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31
Dec

Rain New Years..Then Cooler, How Far North Will Precip Pull?

I’m still watching the trends on the models and overall it still looks like the northern wave will “probably” shear out eastward, instead of backing the flow.  However, it’s still a pretty close call, but the models fail to develop a decent Gulf low.  The models mostly end up looking like this:  The northern wave drops through the Dakotas on Wednesday, and there’s a shearing Baja system that will help pool moisture in southern Texas to the Gulf states where a boundary will lie. But the wave in the Plains looks a little too round and not quite sharp enough to back the flow.

gfs72

Notice the ridge in the northwest US and western Canada is getting ready to get beat down from the Pacific system just offshore. This is the problem for systems that try to amplify downstream and the reason the cold has had a hard time making it to the Southeast this season.  Without a really good ridge out there, the cold air is offset in the Southeast by Southeast ridging somewhat, so systems either shear out or they get squeezed or bypass the Southeast. In this case, there’s so much confluent flow in the east, and with no negative NAO to slow the system down, it looks like it will shear out.

gfs96shears

But like I mentioned if the northern wave can drop down far enough (need a stronger western ridge) then the flow could back from the Gulf….and this would pull the slug of moisture from the Gulf states back northward toward Tennessee and the Carolinas. Right now, it’s still a long shot, and most likely it wouldn’t occur in the Tennessee Valley (although if ECMWF is right, the upper low itself could have a few flakes with it’s passage).

ecmwf120cutoff

The ECMWF last night did separate the Plains wave enough to barely draw moisture northward to graze the Carolinas on Thursday, and then once again with the upper low itself coming through on Saturday.  The GFS just shears the Plains wave, so we’ll have to wait and see how this works out. Even if the ECMWF is right, there still isn’t much moisture shown with it, but it does have a few snowshowers crossing the Apps and some light rain , sleet or snow or mix in the Carolinas and northeast Ga on Saturday, but isn’t a big deal.  I’d be interested to see if the new runs begin to strengthen this upper low in the Plains, but I wouldn’t bank on anything yet.  Regardless, that will bring some cold air over the Friday through Sunday time frame for the Southeast, but following it, a warm up it appears.  The Polar Vortex is still well north, there’s no -NAO anytime soon, and the active Pacific looks to keep on sending systems eastward into California or the Baja region, so we’ll see an uptick in precip chances in the days 6 and beyond time frame.  One other thing to watch for is a suddenly amplifying wave coming across a weak western Canada ridge.  This type of fast flow isn’t modeled right, so any little wave can top the western flat ridge and drop into the Plains or eastern states quickly without much advance notice.

30
Dec

Models Backing Down On Thursday Storm…Still a Close Call

It looks like the models have backed down on the storm potential for Thursday…now they are much more supressed and so are the ensembles.  I should have known the western Canada ridge building was premature, as it’s extremely hard to build that this year so far, and each time the models do so, they end up breaking it down quickly.  The last 2 runs of GFS and ECMWF are breaking down the western Canada ridge immediately, which changes the flow in the central and eastern states.  This won’t allow the flow to back out of the Gulf nearly as much as yesterday’s runs showed, if the last couple of runs are correct.  It’s possible the models are still mishandling the southwest systems, but since this is less than 96 hours away now, and both models agree strongly now, the last runs carry more weight.

ecmwf96

On Thursday the ECMWF (and GFS) both drop a strong Polar wave into the Plains, which still could separate enough from the flow and capture the Southwest system enough to back the flow in the Southeast, but so far both models are quick to pull that wave east, which shears the southern stream. In other words, the northern stream briefly dominates the flow and any system will be pressed along the Gulf states, Florida and maybe southern Georgia to lower SC.  This obviously saves the Carolinas and points north from what could be a Winter Storm.  But as I mentioned, the pattern many times has been for Texas/Ok systems to ramp up in the next few days when models just a couple days before had shown a flat wave, so I would keep the door open atleast for more moisture return than the latest runs and ensembles show. It’s still a very close call.

ecmwf120

The models are still murky on what is remaining in the Southwest after Thursday, so there is potential here for a southern stream system, but also odds are temperatures will be increasing any storm would likely be rain only. So, the odds are that timing would have to be nearly perfect for a Winter Storm, otherwise, most areas will be looking at partly cloudy with a passing southern wave, followed by maybe another passing weak wave, with rain.  Such is life lately in the bulk of the Southeast.

ecmwf168

At one week the models still have plenty of energy working into the West Coast, but timing and the strength and tracks of s/w will most certainly change.  The flow is so fast in the Pacific, it’s really hard to predict much beyond 4 or 5 days in this pattern.  Unfortunately for snow and really cold lovers, the Gulf of Alaska trough is coming back, so no big ridge or +PNA pattern is shown yet….and usually models can get that right. Neither is showing a stout PNA pattern , which is really what is needed to bring serious cold to the Southeast. In addition, the NAO is no longer strongly negative, so without that, the confluent flow in the East is easily replaced with a fast flow in New England and hit and miss cold air masses that don’t stay more than a day in the East.

12zecmwfensnao

So, in this flow, the Southeast can expect rain, followed by a day of cold weather, then average temps,then maybe slightly above temps (but no really warm weather), followed by more rain, rinse and repeat type pattern.

The ECMWF 6 to 10 day ensemble doesn’t show much cold air relative to normals, except under a strong Polar Vortex in Canada, the rest of North America looks about average overall, with fast Pacific Flow and normal heights.  There’s the chance an amplified pattern could come out of nowhere in the 6 day and beyond though, so always take these maps with a grain of salt. Just 2 days ago the models had extreme cold in New England, with temps well below zero. That’s a huge miss.

ecmwfabovenormaltemps

Later on the GFS tries to build a strong PNA ridge where there’s a semi-permanent Gulf of Alaska trough. We’ll just have to wait and see, but eventually I think we will see such a Winter type flow occur….but it will have to wait until deeper in the Winter.

GFSenscoldlongrange

 

29
Dec

Potential For Major Winter Storm Grows

As I mentioned the last couple of days, there is potential with this pattern full of Southwest Lows.  The step down pattern to Winter has occurred much like I thought it would in December, with temps getting slowly colder in the Southeast and some areas on the edges having big Winter Events already, and more is on the way.

Both GFS and ECMWF are still going to mishandle the southwest flow, and the confluent flow in the East, but using the big picture and working inward, I like what I’m seeing for the increasing potential of Winter Storms.  We now have to consider the cold air so prevalent in the nation, even down to Oklahoma and Arkansas and again in the Northeast, and the widespread snow cover.  So any new incoming cold airmasses won’t modify that much, and storm tracks will tend to cut south of the snowcover.  A new cold airmass, the coldest of the season, will be accompanied by a strong high pressure beginning early next week.  First, a weak system will bring more rain across the Tennessee Valley on New Years.  Once again, parts of northern Arkansas, Kentucky and West Va, Virginia and maybe the NC/TN mountains will be game for a little snow or ice, but this doesn’t look like a big deal..maybe an advisory type event.   After this is when the models begin to push the colder air further south.  But like I’ve been mentioning, with the Southeast ridging and southwest flow, the colder air will only get so far.  The pattern mid and late week is very conducive of overrunning the colder air in the lower Plains, Tennessee Valley and eventually the Southeast.  With so much strong high pressure to the north, there is little doubt this will eventually turn into a Winter Weather Event with snow and ice depending on where you are and how the High Pressures evolve.

Let’s look at GFS first.  On Thursday, it has a confluent flow in the East, which will build surface High pressure. I’m not convinced this is right yet (we’ll see ECMWF is different).  But if it’s right in that high, this will be critical for how far the snow and ice will get on the next storm.

gfs120

This is most definitely a Winter Storm look in the Tenn. Valley and NC, possibly including northern GA and upper SC if the low level cold air can bleed that far south.  And right now, I’m noticing each run look slightly colder, and slightly wetter, so this is a trend to watch.  By Thursday morning, the GFS begins to pull Gulf moisture and a weak low into Georgia and the Carolinas and Virginia, but using synoptics, I wouldn’t be suprised to see this MUCH MORE WIDESPREAD than GFS is showing.

GFS leaves the door open to some extremely bitter cold Arctic Air in the Northeast that could be tapped and pushed down the Eastern Side of the Apps Thursday, producing a dangerous Winter Storm that brings ICE to NC and upstate SC, possibly northeast Georgia.  This model shows snow in northern NC and lower Virginia, likely becoming ice, but these details will be ironed out later when the thermal profile is more accurately modeled and the surface ridging.

Notice the GFS dropping temps at the surface into the 20’s in northern NC during the day Thursday, as well as much of Virginia, with extremely cold temps in the Northeast…hopefully none of that type of air will be shoved southward in this damming regime.  The GFS builds the high so strongly, it sends damming into Georgia and eastern Alabama, with 30’s….this is a very strong damming event shown on GFS.

 

GFSthursdaymiddaytemps

gfsthursdaynighttemps

By 168, the GFS begins to roll the Southwest low eastward, and the details are really murky on what could be happening by then.  Again, overall, I like this look as being a classic Winter Storm look in the upper South in general and the MidAtlantic.

Now the ECMWF is pretty similar aloft.  It brings the New Year system through, then begins to ooze down some colder air, but it doesn’t quite push it as far south as GFS but overall it’s pretty similar.  It has a southwest system, a closed ridge in western North America, and strong confluent flow in the East…all of these are tell-tale hallmark signs of a Winter Storm in the Tennessee Valley, Apps and Carolinas to Virginia…if the temps are cold enough.

ecmwf120

The temps on ECMWF on Thursday support snow and ice stratified from northern Texas to northern TN and northern NC, with a close call from Arkansas to northern GA to upstate SC areas….but so far, it’s like GFS and not producing precip in the western regions, only in the Southeast, mostly Georgia, the Carolinas and southeast Virginia.  I think we’ll see this change with time to spread more westward.

ecmwf120temps

By the next day (Friday), the model and GFS begin to roll a deep close cold low eastward.  But they’re not making a big deal on precip. Again, I think this will change.  This look is screaming major Winter Storm for a pretty big region from Oklahoma, Ark, Tenn, NC, SC and Virginia, with the possibility going further south to include northern Ms, Al, Ga areas but it’s impossible to nail down exact tracks and temps right now.

ecmwf144

ecmwf144temps

 

GGEM also shows a Southeast Winter Storm on Thursday…but it’s almost certainly too cold, too far south, which is one of its biggest biases.

GGEM120Snow

Those who were worried about this being another “non Winter” like last year are already incorrect and have baseless fears….obviously, we’ve seen a blizzard with snowfall well over a foot in Arkansas, and a Winter’s worth of snow in northwest TN, western Kentucky, and big snow and ice already in West Virginia, with some minor events in TN, NC mountains and the Virginia Foothills.  The overall pattern has switched tremendously, and will become much more conducive to storms plus colder air coming south with time.  I see signs of split flow continuing, and atleast average cold air covering more of the nation this year than last year.  There is a lot of potential with so many systems coming in with this split flow.  It’s still going to be tough to get the really cold air to press very far south in the Deep South yet, but the longer range continues to ‘step down’ and I’ve always liked that approach to this pattern…not pushing the cold too fast or too far south, instead having a mix of just enough warmth and southwest flow aloft to keep producing storms, and as we get deeper in the Winter, more cold blending with it, to eventually verify my Winter Forecast of above Average snows in the heart of the Tennessee Valley and the Southern Apps.  Unfortunately, I already don’t like the icy look on GFS…as it is a pretty darn good model to catch ice from a distance, and we haven’t seen an ice storm modeled in a few years.

It’s still early, and the details could change…for example, the southwest flow may become so strong , that temps creep upward and more rain occurs where currently I’m thinking snow and ice.  This is very possible, especially with the stout Southeast ridge that keeps showing up, But so far models are looking more like I thought they would…slightly colder, slightly more high pressure, and slightly more moisture working north and west with time.  This is yet another storm to keep forecasters on alert.  This look at 5H has a really big Winter storm potential for some areas.  With time, I’ll nail down the specifics.

 

 

 

28
Dec

Important Update Western NC, VA, Upstate SC, TN, North GA-With Map

Precip. Type Map:

Dec28_29_2012Event

Since this morning models have come in slightly colder and much wetter. As I’ve been mentioning all week, this was always going to be a close call for the mountains of TN, NC and the northern, northwest piedmont of NC, and points north looked more like snow, but drawing the line is critical.  Here’s a look at 3 PM obs showing where the precip shield is, and the 850 temps.

current850

The zero line is near the Ohio River, snow is falling in northern Arkansas to southern Indiana, like last storm. However, the Southern Apps region is around +2 to +4.  But all models have always showed this area dropping to near zero when precip starts after midnight.  Most models show this band of rain being much more than previous, and judging by the radar, it’s hard to ignore.  So a band of rain will move into eastern TN, eastern Ky down to Alabama and northern Georgia then spread east, in tact mostly, but possibly some dimishing somewhere in NC or VA especially, but right now I question how much the moisture will vanish.  Here’s a look at the 18z NAM totals:

nam18zpreciptotals

This is a pretty solid event most areas with atleast .50″ and some areas passing .75″.  Now we can look at how the models are showing the 850 temps dropping in the Mountains and foothills region.

The RAP (lastest run) has the temps at 850 dropping to show an isothermal layer under moderate precip, for western NC and into much of Virginia.  So aloft, this will be SNOW falling, very wet snow. Winds won’t be classically northeast at the surface and surface temps will be middle 30’s in middle areas with wetbulbs not that low.  So the mountains and foothills stand a shot at rain turning over to wet snow in the mountains of NC, VA and maybe even northeast Georgia.  This is a RAZOR thin margin for error, so at times, any particular area could immediately go to snow, or back to rain.  And there will be huge differences from one location in the county to the next location.  It’s a unique setup where cold air trapped in some valleys and the rate of precip could mean everything on Precip Types.  Here’s the 2 AM and 6 AM RAP

RAP2am850

RAP6am850

The High Reso. NAM also shows this from the 18z run. In fact, it’s colder. And further south. It shows a pocket of snow-induced cooling aloft to cover northeast Georgia, upstate SC and much of western to central NC as the night wears on.  Again, this is EXTREMELY close to being a snowfall, but in the end, usually you need some elevation to really help out.  So places like Hendersonville, NC could be rain while Asheville could be Snow at any one time.  Even Hickory could switch to snow in this temp profile.  One other thing to watch will be the higher valleys where cold is at the surface,but the snow melts before hitting the ground, so FREEZING rain would be the issue.  There could be some areas of sleet mixed in, but there’s not that much evaporative cooling going on, so mostly this will be either rain, snow or a mix.

NAM HI RES 2 AM: Notice the cold pool at 850 that develops in the Southern Apps and Lee of the Apps.

NAMhires2AM

the 18z NAM overall has ramped up precip totals esp. where GA, Carolinas where before it was showing substantially less.

 

NAM 18z valid 4 AM:

nam18z4am

For areas west of the mountains, this will be a situation where KY, TN can change to snow at the very end of the event, there’s much more warm advection west of the Apps than east.  For NC and VA, rain to start and depending on where you are it could change to snow overnight.  The line will likely be around Winston Salem/Yadkin Valley region west to the foothills and around Asheville, possibly extending for a brief period into northeast GA mountains.  Further north, from Boone NC and into southwest VA, mostly snow after  rain to start.  Further east into central Va, rain to start but north and west of Richmond will be close to snow.  Not that much accumulations for any area, but the mountains and foothills of VA and NC overnight by early morning could have several inches of wet snow…the precip ends here rapidly by after dawn.  There was  a similar situation in the mountains of NC and VA a couple of Winters ago in December if I recall where the atmosphere was just cold enough ahead of a cold front, so rain quickly changed to snow.  This is a very similar setup. So be safe and be prepared if you’re travelling after midnight into early Saturday morning in these areas.  Most will still get rain, but some will get snow and it could switch either way in a pretty big area from extreme Northeast GA to southwest Virginia.

 

28
Dec

Friday Morning Discussion…Messy Flow Coming

More rain is on the way to the Southeast and East, but some areas will be snow.  This will be a weak system overall, and very fast moving.  The rain /snow line will stretch from western Kentucky to western Virginia and points north, but overall moisture will fade in the Carolinas, most of Virginia and Georgia, with the bulk falling WEST of the Apps on this one. The GFS and NAM  both show this type of scenario.gfsrains

As moisture moves east Friday night, the atmosphere will cool just enough for snow in the mountains of NC, and northeast TN, but most of TN and NC will be rain with this system, except possibly turning briefly to snow in northern TN and northern/nw NC piedmont just before it ends early Saturday.  The best chance of an inch or 2 of snow will be western and northern Kentucky and western Virginia, and again northern Virginia (with several inches in the West VA mountains) but the speed of this system will be so fast, it doesn’t look like much of a deal to write home about.  The bigger news will once again be HIGH WINDS in the mountains, where models show quick, but very strong cold advection Saturday night and Sunday, so unfortunately more tree-damaging winds are likely in northeast TN and northwest NC mountains especially, with some upslope snow showers and very cold temps coming.  The cold doesn’t penetrate much into Georgia or Alabama, except the northern fringes.   So far, it has been extremely difficult to get much cold to penetrate into Alabama, GA and SC this season, thanks to the stubborn Southeast Ridge and the storm track from Texas to Virginia, which leaves the Southeast regions in the continuous warm sector.  This won’t change anytime soon.

The Southwest system is still going to be a tricky issue, and the models are showing a series of Southwest Lows to form, and parts of each one gets ejected east into a confluent flow.  Overall, no model has much cold penetrating south of I-40, so they are remaining pretty adamant on the Southeast Ridge being caught in a squeeze play between the Southwest Low and The Eastern Canada trough, with southwest fast flow aloft in the Southeast.   This will allow two things….Lots of high clouds, periods of precip, and an active stalled or nearly stationary boundary next week.  This will be the area to watch for periods of rain to stretch east across the South. Right now, the models are pretty supressed, but a couple runs still pull moisture north into TN/KY and southern VA but it’s hard to say exactly how far north precip will get.  It’s possible one of these southwest systems could eject enough s/w to phase with a northern stream wave and that could yank the colder air down a little further, and set up an interesting play for the next wave coming out of the Southwest.  But it’s so messy and fast out west, it will be impossible to nail down until you’re only a few days out.  So stay tuned for an active period next week, with some periods having a chance or working just enough cold air with some bouts of moisture.  I still don’t see the cold pushing much further south than I-40 *roughly* for most of next week, unless a much bigger amplification can occur, or unless the flow can get much further supressed.  Here’s a look at ECMWF images, which is being pretty consistent on the southwest systems and the overal 850 temps alignment.

ecmwf96

ecmwf120

ecmwf168

The ECMWF almost phases the southwest system with a Lakes or Ohio Valley wave in about a week, and I’m keeping my open for this. The models most likely wouldn’t get this right, either way, at this point, but it’s a possibility, especially considering how often systems in Texas tend to pull north toward the Ohio Valley.  Right now, they mostly show supressed systems in the Southeast, especially GFS, but I won’t be surprised to see something pull much further north.  If it did pull north, much more rain would occur in most of the Southeast, but the northern shield would be close to snow, especially on the WEST side of the Apps, where the models all show the coldest air, but possibly stretching or arcing east into VA and northwest NC regions, much like this latest storm was, and the Saturday system.  By 10 days, the ensemble means on ECMWF show something interesting, but I don’t know if it’s right (ECMWF has had massive errors at days 7 through 10 for a long time)

It shows a building PNA temporarily and a backing or retrograding flow in Canada, and at the same time Canadas temps drop suddenly, so an Arctic Airmass will be pushing south and it looks like on days 11 and beyond an arctic outbreak could occur in the US.  I am skeptical of this right now, as the flow is so fast, and progressive, it’s hard to trust this far out.  But it also has a strong southern system about to enter the West Coast which **could** take a supressed track after the cold is in place for the central and eastern US, but again, only mentioning it as a possibility.  It would be the first time in a while there has been a really cold airmass in Canada, where it’s currently warm and looks to stay above normal for the next week.

ecmwf240Heights

Just for kicks the GGEM still looks way too cold too far south.

GGEM144

So right now, I’d say it’s still looking like NO really cold air is going to be able to penetrate most of the Southeast, but for part of ARK, TN, KY, NC , VA areas at times there will be the chance that moisture could pull north enough to meet what little cold air is available to produce some snow or sleet, but it’s going to hard to say which days that will be.  With so much southwest flow aloft, clouds (high clouds esp.) will most likely make an appearance on a daily basis for a while.  There is a chance of a very wet time coming overall for the Deep South and Gulf States.   And with so much activity and southwest lows developing, and trying to come east in the active flow, it will keep forecasters on their toes.

 

27
Dec

Watching Two Systems During The Next Week

The first of 2 systems will cruise through the Southeast later Friday and into Saturday before going up the East Coast.  This still looks like a system that won’t have that much moisture, and the cold will be pretty far north and mostly chasing the moisture.  But there is going to be just enough cold air in northern Kentucky, into most of West Virginia, western and central Virginia to the MidAtlantic for mostly snow.  Further south, from the NC/VA border and the TN/KY border those areas are going to be the transition areas, where either rain or snow could fall.  The mountains of TN/NC above 3000 feet will likely be snow or change to snow quickly.  For central NC to Southeast VA, mostly rain, but possibly changing to light snow at the very end, but it won’t be enough to cause any problems.  This storm will wrap up into a very strong storm off the New England coast by Sunday, and then we look at the next system.

For precip totals, the GFS doesn’t show much in the majority of the Carolinas, especially in the lee of the Apps where downsloping and shadowing will be noticed from GSP to CLT regions.  But in Alabama and the Tennessee Valley maybe over .50″ to .75″ of an inch of rainfall, and again in eastern NC when the system gains more moisture as the low develops just offshore Wilmington.

gfstotals

Snow Totals Forecast:

gfssnowfall

The next system is going to be interesting, because the models never know how to handle a Southwest or Baja upper low.  We haven’t dealt with one of these in a while, and I expect some changes to the track of this, which is on shaky ground. It’s impossible to know right now which way this will go, if it will phase with any waves topping the western Canada ridge, or if it shears, or if it holds back and just ejects impulses….all of these are possible.  But right now and the last couple of days, the GFS wants to eject it fully, and the ECMWF waits and ejects southern stream impulses.  With the models showing a good amount of Eastern US confluence, this is an overall Wintery look, but the cold will only press so far. Here’s a look at the ensemble (ecmwf) heights in 144 hours:

ecmwfheights144

The European Operational at 96 hours (Sunday PM) shows a pretty strong s/w dropping into the Northern Plains, and it seems to get stronger each run, so that will have to be watched as it could bring down colder air than the models really show right now, but that could also slide more into the Ohio Valley and New England.  Still there will be some high pressure and X amount of cold pressing south, but probably just “barely” enough to provide a Winter storm next week, if there is to be one.  Lot’s of questions right now in this fast flow.

ECMWF 96 hour:

ecmwf96

ECMWF 144 Hour:

ecmwf144

If the Eastern Canada vortex can hold in place, then this will allow the southwest system to take a southerly track, and moisture will begin to overrun a boundary in the Deep south from Texas to Georgia early next week, and the northern parts of the Precip Shield could be snow or ice.  It will depend on the temperatures and how much High Pressure is pressing southward.  Right now the ensembles and GFS mostly agree that the 850 zero line will run **roughly** along Interstate 40 from NC through TN and Arkansas next week for quite  a length of time.  Any stronger southwest system will tip this boundary some, and that would likely be more from northeast Texas to Virginia type of system, which seems to happen a lot in this pattern, but anything is possible yet.

The DGEX and GGEM, less stellar than GFS and ECMWF also have a southerly system at some point.  GGEM looks too cold and too far south overall, as it always overdoes High pressure.

dgex168

GGEM180

 

So right now, I’d say the odds are this system comes out next week, and areas along central Ark, TN, NC and points north stand a shot at some Wintery Precip….but no guarantees yet.  More rain (and possibly a lot of it next week in the Deep South).  After that system, the pattern still looks very active with more systems coming in from the Pacific.  How cold is the biggest unknown right now…it doesn’t look very cold but also doesn’t look very warm. Probably back and forth between around normal to slightly above to slightly below.

 

 

 

 

 

26
Dec

The Weekend System…Where’s the Cold?

I keep seeing references to models and very cold air, but so far I think it’s an illusion. The flow in this new pattern still isn’t one that will send much cold air to the Southeast and the last areas to really turn cold are going to be the Carolinas, Georgia and Alabama region, sitting squarely under a flat Southeast ridge for a while.  You can see on the 5H maps that a vortex ends up off the Northeast Coast or eastern Canada, with sagging heights in the Plains, so this leads to above normal heights and a little bit of ridginess in the Gulf and Southeast states.  This also explains how the storms continue to cut inland from Texas to Virginia, placing the Southeast in a wet, warmer than average pattern.  I really don’t see any long term changes to that flow yet.

Let’s take a look at the next system. You know you’re in a warm pattern when the GFS (normally supressed and cold) still fails to show the 850 line moving south of NC.  Also, the GGEM keeps the next system rain for most of the Southeast.  I think there will be a weak low with a quick passing wave starting Friday night across the MidSouth and spreading through Georgia and the Carolinas and Virginia on Saturday.  But there is NO HIGH PRESSURE to be found.  This will make it very hard to be snow outside of the higher mountains of NC and VA.  On the west side of the Apps, closer to the lower heights and colder temps, I think the rain snow line will be in central Ky down to northwest Tennessee, much like this current system, but only on the backside and the snow won’t last long at all.  And in the Virginia area, the snow line will probably be near the foothills to just north of Richmond, possibly sagging to the NC border by the time precip ends later Saturday.  This is very bad timing for snow in VA and northern NC on Saturday, with no damming high and no really dry dewpoints or cold air in place, the 850 temps alone in this setup usually means any snow will fall with surface air temps in the upper 30s for most areas, which will be hard to stick.  A nighttime or early morning event (TN/KY/Ark) will offer better chances, and again maybe in eastern Virginia and DC to the East Coast for a Saturday night event, but by then precip is ending quickly and usually cold air chasing the moisture doesn’t work east of the mountains in Va or NC.  But it is possible some snow could fall down to the NC/VA border, but right now I’m leaning against much accumulation since there’s no damming high in place and the temperatures both surface and aloft will be very marginal. As I mentioned yesterday, the ECMWF was looking too cold, too far south, and it’s new run has pulled the 850 further north, and I think it will continue to pull further north, correcting itself.

 

GGEMsatAM

GFSsatmidday

Next, we cast our eyes to what could be in store.  There is potential in this pattern, but I still don’t see good signs of colder than normal air coming anytime soon.  The Gulf of Alaska trough keeps on coming back.  This prevents both a good PNA pattern as well as a good negative NAO pattern, so the shots of cold air are usually fleeting in the East.  This upcoming pattern could have atwist though, with so much energy hanging back and cutting off around the Southwest or the Baja.  If this separation occurs, then more cold will be allowed to come down in the East and we’ll dry out a few days.  Many times in the past a Baja system , when ejected, can be a big Winter Storm in part of the Southeast, but we’ll just have to wait and see if the timing is right, or if it comes out when the eastern trough is lifting out (rain).  If it can come eastward when there is a blocking 50/50 in place, then damming and cold will be forced far south, and it’s a Winter Storm look, but so far, the models aren’t showing that more than one run.  This will be a tricky flow, so be on the alert for changes in the days 7 through 10 time frame.  It’s always extremely tricky when dealing with Baja systems.

Here’s the day 10 Euro Ensemble showing the cold trough in Alaska again, and a Northeast/East Canada cold trough, but mostly above normal temps in the United States.  There could be good or perfect timing though so even without the very cold air, if the timing were right on a southern stream system, there could be some type of Winter event, but overall right now this model doesn’t look cold at all anytime soon to start the new Year.

ecmwfenswarm10day

So the bottom line now is to wait and see how much separation occurs in the flow, between the Baja system that could form, and how much troughing occurs in the East.  Getting any really cold air into the Southeast (or most of the East) has been a hard task so far, and I have my doubts on it turning very cold for a while, but atleast there is some potential.  I’ll have a more definitive rain/snow line drawn in my next discussion for the Ark/Ky/Tn/NC/VA system this Friday night and Saturday.

 

25
Dec

Rainy Pattern Southeast

The active period I spoke of earlier this month has arrived, and now there’s a big storm moving through the Southeast. There will be severe weather and tornadoes tonight and early Wednesday in La, Ms, Al and maybe the Eastern Carolinas on Wednesday. SPC has this area highlighted well with helicity and strong CAPE for this time of year, with the possibility of good shear and turning with height, thanks to that strong ULL moving through the MidSouth. On the northern sides , western edges and the eastern edges, there will be snow and ice, and even a full blizzard on the western edge.
The snow in Arkansas, northwest Tenn, and western Kentucky will approach 6″ in some areas, maybe more in a few spots. Rain and lots of it for most of the Southeast, with a squall line moving through the Deep South overnight, and strong southeast flow into the mountains and foothills of SC and NC will produce localized flooding, dropping nearly a month’s worth of rain in the next 24 hours. Obviously, December has turned the drought around in the Southeast.
ICE will be the word from just north of Roanoke and especially in northwest VA , where temps will only go to freezing right at the very end of the event. Once cold air is locked in at the surface (and all models show it coming), it almost never scours out fully, so I expect northwest VA to be the hardest hit region with ice totals, but some snow to start before giving way to ice. If there were more damming in the East, NC would also have an icestorm, but it seems in this flow it’s hard to get damming to show up strongly enough. The flow so far this month has been southwesterly, and I see no end to that.

We will keep on with this same basic pattern for a while, so be very wary of any model showing snow south of I-40 through TN and NC (although TN will get some snow on the backside Wednesday, even down to northern Al, GA possibly).

The next system is shown to move east, northeast across the Southeast States, but there is no appreciable High pressure to the north. The ECMWF shows the 850 dropping to the SC/NC border early Saturday, with a possible snowfall in most of central to western NC. I’m very, very doubtful of this 850 dropping this far south with no good high to the north. Instead, I think cold air will bank on the western sides of the Apps, so parts of TN and KY will go from rain to snow quickly, as well as Virginia, but for most of NC probably rain with southwest flow and no good damming. It’s possible the mountains are in for a snow event if the low doesn’t pull too far north, but we can pinpoint the rain snow line later. For now, it looks to be in VA and back southwest to northern Arkansas on this system. This system could wrap up strongly off the East Coast, and that may help pull down more cold air, but again at this point, it only looks to be around seasonable, and even slightly above normal in some parts of the Deep South. We keep repeating the southwest flow regimes, and after the next Saturday storm, yet another storm will drop in to the Southwest and most likely will push east.

There are big questions as to where that goes and what the northern stream looks like at this time. If you’re rooting on a Winter Storm, I think once again on that storm the best chance for cold enough air will be from northern Arkansas, across Kentucky and into Virginia, just like the previous systems.

However, it’s far enough out in time that the Southwst low may stay put for a while and allow enough separation in the flow to allow colder air to force down into the East, around the Big Eastern Canada vortex…but it seems like no model keeps the colder air really pushed that far south. A few runs of ECMWF and GFS show a big cold wave, but they always back off on that the next run, so I’m very skeptical of any really cold air pushing too far south into Al, Ga, and the Carolinas anytime soon. We really need to see that PNA ridge out west amplifly tremendously and allow the Vortex in Canada to become massive, to over come the Southeast ridge. Speaking of the Southest ridge, this is the reason that storms continue to focus from Texas to the Southeast and off the MidAtlantic coast. That pattern looks to continue, so atleast we’re now getting a lot of rain

Hope everyone has a Very Merry Christmas…and be patient. I like the stormy pattern and this “neutral” phase, and have never bought into the really cold air like some models and other forecasters have shown. When it does become a real threat for more areas of the Southeast, I’ll be all over it. Until then, enjoy the rains and the very active pattern. This will offer some close calls for TN and NC and points north, and eventually more regions once the colder air is allowed to push far south.

24
Dec

Video Discussion Christmas Storm and Beyond

23
Dec

Beneficial Rains Again in Southeast..Snow Arkansas, Ice northwest VA

Models are in excellent agreement on the track of the storm through the Tennessee Valley late Christmas and redeveloping in eastern Virginia later Wednesday.  This will spread more rains,(cold rain upper Southeast and Carolinas) with damming down into NC, but a strong temperature gradient by Wednesday with temps in the upper 30’s for northern NC, and low 60’s in SC and GA, so some thunderstorms could occur.  All the rain will be welcome news after such a dry Fall, and this is the second major event, with more to come over the next week.

GFSrains

The snow will fall on the northwest side of the storm where it’s going to be cold enough in northern Arkansas into the Ohio Valley, with many areas of western Kentucky and Tennessee turning over to snow just before ending, where an inch or so of accumulation could occur. About 6″ of snow will fall in the synoptic zone on the northwest side of the track.

GFSsnows

Most of the Tennessee Valley will see a few flakes after the main storm has redeveloped east of the Apps, since there will be good northerly flow and there’s still enough moisture around at 850, so even some flakes are possible in the air over extreme northern Miss, northern Ala and much of the state of Tennessee, but no accumulations except in the higher mountains of eastern TN, NC.  The ice part of the storm has shifte more into northwest Virginia since the storm is going to be so strong on the west side of the Apps, and this will bring very warm air aloft which will scatter down through the atmospheric column, or try to, and the high pressure in the Northeast has always been an “on and off” feature, and just won’t hold that strongly for a severe ice storm.  But there will be some ice early Wednesday before gradually lifting and squeezing into extreme northwest Virginia and Maryland, before giving way to snow in Pennsylvania.  It’s possible enough ice could  occur for some damaging totals in extreme western Va, just east of the mountains if cold air gets trapped at the surface as the storm redevelops or “jumps” into eastern Virginia, but temps will be barely supportive, only around 31 to 33 for most areas and won’t be widespread. If there was a stronger high in place, this would have been a much worse ice storm.  Later on this storm will lift into New England and snow will wrap around back into northern Virginia and points north, with accumulations mostly in PA and points northeast. Cold air will once again wrap around into most of the Southeast, but will only be a glancing blow in the Gulf States before westerly flow resumes. Overall, temps look to be about average following the storm.

GFSwedam

 

After this storm, by late next week or weekend we see southwest flow and another system take almost the exact same track. Once again it will have to be watched, but so far the track looks nearly identical, most models taking it west of the Apps, with possible damming in northern NC and into Virginia, with areas in northern TN north of 40 having a close call between rain or mix/snow. So far, it looks predominantly like rain, with more cold air wrapping in afterwards. And once again, rain totals across the Southeast could be substantial.

ecmwf144

ecmwf168

 

GFS ensembles are showing a close enough call again in Ark, TN, NC but with time I think we’ll see this system amp up and most likely run west of the Apps again, with snow chances at the very northern shield most likely around KY, West Va regions.

GFSens144Ptype

 

Finally, if you’re hunting a sustained colder pattern, the PNA looks optimistic. After spening the last few months in negative territory, the forecast is for it to go positive soon and stay mostly positive for a while.  This will finally put a ridge along western North America and a trough in the East, right at the beginning of the new year, so a colder flow is coming.  Right now it doesn’t look extremely cold, but pretty normal January type air over most of the Country, and in addition, there will be some southwest energy lurking around the Baja.  This scenario could be a Winter Storm later on, depending on all the details of course. I’ll keep you posted of the chances.

PNAforecast

 

 

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