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Archive for January 2013

31
Jan

Light Snow in parts of TN, KY, NC, VA….Clipper Pattern

A weak clipper will be spreading light snow across north middle TN, into Kentucky and the mtns of TN and NC overnight, and possibly drop a few flurries east of the mountains in Virginia or northern NC, but won’t amount to much there.  The mtns of ne TN, sw VA and nw NC stand to get 1 to possibly even 4″ , so a general light snow as occurs with most fast clippers.

GFSsnow30hr

 

The next clipper arrives late Saturday and into Sunday and will be more interesting to follow. It looks stronger than models are giving it credit for, and the models turn it strongly neg. tilt right along the East Coast.  That would be too late to drop significant snow in eastern VA or NC, but its close enough to watch.  It also could have a few more flakes (or light rain, depending on temps and time of day) in parts of the Tenn Valley, maybe even northern Alabama and Georgia.  If it dives far enough south, those areas could have a few flakes, even into SC, but it’s too early to say and I wouldn’t expect it. Otherwise, another 1 to 4″ snowfall for the same areas that have been having Winter weather this season…namely, southwest VA, much of West Va, northwest NC, and northeast TN.

g13.2013032.0015_smUS_wv

 

After this weekend, the models are a little fuzzy. A western system will try to work into the west (so a warm up for the East is likely) but there is possibly another s/w that amplifies just before that happens.  We’ll need more time to see how things evolve next week.  Both GFS and ECMWF have a pretty stormy and amplified look, but where the cutoffs are, and the ridges, is yet to be decided.

31
Jan

Colder For a Few Days…Watching Clippers in the NW Flow

The strong south winds are over and now we are in a brisk northwest flow type of pattern. Usually, this pattern is pretty dry in the Southeast but cooler than what we had recently.  It’s also a “clipper ” pattern and there are about 3 minor disturbances that will come through from the lower Midwest toward the Southern Apps then off the East Coast.  Friday Night and early Saturday,  then later Saturday night and early Sunday and another one early next week.  All of these look weak now, but any of them could be a little sneaky and I’ll hone in on them later.

Snow is now falling in Kentucky, TN and NC mostly in the mountains and some flurries could occur with the next clipper as far south as northern Alabama and Georgia, and also along the coast of NC/VA but most areas outside the higher elevations won’t see much accumulation. You will notice the colder air though.

Here’s a look at morning lows tomorrow and afternoon Highs on Friday.  Some areas across northern GA, AL won’t get out of the 30s on Friday afternoon.

FridayLows

 

FridayHighs

The models keep the northwest flow in tact for almost a week, but there will probably be some moderation next week as eventually energy undercuts the western ridge and this will push the trough out of the Eastern US.  Once this happens, a warm up occurs and then more rain could arrive.  Going out past 10 days right now looks active again in most of the Country, but it also gets very volatile with a lot of options. The GFS wants to build a major western ridge.  When you combined that with an active southwest cutoff low , or southerly branch and possible confluence in the Northeast, I think at some point we’ll end up with Winter Weather by Mid February, but there’s nothing to really put a finger on yet.

ECMWF 96 hour: (numerous disturbances in the northwest flow)

ecmwf96nwflow

 

ECMWF 240:  Possible building ridge in the West

ecmwf240_ridgebuilds

29
Jan

Batten Down The Hatches…It’s Going To Get Rough Almost Everywhere!

Nothing’s really changed since yesterday…this is going to be an impressive system for January, and probably end up a record maker in several regards.

Tremendous warm advection will develop (began today if you noticed the temps) but by Wednesday it gets even warmer in some areas.  The flow of the Jets at 250 and 300 are extremely favorable for a strong line to form and SPC has this covered nicely with their outlooks.  This line will travel across the Southern US and reach the East Coast by around dark Wednesday night.  The models have delayed this somewhat today, and this could open the door for more warming and less cloud cover in the Eastern US later Wednesday, which would only add fuel to the fire for the LLJ to come down and also for the QLSC line to wreak even more havoc than it looks like it will.  There are so many factors going into this unique setup it’s hard to cover them all, but if this event with all it’s special upper air support were to occur in March, this would be one of the worst tornado outbreaks in history.   The limiting factor is CAPE.  Shear and Helicity are phenomenal.

The GFS and NAM have a little differening views on the squall line itself, and for now I lean toward NAM.  THe GFS takes too long to organize the line nicely.  Both are still major weather producers.  It begins tonight for the lower Mis. Valley then it spreads northeast, and will grow the southern flank down to the Gulf.  By Wednesday, the line will rake across the entire Southeast.

day1otlk_1300

day2probotlk_1730_any

 

the High Res. NAM valid 1PM

namHiRes1PM

 

 

NAM 3 PM

namsquallline3pm

The NWS and other forecasters are now taking notice of the LLJ that I mentioned on Monday. The models still have that, and we’ll just have to wait and see if the conditions just before the squall line arrives will fully max out to produce a rare event where the LLJ actually comes down to near the surface just before the line arrives.  The more sunshine and less rain, the more likely this would occur and this looks to me to be offering the best chances of the LLJ to hit in GA, SC, NC, VA and MD and DE, but any area ahead of the strong front is susceptible.

Even without the LLJ reaching down, the winds aloft are extremely strong and there’s almost no doubt some of this will work down in the squall line, so the winds are definitely coming.  The only question is whether there will be 35 to 40mph gusts, or whether there will be 50 to 60mph gusts (and strong sustained winds for several hours).

High wind watches and flood watches are going up in several spots. The Southern Apps looks to get strong upslope in the southern facing slopes in north GA nw SC and sw NC…as well as being elevated Wednesday so the strong winds will be even worse in the mountains.

Numerous Tornado Watches will likely go up soon. Take care and have a plan in case the worst case scenario comes to pass.  For some areas, there WILL be tornadoes with this event somewhere in the Southeast, despite the fact that it’s only January.

A look at the totals rainfall projections per GFS.  I see slight shadowing in northeast/east TN thanks to some blocking of the Smokies and a slight minimum in eastern Carolinas as the GFS thinks this line will speed up as it moves toward the Coast.

GFStotalrains

Snowshowers come in to the NC, TN and West Va mountains by dawn…but won’t amount to much.  The temps will be drastically reduced for Thursday and Friday in the entire Eastern US.  The longwave trough looks to stay for a while, and be coldest relative to normals in the Northeast, and gradually warming further south and west.  From Ark, MS, LA and TX region, those areas will be at or even above normal for a while as the trough is too far east to allow much cold air that far south and west.  A couple of clipper systems will dive into the trough the next few days and into the weekend, with some light snow possible again around the Apps, but it doesn’t look like much.  We’ll watch those systems later.

 

28
Jan

High Wind Event Tuesday PM Through Wednesday PM And Squall Line

AnimationWindsJan30_2013

Above are the wind fields shown by GFS for early morning to late evening roughly 10 AM to 10 PM across the Southeast, at the surface.  The NAM continues to be much greater than this, with 60 to 70mph gusts.  I lean toward GFS as its usually tough to realize the worst winds at the surface but this has strong similarities to past high wind events with warm advection.

The SPC has outlined the lower Miss. Valley to western TN region with a severe threat, and has extended it further into the Southeast for day 3 (Wed).  The SPC is very confident on a high impact Severe Weather Situation and will be only a few times that this setup has occurred in January. After looking at all the data, this setup is most definitely a severe setup, even though CAPE is small, there is still a coupled jet, and the Southeast region to TN valley lies squarely in perfect alignment under the entrance region of the upper jet, and the lower left exit region for a time, so this will be a case of a solid Squall line with embedded meso twisters possible (even likely) that runs east and holds together nicely.  The only impediment could be when it crosses the mountains but then, I expect redevelopment of the line again.

Before this hits, there is a 1 to 3 hour window of sustained high winds with the LLJ I have been mentioning, and if all factors come together just right, then this LLJ will wreak havoc even before the severe line arrives.  I’ll have to monitor observations Wednesday to get the best idea of how it unfolds, but regardless, severe weather is coming to many.

By Thursday, the front has cleared, and there could be snow showers in the mountains, and turning much cooler…around normal for early February.

More on the longer range later..which looks pretty interesting.

day2otlk_1730

day3otlk_0830

NamCarolinaSquall

28
Jan

Weather Alert ***Low Level Jet HIGH WIND Event Wednesday***

Besides the actual Squall Line that will likely develop ahead of the strong front later Tuesday and spread into the Southeast Wednesday, the models also show a very strong and well organized low level jet.  This sometimes happens when there is a full-latitude trough and when the 300mb and 250 mb jets couple.  This happened in January 17, 2006 in the Southeast, where many stations had a high wind event AHEAD of the squall line and just before the showers arrived.

Jan17_2006_CLTwinds

The January 17, 2006 Event was very similar to this upcoming event at the jet stream level, with a couple 250, and 300 mb jet that arrived in the East with anomalously warm air and a strong cold front, with a squall line.  The highest winds occured just ahead of the Squall line itself, under partly sunny skies, much like this one is progged to do.  Sometimes the sky condition can help or hinder the development of winds at the surface, with maximum heating allowing a stronger low level jet to form just ahead of the squall line.

Here’s a look at Jan 17, 2006:

Jan17_2006_18z

Here is the GFS prog for 18z on Wednesday at 250 and 300mb levels.  Notice the coupling of the upper jets in the Mississippi Valley associated with the strong front, and the time of day for the Tennessee Valley and the Southeast is almost perfect to allow maximum heating which could aid the development of the low level jet.

GFSwedmidday250jet_60hr

GFSwedmidday300jet_60hr

 

The GFS and NAM models are showing a ribbon of sustained winds just ahead of the cold front to begin early Wednesday in the western Tennesee Valley and quickly work east with the front. This will be a strong southerly wind event, where the winds at the surface can reach up to 50 mph sustained (likely the max) just ahead of the cold front and squall line arriving, and lasting from 2 to 3 hours in any one location.   The timing looks to be the Al/mid TN corridor first, then spreading into GA and western NC/SC corridor by midday then the Eastern Carolinas and southeast VA by early Evening, before heading offshore the East Coast just after night fall.

GFS Surface Wind Gusts Below:

Wednesday morning:

windswedam

windswedmidday

windswedpm

The NAM almost always overdoes surface winds, no matter which synoptic setup it is.  The GFS looks much more realistic, but we’ll have to watch the trends and see if it can become stronger like the NAM.  The NAM would be a massively destructive High Wind event on a large scale.  Even the GFS alone is a harbinger of some damaging winds, but nowhere near the NAM.

NamwindswedAM

NamwindswedMidday

More updates later as I follow this Potential Low Level Jet High Wind Event.  Regardless of whether the low level jet truly materializes, there will be high winds with the Squall line, sometimes this is preceded with LLJ events, and in this case it looks very possible to something similar to January 2006 LLJ event, where the worst winds were ahead of the Squall line, rather than with the Squall line.

 

27
Jan

Light Ice Overnight..Then Warm Up, Then Major Cold Front

A weak system will cross the Apps overnight and spell a little trouble for northern NC, much of interior VA and eastern West Va, and into Maryland.  This won’t last long, and temps won’t go nearly as low as the last event, but here’s a look at the GFS forecast temps tonight. Notice upper 20′s, and north of I-40 and points north have the best chance at seeing enough moisture, and there will be more moisture in northern VA than in NC, around a tenth is possible.

GFSfreezingraintemps

GFSfreezingrain

freezingrainadvi

Some drizzle or light rain is possible further South in the Carolinas and Georgia overnight, but after this , here comes the warm advection.

The new week starts off near normal but gets warm, with thunderstorms by midweek as a deep western trough moves steadily along and phases with energy topping the ridge.  The Gulf will open up , so all of the lower Miss. Valley will get into some rain, and an embedded line of thunderstorms, possibly severe, could erupt either Tuesday or more likely on Wednesday.

day3otlk_0830

This front will usher in another very cold airmass, but once again THIS WILL NOT BRING THE DEEP FREEZE TO THE DEEP SOUTH.…instead, there will be another tight thermal gradient, so areas from Jackson MS to Macon GA will be around normal, while areas just north across the Tenn. Valley to NC and points north go very much below normal.  This has been the theme so far this Winter, with the Cold Air Advection not impressive at all from eastern Texast to much of Georgia or Florida.  This looks to continue for quite some time.  There simply isn’t a tall PNA ridge out west, as there is way too much fast flow that keeps crashing through the ridge.  Also, there is no southern Greenland block (or any Greenland blocking–which would help supress the cold further south).

There will be several minor impulses coming across the ridge by Friday and into the weekend, that the models will be hit and miss on.   One could arrive Thursday night or early Friday across the TN Valley to Apps maybe VA, NC region, but it looks light and some runs don’t have any moisture at all with it.  It should be a minor event , if anything.

Then the ECMWF has another one right after that, so this could become a clipper type pattern.  Basic northwest flow, cold in the East, ridging out west.

Of more importance that I’m watching is the chance that a system could eventually undercut the western ridge and slide east across the Deep South.  It’s too early to say what temps will look like then, but there is the chance this happens, as a weak Split Flow has shown up in the extended range on GFS and has now worked under the 192 truncation hour….so I’ll keep on watching for that possibility.

 

 

26
Jan

Warming Up, Strong Front Wednesday…Then Colder

We’ll see improving weather over the next 4 days across the Southeast, with gradual warming, and then marked warming just ahead of the cold front Tuesday and into Wednesday. The front will begin to tap the Gulf on early Wednesday and spread across the entire Eastern US,and will drop a good line of showers (maybe a few rumbles of thunder) before exiting up the East Coast early Thursday.  Here’s the GFS rainfall progs for the next event, which looks reasonable.  A very good rain event for many.

 

GFStotalprecip120

This storm will really deepen in eastern Canada, going down into the 930 mb range, which is extremely deep even for Winter Storms in Canada.  This will feed the PV in Canada and help increase the cold air suppy their…it’s been quite a hard Winter in Canada this year, with severe cold and lots of snow.  Unfortunately for snow lovers in the East, the track of the storms still hasn’t helped develop strong Greenland ridging yet, and a cold Greenland usually means only transient cold in the Eastern US..and so far, that’s what keeps happening. We have strong cold fronts move through, but temps quickly rebound as the cold increases in eastern Canada and Greenland.  Without a negative NAO pattern, that’s what happens.

There could be a clipper type system in a week to watch for some areas, as the western ridge holds on through that period, and there will be some energy (not yet seen too well) topping the ridge and dropping into the East. More on that once it becomes clearer.  Also, on thing to note is how the cold continues to miss eastern Texas and the Gulf Region.  So far the cold air hasn’t been penetrating too far south, and there’s been some strong temp gradients from Jackson MS to Jackson TN for example..the further north you go, the more quickly temps fall.

Another look at the strong front on Wednesday:

GFS108strongfront

There’s hardly any chance at the southwest system closing off. Earlier the ECMWF and GFS hinted it could but now it looks to phase into just a  single longwave moving west to east. Usually big longwaves like this are great precip makers.  There’s still a slight chance the models are missing the southern part of the trough, and it could still cut off (like the big snowstorm ECMWF) but with all models trending the other way, its very unlikely.

 

GFS96Not much reason to look into beyond 10 days right now on the operationals since they will change a lot…February looks very active though. The western ridge will come and go, and shows signs of bouncing back and forth, and several systems will come across the Country during this period.  With so much cold in Canada coming down from time to time, we’re certainly not done with Winter Storms yet.  As long as we don’t head back into the West Trough/East Ridge regime that dominated Dec and early Jan, then I think we’ll see one or two good potential Winter storms showing up in February.  But also I don’t see cold air sustained in the East.

 

24
Jan

Friday Won’t Be A Big Event…Meager QPF

The models continue to trend less and less for anythng significant on this warm advection event.  The NAM is the most significant, and the GFS is the least, so I’d take a blend, but lean toward GFS on the precip amounts and the 850 profile.

This means light snow quickly changes to light sleet then quickly to light freezing rain in middle Tenn early Friday and spreads to eastern TN and sw VA by noon.  All of this will switch to light freezing rain (plain rain in middle TN) by shortly after this begins, as the GFS brings surface temps to just above freezing except in northeast TN and sw VA.  That region is the highest impact potential on this system where the surface temps are cold enough for most of the event, and the most moisture occurs.  There could be 1 to 3″ of snow and sleet there, topped off by some minor glazing.

For western NC, Upstate SC and all of Virginia….light snow north of I-40 quickly goes to sleet, then quickly to light freezing drizzle.  But for Upstate to lower NC and northern GA the amounts are practically nothing and there is a virga hole showing up rapidly. It wouldn’t surprise me to see absolutely nothing fall to the ground in parts of the foothills and upstate Region of SC to western NC just east of the Apps.  The western VA region also quickly shows a virga downslope taking over, but that region near the NC/VA border stands the best shot at a few hours of precip, but from southwest VA through all of NC, it quickly goes from snow to sleet to ZR (or freezing drizzle).  Temps stay below freezing from the northern Upstate through central and western NC to central VA for the event, so what little bit falls will stick.  There just won’t be much of anything.

The NAM and GFS both show the lee areas with a hole opening up quickly after the initial burst.  Keep in mind these reflectivity simulations don’t account for the dry air on the initial burst, so that means it’s possible that first burst goes mostly into virga and dry air as well, so by the time there is a second burst of precip, already the downslope is kicking in.  So it’s possible nothing falls in northwest VA and western to central VA as well.  Such is life living east of the mountains with a westerly flow and not much moisture (and the dewpoints are extremely low).

namdownslopecombined

The GFS total snowfall: Once again, it’s not much really anywhere, but West VA, southwest VA and maybe ne TN region has the best shot at snow and sleet accums.

GFSsnowfall

NAM has more snowfall in southwest VA and ne TN than GFS , but it too has more in West VA and northern VA, MD regions and even there it’s probably only a couple inches at best.

namsnowfallA look at the NAM and GFS total QPF..trace amounts most of the piedmont of NC, VA and SC, a little more in northern Ala, TN and northern GA possibly.

newnam

newgfs

 

Bottom line is this is a small event overall, a few spots will get a couple inches of snow (mostly southwest VA to possibly ne TN and into West VA.  For NC, SC and northern GA, brief chance of sleet then freezing drizzle, which will stick and make things slippery since temps are cold enough, but amounts are extremely light, and some areas will remain totally dry in the Lee.  The coastal sections of VA and NC could have a burst of sleet and ZR and the moisture may be more meaningful there but the temps will rise toward the end and it could be rain for the last couple of hours.

 

24
Jan

Windy/ Cold Carolinas/VA Today…Models Trending Lighter With Precip

Strong cold advection behind the departing MidAtlantic clipper will usher in strong high pressure and some gusty winds today, and parts of eastern VA and NC will experience really cold temps and high winds today, with a strong pressure gradient showing up in VA , NC, SC region today as the Arctic High builds in.  Some wind advisories are being issued.

 

I’m not at all suprised that this is trending lighter and lighter east of the Apps (and a little lighter in north Ala, GA and much of TN) .  For areas that would stand to get ice, thats a  good thing.    Still, only a tenth of QPF in ice form is very slippery and dangerous to drive on, but I think overall this will be more a nuisance event, not a Winter Storm Warning type of event for most.

The models have eased up on amounts in northern AL, GA and much of lower TN, as well as the Upstate SC, lower piedmont NC and central and western Virginia in the lee of the Apps.  This happens frequently as you know if you live in these areas with westerly or northwest flow systems.  And this system is so fast moving and just doesn’t tap much moisture, plus there is going to be extremely low dewpoints in place for the Carolinas and Virginia to start, so the initial hours of precip will likely be virga.  And what does fall, will probably be light.  I still think northern NC and points north are mostly snow, and central to southern NC and points south will be sleet to freezing drizzle, but just not much of it.  The maximum snowfall anywhere probably won’t be more than 1 to 2″ , except some higher mtns of NE TN and into the Apps of West VA where maybe 3 to 4″  of accumulation, as thats where there is more moisture and no downsloping to eradicate precip downwind of the Apps.

virga

 

NAM and GFS both show trace to a tenth of total QPF in some areas downwind the Apps, (NAM still overdone )

nam48totals

GFS:

GFSnewtotals

Current Advisories

advisoriesnow

 

23
Jan

18z Runs…About the Same

Nothing new so far..this will be a watching and waiting to see exactly what happens and for which areas. All the areas I outlined earlier are under the gun for Winter Weather, and for some of these areas (northern GA, Upstate SC, lower NC)  it has been over 2 years now since there has been any Winter Weather.  For northern NC, and much of VA this will be the 3rd event in 2 years.

One area I am especially concerned about on the precip is the Tenn. Valley, from northern Alabama, middle to eastern Tennessee and northern quarter of Georgia.  The models all have the most moisture here, and there are no mountains to block the moisture or have any downslope issues.  The question here is how quickly temps at the surface will go above freezing.

So far, northern Georgia, and much of eastern TN is in a WW Watch…but I think I’d add northeast Alabama , maybe all of northern Alabama in one as well, since all models have very significant amounts of glazing there.  Same for middle Tennessee.  The models start this event very early Friday morning and the amounts grow quickly, so the moisture coming down could easily fall before the surface temps rise above freezing.  Eventually, most of this region will go above freezing, but there is a good chance by then there will be a moderate Winter Storm to have hit the region, with up to 1/2″ of sleet and freezing rain.   Some areas of the Northern GA mountains could experience up to .75″ of just mostly freezing rain, which would actually be a devastating Ice Storm.  This continues to be a tricky situation and it’s best to stay prepared, and of all the place to forecast precip on this storm, this region looks to be a no-brainer—-its going to precipitate.  And likely most of which will be ICE.  Further east of the Apps, we’re still watching for where the most precip falls and the chances of mostly virga in the very dry air…so that area has the sustained low temps, but questionable moisture. It’s always tough in the Southeast forecasting Winter Storms.

TNvalleyconcerned

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