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Archive for May 2012

31
May

Severe Weather In Some Form (QLSC or Twisters) On The Way!

Lots to go over Thursday afternoon. First, the usual caveats to preface a potential big event. Factors like where the best heating occurs, best CAPE and types, worked over environments and interactions with meso- features all conspire and work together to deliver the ultimate final outcome on who exactly gets what. So I’ve pinpointed as much as possible, and following all the latest data from SPC, obs, etc, and come up with an outlook for this afternoon and tonight.

The incoming upper trough is very stout, and leading to a strong low pressure that models continue to deepen. By 6 AM Friday, the RUC (or RAP) has a strong vort about to round the bend in Kentucky, and will work with the secondary s/w axis in the Gulf States to form a pretty negative tilt trough in Eastern Tennessee Valley.  By then, I think a solid line of severe could have formed in the region below, and hold for most of the night. So severe is likely to get going in parts of Ill, Ind, Ohio and Ky, down through mid Tenn and into Alabama and Mississippi as Thursday and Thursday night wears on.

Latest RUC/RAP has a strong vort rounding the bend of the major trough, and has very strong divergence over the Ohio Valley to Apps of East Tennessee and north Georgia by 6 AM Friday.

NAM has a developing negative tilt to the trough as it approaches the East as well. Strong height falls, divergence, cold aloft and strong instability with a well developed severe line (or broken line) should be ongoing roughly for Ohio, Kentucky, Tennessee, Alabama and spreading into Georgia and the Carolinas to West Virginia, eventually into the piedmont of Virginia during prime heating. There’s a question on timing as forecasting moving lines of severe is difficult, and a lot of factors will determine how widespread and the overall strength of the outbreak could be on Friday.  But Friday could be very severe in the Eastern Ohio Valley, Carolinas and Midatlantic during the day and reaching northern Virginia through the Tri State region later Friday as strong dynamics come into play with this strong (anomalous) shortwave trough.

WxSouth Map Call for Thursday into 6 AM Friday.

31
May

Strong Storm Development West of Apps Thursday, East of Apps Friday

The system I posted about May 24 is developing nicely and already severe is developing from Texas to Midwest. Here’s the map I posted a week ago, and below is current Water Vapor image:

SPC is highlighting the Carolinas to  Midatlantic Friday with some high probablistic severe chances.  Keep an eye on future updates…I think severe watch boxes will begin to be issued soon and this could end up a pretty significant event. Beyond this, a nice weekend, but already signs of an active week next week from Ohio Valley into part of the Southeast.

The medium range (next week) looks like it will get active too. Very unusual flow shaping up, after we get past the Thur/Fri deep trough and severe then a nice weekend but nw flow MCC events next week usually occur in this type of flow. Rex Block shaping up on both major globals. All it takes is weak upper air disturbances to get the ball rolling then if conditions are right the storms evolve into these complexes….so far, looks to start Sunday night or Monday, and there may be more than one that rolls from Ohio Valley through the Apps and part of Southeast (usually a couple states wide).  With all the blocking still going on, we won’t be seeing major long lasting heat wave for a while. Current airmass in Midwest is coming our way this weekend for a nice, cooler change, some record lows might be possible a few areas since the Dakotas and Lakes are nearly 20 to 30 deg. below normal. (GFS ECMWF are at odds for next week to some degree) but both have a Rex Block.  Currently I think ECMWF is overdone by day 10 with it’s unusual flow.

30
May

Next Big Weather Event (Severe!), More Rains Southeast, Then Rex Block

Beryl’s rains were very beneficial to southern GA and northern Florida, as well as (soon will be) for SC and NC into VA.  Up to 10″ is shown in rain totals across north FL and south GA. Unfortunately a very tight cutoff was observed west of Macon GA.

Next up is the big event I mentioned 5 days ago.  The GFS is holding on to the idea of a deeper than normal trough arriving through the Plains and Mid South beginning Thursday night.  ECMWF has got much deeper and slower with it recently.  Now, HPC is noticing it, and mentioned it on Tuesday discussion:

“ANOMALIES SHOW A QUASI-STATIONARY BLOCKING REGIME OVER THE
N-CENTRAL ATLANTIC WITH OBSERVED AND FORECAST NAO INDICES
APPROACHING MINUS 3 WHICH IS RARE.

By Thursday night, a strong upper low will begin to form in the Missouri region and be attended by a trailing vort max that sweeps through the MidSouth, really affecting the Gulf states to the Ohio Valley with a frontal system and convection. The SPC is already highlighting this area now with moderate risk, and slight risk. Usually, when a deep trough like this (notice 546 thickness!) comes through the Ohio and Tenn Valley in early June this is a severe weather maker, as well as a general rain maker. There is pretty strong divergence and negative tilt over the heart of the Southeast Thursday night and into Friday for the Apps and Piedmont, so convection should have no problem surviving the night and continuing unabated through its’ lifetime approach going to the East Coast by Friday night. Be on the lookout for Tornado Watches anywhere from eastern Ok/TX to Ill, In, Ky, and all points south and east beginning later Thursday and into Friday. This could be a very significant severe weather system. Heights will be crashing well below normal for early June standards, so instability will be great, combined with other supporting factors. Very large hail could be observed in some storms.

Here at WxSouth, I like to keep my readers abreast of what lies beyond..so already I’m looking at the pattern just beyond this event. There’s good agreement that the East Coast trough is here to stay a while. Strong blocking will lead to a negative anomaly in the Northeast, so that will setup a northwest flow regime, via Rex Block. (see image below)

In Summer, NW flow regimes aren’t quite the same as they are in Winter (dry). If the models are right in the flow, and there’s pretty good agreement, then what happens next will be a cooler, drier airmass but also the chance that MCC systems begin to generate by Sunday night in the central Plains or Midwest, and take a track through the Tenn Valley to MidAtlantic Later on next week, the constantly redeveloping pattern of MCC’s in the Plains or Midwest will possibly affect more of the Southeast , at different times and trajectories. The basic emphasis is that next week looks conducive to atleast one, if not several, MCC developments that sweep across many states, all the while the Southeast and East Coast is in a general cooler environment. Its a big switch from last June when a heat wave was in progress and a dry hot ridge ruled most of the area. It could be that this is the first time a long time that Summer Temperatures are closer to normal, rather than being extremely above normal.

Speaking of last year and this year, here’s a look at a comparison. Last year featured 850 temps +21 roughly in Ky, Tn…this weekend brings down+3 to +6…VAST difference.

27
May

Beryl To Bring Rain To Ga, Fl, Carolinas…Then Extreme Supressed Flow

Quite an exciting pattern, especially compared to the previous 3 Summers.  The second named storm (Beryl) has formed and will make landfall between JAX and the GA coast, near the GA/FL border late Sunday. It’s not very well developed with most convection concentrated on the east side, but clearly some convection will be entering southern and central SC coast, down through the GA coast and north Florida later on today. The models all stall this system in southwest Ga, before making a turn northeast toward southern SC again later Tuesday.

Rainfall totals will be very decent in north Florida and much of central and southern half of GA and southeastern third of SC.  But showers will rotate into much of the Carolinas, starting late Sunday and especially Monday and again Tuesday. By Tuesday evening, a front will be impinging on the Southeast, so some convergence should create much more numerous storms in most of the Southeast.  The remnants of Beryl could linger a while in GA/southern SC through Wednesday and the total rains could be up near 5″ some areas, and perhaps several inches near the Apps as well, with lower amounts in between.

One of the most impressive 5H looks this forecaster has ever seen in late May/June is showing up. So far, only WXSOUTH is talking about it.   For a few days the GFS has been the most adamant about it, now ECMWF also joins it whole-heartedly beginning mid to late week.   A double block, combined with very strong negative anomaly off Newfoundland, will force a deeply supressed flow in the central and eastern states beginning Wednesday and culminate late this week (atleast “peak” on Fri/Sat)

Again, I’ve said several times last couple of months  that all the blocking and slightly neg. NAO pattern , with baggy troughs in the Tenn Valley to Carolinas lately , had this occurred in Winter, it would be an Extreme Winter Pattern, but being in this time of year the net effects aren’t nearly as pronounced.

Still, what’s coming up is very unusual.  A strong low pressure will begin to get organized in the lower Mississippi Valley and develop rapidly through the Tenn. Valley and Southern Apps/Carolinas.  The system will deepen very rapidly for a June storm, similar to what happens in Cold Season Cyclogenesis.  The GFS has the low travelling up the East Coast in Nor’easter fashion, complete with cold advection in its wake, strong warm advection, and almost complete “bombogenesis”…so there will be very notable weather changes.

The system will feature strong height falls Thursday across the Deep South, so rain and thunderstorms will be in the developing stages all through the night, not on the decrease after dark, which is typical of Summer storms.  A strong 850 low develops, and aloft there will be very strong diffluence, so the system is loaded with energy and precip-making ability.  I think severe will come from this under its track, along with tornadoes, hail, high winds and heavy rains.  Not every where, but widespread enough to be very noteworthy…a VERY Impressive Summer system.

If the blocking and neg. NAO type of regime continues to repeat, the Southeast won’t have nearly as hot a Summer as the previous several years.

Current Double Blocking, per ECMWF:

24
May

Interesting Weather Pattern Shaping Up…

Don’t hear that much for May and early June. But if you’re a weather enthusiast, that’s what’s coming up. This will make about 3 times in a couple of months that a hardcore blocking pattern sets up in Canada and Greenland.  I hate to keep saying “If this was only Winter time”…but I have to admit how impressive the 500 mb pattern truly is for the Southeast in particular. This time, the GFS and to some degree ECMWF, have a very impressive Greenland block, and works in tandem at one point with a very strong northwest US block, so the result is low heights and a deep trough in the Deep South near day 7 through 10.

This type of flow (which GFS has been excelling at for over a year now) would carve out a rare early June cold season type of cyclogenesis.  The model responds with a Rockies low that moves into the Plains and then through the Deep South and up the East Coast later on…something like what happens in a Winter Suppressed Flow.  The net result would be widespread rain, severe weather since heights are low and temps aloft are colder than normal, and a good temperature clash or thermal gradient to work on. Unfortunately, large hail would be a guarantee in some cells with a system like that. Make sure your insurance is up to date.

Here’s a look at the Northern Hemisphere height anomalies during this time.

Before we get there though, there’s more to watch. There is a low developing in the Bahamas that will come to a stall offshore the Southeast Coast around Sunday.  The building heat ridge to the west will develop on top of this system and force it to work back southwest, just like “Alberto” did, and possibly affect coastal SC, GA and the Florida peninsula near Jacksonville.  There’s even the chance it continues to work west into the Gulf and gets pulled north into the Southeast next week ahead of an incoming cold front. I’ll monitor this and we’ll talk about it’s track once it becomes clearer, but either way, more rain and another front is coming through the Southeast early next week, and that gets the pattern started to wetter and maybe a little cooler. Probably mostly wetter though.

The heat and humidity will steal the headlines this weekend, especially west of the Appalachians. Temperatures in the 90s and high humidity will lead to Heat Index values near 100 in parts of the Tennessee Valley. It appears there will be too much northerly flow around the ridge east of the mountain chain to really crank up the heat. In fact onshore flow for the Carolinas Beaches down to northern Florida each day could be the impetus for strong seabreeze storms. Any storms that form in the Piedmont or Mountains this weekend will be slow movers and be capable of dropping a large amount of rain, since usually in heat dome type of situations, cells that form are far apart but require more height to bust the cap in place. These are the types of thunderstorm cells that produce the biggest rains of all if you go back and look at old Co-op weather records county by county. They will be few and far between however.

21
May

Another Cutoff Low–Then Big Heat/Humidity

Yet another cutoff will form in western North Carolina on Tuesday.  The system is diving now west of the mountains, so Monday and early Tuesday the rain showers and storms in the Tenn. Valley will translate to the Apps and the Piedmont by Tuesday afternoon.  I think for the Carolinas and Virginia, this could end up being another wet week.  Also parts of Georgia and Florida will have a good coverage by Tuesday afternoon.

All global models build a 588 ridge over the Tenn. Valley by Friday and expand it to cover a lot of the East and Ohio Valley by the weekend.   Directly under the ridge is where the heat and humidity will be the most pronounced and that appears to be the Tennessee Valley and much of Kentucky, where Heat Indices could top 100 pretty easily on a couple of day. 850 temps soar to +21 in eastern Kentucky, that combined with the location of the ridge and the high heights will mean temps in the upper 90s and apparent temps over 100.

An interesting aspect of the late week and holiday weekend is the offshore eastern trough. Right along the east coast and especially toward the Carolinas, there could be strong northerly flow at 500, so moisture usually gets stalled along the eastern Seaboard and piedmont in a situation like this. Therefore, I think afternoon thunderstorms will be a good bet, especially in the Apps themselves, and into the piedmont. Anytime there is a ridge over Kentucky, storms on the east side of a ridge can get viciously strong and be mega rain dumpers, so I think for some counties that get lucky enough to have a storm over the weekend, there would be big ones.  Any area is game from north central Ga through Virginia and Maryland this weekend for the afternoon Cap-breakers, but otherwise, hot and muggy will be the rule.

The good news is already a new front is showing up for the following week, so this is NOT the beginning of unrelenting heat in the Southeast.  More showers and storms, and cooler weather is within sight.

 

 

20
May

First Tropical Storm, First Heat Wave of 2012

The upper low and baggy trough over the East Coast this weekend spawned a weak tropical storm, and as WxSouth mentioned a few days ago, there was a big question mark on how the east coast trough or any low that formed would track. Its not a very good environment for this to strengthen, since there are three circulation centers relatively close together. But it appears these three centers will graze the east coast the next day or two. So from north Florida, eastern Ga to eastern Carolinas that area could be affected by a weak Alberto, and for eastern Virginia to Maryland, a seperate low may retrograde over the next couple of days and bring showers.

A new front will drop down to the Tennessee Valley and be close enough to generate some thunderstorms in the Valley to the Apps Monday afternoon, then become more widespread in northern Ga through the Carolinas and Virginia by Tuesday evening.

After this, the attention goes to what the ECMWF and GFS are cooking up aloft by late next week and the Holiday Weekend. Our first widespread heatwave.  A deep trough will settle into the west and again in the far Northeast, so that means a major closed high aloft will form somewhere over the Southeast.  Closed highs at 5H mean heat waves usually in the warm season, and the models respond with actual surface temperatures near 100 in Kansas on Friday and then in the middle to upper 90′s in the Southeast by next weekend. It will be hard to actually touch 100 in the Southeast, since ground moisture is very high under the location of the ridge and humidity levels will be very high as well (Dry air can warm much more). But, the heat index will be near 100 and pass 100 in some areas, thanks to the very high dewpoints in the 70′s.  Downslope flow in SC and southern NC will first occur for Columbia and Fayetteville Friday and Saturday, so Heat Indices will be near 100 there, and then spread west with the high humidity to produce apparent temps near or over 100 many areas of the Tenn. Valley lower elevations by the Weekend.  There’s a chance that negative NAO and a northeast trough could make this a short lived event for the Carolinas and Virginia, and speaking of the NAO, it appears there could be another decent sized eastern trough shortly after this period, meaning more rain and a return to near normal temperatures. But first, get set to sweat!

18
May

Upper Low Carolina Coast, Next System Mon/Tue. First Heat Wave Soon?

The pesky upper low that brought the rain and storms, especially to the Carolinas and Georgia will slowly pull to the coast this weekend.  Most models keep it along the coast , as opposed to working back west which is a slight possibility.  This will keep rain chances in the forecast for the eastern half of the Carolinas and Virginia, with a few showers on the western edge toward the Apps and into central Ga this weekend, before pulling totally out to sea.

Other than that, temperatures will be near normal, and even below normal in parts of the piedmont early mornings thanks to a damming type of high around the low, with northeast surface winds.

The next system to watch will approach from the Midwest on Monday afternoon for the Tennessee Valley. Showers and storms will accompany this front by Monday night, and cover more of the Southeast by Tuesday afternoon.  The front will intercept a deep southerly flow around a Bermuda high, so temperatures and dewpoints are going to go up dramatically early next week.

GFS and ECMWF are developing a deep western trough, eastern ridge couplet, slated to begin in about a week and maximize by day 10.  It’s still way too early to bank on this agreement, but if it happens, this will be the first real Summer type of heat and humidity.  The GFS develops a 594 ridge briefly in the heart of the Southeast.  This particular setup still looks like a ton of low level humidity, but since capping would be present, afternoon storms would be limited. It appears once the humidity and Gulf inflow arrives next week, it could be around a while.

 

15
May

Another Active Day Georgia/Carolinas/Florida/Va and Texas

After a very active day Monday, we’re in store for another today. There are two weak upper lows, one in Texas and one axis near the Appalachians, both are very slow moving. Eventually they both will continue to weaken but it’s not clear whether or not this baggy trough will fill. The models keep some sort of weak trough in place in the Southeast most of the weak, and eventually close off yet another weak upper low near the Ga or Fl. coast by Friday or Saturday. This could back inland if a ridge builds to it’s north, so I don’t think the Southeast is going to get into a totally dry pattern any time soon.  The wettest areas looks like in and near the Appalachian chain into northwest NC, and again in Florida.  The rains in Texas should slide east toward the Gulf coast the next several days.

Again today, if there is enough sunshine to break through by afternoon in Georgia and parts of the Carolinas to Virginia, the mid levels could become dry enough to support quick developing updrafts. Without the drying action of the sun, then the towers won’t be allowed to develop fully, so there’s a lot that depends on breaks in the clouds. Still, the PWAT is near 1.5 to 2″ along the Gulf and into Central Ga, and the eastern Carolinas, and with cyclonic flow, any showers will be slow moving and generally move southwest to northeast.  Any heavy rains again in the foothills today would lead to more flooding problems, on top of the 3″ to 5″ that fell yesterday in a large region.

There’s also a chance the baggy trough or cutoff late week or weekend could sit a while near the coast, pulling in copious rains for the coastals Carolinas and especially into Georgia and possibly even Alabama and part of Tennessee. Florida looks to remain wet for a while.

If you’re interested in when things dry out and turn more Summer like, the long range has hints of a trough in the east continuing. As WxSouth predicted in late April, the month of May is turning out to be quite wet and cooler (relative to the major heat lately), and so far there’s no signs of a big warm up in the Southeast yet.

11
May

Strong System Weakens Slowly Crossing South…Some Areas Copious Rains

A few days ago the models didn’t explicitly show this system being as strong as it is, and several AFD’s, including national outlooks, really tended to weaken this strong comma shaped cutoff as it progressed through the Southeast. Now offices are struggling to keep up with flood watches and hydro outlooks across Texas, Louisiana and soon will be in Tennessee and Alabama.  Wxsouth mentioned a few things a while back to the opposite, hedging our bets this would be a very significant system.  I hate to mention this but some outlooks even used the ECMWF to tell of a heat wave enveloping the Southeast from Texas to Virginia by later next week, and nothing could be further from the truth. I read a lot forecasters and national organizations, etc, taking models at face value most of the time.  “Such and such guidance indicates this or that…and the models show this”.  Truth is, it’s always up to the forecaster to make the call and use a variety of ways to support a forecast, not just MOS guidance or any guidance. And to know when a model is bogus.  Once again, synoptics and pattern recognition are absolutely crucial to this for this Synoptician…always has been and always will be, despite great advances in modeling. You can use those great tools of synoptics to actually predict well ahead of time when the models are going to be wrong on something and to know when the models will eventually fall in line with your thoughts. I’ve seen it happen most of my forecasting career.  Aren’t you glad you’re a WxSouth subscriber  :-)

The GFS has even strengthened the system’s structure a little more, holding it together much longer, but holds on to the basic speed and path. This will be a copious rain maker just ahead of the comma shaped spin, as it pulls in slow moving moisture and spreads it across the mid South. Tennessee and Alabama really lies in the heart of the path and dynamics, so I still think several inches of rain could occur in a large area, atleast 2″ and possibly much more in spots that get trained on.  Here’s a look at the GFS moisture fields and geopotential heights as the system slowly marches east from Saturday through Monday.

 

Heavy rain will pull north in a north-south band through Alabama into Tennessee and Kentucky, before lurching northeast. Unfortunately , the heaviest stuff once again may bypass central to South Georgia and central to eastern Carolinas atleast early on (but there’s signs a cutoff could re-develop eastern NC later on).  The lions share will drop along and west of the Apps and through the heart of the Tennessee Valley.  The good news for areas that need rain in the Carolinas and Georgia, is that even though it will take a while to get the solid shield to arrive, once it does, there will be no really quick end to it, like in previous rain events.  That’s thanks to how the Southern Plains system comes in and “tugs” on this one, instead of totally pushing it out.  This means a general weakness in the height field could exist most of the weak somewhere in the Deep South or Gulf coast area. It’s something to watch.  And the GFS wants to create a weak cutoff along the east coast somewhere near coastal NC later in the week.

All in all, every where in the green shading should be in line for atleast some measurable rain and the darker regions indicate my highest potential for the most rain fall.  The southern Apps could also have the benefit of persistent upslope southeast flow, so the usual spots in extreme northwest SC, southwest NC and northeast GA could be a secondary max of rain.  Have a great Mother’s Day despite the rain!

 

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