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29
Jun

On The Brink Of A History-Making Airmass Today

As I write this morning, the sun is just rising and the mountain peaks of Virginia, Tennessee and North Carolina are just getting into a truely historic HOT airmass, sending temperatures into the middle 80’s….at Dawn !

The RUC model captures this hot airmass well at 850 and by 5 PM it has a few pockets of +30 degrees in TN, SC and GA.  Today is the day that will set some new All-Time Heat Records in the Southeast.  The heat ridge in the Plains has now rolled to the Southern Appalachians and as the afternoon sun works on the airmass, a very unique phenomenon called a “heat burst” will develop in the lee of the Mountain Chain.  The bubble of hot air will roll down the front side of the ridge, across the mountain chain and go through a quick process of deep mixing and extreme compression.  This is common in the Rockies, but extremely rare in the eastern states. For western and central parts of Virginia, NC, SC and north and east Georgia, this heat burst is going to be like opening an oven door this afternoon and evening. Hot winds will scream down the mountain and sending scorching, searing winds across the region, enough so that 105 degrees could be very common in places like Atlanta, Athens, Spartanburg, Charlotte, Greensboro and Danville. Some areas could even surpass the 105 mark. We’re literally in unchartered waters so to speak…I’ve never seen this type of airmass progged for any part of the Southeast…and can’t find anything close to it in 125 years of records.

Even though the airmass will dry out in the lee of the mountains and dewpoints will crash into the 50s and possibly even 40’s, with relative humidity in the teens and 20 percentile, the actual temperatures will soar into triple digits, while in the eastern sections of Va, NC and SC, the humidity will pool much higher, leading to some extreme heat index values there.  It’s a tale of “dry heat” or “tropical heat” both are deadly.

Stay cool!

All-Time Records:

RUC valid 6 PM Friday June 29 2012:

28
Jun

Shades of August 2007

The upcoming heat wave looks similar to August 8-12 , 2007 when Charlotte hit it’s all time record of 104. The GFS has +25 to +28 at 850 coming to the western and central Carolinas and north Georgia Friday afternoon. The numbers in the northern Upstate to western NC are the highest I’ve ever seen, and easily surpass the +23 to +25 of August 2007, but in this case the 5H ridge isn’t as pronounced or long lived, or as deep, so this could just be a tradeoff. The numbers may shake out to be about the same, but one could use the argument that 2007 had the region in an extensive, unprecedented drought, as many areas like Greer and surrounding areas had the driest year on record.  So in the end, its a tradeoff, but only time will tell if the higher 850 temps translate to overwhelming the slightly wetter ground this time (still a drought).

Either way, it’s going to be extremely hot.  In the lee of the Apps, the models have northwest and westerly winds which will mean the low levels will mix out dewpoints into the upper 50s and near 60 (occasionally the models underdo the mixing, and dewpoints fall in to the 40’s!).  Further east toward the eastern Carolinas and southeastern third of Virginia, the dewpoints will be much higher and heat indices will be near 110 and even 115.

This is going to be long lasting heat wave, with strong ridging holding firm in the Southeast, but gradually loosening it’s grip as the ridge retrogrades by the early or middle next week. This may allow thunderstorms and a front to approach the eastern states, but the western sides of the Mountains, in the Tennessee Valley to the Plains are going to continue to bake in nearly 100 or above temps for about a week.

 

The hottest 850 temps on record are predicted for Upstate SC, Northeast GA and southwest NC Friday afternoon.

27
Jun

SEVERE HEAT WAVE ABOUT TO HIT ENTIRE SOUTHEAST

The only escape from this impending heat wave will the be the high mountains of West Virginia, VA and NC, TN, and again the western peninsula of Florida and the immediate Gulf coast region. Otherwise, this one could eclipse both August 2006 and August 2007 in many areas.

Here’s a look at the GFS model, which is about the best model for portraying 850 temps and surface predictions in the last few years (especially during heat and cold events).

The model shows a 594 ridge over the Southern Apps, and widespread 500-1000mb thickness values of 582 very widespread (very unusual to see it cover this much ground) in addition to 850 temps at around +24 to +26 degrees…again, covering a large chunk of the Tennessee Valley east to the Carolinas and most of Virginia and northern half of Georgia.  The location of the closed ridge in this area is the prime spot for sending scorching downslope flow into the heart of the Carolinas, where the models all respond with record breaking 100 to 105 surface temps.  I think one of the reasons the GFS and ECMWF are so intense this time with the heat wave is the location of Debby’s remnants offshore and the fact that extremely strong mixing will occur in tandem with the strong downslope and subsidence, in other words, we have a very unique setup at the surface and aloft….one that is poised to be almost exquisitely designed to deliver the most heat possible.

On forecasting heat waves, there are a few things that can prevent reaching numbers like 105 on a widespread basis…such as the location of any upstream cirrus debris (and the chance at any localized mountain convection breaking the cap). Also, local soil conditions antecedent can eat away at the first couple of days of strong heat, turning the ground level heat immediately into transpiration and low level humidity.  Parts of Virginia and North Carolina are especially prone to see the first day or two of the heat wave turn the energy of the heat into low level humidity rather than intense heat, but it’s iffy on a big scale…some drier areas will still be able to achieve 100 or 102 Friday and even more areas will hit over 100 by Saturday.

However by Sunday, there are signs of MCC debris working south quickly from the Ohio Valley around the ridge. So even with +24 degree at 850 still in place in the Carolinas by that time, it could actually be hotter in the Tennessee Valley because of more sun there, and a  thin cirrus shield dropping south and spreading a thin canopy over Virginia, West Va and maybe NC as well late Sunday, but again thats just way too far out to know for sure. The more sun, the more heat. The less sun, the less heat. As usual there are a lot of small factors that have big impacts on just how hot any one city can get. Another thing that stands out is the mixing of the dewpoints east of the mountains in Va, NC, SC and northeast Georgia. The GFS shows this well, and has absolutely nailed dewpoints in every heat wave I’ve studied and predicted since 2006, and synoptically, it makes sense.  However once you get to the Fall Line roughly in the eastern third of NC, SC and VA, the dewpoints suddenly increase to mid 60s and low 70s just east of there. West of there, in Charlotte and Hickory and Winston Salem to Roanoke, the dewpoints should mix out daily into the upper 50’s atleast Friday and Saturday when the surface winds are west and northwest. However, that also aids the heat formation through compressional heating at the surface, so while actual humidity may go down in the afternoons, actual numbers on your thermometer can get that much higher since dry air warms more quickly than moist air. It’s a trade off. In terms of apparent (feels like) temps , then the areas around Raleigh to Norfolk are in for some extreme heat indices of over 110, thanks to increased humidity several days.

Above image is 850 temps , and the arrows are surface winds.

 

25
Jun

Historic Flooding Likely Big Bend Region of Florida

While the NHC, and other forecasters across the Internet and Various National Markets, including the NWS went mostly with a western track on Debby (ECMWF version), only WxSouth went with more of a Florida likelihood. The battle was always a challenge as to which entity would steer the system 1) the Plains ridge, or 2) the Eastern trough.  The GFS was always steadfast in maintaing that the system would slowly approach the Florida panhandle and only slowly cross the peninsula midweek, with part of the system getting shredded and WxSouth saw this in the model, and other subtle cues.

It’s still nowhere near certain, and I’m very willing to cut a generous amount of slack for tropical forecasting, but the GFS has certainly proved the last 18 months more often than not, it has the hot hand, both in general, and now with 3 Tropical storms recently, the tropics as well.

The RUC and GFS has the system becoming nearly stalled in the big bend of Florida, and Monday brought severe flooding, with no end in sight. Unfortunately, there will be devastating video and pictures coming in very soon from several big counties in Florida.

Gulf, Franklin, Liberty, Leon and especially Wakulla Counties are all experiencing a nearly once in a lifetime flood.  See the image below to view the Doppler estimated totals since earlier Saturday. By midday Monday, only a small part of Wakulla Co. had 15″ of total rain, now the entire county and parts of surrounding counties are over 15″ of accumulated rains and WxSouth. com predicted 3 days ago that a major flood event would be likely for this region of Florida if the system didn’t get fully picked up by the Eastern Trough.

The worst could be yet to come as more rain continues to pile up thanks to a “perfect storm” of ingredients that is placing direct aim on this part of the Panhandle and extending up into extreme Southern Georgia.  The eastern trough will lay down a front so that will act as a convergence zone, and the circulation around a stalled “Debby” and in conjunction with the jutting landmass near Apalachicola all point to continuous rains re-developing, in never ending heavy bands.  The longer the storm doesn’t make a move (either east or west) the worse this flooding will become.  And if the system actually wobbles slightly south and west, the flooding will spread a little more west, possibly after spreading east, and the same areas will go through the entire process again.  Some parts of this area near the Big Bend may end up with 30″ or more of rain this week.  Already, more rain has fallen here than most of the entire year of 2007.

 

 

24
Jun

GFS Versus ECMWF…Both Show MAJOR HEAT WAVE LATE WEEK

If you’ve been following WxSouth forecasts you know I have a method to forecasting and I put model biases aside. However, I continue to see many Internet Forecasting Legends, National Outlets and many forecasters in general relying too heavily on the formerly great ECMWF model.  It’s too early to call victory on the GFS adamant forecast for Debby, since this is a particular hard call, but most models are now trending toward the GFS. ECMWF has had a few breaks on Debby but has mostly been Texas-bound. GFS has been mostly Florida-bound and now it looks like it will be correct. Either way, as a synoptic forecaster, I’m very willing to cut any model slack on errors, and be very gracious regarding Tropical systems because of a lot of complex factors. In this case, this has always been a factor of whether or not the Plains heat dome would do the steering, or the Eastern US trough would pick up the system. So far, GFS has had this system lolligagging in the northeast Gulf and slowly crossing the FL peninsula, then getting absorbed in the trough, and its hard to argue right now with that logic. But, the door is still open to the possibility it doesn’t get picked up, and actually would reverse course and hit coastal Texas or even Louisiana.

That said, it still doesn’t matter which model ends up being right, but the unrealistic heavy-duty levity that ECMWF holds is totally unfounded. GFS has led the way for 18 + months now in many, many ways, even when you consider the “verification charts” that show otherwise.  All the MCC events, the tornado outbreaks, the heat waves, the damming events, the drought regions, and many other local meso type of events, for the most part, the GFS has shown them over a week out, whereas looking at ECMWF model would leave you guessing.

Enough with which model is best (it doesn’t matter because different models perform better in certain patterns anyway).

Next up, after the deluge in northern Florida, and southern Ga from Debby, a quick cool down hits the East Coast. Subsidence and a cooler airmass, will take over about Tuesday and Wednesday, but quickly get replaced with a heat dome. The heat dome in the Plains is forecast to slide east and flatten between the Southern Plains to the Carolinas on Thursday, Friday, Saturday time frame.

The GFS actually shows +24 at 850 in a wide region on Friday, and actually goes to the rare +27 near Raleigh at one point.  The GFS has been deadly accurate, and long gone is the “cool bias”, so when this model reaches +27 at 850, I take quick note.  The heat wave is most definitely coming from Dallas to Richmond to Birmingham, and all points in between.  There’s always local effects that can affect the actual ground temps, among them are any high cirrus clouds, which sometimes develop well upstream, and local soil moisture readings, surface winds, and many other factors. For now, it appears this has the chance to spread 100 degree air across a HUGE region, and again east of the mountains when northwest and westerly surface diabatic heating gets involved, I won’t be surprised to see 105 to 107 degree actual temperatures occur between Raleigh, Fayetteville and Columbia by Friday or Saturday.

Once this heat wave is over, I’ll look down the road at what’s next. Until then, get ready for some serious, record breaking temperatures across a very large region of the Southeast states by late week.

 

23
Jun

“Debby”, Eastern Trough, Then First True Southeast HEAT WAVE

On Saturday, a stalled front in the Carolinas and northeast GA will be the focal point for afternoon storms to develop. Meanwhile, the Florida peninsula, especially central, western and southwest parts are in for a major rain event from the circulation in the Gulf (soon to be “tropical storm Debby”.

For a while now, the models have had this system developing, but are at odds as to where it goes. I don’t think it will reach Hurricane strength, but the NHC does give it good odds at becoming  a Tropical Storm within the next few days.  Then, the big question is where does it track? The steering currents are weak, but the GFS has always had the system crossing the Florida peninsula and then ending up offshore the Southeast, and has this feeling the effects of the Eastern trough early next week. If this happens, obviously a Texas hit won’t happen, as the ECMWF has been showing a while.  This is a tough call, as most Tropical systems in a weakly steered environment.  The reason this is particularly hard to forecast is because of how the ridge to the north of it (notice a 594 dm ridge in the Plains) and the proximity of the developing Northeast trough, both could tug on the system, and where it actually develops means everything as to which winds will end up being the primary driver. The ECMWF thinks the Plains ridge will be the main driver, and steer her to the west, under the ridge, and hitting Texas later next week. The GFS exerts more influence from the Eastern trough , and allows her to feel the influence and get nudged east across Florida, then out to sea.  Either option is very possible, but it’s hard to ignore the GFS’s superiority in major weather events (and the ECMWF model’s inconsistency ), so this forecaster is leaning more along the lines of a GFS solution.  However, it’s still very early, and probably no model has this right. It’s also possible Debby gets split, and a new circulation develops east of Florida early next week, and leaves part of the circulation back in the central Gulf, the GFS is hinting at that lately.  Either way, Florida is in for a major, drought-busting rain event, except the northern nw Panhandle region.

 

GFS forecast rain totals 120 hours:

 

A look at next Wednesday night on the GFS and ECMWF models.  Huge difference in tracks.  Which way Debby goes will be a function of either the trough in the East being the primary driver, or the heat ridge in the Plains being the main steering current.

After a brief cool down in the East Tuesday and Wednesday, the first Major Widespread Heat Wave of the Season is coming to the Southeast…all of us.  The GFS and ECMWF both have 850 temps reaching +24 and combined with a closed ridge aloft of 592 heights, that stretches quickly from the Plains to the Carolinas and Virginia beginning Thursday, this will be the makings of a true Furnace type of heatwave, equal to that of the previous couple of Summers when 100 degrees was very widespread.  The ECMWF has falsely showed +24 at 850 twice over the Carolinas earlier this Summer season,  but instead, a trough resulted. Now, GFS is finally also showing a heat wave, so the believability factor has gone up on this threat.  By late week, after a brief trough, the heat ridge in the Plains is forecast to lurch eastward quickly, so our first major heat wave is likely for atleast 2 to 3 days, before another bout of troughing comes back…but that’s getting too far out. I’ll touch on the changing pattern soon, one that offers a cool down, and better rain chances in Texas through the Southeast for July….stay tuned!

20
Jun

Heat Dome MidAtlantic to Be Short-Lived…Another Greenland Block. Tropics?

Lots to talk about again. The GFS began to hone in on yet another pretty strong Greenland block, working in tandem with western Canada ridging a few days ago, and today it’s really amplifying yet another Eastern US cool down. The ECMWF , which has had some major problems with consistency, is now joining it in it’s ensembles atleast.  It’s still just a little bit early to know for sure how deep the Eastern trough will get, but the operational 12z and the ensembles from GFS are pretty remarkable for late June.  That is one very impressive closed Southern Greenland ridge going up soon.  That always lays the groundwork downstream, especially if there is some western ridging, so the model shows 546 thickness coming all the way down into Ohio…pretty impressive!  Unfortunately, it still doesn’t look like much rain in the Southeast, however the sunshine state of Florida is going to get drenched thanks to the deep easterlies currently in place running around the periphery of the MidAtlantic heat dome.  That area could evolve into a low level circulation in the Gulf of Mexico and eventually it could get caught up into the Eastern trough, or just offshore, somehow interacting with it, but that is very much speculation right now. A lot could happen here with how the trough and any possible system in the tropics interacts, so I’ll update on that aspect as soon as more is really known.

One thing that is very likely is the GFS will likely score another major coup regarding the Blocking Episodes that have occurred so frequently in this negative NAO state since April.  Contrary to popular opinion online and among many old fashioned “stick in the mud” forecasting personalities, the truth is, the GFS has had the hot hand since just after the Christmas storm of 2010, for the most part.   It will be interesting to see how the roles reverse among the major two Global Models once another El Nino pattern gets established. Both models have had good and bad periods, but this is one of the most prolonged periods in which the model usual biases have been absent and represents a bit of an upheaval… we’ll have to wait and see if ECMWF has better luck with the next Nino pattern and if the GFS once again reverts back to ultra supressed or overdeveloped looks , like used to occur frequently.

In the graphics below the ECMWF isn’t quite as deep with the eastern trough, therefore allows more tropical potential development in the northeast Gulf which could affect part of the Southeast next week. GFS has a much more pronounced trough, which would quickly pick up anything that develops. It remains to be seen how any possible tropic. development interacts with the Eastern Trough.  A lot of options are possible here.

18
Jun

Not Much Rain Most of Southeast-Trough Returns late Month

The dry, cooler weather we’ve had lately (esp. Tenn Valley and points east) will subside as a minor ridge develops this week. This will bring the upper level temps upward, and correspondly, the surface will heat up as well, especially in the Tenn. Valley under the heart of the ridge. The flow at the surface will offer a chance of daily afternoon storms around the Apps and possibly parts of the piedmont of NC, VA and again around the Florida peninsula and southeast Texas, around the “edges of the ridge. But most areas are in a bit of a dry spell, but with increased levels of humidity.

At one point, the European model wanted to bring major heat east from the Rockies across the southern and central Plains to the MidSouth region to the Carolinas by late week, but has since backed off on the big heat. Both it and GFS have double blocking once again, showing up soon, and this blocking will result again in a pretty deep trough for the East.  Basically, the further west of the Apps you are, the warmer you’ll be and the further east and north, the cooler and more substantial the effects will be. But nobody looks to cash in on any major wetness too soon, since right now we’re at the northernmost trajectory of fronts, cool air and the westerlies can only dip so far south in June and July.  The one area of increased rain chances for a while could be Florida and coastal Texas, and briefly the Apps. region.

The double blocking signature that keeps returning (this event must make around 7 times since April) is nothing short of amazing, and I’ll say again, since it’s the late Spring and Summer months now, the effects are muted this far south. But, one of the effects has been periods of rain and drastically reduced temps, compared to previous Summers especially, and if this type of blocking occurs in the December through March time frame, it almost always delivers Winter type weather events to the Southeast and Mid-Atlantic, such as what happened the previous 3 Winters (minus Winter 11/12, when there was no blocking).  This certainly would have been very interesting to see play out, as it’s been many, many years or even decades since this type of pattern has really occurred so repeatedly.

Here’s a look at how the evolution of the next Eastern Trough occurs. There’s a ridge in the Rockies stretching north to western Canada, and again in Greenland. Sandwiched between is  an East Canada trough, that grows and sinks southward. This time it may not develop as deeply southward as the previous troughs, basically since we’re in the Summer months now. Occasionally, the western ridge may try to flatten out and sneak under the eastern trough briefly, giving us a taste of true Summer heat, but it seems to always be short lived, as the east Canada trough seems to amplify and push south repeatedly, thanks to all the blocking that keeps occurring.  Unfortunately, the lack of rain is going to be a problem soon, since many areas of the Southeast are still in a drought, especially Ga and SC and those areas look to remain mostly dry until the next phase change. Even with two fronts slated to pass through over the next week, the flow is very much northwesterly and mostly dry, unless an MCC can organize and right now the MCC pattern doesnt’ look to strong with this type of flow. However by early July, there are signs of a stalled front and deep southerly flow in the Southeast, so that’s a time frame to watch for decent, widespread rain to return.

14
Jun

A Break From Very Active Weather in Southeast

After several strong blocking episodes, and resulting severe weather, heavy rains and 2 tropical systems, the Southeast will go into a more tranquil period for about a week.  The closer to the East Coast, the more northerly the winds aloft, and some dryer air will be found. But there is a chance of a weak cutoff at the base of the trough just offshore the Carolinas this weekend, and we’ll have to see how closely this pulls moisture west toward the beaches of Virginia down through SC.  Other than that, deep northerly flow and even easterly flow further south toward Alabama and part of the Tennessee Valley will mean daily afternoon storms are few and far between, but some will form daily especially on the western side of the Apps and those storms will push south and southwest each afternoon, so parts of Georgia, Tennessee and west and south will experience some afternoon storms in this type of flow.

Also, the temperatures will be going up to around normal perhaps a couple degrees above normal by most of next week, as a ridge aloft builds.  Meanwhile, another strong to severe outbreak could occur in the Plains and especially Midwest region early or mid next week as a strong Pacific storm takes a track across the northern states and encounters hot air and return flow.

If you’re wondering when the next major weather event is for the Southeast, there’s a couple things going on: First, the tropics could generate something later next week in the deep easterlies I mentioned, either side of Florida in the Atlantic or even in the Gulf.  Usually deep easterlies, if not too strong, can turn into a low level spin, and so far we’ve seen 2 developments at the bottoms of deep troughs, and I won’t be suprised to see our third named storm develop by late next week.  By then, there’s also going to be a change in the jetstream pattern, one that favors the trough coming back to the East.

I’ll be working on some old case studies during this tranquil period and hopefully get some good reading  info for the Southeast region, re: snow and Winter.

10
Jun

Flooding Continues Ala, Fl. Panhandle…Periods of Rain In Southeast Through Wed.

The water vapor and infrared shows a steady stream of more heavy rain concentrated in the northern Gulf, about to stream back into the central Gulf Coast region. The Fl. panhandle to Mobile and eastern La. will continue to be hit hard with steady showers and pockets of training for the next 24 to 36 hours. Meanwhile further inland, several rounds of heavy rain and some thunderstorms will develop in Georgia and Alabama, possible entering western SC and the mountains of NC/TN by Sunday night.

The biggest unknown is how much robbery takes place further north in TN/VA andNC , that results from lines of convection that keep firing up along the Gulf Coast. Usually, a very wet Gulf is not a very wet Appalachian or Piedmont region. But still there will be periods of rain, possibly heavy rain, especially since the PWATs will become very high on Monday in northern Ga, and most of the Carolinas and eastern Tennessee. Further west into the Tn. Valley, showers will be more sporadic at first, but by Tuesday, the entire Southeast may line up once again with steady, organized rains and storms just ahead of the next incoming front.  All in all, a very active period for most.

By late week, High Pressure will clear out most of the South, with slightly cooler and noticeably drier air.  However, the front could stall near the Gulf and into Central Texas, offering a focus for more rain in those areas. Unfortunately, this will place some areas with unneeded rain again late week, around southern sections of Louisiana, Ms, Al, and the Florida Panhandle.  Some counties in Ms, Fl, Al are going to have about half a year’s worth of rain this week, when all is said and done.

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