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Another Strong MCC or Even Derecho Possible Monday into Tuesday

We’ve been in a pattern of MCC development several times this season and a couple have turned extremely severe. The culprit is the strong 594 closed ridge in the Plains. As disturbances in the jet move around this major ridge, they sometimes dive nearly due south or southeast toward either the TN Valley or the MidAtlantic. Depending on how the flow is in Canada, they can either gather great support and maintain themselves but many times they fall apart or are just a moderate complex.

The NAM model has a textbook case for a strong Derecho event evolving Monday night in the eastern TN Valley and then spreading quickly southeast, arcing in a very long arc from Virginia, through the Carolinas, through Georgia and eastern Alabama by Tuesday morning, sweeping east as the day goes on.

What to look for to predict MCC? A few rules of thumb I learned years ago (and have been adding to it greatly since the science is evolving) are:

1) A closed 588 to 594 ridge in the Plains, Midwest or TN Valley.  If there is a splitting or divergence showing up on the 1000-500mb thickness charts, then development usually rides between these lines.  NAM has this

2) Upper jet streak or jetlet and 5H vort juxtaposed on north or east side of ridge.  NAM has this. This is the fuel to feed the system as it goes, to sustain the complex.

3) Strong low level warm advection (between surface and 850mb), and strong northwest flow aloft, on the east side of the ridge. NAM has this and actually shows extreme warm advection for a Summer event. Notice the +24 temps  that works under the warm front in western TN/KY and Arkansas for a period.

4) Meso low or Meso Convective vort showing up at the surface. NAM has this as well.  GFS does not but shows signs of convective feedback, so there’s a “hint” of it.

There’s a couple more things to look for I’ll put in the MCC menu of the page soon.

Comparing NAM to GFS , the GFS has all of the above as well, but none of the parameters look quite as well as they do on NAM, however for the most part GFS does still strongly indicate some type of MCC developing, but doesn’t take it to the Derecho level.  Also GFS is slower to develop the complex.  GFS also strongly hints at another MCC event further south and west than the first one, focused mored on TN, MS, and LA and AL by Wednesday.

Here’s a look at 30 hour NAM , valid midday Monday July 30.  Notice the classic warm advection and surface low, similar to a Winter Event (Clipper).  Very rare to see this in dead of Summer.


Animation of GFS 200 Jet.

GFS is later on Tuesday and not as strong with the development.

So far , SPC was hesitant to even give 5 % hatch mark for possible development but now has a “See Text”. However, they remain skeptical on a day 2 or day 3 event.


I think synoptically, something significant will develop because it has almost every time this Spring and Summer
when the opportunity was presented. Synoptically, for the reasons I mentioned above (what I look for), this even
has about every ingredient, but of course, weather doesn't always work like theories do. Overall, in general it
is my opinion that MCC events curve sharply south and west of where models or forecasters want to track them..
something to keep in mind. Either way, an area from Missouri, Kentucky and points due south and east are at risk
from the first MCC event, and areas slightly further west and south are likely candidates for MCC event number two.

I'll update again Monday with my graphics and call maps.

Wet Gulf And Southeast Coast…Northwest Flow Next Week

The action is going to shift mainly toward the Gulf Coast from Louisiana, Alabama, Southeast Georgia and Coastal Carolinas, although storms will still be possible in the Interior Southeast, just not as numerous as they will be further south.  There is a stalled front that lay between the Offshore Bermuda Ridge and the big Heat Ridge in the Plains.  This pattern will basically remain unchanged most of next week, but the coastal front will die out, and the storms will become more typical Pop-up storms in a broader region of the Southeast.  Georgia and SC look to be in a particularly good spot over the next few days, especially central and eastern sections of those states, but as next week goes along, we will have to watch any possible MCC development because the pattern will be conducive to a couple of those events that travel from Chicago and Iowa , southeast toward the TN. Valley, and maybe affect more of the Southeast, especially mid and late week.

For temps, the heat dome will stretch toward the western Tenn. Valley, places like western Kentucky and western Tennessee will still be very hot, with slightly cooler further east, but eventually by late week there’s a chance that the heat ridge weakens and shifts slightly further west.  One other thing to watch later next week is a disturbance in the Atlantic or a new developing one that could rotate around the Bermuda Ridge and by early August be somewhere offshore Florida.

Meanwhile, Canada is going to turn very cold! Hudson’s Bay will be the first to get hit with an unseasonably cold airmass late next week, and then northwest Canada will have a slug of very cold air. None of that refreshing air will come this far south anytime too soon though.

precip through Tuesday Night



Heat Wave 2012: June/July Detailed Synopsis of All-Time Heat Wave

The heat wave that began in the Plains during late June of 2012 and spread through the Ohio and Tennessee Valley eventually encompassed the entire interior Southeast and became the All-Time record breaking heat wave on record. Until this period, the previous Heat Wave of August 2007 ( a severe drought year) was the hottest period on record.

In forecasting strong Heat Waves, weather forecasters look at several factors that can help reach the hot numbers the models are indicating.  Some of these factors include looking at the upper flow (500 mb), also called “5H”.  Usually a heat wave is associated with a closed ridge aloft and heights ranging from 588 to 594dm at the 5H level.  The ECMWF and GFS model began showing the big central Plains ridge, where unusual heat was already occurring, to spread east and encompass the upper Southeast by the weekend of June 30 and July 1st.  The ECMWF was garnering major national attention as forecasters began to see numbers that had never been shown before in the Southeast, both aloft and at the surface, for parts of the Southeast.  The GFS also had high numbers, indicating the 850 temperatures to rise to around +27 , as shown on several runs, bouncing between Tennessee, northeast Georgia and parts of the Carolinas.  The ECMWF had shown +30 at 850 to spread across the Tennessee Valley to the heart of the Southern Appalachians.  This was a clear, historic first, as at no time in weather record history had this part of the Southeast come close to either +27 or +30 at the 850mb level.



At the surface, from 120 hours before the Heat Wave was to arrive in the Southeast US, the ECMWF model as already showing 105 degrees over an enormous region, and large sections of 110 degrees, on both sides of the Appalachian Chain. Most past heat waves were concentrated over a smaller area and had lower temperatures.  This was a well-advertised Massive Heat Wave.

ECMWF Surface Temperature Forecast For Friday June 29, 2012

As we’ve seen, the strong 594 ridge aloft is one aspect of attaining record heat at the surface.  Already in a very warm year, the bulk of the United States by the end of June as under extremely high heights aloft, with a strong 594 ridging out west and again in the Southern Plains, with the jet stream far removed to the north.  The large 594 ridge was forecast to spread east into the Southeast by Friday, June 29.

The location of the closed ridge aloft is also important in forecasting high heat and exactly where the ridge is placed determines what areas experience the hottest temperatures. Like in August 2007, this ridge was poised to be in exactly the correct spot to ensure both sides of the mountain chain gets into the heat. A closed high aloft over the Tennessee Valley and Southern Appalachians with 850 temps of atleast +21 is always the first signs of a major Heat Wave, and this particular event had even hotter forecast temperatures.  Downsloping compressional surface winds were also a big factor in what would end up sending the hottest air ever recorded for areas east of the mountains in areas like Athens to Charlotte.

As the weekend approached, the ECMWF model toned down the +30 to around +27, still very adequate hot air to pull off the worst heat wave, so long as other conditions didn’t interfere with the setup.  Any high cirrus clouds from upstream convective debris, along with wet grounds or too much low level moisture could alter the high progged temperatures, but in the end, the Heat Wave of 2012 arrived as forecast over many areas of the Southeast.  By Thursday afternoon, the event was in the RAP model window, and that model also began to crank out never-before-seen temperatures , and an expansive closed 594 + ridge in the Southeast.


All models agreed within a few degrees, that 105 to 110 degrees was a strong likelihood in the interior Southeast between Friday and Sunday. In contrasting and comparing the models at the surface, it appears the RAP was only slightly too warm at the surface, along with ECMWF and perhaps GFS is given the nod overall as being more correct, but all models handled the evolution of the heat wave in nearly the same form and come up with 110 degrees as being the upper bound limit and many areas located with the 105 to 110 isotherms as being the locations that had the best shot of attaining record heat.

RAP model forecast 110 degrees Friday, Saturday and Sunday in parts of the Southeast:

NAM model also had +27 degrees at 850 across the Tennessee Valley to northern GA and western SC.


Until this Heat Wave, the hottest air at 850 to ever cross the Mississippi and reach the Appalachian region was around +25, and that number is extremely rare.  By early Friday morning, the RAP model had honed in on a bubble of +30 in Illinois and was forecasting for the first time that +30 degrees would indeed arrive in parts of eastern Tennessee, northern Georgia and the western Carolinas: An Historic First.

Early morning meso-analysis captures a first: A bubble of 30 degrees (850) east of the Mississippi River.


By later on Friday, the RAP model held on to this region of hot air aloft and shunted it around the Tennessee Valley ridge. By 6 PM the model was forecasting +30 at 850 over portions of eastern Tennessee, northern Georgia and the western Carolinas:

Rapid Update Cycle (RUC) Was Predicting All-time Record Heat Within 18 hours

By 6 PM on Friday, all conditions were go for the Historic Airmass to maximize the heat to all-time levels. The surface and upper winds were at just the right trajectory to aid in downslope heating, the cirrus canopy was far enough north to not impede surface temperatures and the time of day and arrival of the +27 to almost 30 degree air was timed with afternoon heating to culminate in perfect timing. It was the “perfect scenario” for the records to be shattered. And as you’ll see below, records did indeed fall on a massive scale.

At one point, just before the Heat Wave was set to pounce eastward, much of the central and southeastern sections of the country was under excessive heat warnings, heat watches and advisories…perhaps one of the largest, most extensive regions ever to be gripped at the same time by a super heat wave.

The Record Setting Heat Wave of Late June 2012 Was Expansive


Another look at the GFS forecast 850 temperatures.  As it turns out, the model was very close to portraying an accurate 850 field.  Here’s the 36 hour map valid 00z June 30, showing the expansive heat across the interior Southeast:


Actual analysis for July 1st, 00z.  Notice the area of temperatures greater than +26 covering east Tennessee, northeast Alabama, north Georgia and western Carolinas.  This is actually the hottest it’s ever been in recorded history for this region:

* Actual Analysis* All-Time Hottest 850 Map (in recorded history)

Another look at the actual analysis from 00z July 1.  Atlanta reached +26 at 850. Parts of western SC on meso analysis indicated close to +28.

Raw 850 Grids


The result of the unique atmospheric conditions and the extreme levels of the upper level heat combined with otherwise perfect conditions to deliver All-Time Records to much of the Plains and Southeast.

All-Time Heat Records Southeast Close-Up


Finally, a comprehensive list of all the cities in the Southeast that set records. Click to enlarge.


Strong MCC or Several Smaller Linear Lines of Convection to Race South Today

Current development in Indiana has worked out as I thought yesterday, and now there is a new line forming quickly ahead of the main line for east Ky, stretching across southern West VA and into Virginia. It’s hard to say which line will become the dominant, but if there’s enough separation and the second line doesn’t have to fight an already worked over airmass, both could hold their own in a strong MCC outbreak. If nothing else, several large clusters of storms could affect a lot of places today.

The SPC has outlooked the area, but overall MCC’s tend to drop further south and west, so I’m including northeast TN and north GA in the area of concern as well, in addition to Ky, West VA and most of Virginia today.  Already a new line appears to be developing and dropping south toward the Smokies and maybe Piedmont for this afternoon.  By late night, on the western edges of the first line, new convection could develop and affect more of the KY and TN region than this one does, and that also could make it very far south, or the outflows from it could generate development even further south toward northeast Al, north and central GA and into SC.  Timing means a lot today for the Carolinas, if the sun hold out all day and the instability can work up into high CAPE then storms or lines that survive east of the mountains could become extra severe as well.



Dying Front in Southeast…Then Northwest Flow

Over the weekend, the front will stretch from eastern Texas to southeast Virginia and wash out. This entire zone will be the shear zone along which daily storms will focus, and many areas are under the gun for “shotgun” type of pops, but overall a general max of storm formation will be along the front from southwest to northeast.  Meanwhile Bermuda return flow will help keep the frontal zone in this position until Monday when the overall flow begins to switch.

The ridge in the southern and central Plains will become the main steering force as we head into the next 10 days, so we are heading back to where much of the Spring and Summer has been…namely, strong drought in the Plains with a definite propensity for systems to roll around that major ridge and try to drop southeast toward TN and NC as next week wears on. There will still be scattered storms about anywhere in the Southeast next week, but not nearly as many as recently, and the focus will become what could be MCC type of systems, beginning Tuesday and onward.  At 5h, the flow bends sharply south once you get east of the ridge, and everytime this Spring and Summer that this flow has shown up, inevitably MCC systems, some of which are large, have raked the Ky/TN region and sometimes worked entirely to the Gulf Coast.  I expect next week we will once again see that scenario play out, but I’ll have to wait to fine tune the track.  Otherwise, still hot temps, but not quite heat wave level.  Generally, the further west and closer to the ridge, the hotter it becomes. The further north and east, from eastern KY to VA, the generally cooler, relatively speaking.  The Great Lakes and Northeast once again will enjoy being much more embedded in the northern stream troughs, where much cooler air resides.

Making plans for beyond next weekend? Most models still insist the big ridge stays put or works slightly west, which may allow another front to die out, this time further north, so overall the pattern looks about the same as next week’s, but maybe a bigger focus for storms if another front dies in the region.



Very Active Pattern Stays

Practically every state in the eastern half of the country will have thunderstorms today and again Friday. There’s not many times in the Summer that this happens, but it’s indicative of all the low level moisture and upper level triggers that are abundant in this pattern.

Another front is on the move in the Upper Midwest and will work south, stretching east to west, and settle across the upper Southeast by Friday night and Saturday. Ahead of this feature, once again very widespread coverage of storms will occur. By Saturday and Sunday, a weak damming situation could cool down the areas east of the Apps from NC and Va northward. Before that happens, enough dynamics and even an 850 low will develop on the front in West Va, and most of Virginia by Friday, and become the impetus to trigger very strong thunderstorms in the Old Dominion.

After we get through the weekend, the action continues. The front in the Southeast will become a shear zone stretching from NC back to Louisiana early next week.  The GFS has a strong Bermuda high setting up for a day or two.  The winds will funnel moisture and winds and focus more storms on this decaying front (along with abundant heat) but anywhere in the Southeast is once again game for storms on a daily basis.  And by early to mid next week, yet another front will rotate down the eastern side of the Rockies/Plains ridge, and there’s even a chance at a major MCC event occurring just before the front arrives. So not one, but two distinct rounds of thunderstorms will slide from the Midwest toward the Tennessee Valley and east Coast once again.  The models show this front stalling similarly to the recent once, keeping daily convection around, really for as far as we can see.


Heat? No. More Storms? Yes.

The rainier pattern is here to stay, I’m glad to inform the Southeast subscribers.  About a week ago I issued an alert and detailed how a wet pattern would be arriving this week from east Texas through most of the Southeast states.  Here’s a look at the weekly rains ending Friday night.

You can see that most of the rain in the US has been concentrated in the Southern and Southeast third of the Country.  Here’s a closer look at the Southeast (notice a few areas in Alabama, Georgia and north and east Florida haven’t been hit with storms).  It’s unusual for the entire region to be hit at once because of how the atmosphere works, and in this case, the best lift associated with the weakness aloft has been stretching from the Carolinas and arcing back across the Apps and southwest through the Gulf states to east Texas. The weak upper low didn’t want to budge any eastward so part of Alabama, Georgia and Florida didn’t receive as much rain as just to the north and west did.


Now where do we go next? If you’re looking for some drying out or a heat wave, you’ll be disappointed over the next 10 days. The ridge and heat will remain west in the Plains and eventually retrograde even further.  Meanwhile for the Southeast, a Bermuda High will continue to pump ample moisture and high PWAT air into the Southeast for a while. This will continue to build daily afternoon storms, a rather typical Summer pattern from years ago (but not too common over the last decade).  This pattern favors a good bit of rain in the Carolinas, especially South Carolina where the northwest flow of recent Summers has done a number on the drought. Not every location will see a storm on a daily basis, but some will, and the coverage is going to be pretty high for the Southeast as a whole.  Here’s a look at GFS next 7 days cumulative rainfall…for general purposes only. Again, the Tennessee Valley and Southeast is the wettest location on the map.


In about a week, we may lose the true Bermuda Ridge flow, and replace it with more northwest flow. However there is plenty of evidence that a front will stall once again in the Southeast, from Texas and points east, which will be the focus yet again for daily storms, some even lasting beyond the usual afternoon/evening type of stuff. Similar to what we just went through.  That would be the day 7 through 10 period. And just beyond this period, as the ridge out west possibly works even further west, a weakness could form again in the Southeast between  a Bermuda ridge (forecast to develop again) and the western ridge, which would place the Southeast squarely back into the pattern we’re currently in: Numerous, widespread storms with buoyant , moist air.


There’s also a slight chance of a system developing in the Caribbean or Atlantic that would work west under the ridge and into the Southeast or Gulf states…too early to say on that yet, but there are a couple weak upper lows that could become warm core, not likely yet though.

GFS cumulative rain totals through 384 hours:




Muggy, Typical Summer Pattern Here To Stay A While

Normal Summer-like pattern of a weak Bermuda Ridge and a weak Gulf Coast weakness will hold in place for about another week.  Thursday will see a weak damming pattern east of the Apps, while west of the Apps the cyclonic spin will continue to focus heavy rains from East Texas through the Tennessee Valley including northern Louisiana, Mississippi and Alabama. By Thursday afternoon, the RAP model has Georgia getting into heavy rains by afternoon possibly reaching the western Carolinas. Further north into Virginia, High Pressure will keep most convection to a min, except in the mountains of southwest Va.

There are a couple items to watch regarding tropics, that all models could be mishandling. One is a weak upper low east of Florida, and the other is a weak upper low in the central Gulf of Mexico. Both of these could gain some tropical characteristics with time, and if they do, the moisture would be forced to come into the Southeast thanks to the building Bermuda High pattern, a pattern that looks to lock in for a while. The central Plains will be the hottest place in the US for about the next 10 days, while the Southeast has average temperatures thanks to the weakness buried in the region, many clouds and low level moisture. Don’t be looking for another heat wave around here too soon thanks to the above, and the wet grounds.


Cooler Week…Wet Pattern Begins

The much advertised wetter and cooler pattern is arriving on schedule. The front will stall in the Tennessee Valley, stretching from Oklahoma to the Virginias, stretching east to west, before rotatating more north to south later this week, and eventually washing out.  A weak 850 low is forecast to form in Alabama at some point, causing ripples of upper level energy to occasionally enhance some totals in the Apps region by midweek. It will be slow to start raining in Georgia to SC because of the still strong Upper High and anti-cyclonic flow, but by midweek, cyclonic flow and southeast upslope winds will do the trick at opening up the skies by afternoon with downpours

For the Ky/TN region, the rains have already arrived and will re-form on a daily basis. The rest of the Southeast will get wetter and wetter as the week goes by with plenty of dynamics, good Gulf inflow and no capping in the atmosphere. The lifting condensation levels will be dropping low enough, so this is going to be a classic “puffy” blue sky with low cloud bases that once enough heating forms, the rain droplets can no longer be suspended in the clouds, but instead drop down in buckets of water.

I still think there could end up being too much rain in some parts of Texas to the Southeast by the end of the week, but for now there’s nothing to worry about since the entire area is in drought conditions (save north Florida where Debby made an appearance).

Here’s a general outline of where the rains will be, and 5 day totals from HPC/NCEP. However, this won’t be stratiform rains so I caution not to really expect a final totals map to not really resemble this map too much. One county can easily get 4 times the amount of rain of any adjacent county, but the general idea is a very wet Southeast, where some counties could get over 6″ of rain this week.  I wouldn’t be surprised to see some smaller localized areas get up to 10″ of rain by Friday night (cumulative), but it’s very hard to narrow down the locations. WxSouth’s first pick for a rain max is northeast Georgia, northwest SC/southwest NC, owing to the location of the 850 low, moisture transport and orographics. But parts of the Tennessee Valley or Cumberland Plateau could easily match it, as could southeast Texas.


GFS totals through Sunday Night:



Hot Weekend…Then Classic Wet Pattern Next Week

The atmosphere over the Globe is undergoing change as we speak, and part of it is the changing MJO and El Nino cycling. This could be the beginning of a long term pattern shift, but I’m not forecasting that just yet with any certainty. One thing I am certain about is the upcoming Wet Pattern, and return to near normal Summer temps.

First, a cold front will begin to approach the Midwest and eventually reach Texas through the Tennessee Valley to MidAtlantic by Sunday. Ahead of this feature, one more strong push of very hot air, especially in Tennessee, Kentucky through the Virginias and North Carolina, where 850 temps soar to +21 to 24 again (not quite as hot as the previous +27). However, for Virginia and Maryland, on Sunday if the clouds hold off, this could be the hottest weather of the year there.

As I mentioned the atmosphere is changing alignment, with a big ridge about to set up in the West, where some areas have been cooler than normal, as the midsection and east has baked.

A record 55 % of the lower 48 states landmass is now covered under drought conditions.  This eclipses the 2002 and 2007 droughts , but for central Ga, eastern Al, and western SC, the drought is nearly as bad as those years.  The good news is the incoming front will stall, and allow a southerly flow to develop.  The moisture coming in from the Gulf over a long period of time (atleast 7 days) represents a big change from Summers past. It’s actually closer to more normal Summers, with the mean flow being southwesterly. When we lost this mean flow, drought began to take shape. Thats because more often than not, the Summers since 1998 in the Southeast have been dominated by higher than average heights, and winds aloft and at the surface from some component of westerly.  West and northwest winds aren’t good for rain chances since theres a large landmass west of this region, and the mountains create a block to intercept what moisture there is, and also further dries out the region downstream in Georgia and especially the Carolinas. Depending on where any specific ridge is at any specific time changes which region is the dryest. Currently, the mega ridge that has sweltered the Plains favors extreme dryness and northwest flow that blocks most of eastern Alabama, the heart of Georgia and South Carolina from receiving much rain, especially compared to climatology.

The flow is about to undergo massive change, assuring that the entire Southeast returns to atleast 30 year normal rain patterns, atleast on a short term basis.

There’s strong reason to believe (for this forecaster) that the pattern will actually bring extensive moderate rains, and in some broad areas possibly some flooding rains by late week. The long lived nature of the southerly flow and weakness aloft in the lower Mississippi Valley could evolve into a weak upper low that gets caught and remains stationary between Louisiana and Alabama.  This type of 5H flow, combined with the big Bermuda Ridge to the east, pumping in moisture all the way from the Caribbean, the cooler upper temperatures and the flow from the warm, rich Gulf will most likely ensure a drought-busting wet pattern for a broad region from Texas through the heart of the Southeast up into the MidAtlantic region.  Usually, the southern Appalachians, especially the south and east facing slopes, end up with too much rain in this type of pattern.  The dewpoints are progged to be in the 70 to 75 degree range over the entire Southeast, so the afternoons will see the moisture bubble up into puffy cumulus, against a rich blue sky, and once the LCL’s are reached, the skies open up and downpours are unleashed.   A similar pattern to what’s on tap is June 2005, where there was major rain totals in the Southeast.

Dewpoints Next Tuesday  (GFS)


We could be heading (atleast briefly) back to a Pre-1998 type of surface wind flow.  Mean winds from the Gulf.


GFS animation Monday through Sunday Next Week.  A weakness in the 5H height field, possibly even evolving into a weak mid level cutoff low, ensures daily storms and showers from most of central Texas, and all points east south of the Ohio River, with a concentration around the Appalachians and Deep South.

June 2005: A wet Month in the Southeast. Up to 20″ in the southwest mountains of NC, northwest SC, extreme northeast GA and parts of central and south Florida.


GFS rain totals through July 15.  *Always use caution on a Ptotals map that’s convective. This isn’t stratiform precip, but the idea is a wet pattern from Texas through the Southeast. Some areas will get much more rain than shown, some will get less.

On the tropics….there’s nothing to report now, but if something develops, the flow would be around the Bermuda ridge and into the Gulf, which would place the Gulf States and Southeast into the track. As of now, the region stands to receive a lot of rainfall without any tropical involvement.