east GA Glascock, Warren and Jefferson Counties hit hard this morning with stationary heavy rain on sw side of Andrea. More 2 come #gawx
Lots to talk about. First, just when it appeared to be dry and boring for the Southeast for a while, things have changed. The NAO forecast was nebulous over the last week, but now its clearly locking into a negative look, with 2 possible blocks and one likely block atleast (in southern Greenland). GFS is more adamant about this than most models, but the short range models have this look beginning soon, so it’s hard to ignore. And it appears to last a long while, even though the flow may change in the high latitudes through the month, the likelihood overall is that there will remain some type of northern latitude blocking most of the month, atleast enough so that it will impact the departures (both temps and precip) for our region.
Usually, this type of flow means a split out west, and a forcing south of the westerlies for the Eastern States. This time there is a unique setup with a Gulf inflow that is almost always open. If this happens, then the Southeast will be the beneficiaries of much needed rainfall on numerous occasions during the month of May. Our warmest temps of the month may occur during the first week, with temperatures dropping to at or even below normal for much of the remainder of the month. Looking back to last Summer, Fall and Winter, this almost never happened. So I’m in a dangerous territory now, to predict below normal temperatures and at or above normal rains for a broad region. But all signals are pointing that way. Still I won’t say all the Southeast gets into the above normal rains but enough will to help with drought conditions.
The Month of April saw a continuation of the drought. Many areas only had 5% to 25% of normal monthly rains, and this time the dry areas spread from SC and GA northern Fl to more inland areas of the Tennessee Valley and in central Texas, after those areas had a wet Winter. The next few days offers heavy rain potential in Florida, especially south and southeast, then working toward the western half of the Peninsula early next week. This inverted trough has to be watched for development, as SREF models bring it northward into the Gulf States, again offering much needed rains. This could keep temperatures down in GA and SC where early on it looked like 90’s were likely this week.
The net result of the upcoming pattern change puts the Southeast/Lower Midwest/MidAtlantic into the heart of convergence, which means gulf moisture is going to get intercepted numerous times with frontal systems…this time situatied more in the Southeastern Third of the US, possibly including the really dry areas of Florida, Georgia, Louisiana, South Carolina and Virginia.
Even if a truly wet pattern doesn’t emerge this month, I don’t see the Southeast as being nearly as dry as April was. Usually, a long lived area of northern blocking leads to some kind of lower height fields over the Southern/eastern US…sure enough , GFS has that as well, but it takes a while to show up.
The cooler temps/wetter weather for the Southern Region begins to kick in around 168 hours and persists thereafter. Many years recently the heat began in May, and that month was nearly as hot as any Summer month…looks like we may avoid that this time. I’ll be able to pinpoint the locations in a later post as to the best chances of rain and cooler weather, but for now broad brushed the South including Florida. Another note, if the double blocking occurs as per GFS, I wouldn’t be suprised to see a stationary cutoff in the Southeast at some point. In May, with the strong sun and ample Gulf inflow, that leads to numerous widespread showers and storms. We’ll see how this evolves.
As the westerlies move north beginning tomorrow, by next week we will really start to feel the effects of a warmer mid and upper level atmosphere, and building heights from Texas to the Virginias and down to Florida. Other than a brief back door front in the Carolinas and VA on Monday, the winds will quickly turn from the south as a Bermuda ridge begins to develop just off the Southeast Coastline. The storm track will shift north toward the northern Plains and Lakes next week, so there won’t be much in the way of dynamics , a front, or any lifting mechanism to generate rain, other than instability caused by the sun’s heating and a buoyant, rich moist airmass surging in from the warmer than normal Gulf.
The big news will be the developing H-E-A-T . Unfortunately we’ll be turning dry and warm, much warmer than normal, to the tune of qualifying for HOT if the ECMWF is right. Parts of Georgia, South Carolina and Florida could reach the low 90s the latter part of the week, and even flirt with 90 sometime this weekend. Where the ground is the driest (drought) over central to south Georgia to around Columbia, SC, it appears the best chance of 90’s will first occur there, and again in western Texas.
The first heat waves are usually squelched where the ground is wet or saturated and right now areas of the Tennessee Valley and Arkansas to central Texas will see the airmass remain below the truly hot threshold thanks to an initial few days of heat going into the transpiration process.
Bottom line for next week for the Southeast third of the country:
Increasing temps…mid/upper 80’s to low 90’s.
Increasing in diurnal Summer type convection (widely scattered)
The setup is still there tonight and most likely the next 48 hours (can’t rule it out) for northwest flow MCC events. The SPC and RUC are in good agreement here with synoptics: There’s a stout 5H wave dropping through Kentucky, strong low level warm advection west of the Apps, and a strong splitting of the 250 and 300mb jets, which is splitting directly overtop the dynamics of where the 2 current outbreaks have occured, ie, Ky, Tn and western NC. This will continue to repeat unfortunately. Eventually the heights will rise, the 5H vorts will move out in to the Atlantic and we won’t deal with the repeating MCC tracking through the region. Until then though, a few more rounds are possible with any weak upper disturbance. Stay alert..high winds, hail, embedded tornadoes and severe storms are possible in the lines.
GREATEST SEVERE POTENTIAL SHOULD REMAIN WITH TSTMS DEVELOPING ALONG THE SURFACE COLD FRONT STRETCHING FROM NEAR HTS TO 40 S PAH AS OF 20Z...WITH INITIAL SUPERCELL CENTERED AROUND 30 N LOZ. STRATUS DECK OVER NRN TN HAS BEEN ERODING AHEAD OF THE FRONT...LEAVING A 50-70 SM WIDE ZONE OF GREATER INSOLATION. THIS WILL SUPPORT FURTHER DESTABILIZATION JUST AHEAD OF THE ONGOING STORMS AND LIKELY RESULT IN PROPAGATION OF A FEW SUPERCELLS ACROSS SRN KY AND EVENTUALLY INTO NRN TN. LARGE HAIL /WITH ISOLATED SIGNIFICANT STONES/ WILL REMAIN THE PRIMARY THREAT. FARTHER E/SE...TSTMS HAVE PERSISTED FOR THE PAST FEW HOURS AND HAVE RECENTLY INCREASED IN COVERAGE ACROSS THE SRN APPALACHIANS WITHIN A WAA REGIME IN THE WAKE OF OUTFLOW FROM AN EARLIER MCV ACROSS SERN VA...REINFORCED BY A TSTM CLUSTER APPROACHING THE NC/SC COAST. WITH DIURNAL HEATING HAVING BEEN LIMITED BY THE ROUNDS OF CONVECTION/PERSISTENT CLOUD COVERAGE...TSTMS WITHIN THIS ZONE SHOULD CONTINUE TO STRUGGLE TO APPROACH SEVERE INTENSITY. STILL 40-50 KT EFFECTIVE SHEAR MAY SUPPORT A MARGINAL HAIL THREAT WITH THE STRONGER CORES ON THE SRN/WRN PERIPHERY OF THIS CONVECTION.
A strong line of well developed storms is bowing out as it approaches the southern Apps. This is a classic shaped MCC that began overnight, but the models missed it. I mentioned afew days ago the chance of MCC type of events though, so my readers atleast were aware that the pattern supported it .
A watch is possible, and several warnings are in place. The areas under the gun will soon be north Georgia, western Carolinas, southwest VA, and already damage is done in east Tn, and southeast KY. From SPC:
NWS STORM PREDICTION CENTER NORMAN OK 0624 AM CDT THU APR 26 2012 AREAS AFFECTED...MIDDLE/EASTERN TN AND FAR SOUTHEAST KY TO WESTERN PORTIONS OF VA/NC/SC CONCERNING...SEVERE THUNDERSTORM WATCH 189... VALID 261124Z - 261300Z THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 189 CONTINUES. AN EAST-SOUTHEASTWARD MOVING MCS WILL CONTINUE TO POSE A SEVERE HAIL/DAMAGING WIND THREAT OVER THE NEXT SEVERAL HOURS. AN ADDITIONAL WATCH MAY BE NEEDED TO THE EAST OF WW 189 ACROSS PORTIONS OF WESTERN VA/NC/SC. AFOREMENTIONED QUASI-LINEAR MCS CONTINUES TO MAKE A STEADY EAST-SOUTHEASTWARD FORWARD PROGRESSION AT AROUND 50 KT ACROSS EASTERN TN AND ADJACENT SOUTHEAST KY/EXTREME WESTERN VA AS OF 1115Z. THIS SYSTEM HAS REMAINED VERY WELL ORGANIZED OVERNIGHT WITH AN MCV AND MCS-TRAILING WEAK ECHO CHANNEL/REAR INFLOW JET EVIDENT IN OBSERVATIONAL DATA. EVEN WHILE THIS MCS WILL TEND TO OUTRUN THE PRIMARY WESTERLY FEED OF UNSTABLE AIR/STEEP LAPSE RATES...THE EXISTING ORGANIZATION OF THE MCS/ITS FORWARD MOMENTUM WILL LIKELY AT LEAST MAINTAIN A SPORADIC SEVERE HAIL/WIND THREAT TOWARD THE SPINE OF THE APPALACHIANS. PENDING SHORT-TERM TRENDS...AN ADDITIONAL WATCH COULD BE NEEDED SOON FOR WESTERN PORTIONS OF VA/CAROLINAS.
After we get through with the northwest flow type of disturbances (mainly Ky, Tn, NC, VA, West VA) then the Southeast will be getting into southwest flow. By late next week, the GFS and ECMWF show the likelihood of a Bermuda type ridge and a decent flow off the Gulf, but no strong surface boundaries. So this is the hallmark of buoyancy type of “Airmass” storms…probably the first of the season. As opposed to ones that are forced from a strong front. The actual low pressure will be very far north next week in the Plains and Midwest near Chicago, with not much lift or dynamics in the South….only a flow off the Gulf, increasing dewpoints and muggy air and a strong afternoon sun to stir up some weak lift. So anyone west of the Appalachians down to eastern Texas is game for the first Summer time type of Pulse storms.
One thing to watch Sunday and Monday for the East will be the backdoor front. Models clearly show an Eastern Canada or Northeast US vortex closing off, and a surface high building down the east side of the chain into Va , and the Carolinas beginning Sunday. This won’t be a big rainmaker, but it always (or usually) is good enough to drop temps well below average in Spring. There will be damming, northeast and east winds and drizzle to light rain in the MidAtlantic and down to eastern GA for a couple of days around Sunday and Monday, before the high slides offshore and southwest winds warm everyone up.
The long range shows another ridge closing off in western or central Canada, but that’s far out. If it happens, we may see a cutoff develop in the Southeast by the first or second Week of May, bringing much needed steadier rains. We’ll see though.
The flow will lift north, and put most of the Southeast in west or northwest flow. Several disturbances will cruise through, originating in the northern Plains states starting Wednesday. The bulk of the Southeast states will miss the moisture and dynamics, but north of the boundary, there will be showers and maybe thunderstorms, in several different waves. The best chance of getting wet will be from northern Arkansas, northern and eastern TN and Virginia and points north. It’s possible enough moisture streams southeast toward northern Georgia or NC, but right now its looking doubtful atleast until the weekend. Kentucky and Virginia will get into some very decent rain totals over the next 5 to 7 days.
With the flow lifting north, there will be strong southwest winds eventually taking hold, so warm air will return quickly. Temps will be comfortable to a little too warm, with upper 70s to mid 80’s very common by late week south of the rain-hit areas. There’s a building ridge and alittle split type of flow in southern Canada, enough to create the possiblility of another east coast storm early next week, or the very least, another strong northerly push of cold air reaching southward, especially in the Carolinas where a back door front could bring in cold, damp air, but that’s far out.
Unfortunately, areas that really need the rain from La, Miss, Ala, Ga and SC won’t find much in the forecast for a while.
Looks like the NAM is going to be a little too far west and south with its depiction. The GFS looks more realistic at this point, so by Monday morning the surface low will be strengthening near Philadelphia, and there will be wrap around snow for western Pennsylvania and through most of West Virginia. Even a period of snow showers for northeast TN and northwest NC mountains during the day Monday. Also, steep lapse rates and some moisture will roll through most of central Virginia into central NC during the day and reach the coast by afternoon, so low topped convection with showers or mixed precip can’t be ruled out there.
Other than a possible record snowfall in northeast West Va, wstern Maryland and western PA, the big news will be the winds. Strong mixing and a tight pressure gradient, plus some downslope enhancement could lead to enough winds to cause some minor damage. The GFS has winds of 3o to 40 mph,and its possible gusts could hit 50 mph in some areas of the mountains of West Va, western Va and northern NC.
The next few mornings will feature surface high sliding across deep South, and settling over the Florida Peninsula Wednesday and Thursday. Some record cold is possible in GA and Florida these mornings. By Thursday, a strong disturbance coming southeast from the Ohio Valley will be spreading showers and thunderstorms, and possibly an MCC type of system approaching parts of Kentucky, TN and western NC/VA. This area looks like where the front will stall next Friday and Saturday, with unsettled weather.