April 15-16 Severe Weather threat

[ATL_Militarypolice]

SPC has already outlined most on Alabama into parts of Central TN, Eastern MS and far NW GA for Day 4 (Friday).

DAY 4-8 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0359 AM CDT TUE APR 12 2011

VALID 151200Z - 201200Z

THE MEDIUM RANGE MODELS BEGIN THE DAY 4 TO 8 PERIOD WITH A

NEGATIVELY-TILED UPPER-LEVEL LOW IN THE CNTRL PLAINS. THE MODELS

MOVE THE LOW ENEWD WITH THE ECMWF SLOWER AND FURTHER SOUTH THAN THE

GFS. THE FURTHER SOUTH SOLUTION WOULD SEEM THE BEST DUE TO THE

TENDENCY OF CLOSED-OFF LOWS TO BE SLOWER THAN FORECAST. AHEAD OF

THIS SYSTEM...THE ECMWF FORECASTS THE DEVELOPMENT OF AN MCS ALONG A

MOIST AXIS IN THE CNTRL GULF COAST STATES AND TN VALLEY FRIDAY

AFTERNOON/DAY 4 WHERE THE MODELS ARE FORECASTING MODERATE

INSTABILITY. HAVE OUTLOOKED A SEVERE THREAT AREA IN ERN MS...AL AND

MIDDLE TN. THE ECMWF MOVES THE UPPER-LEVEL LOW INTO THE WRN GREAT

LAKES REGION SATURDAY/DAY 5 WITH A POWERFUL LOW-LEVEL JET LOCATED IN

THE ERN STATES. A SEVERE THREAT WILL BE POSSIBLE ACROSS THE SRN AND

CNTRL APPALACHIAN MTNS INTO THE CAROLINAS ALONG THE MOIST AXIS

SATURDAY BUT CONFIDENCE IS NOT ENOUGH FOR A THREAT AREA. BY EARLY

NEXT WEEK...THE MODELS DEVELOP AN UPPER-LEVEL TROUGH IN THE WRN

STATES BY MONDAY/DAY 7. LOW-LEVEL MOISTURE RETURN COULD BE STRONG IN

THE SRN PLAINS AHEAD OF THIS SYSTEM RESULTING IN A POTENTIAL FOR

SEVERE WEATHER. HOWEVER...THE GFS AND ECMWF ARE DIFFERENT IN THE

TIMING AND AMPLITUDE OF THE UPPER-LEVEL TROUGH MAKING UNCERTAINTY

HIGH THIS LATE IN THE DAY 4 TO 8 PERIOD.

This time it looks like we may be dealing with a more discrete cell setup than the previous linear setups we have had.

Here are some AFD's edited for emphasis.

FFC this afternoon:

ANOTHER STRONG WEATHER SYSTEM SLATED TO IMPACT THE CWA LATE FRI-SAT.

YET ANOTHER DEEP CLOSED UPPER LOW WILL EVOLVE IN THE CENTRAL U.S. BY

THU...TAKE ON A NEGATIVE TILT...AND LIFT NORTHEAST INTO THE GREAT

LAKES NE U.S. BY SUN.MODELS ARE TRENDING STRONGER AND

FURTHER SOUTH WITH EACH RUN...WHICH IS NOT GOOD. ECMWF/GFS IN

GENERAL AGREEMENT ON TIMING AND DYNAMIC/THERMODYNAMIC PARAMETERS

ASSOCIATED WITH THIS SYSTEM. DYNAMICS AND INSTABILITY APPEAR MORE

THAN SUFFICIENT FOR SEVERE WEATHER WITH THIS SYSTEM. INSTABILITY

IS SOMEWHAT MORE IMPRESSIVE THAN WITH YESTERDAY`S

SYSTEM...ALTHOUGH SHEAR LEVELS ARE ANALOGOUS. SLOWER MOVEMENT OF THE BROAD

UPPER LOW...AND RELATIVELY COLD TEMPS ALOFT...WILL FAVOR MORE OF A

DISCRETE CELL CONVECTIVE MODE AND GREATER THREAT OF HAIL THAN WITH

PREVIOUS SYSTEMS. HOWEVER...GFS ESPECIALLY HINTS AT SOME INITIAL

THREAT OF A LINEAR/QLCS SYSTEM. AT THIS POINT...IT WOULD BE WISE

TO CONSIDER ALL SEVERE THREATS...AS WELL AS HEAVY RAIN.

BMX from this morning:

THE BIG DEAL COMES ON FRIDAY AND FRIDAY NIGHT...HOWEVER. LATEST

MODEL OUTPUT HAS RAISED MY LEVEL OF CONCERN FOR THE POTENTIAL OF

SEVERE STORMS DURING THIS TIME. CONDITIONS ARE FORECAST TO BECOME

QUITE UNSTABLE...WITH CAPES RUNNING FROM 1000 TO 1400 J/KG FRIDAY

AFTERNOON. MODEL BUFR SOUNDINGS SHOW A MORE MOIST LOW LEVEL SYSTEM

COMPARED TO THE ONE WE JUST WENT THROUGH...WITH LCLS MUCH LOWER.

BULK SHEAR AND SRH VALUES ALSO SEEM SUFFICIENT FOR ORGANIZED

UPDRAFTS AND ROTATING STORMS. FINALLY...SHEAR ORIENTATION AND

HODOGRAPH PATTERNS SUGGEST A GREATER DISCRETE CELL THREAT COMPARED

TO THE LARGELY LINEAR FORCED SYSTEMS OF LATE. ALSO NOTICED THAT

SPC HAS INCLUDED OUR AREA FOR SEVERE IN THE DAY 4 OUTLOOK. FOR

THESE REASONS...WILL INTRODUCE A TORNADO THREAT FOR FRIDAY IN THE

HAZARDOUS WEATHER OUTLOOK PRODUCTS AND MULTIMEDIA BRIEFING. LOTS

OF DETAILS TO HAMMER OUT...BUT DEFINITELY SOMETHING TO KEEP A

CLOSE EYE ON.

[ATL_Militarypolice]

As soon as I finish typing BMX comes out with their afternoon diso and make a complete 180^o turn. Now they mention more of a linear threat than discrete supercell threat.

AT THIS TIME...STRONG DAMAGING WINDS IN THE FORM OF A SQUALLINE

WILL BE THE MAIN THREAT. GIVEN THE STRONG UPPER LEVEL LOW...LARGE

HAIL WILL BE POSSIBLE DUE TO THE COLD AIR ALOFT. THREAT OF

TORNADOES LOOKS LOW AT THIS TIME. ALTHOUGH THERE IS SOME MID LEVEL

SHEAR WHICH WOULD SUPPORT SUPERCELL DEVELOPMENT...SURFACE WIND

LOOKS LIKE IT WILL BE STRAIGHT FROM THE SOUTH. ALTHOUGH THIS IS

NOT A SHOW STOPPER...IT WILL MINIMIZE THE THREAT OF TORNADIC

SUPERCELL AND WILL CONFINE ANY KIND OF ROTATION ON THE SQUALLINE

ITSELF. FOR MODERATE TO WIDESPREAD EVENTS...A SOUTHEAST WIND WOULD

BE MORE FAVORABLE TO TORNADIC ACTIVITY. MODELS DO SHOW A

TREMENDOUS AMOUNT OF SHEAR IN THE MORNING AS A SOUTHEAST WIND

COMPONENT IS IN PLACE. HOWEVER...THIS IS WELL BEFORE THE SEVERE

ENVIRONMENT MOVES IN. BY THEN...WINDS ARE EXPECTED TO BECOME

STRAIGHT SOUTH. DEFINITELY SOMETHING THAT WE WILL KEEP AN EYE OUT

AND WILL MONITOR. FOR NOW...THREAT OF TORNADOES WILL BE LOW.

[Gastonwxman]

At least for the folks that missed out from last night's event will have a much better chance this go around since this appears to be a case where squall lines tend to hold on better. You have a decent setup already with the ULL in place and an ideal track, which we all know can provide some interesting situations regarding severe or winter weather threats. Wouldn't surprise me if another surface low rears its head again like it has done so recently; once from last week's cold frontal passage and again from yesterday. The southeastward flow from said surface low could provide the necessary turning of the winds for more rotation assuming it develops in the right spot but I'm just speaking of possibilities here. Still, this looks to stand a better chance to provide storminess for areas further east in the Southeast this time, especially if Saturday becomes the focusing period for storms if the front were to slow down some more to where it occurs during the afternoon and not Friday night-early Saturday. I don't think it's set in stone as far as how super cellular development goes considering that we're so many days out (linear or discrete) but bears watching indeed. A small change to timing, changes regarding the pre-frontal trough, or the dynamics out ahead of the front can be a break or make kind of deal (like yesterday for example).

[ryan1234]

At least for the folks that missed out from last night's event will have a much better chance this go around since this appears to be a case where squall lines tend to hold on better. You have a decent setup already with the ULL in place and an ideal track, which we all know can provide some interesting situations regarding severe or winter weather threats. Wouldn't surprise me if another surface low rears its head again like it has done so recently; once from last week's cold frontal passage and again from yesterday. The southeastward flow from said surface low could provide the necessary turning of the winds for more rotation assuming it develops in the right spot but I'm just speaking of possibilities here. Still, this looks to stand a better chance to provide storminess for areas further east in the Southeast this time, especially if Saturday becomes the focusing period for storms if the front were to slow down some more to where it occurs during the afternoon and not Friday night-early Saturday. I don't think it's set in stone as far as how super cellular development goes considering that we're so many days out (linear or discrete) but bears watching indeed. A small change to timing, changes regarding the pre-frontal trough, or the dynamics out ahead of the front can be a break or make kind of deal (like yesterday for example).

Seems like a good chunk of us missed out yesterday. The westside of Atlanta got hit pretty hard, and as always the storms weekend as they approached Atlanta. Then they just became heavy isolated rain showers as they approached the Charlotte metro. I am not complaining as we have done very well here. Considering that Charlotte's main severe weather season is late April through May, I would say we are well ahead of schedule. I have a feeling that this will be one of the more active season we have had here in a while!

[FoothillsNC]

the upper low has been shown to cut off strongly in the MO area, and that usually equates to 2 lines of severe for GA and the Carolinas. I'm not sure yet which way I'm leaning on this, on the one hand a primary line could come through and begin to lose steam in central Carolinas overnight Fri. Night, and then another develops to the west a few hours later. It depends on how quickly and where the ULL cuts off. Also, usually this is a big rain maker at the GA/NC/SC conjoinance region, IE, southern APPS. Already the GFS has been showing this several runs. Hopefully its a little more progressive to help the central and eastern Carolinas get into some action where they've missed out a lot already. Either way you slice it, GA is gold once again. I could see the first line making further progress east and earlier than shown, which would help out the eastern friends on much needed precip. And with the ULL shown still so far back, there could be a case for re-development. Its a rare setup, but its happened before.

[LithiaWx]

Either way you slice it, GA is gold once again.

After so many years of drought I can't complain. Bring it on, and keep it coming.

[Gastonwxman]

Latest guidance continues to keep our threat in tact throughout the Southeast particulary in MS, TN, AL, and parts of GA during the day Friday. The ULL still looks nice and healthy and our 0-6km shear is still strong with speeds near 100 kts thanks to a powerful mid level jet that will be present and allow the environment for plenty of severe weather to develop. We also seem to have yet another setup that allows a MCS feature to make itself known developing back in the mid region of the MS Valley eventually crossing into TN. With plenty of sufficient instability produced throughout the afternoon hours, this will allow the initiation of convection along portions of the Gulf States. Taking a look at more of the parameters, there is some strong indication of speed shear with winds forecasted to be around 60 kts in the deep layer and SRH values >350 and would highly support supercells but again, being a few days away it will depend on whether we see QLCS or discrete super-cellular action. However, taking note of what the Euro has done, the LLJ is displaced further south than where the GFS/NAM places it and assuming moisture level is high, there could be more tornaodes to be concerned with. No guarantees of course but the chance for a widespread tornado event is in the cards. Just gotta watch how things unfold for the next 3 days.

[ATL_Militarypolice]

SPC has issued a slight risk including a hatched area.

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE LOWER TO

MID-MS VALLEY...CNTRL GULF COAST...TN VALLEY AND OH VALLEY...

...LOWER TO MID-MS VALLEY/CNTRL GULF COAST/TN VALLEY/OH VALLEY...

A STRONG NEGATIVELY-TILED UPPER-LEVEL LOW IS FORECAST TO MOVE FROM

THE CNTRL PLAINS EWD INTO THE OZARKS ON FRIDAY. THE EXIT REGION OF A

WELL-DEVELOPED 80 TO 100 KT MID-LEVEL JET IS FORECAST TO SPREAD

ACROSS THE CNTRL GULF COAST STATES DURING THE DAY CREATING STRONG

DEEP LAYER SHEAR PROFILES FAVORABLE FOR SEVERE STORMS. THE

GFS...ECMWF AND NAM BEGIN THE DAY 3 PERIOD WITH AN MCS LOCATED IN

THE MID-MS VALLEY DRIVING THIS FEATURE EWD INTO WRN KY AND WRN TN BY

MIDDAY. SOUTH ACROSS THE WARM SECTOR...THE MODELS DEVELOP MODERATE

INSTABILITY ACROSS MUCH OF THE CNTRL GULF COAST STATES AND INITIATE

NUMEROUS THUNDERSTORMS FROM MIDDLE TN SWWD INTO NCNTRL AL...MS AND

SE LA DURING THE AFTERNOON. THE DEVELOPMENT OF A SEVERE MCS SEEMS

PROBABLE ACROSS THE CNTRL AND SRN PARTS OF THE SLIGHT RISK AREA

FRIDAY AFTERNOON AND EVENING.

FORECAST SOUNDINGS IN CNTRL MS AND WRN AL AT 21Z ON FRIDAY SHOW

IMPRESSIVE WIND SHEAR PROFILES WITH 50 TO 60 KT OF 0-6 KM SHEAR AND

0-3 KM STORM RELATIVE HELICITIES AROUND 400 M2/S2. THIS ENVIRONMENT

SHOULD SUPPORT SUPERCELL DEVELOPMENT WITH A THREAT FOR STRONG

TORNADOES POSSIBLE. HOWEVER...THE MAGNITUDE OF THE TORNADO THREAT

WILL BE CONDITIONAL UPON STORM MODE. IF A SQUALL-LINE WERE TO

DEVELOP INSTEAD OF MORE DISCRETE CONVECTION....THEN WIND DAMAGE

COULD BE THE GREATER THREAT. THE UPPER-LEVEL SYSTEM IS QUITE

IMPRESSIVE WITH A WELL-DEVELOPED LOW-LEVEL JET IN PLACE ACROSS THE

ECNTRL STATES. THE GFS AND NAM SOLUTIONS FOCUS THE LOW-LEVEL JET

FURTHER NORTH IN TN AND KY BY LATE AFTERNOON WHILE THE ECMWF SHOWS A

STRONG COMPONENT OF THE JET IN THE TN VALLEY AND CNTRL GULF COAST

STATES. IF THE ECMWF SOLUTION IS CORRECT AND MOISTURE RETURN ENDS UP

BEING STRONGER THAN FORECAST...THEN A TORNADO OUTBREAK COULD OCCUR

IN PARTS OF WRN TO MIDDLE TN...MS AND AL FRIDAY AFTERNOON. AT THIS

POINT...THE POTENTIAL FOR AN OUTBREAK REMAINS CONDITIONAL AND

DIFFERENCES IN THE MODEL SOLUTIONS RAISE UNCERTAINTIES CONCERNING

THE EXACT SCENARIO.

FURTHER NORTH ACROSS THE OH VALLEY...SEVERE STORMS WILL ALSO BE

POSSIBLE FRIDAY AFTERNOON AS THE UPPER-LEVEL LOW APPROACHES FROM THE

WEST. IN SPITE OF WEAKER INSTABILITY...A STRONG WIND FIELD IS

FORECAST WITH COLD TEMPS ALOFT. THIS WOULD RESULT IN A POTENTIAL FOR

HAIL AND WIND DAMAGE WITH THE MORE ORGANIZED CONVECTIVE CLUSTERS. A

TORNADO THREAT WILL ALSO BE POSSIBLE IN THE OH VALLEY DUE TO THE

STRONG LOW-LEVEL SHEAR FORECAST BUT THIS POTENTIAL SHOULD BE

DEPENDENT UPON MOISTURE RETURN.

[buckeyefan1]

the upper low has been shown to cut off strongly in the MO area, and that usually equates to 2 lines of severe for GA and the Carolinas. I'm not sure yet which way I'm leaning on this, on the one hand a primary line could come through and begin to lose steam in central Carolinas overnight Fri. Night, and then another develops to the west a few hours later. It depends on how quickly and where the ULL cuts off. Also, usually this is a big rain maker at the GA/NC/SC conjoinance region, IE, southern APPS. Already the GFS has been showing this several runs. Hopefully its a little more progressive to help the central and eastern Carolinas get into some action where they've missed out a lot already. Either way you slice it, GA is gold once again. I could see the first line making further progress east and earlier than shown, which would help out the eastern friends on much needed precip. And with the ULL shown still so far back, there could be a case for re-development. Its a rare setup, but its happened before.

This is what I'm afraid of. Central NC and east to the coast looks to be in a good spot for Saturday afternoon and as you pointed out GA appears to get rocked As long as the threats keep coming, there will always be a chance and I'll be happy with anything close to .25 in the rainfall department

[kanc2001]

going to most likely be in Birmingham friday-saturday for a family event. good timing although we may get there too late friday.

[eyewall]

Out of RAH for central NC on Sat:

PACIFIC JET ENERGY DIGGING ACROSS THE ROCKIES WILL DEEPEN A SYSTEM

FROM THE LEE OF THE ROCKIES TO THE MID MS RIVER VALLEY REGION ON

FRIDAY. THERE HAS BEEN GOOD GENERAL AGREEMENT BETWEEN THE GFS/ECMWF

ON AN UPPER WAVE CUTTING OFF AND THE SYSTEM BECOMING VERTICALLY

STACKED AS THE A ~995MB SURFACE LOW LIFTS NE FROM MO TO THE

GREAT LAKES BY SATURDAY MORNING. AN ONGOING QLCS FRIDAY IN A

MODERATELY UNSTABLE AIRMASS OVER THE DEEP SOUTH...FURTHER SUPPORTED

BY THE SURFACE COLD FRONT/PREFRONTAL TROUGH AND INCREASINGLY

DIFLUENT UPPER LEVEL FLOW AS A SPEED MAX SURGES INTO THE BASE OF THE

UPPER LOW...SHOULD BE APPROACHING THE SOUTHERN APPALACHIANS BY 06Z

SATURDAY. MODELS HAVE SLOWED ARRIVAL TIME OF THE CONVECTIVE LINE BY

6-12 HOURS...MORE TOWARD THE DAYTIME HOURS SATURDAY. THIS MAY SPELL

A GREATER SEVERE THREAT AS MODEST DESTABILIZATION WILL BE POSSIBLE

VIA DAYTIME HEATING AND A SURGE OF 60F+ DEWPOINT AIR FROM THE SOUTH.

AS THE UPPER TROUGH BECOMES NEGATIVELY TILTED...DEEP LAYER SHEAR IN

EXCESS OF 50KT AND AND LOW LEVEL VEERING PROFILE/HODOGRAPH

SIGNATURES ARE A BIT CONCERNING. TIMING AND DESTABILIZATION WILL BE

KEY WITH THIS SYSTEM...AND THOSE DETAILS WILL HOPEFULLY BECOME MORE

CLEAR IN SUBSEQUENT FORECASTS. GIVEN THE AMOUNT OF MID LEVEL

FORCING AND STRENGTH OF THE LOW LEVEL JET... RELATIVELY QPF AMOUNTS

ARE FORECAST TO RANGE FROM 0.5-1.0" ON AVERAGE...WITH HIGHER AMOUNTS

CERTAINLY POSSIBLE.

[FoothillsNC]

The NAM is showing a setup for flooding in the Apps again. Esp. right around northeast GA/western Carolinas, and even the Apps in general. The strong confluence in the Northeast shown on all models now, has a strengthening slow moving surface high sliding offshore and that will focus 850 winds perpendicular to the escarpment. Combined with a pretty slow moving, deep, and strong cutoff to the northwest, all factors combined show this is usually a big deal for the region mentioned above. The one thing that can and sometimes does disrupt this or diminish this some , is the convection that outruns and robs the area from a lot of rain, but right now theres signs that the convection will backbuild and keep training right over northern GA, northeast Alabama, and far western SC and southern/SW NC area. Probably over 3" of widepsread rain if that happens. Be interesting to see if the GFS is similar again or faster, as I'd give it much more weight than NAM, but so far its a decent event too.

[ATL_Militarypolice]

I have a question for any of the mets/experts. Would steep-lapse rates in the lower and mid to upper levels help increase instability. Was wondering this while I was looking at soundings for KAHN involving this severe threat, the overall CAPE was low, but there is steep low-level and upper-level lapse rates being shown during the afternoon hours (from 1pm to 6pm). Would this help increase instability to be higher than what is being modeled, if not what do the steep lapse rates signify?

[Gastonwxman]

I have a question for any of the mets/experts. Would steep-lapse rates in the lower and mid to upper levels help increase instability. Was wondering this while I was looking at soundings for KAHN involving this severe threat, the overall CAPE was low, but there is steep low-level and upper-level lapse rates being shown during the afternoon hours (from 1pm to 6pm). Would this help increase instability to be higher than what is being modeled, if not what do the steep lapse rates signify?

Indeed they can. Steep lapse rates can occur when there is strong surface heating, which we know can aid in creating an unstable environment. If the air is said to have a steep lapse rate throughout the lower to upper levels, we know this means that temperatures are rapidly decreasing the higher you go and would indicate that air to be considered unstable. The higher the lapse rate, the greater the instability that is produces. The parcels of air in this case would be warmer than its surroundings and thus will have a better chance of lifting. So in short: Steep lapse rates help in the creation of instability. Did this help?

[ATL_Militarypolice]

Indeed they can. Steep lapse rates can occur when there is strong surface heating, which we know can aid in creating an unstable environment. If the air is said to have a steep lapse rate throughout the lower and mid levels, we know this means that temperatures are rapidly decreasing the higher you go and would indicate that air to be considered unstable. The higher the lapse rate, the greater the instability that is produces. The parcels of air in this case would be warmer than its surroundings and thus will have a better chance of lifting. So in short: Steep lapse rates help in the creation of instability. Did this help?

Yes it did thanks.

[ATL_Militarypolice]

0-3KM CAPE

54 hours

60 hours

66 hours

[eyewall]

In addition to what was said earlier steeper lapse rates in the mid levels will also usually mean larger hail size (if in the -10C to -30C layer) and more vigorous updrafts "fat vs. skinny CAPE" comes to mind here as well.

[Gastonwxman]

Just going by the 12z Euro, we have a nice look to a negatively-tilted 5H trough as it swings through the country. Strong upper level divergence/diffluence can be seen across the eastern third of the U.S. as energy gets pivoted underneath. The ULD will aid in allowing more rising air to take place from below since the air aloft is too sparse and would indicate some good lifting going on, increasing the chance of severe weather for the Southeast.

[jrips27]

Some very impressive images for MS/AL/TN on today's model runs. SPC may go with a moderate risk in this area tomorrow morning.

[Cheeznado]

00Z NAM has some scary dynamics and LL shear in MS/AL and even into GA, in some respects this reminds me of the April 8th, 1998 situation. One really bad thing- there are a TON of events in KTCL and the BHM area Friday night, folks will be camping, there is a NASCAR race in Talladega- this could be pretty serious. Even ATL could be under the gun, SRH values off the charts at 06Z, despite low CAPE a tornado cannot be ruled out this far east. I agree a MDT risk and maybe even a high is in the cards for Friday.

[audioguy3107]

00Z NAM has some scary dynamics and LL shear in MS/AL and even into GA, in some respects this reminds me of the April 8th, 1998 situation. One really bad thing- there are a TON of events in KTCL and the BHM area Friday night, folks will be camping, there is a NASCAR race in Talladega- this could be pretty serious. Even ATL could be under the gun, SRH values off the charts at 06Z, despite low CAPE a tornado cannot be ruled out this far east. I agree a MDT risk and maybe even a high is in the cards for Friday.

April 8, 98 was a pretty scary night.......there was a large part of the SE under a high risk that day. I remember that night, it was extremely muggy and hot. Posted a SPC risk map for that day......I love severe weather, but hope it doesn't pan out like that day did.

[Cheeznado]

I think that the CAPE will be lower (especially in GA) than in 1998, but the dynamics are a bit stronger.

[Gastonwxman]

00Z NAM has some scary dynamics and LL shear in MS/AL and even into GA, in some respects this reminds me of the April 8th, 1998 situation. One really bad thing- there are a TON of events in KTCL and the BHM area Friday night, folks will be camping, there is a NASCAR race in Talladega- this could be pretty serious. Even ATL could be under the gun, SRH values off the charts at 06Z, despite low CAPE a tornado cannot be ruled out this far east. I agree a MDT risk and maybe even a high is in the cards for Friday.

It's especially a scary situation given the time that this occurs. With a secondary surface low developing amongst all other things, this only further increases the tornadic threat with the backing winds. Indeed the shear and SRH is looking quite strong, especially the Energy Helicity Index which was forecasted to be near 4 at 1km and around 6 at 3km for some locations across the Gulf Coast States! All indicative of dangerous super cellular development. The parameters are quite impressive to say the least...

EHI (1km and 3km) values at hr. 45:

[GaWx2688]

This is also race weekend in Talladega. Yikes!! I hope everyone in campers there take shelter if those sirens go off, and are not too intoxicated to realize what's going on.

[ryan1234]

I really hope the Carolina's can get in good on this. I think we will, but you never know around here. Looks like Alabama will once again be slammed, but that always seems to be the case. Gaston, what do you think?

[GaWx2688]

Mod. risk now up for parts of Alabama for Friday already. Some even hint they could go high risk. I am in western Ga not far from I-20 and only 10 miles from the AL line. I always pay close attention to what they say for eastern AL. I just wonder how it is looking for the Atlanta area now, because from what I am reading Friday is going to be one rough day on the severe weather front.

[Gastonwxman]

I really hope the Carolina's can get in good on this. I think we will, but you never know around here. Looks like Alabama will once again be slammed, but that always seems to be the case. Gaston, what do you think?

The chances are increasing with each new set of data that's coming in for a more dangerous severe weather setup. After a review of tonight's guidance, it seems as though the tornado chances have ramped up a good bit per some of the sounding data (say KCBM in MS for example, which had some very impressive severe wx parameters from the 0z NAM) but this high threat is more for the folks further west of you and I. We continue to keep our negatively tilted trough that traverses across the Gulf Coast States with the upper level low going from the Plains and eastward into portions of MO and AR. Dynamics are still strong, especially CAPE (values +2000 in spots), deep layer and low level shear, 3km SREH values going off the deep end (400-500) ,mid-level jet (which looks to have a favorable exit with winds near 90kts max (or 135mph)), and a progressively deepening surface low that will head NE through TN and into the OV with the next cold front pushing through MS (and aid in backing winds). During the afternoon, convection should fire off back west in the western section of the Southeast (being western TN, MS) and move eastward in the evening. I expect areas from MS-AL and parts of TN to receive the hardest hits with a good threat for plenty of super cellular action. In fact, basing it just on these parameters alone, I wouldn't be surprised if a few of these super cells had a "long" life after they erupt. This is based on some of the hodographs that I've seen which have that looped look to them and therefore indicates that any tornadoes that do develop could have increased longevity ( or simply long-tracked), which that alone is threatening enough. The hail is another thing to be concerned with. With such strong updrafts and steep lapse rates, large hail will definitely be an issue for some; very large in spots. At the mid levels, temperatures are definitely cold enough to support very large hailstones and have a good chance of reaching the surface with some or little melting similar to the event that occurred across NC over the previous weekend, and this is in combo with such strong deep layer shear present and of course any of the supercells. Still, in terms of what the convective mode will be, it does seem that discrete supercells will be available but eventually the storms will organize into a QLCS later on during the day Friday but the environment would still support a few tornadoes nonetheless.

As far as what eventually happens in the Carolinas (and I suppose I'll include GA in this), while I don't think it will be nearly as bad as it it most likely would be back west in MS, parts of TN and AL, we could still be dealing with some rough action ourselves despite the timing of the arrival of the front (which was the issue last time with low instability) since dynamics are still looking good for a part of Saturday. There is room for a few discrete supercells (if you're to believe that the MCS breaks before arriving in our neck of the woods). If the squall line were to make it into GA and the Carolinas, straight line winds, hail, and a few tornadoes will be the threats, more-so the wind and hail (think the event from the early part of last week). Despite the solutions amongst the modeling (the NAM in particular showing those turns in the hodographs), it's still uncertain as to what will eventually play out further east. Many times something will look good and then suddenly it falls apart when you least expect it. I don't think that will happen this go around (IMO)...at least not for most folks but we'll see. Not much more to say except keep in mind that things can and will change...down to the last minute if it happens. I wouldn't be surprised if the risk of severe weather gets raised to moderate status here given the load of potential that's on the table. Latest on the timing for us further east would be late friday and half of Saturday, although if you're to believe the Euro and NAM, it'll arrive slower and would persist for a part of Saturday afternoon until the evening pushing through eastern sections of NC/SC.

[GaWx2688]

This is the 1st system so far other than the Jan snow/ice storm that I get a bad feeling about, after all that I am reading. I am now reading about super cells ahead of the main front squall line around rush hour on Friday. Not so much for where I live, but over into western Alabama. Of course the Atlanta news is making this look like nothing. When they do that, is when we get slammed. When they tell us to bring out the helmets is when nothing happens.

[eyewall]

RAH is saying we could get the shaft via cloud cover and hence lack of instability:

STRONG TO SEVERE STORMS WILL BE POSSIBLE SATURDAY MORNING AND

SATURDAY AFTERNOON AS THE AFOREMENTIONED SYSTEM CROSSES THE AREA

FROM WEST TO EAST. WHILE THE BULK OF THE UPPER LEVEL FORCING WILL

LIFT OFF WELL NORTHWEST OF NC.. DEEP LAYER FORCING FOR ACCENT STILL

APPEARS TO BE FAIRLY STRONG AS AS THE UPPER TROUGH BECOMES

NEGATIVELY TILTED OVER THE CENTRAL APPALACHIANS AND OHIO VALLEY

REGION...WHILE FORECAST SOUNDINGS SHOW STRONG LOW LEVEL WARM

ADVECTION PROFILES. DEEP LAYER SHEAR WILL ACCORDINGLY STRENGTHEN AS

A SPEED MAX SURGES THROUGH THE BASE OF THE UPPER TROUGH AND ACROSS

THE SOUTHEAST US SATURDAY MORNING. OPERATIONAL NWP AND SREF PLUMES

ALL INDICATE A 45-55KT OF 0-6KM BULK SHEAR WITH STRONG 0-1KM SHEAR

IN EXCESS OF 40KT AS A 50KT+ LLJ TRANSLATES ACROSS THE AREA DURING

THE DAY. BACKED SOUTHEASTERLY NEAR SURFACE FLOW WILL ALSO SERVED AS

A FOCUS FOR 0-3KM HELICITY VALUES IN EXCESS OF 300 M2/S2 AS A WARM

FRONT RETREATS TO THE NORTH SATURDAY MORNING. THE MAIN QUESTION IN

THE FORECAST WILL BE INSTABILITY..AS MODELS ARE INDICATING ONLY

MODEST DESTABILIZATION WITH AROUND 400-800 J/KG OF MLCAPE

DEVELOPING. THIS APPEARS TO BE MAINLY A RESULT OF WARM ADVECTION AS

INSOLATION WILL LIKELY BE HAMPERED BY WIDESPREAD CLOUD COVER AND

ONLY MARGINALLY STEEP MID LEVEL LAPSE RATES AROUND 6-6.5 C/KM. THE

MAIN THREAT FROM THIS SYSTEM APPEARS TO BE DAMAGING WINDS...BUT

GIVEN THE STRONGLY SHEARED PROFILES AND POSSIBLE INSTABILITY AXIS

DEVELOPMENT...DISCRETE SUPERCELLS AND A CONDITIONAL TORNADO RISK MAY

ALSO EXIST. HEAVY RAIN WILL ALSO POSE A THREAT AS PW VALUES EXCEED

1.5" WITH STRONG WARM ADVECTION. MODEL QPF HAS BEEN CONSISTENTLY IN

THE 0.75-1.0"...THOUGH THE MOST RECENT 00Z NAM RUN IS A BIT DRIER.

SPC also hinting at more of a linear mode here.

[ATL_Militarypolice]

Strong wording coming out of SPC in their Day 2 moderate outlook talking about long-tracking strong tornadoes. A high risk defiantly seems in the cards by Day 1.