Severe Weather Potential Friday the 13th and MLK Day?

[wxmann_91]

That big huge low which has been so hard to predict may not only bring one heck of a blizzard in the northern portions of the country, but severe as well.

Models continue to flip-flop, but SPC does have a risk area for the southeast.

http://www.spc.noaa.gov/products/exper/day4-8/

Still have many days to watch this, though, and as we have seen so far with this progged system, things can change drastically in two days.

[WaitingForSiren]

I was actually just talking about that storm. I live in MN and it looks like we may get some good snow out of it if enough cold air gets worked in. I also think a pretty good severe weather event may occur. I guess it'll depend on the strength/negative tilt of the storm and how much moisture gets pulled northward. Shouldnt be too hard though considering the storm in the south right now should draw some moisture northward.

[Brent]

It's something to watch... after the recent non-events I'm a bit reluctant to get overly excited right now. Too much uncertainty.

[WaitingForSiren]

Hmm, still looks tough to call. The issue I have is that the storm will be rapidly strengthening and since the cold front should flare up Thunderstorms thursday night, there should be plenty of precipitation along the fast moving front. this'll probably result is mostly low-end wind damage or isolated tornadoes embedded in the line maybe in Alabama or Georgie where the best moisture will be.

[jkt21787]

I am beginning to think the Fri event is not much of anything, but there are still some wildly varying model solutions to make a solid guess. GFS came in with crapped out solution, with NAM leaning toward it but not as bad. UKMET and ECMWF maintain a strong system. So indeed a tough call.

Personally, my attention is beginning to focus on the system slated for Monday and Tuesday. Here locally, this will probably have better chances simply for timing (morning event for Fri vs evening event with this one). Still far out, but it looks impressive, and CPC analogs run off the GFS have the top analog dates at 1/21-22 1999.

[WaitingForSiren]

I am starting to agree with you, the storm next Monday looks impressive. Good timing, rapid strengthening and ejecting northeastward. Looks like a big time tornado outbreak is possible for Monday...

[conestogo_flood]

Where will the Monday event be? In the southeast USA?

[WaitingForSiren]

Looks like Lousiana, southern arkansas, mississippi and perhaps western alabama into extreme southern Tennessee. Best bet for tornadoes looks to be in Northern Lousiana into northwestern missippi/southern arkansas. Should be quite interested, but then again its still a good 5 days away so we shouldnt get too excited.

[jkt21787]

Where will the Monday event be? In the southeast USA?

Early guess for me could include the states of AR, TN, MS, MO, KY, LA, perhaps Eastern TX and OK on Monday, perhaps shifting east of there on Tuesday. The exact track of the surface low will determine this in the end.

12z models remain impressive. GFS shows screaming wind fields (110+ kt upper jet streak and 50-60kt LLJ). Moisture return could be a problem with 60 dewpoints only reaching up through portions of the MS Delta up to near Memphis accord to the GFS, but this remains to be seen.

GFS and GGEM were a little south with ECMWF and UKMET not showing much change.

At least low topped damaging squall line could be a threat, and given enough shear, we may have supercells/tornadoes to deal with. Its way too soon to speculate on this, however, as this will be strongly dependant on the exact orientation of the wind fields, surface instability, and moisture return, which won't be known in great detail for several days still.

SPC Day 4 through 8 mentions the situation but cautions its still too soon to forecast a decent risk of severe storms, whcih I do agree with at this point.

Nevertheless, this is something that people in the aforementioned areas should continue to monitor. There will also be potential for rains in drought stricken areas of TX and OK, as well as winter weather from the Rockies into the Plains on the backside. Stay tuned...

[conestogo_flood]

What weather models does everyone use to see this?

[jkt21787]

What weather models does everyone use to see this?

Like said above, I've looked at the GFS, UKMET, ECMWF, and GGEM here. There's also the DGEX and NOGAPS but I haven't looked at them much for this system. We are not within the NAM, WRF, MM5 range yet.

[conestogo_flood]

Are there any links is more what I meant.

[jkt21787]

Are there any links is more what I meant.

Well a general view of the globals can be found here...
http://meteocentre.com/models/models_e.html

You can follow this link to the GFS runs and its various products which I got the wind field info from...
http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/

And another great site for model info...
http://www.meteo.psu.edu/~gadomski/ewall.html

[wxmann_91]

Well, now that the system for Friday seems to have crapped out, this thread will now also deal with Monday.

[WaitingForSiren]

Great site JKT. And yeah, the system for Friday appears to be more of a marginal forced squall line with marginally severe wind and hail. I could still see a few tornadoes in southern georgia, though.

[wxmann_91]

Well, if the 0Z run of the GFS verifies, another one will bite the dust. This run features LI's of an astouding 2 across the area next Monday. Severe weather can't develop in that.

[Brent]

...SERN U.S THROUGH CAROLINAS AND MID ATLANTIC AREAS...

CURRENT OBSERVATIONAL DATA SHOW DEWPOINTS IN THE LOW 60S OVER THE
WRN GULF AND SOUTH TX EXTENDING EWD THROUGH THE CNTRL AND NERN GULF.
A SWLY LOW LEVEL JET WILL INTENSIFY TONIGHT INTO THURSDAY OVER THE
CNTRL PLAINS AND LOWER MS VALLEY EAST OF DEVELOPING LEE CYCLONE AS
THE UPSTREAM SHORTWAVE TROUGH AMPLIFIES SEWD. THIS SHOULD RESULT IN
THE ADVECTION OF PARTIALLY MODIFIED GULF MOISTURE NEWD INTO THE
LOWER MS VALLEY AND SWRN PARTS OF THE SERN STATES BY EARLY FRIDAY.
LOW LEVEL MOISTURE SHOULD REMAIN MORE LIMITED FARTHER NE INTO THE
SERN STATES DUE TO LESS TIME AVAILABLE FOR ADVECTION TO OCCUR. LOW
LEVEL DEWPOINTS ARE EXPECTED TO RANGE FROM THE LOWER 60S OVER SWRN
PARTS OF THE SERN STATES TO 50S FARTHER NE. THE EXPECTED MODEST LOW
LEVEL MOISTURE RETURN WILL DEVELOP BENEATH -17 TO -19 C AT 500 MB
AND SHOULD CONTRIBUTE TO AT LEAST MARGINAL INSTABILITY WITHIN
PRE-FRONTAL WARM SECTOR...ESPECIALLY WHERE ANY HEATING DEVELOPS.
HOWEVER...A POTENTIAL LIMITING FACTOR FOR WIDESPREAD HEATING COULD
BE MIDDLE AND HIGH LEVEL CLOUDS THAT MAY ACCOMPANY THE SUBTROPICAL
JET.

STORMS WILL LIKELY BE ONGOING WITHIN ZONE OF ASCENT ALONG AND JUST
AHEAD OF FRONT COLD FRONT EARLY FRIDAY. FORCING ACCOMPANYING FALLING
HEIGHTS AND INTENSIFYING LOW LEVEL JET WILL LIKELY MAINTAIN
CONVECTION ALONG AND AHEAD OF THE FRONT DURING THE DAY. SWLY LOW
LEVEL JET AND VERTICAL SHEAR PROFILES WILL STRENGTHEN DURING THE DAY
AS MID LEVEL JET DEVELOPS SEWD INTO BASE OF AMPLIFYING UPPER TROUGH.
POTENTIAL WILL EXIST FOR ORGANIZED LINES AS WELL AS SUPERCELLS AS
ACTIVITY CONTINUES EWD. WILL MAINTAIN A GENERAL 15% SEVERE
PROBABILITY AREA AT THIS TIME. HOWEVER...AN UPGRADE TO HIGHER
PROBABILITIES MAY BE NEEDED FOR PORTIONS OF THIS AREA ONCE
UNCERTAINTIES REGARDING THE EVOLUTION OF LOW LEVEL MOISTURE AND
INSTABILITY HAVE BEEN MITIGATED.

[jkt21787]

Well, if the 0Z run of the GFS verifies, another one will bite the dust. This run features LI's of an astouding 2 across the area next Monday. Severe weather can't develop in that.

I've been told by several pros on another site that the GFS is way way off there. If the system is as strong as GFS is depicting, LIs will be much lower, as will dewpoints be much higher. Basically it makes no sense for the dynamic of this system to feature so paltry numbers. I was surmising on this myself earlier today and the Jackson MS NWS did too:

MODELS HAVE SFC DEWPOINTS SUSPICIOUSLY LOW FOR SUCH A
DYNAMIC SYSTEM AND HAVE A FEELING THAT THEY ARE AS MUCH AS 4-7F TOO
LOW. WITH DEWPOINTS IN THE MID 60S (RATHER THAN AROUND 60F)
INSTABILITY WOULD BE GREAT ENOUGH TO SUPPORT SEVERE CONVECTION
ACROSS THE ARKLAMISS. HOWEVER...AM UNCERTAIN HOW THUR NIGHT/FRIDAY`S
FRONTAL PASSAGE WILL AFFECT MOISTURE SOURCE OVER THE GULF. WILL
CONTINUE TO MONITOR LATEST TRENDS IN SUBSEQUENT PACKAGES AND KEEP A
CLOSE EYE ON TS POTENTIAL FOR MONDAY.

[WaitingForSiren]

I agree, I think dewpoints will advect further northward than currently forecast. Even if for some unusual reason they dont, the dynamics suggest a fast moving squall line with damaging winds at LEAST.

[Brent]

BY 12Z FRIDAY...HIGH AMPLITUDE UPPER TROUGH IS PROGGED THROUGH MUCH
OF THE MISSISSIPPI VALLEY. AS A MID-LEVEL LOW DEVELOPS/DEEPENS
ACROSS THE LOWER OHIO/TENNESSEE VALLEYS...SYSTEM WILL SLOW...BUT
TROUGH AXIS IS FORECAST TO SHIFT EASTWARD THROUGH THE APPALACHIANS.
LATEST NAM/GFS INDICATE A 100+ KT 500 MB JET STREAK DIGGING INTO
BASE OF THE TROUGH WILL SUPPORT SOUTHEASTWARD DEVELOPMENT OF
MID-LEVEL CIRCULATION INTO THE SOUTHERN APPALACHIANS BY 12Z
SATURDAY. A DEEPENING SURFACE CYCLONE WILL ACCOMPANY UPPER SYSTEM
THROUGH THE OHIO VALLEY...WITH A SIGNIFICANT TRAILING COLD FRONT
SURGING THROUGH MUCH OF THE MID SOUTH AND SOUTHEASTERN STATES.

ALTHOUGH SOME CONCERNS STILL EXIST ABOUT DEPTH OF MOISTENING
BOUNDARY LAYER ACROSS THE GULF OF MEXICO...SURFACE DEW POINTS OVER
THE OPEN WATERS OF THE WESTERN GULF ARE NOW IN THE MID/UPPER
60S...WITH LOWER 60S OVER THE NORTHEAST GULF. WITH FURTHER
MODIFICATION LIKELY THROUGH FRIDAY...RETURN FLOW...GIVEN STRENGTH OF
UPPER FORCING...SEEMS LIKELY TO SUPPORT SUFFICIENT DESTABILIZATION
FOR SEVERE THREAT. AN OUTBREAK OF SEVERE STORMS APPEARS POSSIBLE
ACROSS PARTS OF THE EASTERN GULF/SOUTH ATLANTIC COAST STATES.
DAMAGING WINDS MAY BE PRIMARY THREAT...BUT SHEAR PROFILES WILL
BECOME MORE THAN SUFFICIENT FOR SUPERCELLS WITH TORNADIC POTENTIAL.

...EASTERN GULF/SOUTH ATLANTIC COAST STATES...
MOISTURE RETURN/DESTABILIZATION AND STRENGTHENING LOW-LEVEL WARM
ADVECTION SEEM LIKELY TO SUPPORT INCREASING CONVECTIVE DEVELOPMENT
FROM PARTS OF SOUTHEAST LOUISIANA INTO SOUTHERN MISSISSIPPI
BY/SHORTLY AFTER 12Z FRIDAY. BOUNDARY LAYER BASED CAPE MAY BE
CLOSER TO 500 J/KG THAN 1000 J/KG...BUT LARGE CURVED HODOGRAPHS
BENEATH DIFLUENT AND STRONG MID/UPPER FLOW WILL BE FAVORABLE FOR
ISOLATED SUPERCELLS. AS SURFACE WARMS BY MID TO LATE MORNING...RISK
FOR ISOLATED TORNADOES WILL INCREASE...BEFORE ACTIVITY BEGINS TO
DEVELOP EASTWARD THROUGH THE REMAINDER OF THE GULF STATES. THIS
SHOULD OCCUR AHEAD OF INCREASINGLY ORGANIZED SQUALL LINE...WHICH IS
EXPECTED TO ADVANCE THROUGH MUCH OF MISSISSIPPI/ALABAMA/WESTERN AND
CENTRAL GEORGIA AND THE FLORIDA PANHANDLE BY LATE FRIDAY AFTERNOON.
ACTIVITY IS EXPECTED TO DEVELOP EASTWARD INTO SOUTH ATLANTIC COASTAL
AREAS...THROUGH THE CAROLINAS AND ACROSS NORTHERN FLORIDA...WITH A
CONTINUING RISK FOR DAMAGING WINDS/ISOLATED TORNADOES FRIDAY
EVENING.