ETA/GFS comparison ... Interesting Setup for the MID-ATL

[Stormsfury]

Both the ETA and GFS are developing a storm system in the Southern Plains rapidly moving NE in the short-term ... with the potential of squall line development for the Middle-Atlantic States on Thursday/Friday of this upcoming week ...

ETA vs. GFS model comparison

[JCT777]

My local forecast calls for rain late Thursday into early Friday. Followed by a very windy day on Friday.

[PTrackerLA]

My forecast has hinted at possible severe storms tomorrow night.

[Lightning_Storm]

I doubt there is much of a chance up here for severe weather...maybe a slight chance for DC and south... Since it will be rather cool and cloudy

[Stephanie]

Sounds a fun Black Friday!!

[breeze]

It's gonna rain on our gobblers.

That's a fact!

[Stormsfury]

I doubt there is much of a chance up here for severe weather...maybe a slight chance for DC and south... Since it will be rather cool and cloudy

Both the ETA/GFS continue the threat for a narrow squall line, with a primary threat likely being gusty winds ... both in the short term are indicating quite a surge of WAA which could destabilize the atmosphere just enough to produce convection that's able to tap into the strong low-level southerly jet seen by BOTH of the models ...

And even better, as I finished typing this, I checked SPC's outlook and darn, if they are seeing the same possible threat as I am ...

SPC Day 3 Outlook

DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0232 AM CST TUE NOV 25 2003

VALID 271200Z - 281200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...
DEEP TROUGH WILL CONTINUE EWD THURSDAY WITH AN AXIS EXTENDING FROM
THE GREAT LAKES INTO THE GULF COAST STATES BY THE END OF THE PERIOD.
SEVERAL STRONG VORT MAXIMA AND ASSOCIATED MID LEVEL SPEED MAXIMA
WILL BE EMBEDDED WITHIN THE TROUGH...WITH LEADING SYSTEM EJECTING
INTO THE MID ATLANTIC/NORTHEASTERN U.S. BY FRIDAY MORNING. AT THE
SURFACE...A COLD FRONT WILL MOVE QUICKLY EWD ACROSS THE APPALACHIANS
AND EXTEND ALONG THE MID/SRN ATLANTIC COAST AND NRN FL BY THE END OF
THE PERIOD.

...CENTRAL GULF COAST STATES INTO THE SRN ATLANTIC...
LINE OF THUNDERSTORMS WILL LIKELY BE OCCURRING EARLY IN THE PERIOD
FROM THE TN INTO THE LOWER MS RIVER VALLEYS...WHICH IS EXPECTED TO
MOVE STEADILY EWD THOUGH THE PERIOD. THOUGH LOWER AND DEEP LAYER
SHEAR ARE FORECAST TO REMAIN FAIRLY STRONG...AND CERTAINLY SUPPORT
ORGANIZED CONVECTION...INSTABILITY MAY BE LIMITED WITHIN THE WARM
SECTOR. THE ETA IS MORE AGGRESSIVE THAN THE GFS IN DEVELOPING
MODERATE INSTABILITY AND 70+F SURFACE DEW POINTS INLAND INTO THE FL
PANHANDLE/SERN AL/SWRN GA DURING THE AFTERNOON. GFS ONLY ADVECTS
64+F SURFACE DEW POINTS INTO THIS REGION. WILL OPT TO ONLY FORECAST
LOW PROBABILITIES OF SEVERE ATTM DUE TO DEGREE OF UNCERTAINTY
REGARDING INSTABILITY.

...MID ATLANTIC...
A SURFACE WAVE ALONG APPROACHING COLD FRONT MAY LIFT ACROSS THE MID
ATLANTIC LATE IN THE PERIOD IN RESPONSE TO SHORTWAVE TROUGH/SPEED
MAXIMA EJECTING INTO THE NERN U.S. THIS SHOULD SUPPORT VERY STRONG
LOW LEVEL SHEAR WITH ETA FORECAST OF 50-60 KT WIND JUST ABOVE A
SHALLOW...STABLE BOUNDARY LAYER. GIVEN PROXIMITY OF SUCH STRONG
WINDS JUST OFF THE SURFACE...AT LEAST LOW PROBABILITIES OF SEVERE
THUNDERSTORMS ARE WARRANTED ATTM AS A FEW DOWNDRAFTS WITHIN EWD
MOVING LINE OF CONVECTION MAY TAP THESE VERY STRONG SLY WINDS.

..EVANS.. 11/25/2003

[RNS]

...MID ATLANTIC...
A SURFACE WAVE ALONG APPROACHING COLD FRONT MAY LIFT ACROSS THE MID
ATLANTIC LATE IN THE PERIOD IN RESPONSE TO SHORTWAVE TROUGH/SPEED
MAXIMA EJECTING INTO THE NERN U.S. THIS SHOULD SUPPORT VERY STRONG
LOW LEVEL SHEAR WITH ETA FORECAST OF 50-60 KT WIND JUST ABOVE A
SHALLOW...STABLE BOUNDARY LAYER. GIVEN PROXIMITY OF SUCH STRONG
WINDS JUST OFF THE SURFACE...AT LEAST LOW PROBABILITIES OF SEVERE
THUNDERSTORMS ARE WARRANTED ATTM AS A FEW DOWNDRAFTS WITHIN EWD
MOVING LINE OF CONVECTION MAY TAP THESE VERY STRONG SLY WINDS.

i doubt we will see any widespread severe weather aside from isolated convection which is able to tap the very strong winds just above the surface. given shear profiles...another pre-cold frontal rain band is probably the prefered convective mode. instability will be the biggest problem (as it will be lacking...significantly). the development of the pre-cold frontal rain band will likely depend on the strength of the pressure rise/fall couplet.

in last weeks severe event, a very strong pressure rise/fall couplet forced the strengthening of the squall line across MD and northern VA, which due to favorable shear and wind profiles (SRH was around 750 m2/s2)...even despite little in the way of thermodynamic support...convective initiation took place anyway. This may once again occur.

[Colin]

Well, we'll see! I agree with RNS, probably another rain band ahead of the main front.

[Stormsfury]

...MID ATLANTIC...
A SURFACE WAVE ALONG APPROACHING COLD FRONT MAY LIFT ACROSS THE MID
ATLANTIC LATE IN THE PERIOD IN RESPONSE TO SHORTWAVE TROUGH/SPEED
MAXIMA EJECTING INTO THE NERN U.S. THIS SHOULD SUPPORT VERY STRONG
LOW LEVEL SHEAR WITH ETA FORECAST OF 50-60 KT WIND JUST ABOVE A
SHALLOW...STABLE BOUNDARY LAYER. GIVEN PROXIMITY OF SUCH STRONG
WINDS JUST OFF THE SURFACE...AT LEAST LOW PROBABILITIES OF SEVERE
THUNDERSTORMS ARE WARRANTED ATTM AS A FEW DOWNDRAFTS WITHIN EWD
MOVING LINE OF CONVECTION MAY TAP THESE VERY STRONG SLY WINDS.

i doubt we will see any widespread severe weather aside from isolated convection which is able to tap the very strong winds just above the surface. given shear profiles...another pre-cold frontal rain band is probably the prefered convective mode. instability will be the biggest problem (as it will be lacking...significantly). the development of the pre-cold frontal rain band will likely depend on the strength of the pressure rise/fall couplet.

in last weeks severe event, a very strong pressure rise/fall couplet forced the strengthening of the squall line across MD and northern VA, which due to favorable shear and wind profiles (SRH was around 750 m2/s2)...even despite little in the way of thermodynamic support...convective initiation took place anyway. This may once again occur.

I definitely agree ... nothing widespread, but a narrow squall line seems feasible with the possibility of isolated low-topped (discrete) supercell activity given the shear profiles ... hence the risk is under (less than) slight categorical risk and too isolated in nature to warrant such ...

As for last week's severe event, that strong rise/fall couplet almost resembled as such as one would see in a "Gravity Wave" scenario ...

For those who haven't seen anything on "Gravity Waves", I suggest you read this event (from GSP) last year with links to the science of how they might form ...

http://www.stormsfury1.com/Weather/GravityWave.html

SF

[RNS]

if a gravity wave is to develop it would do so at the mouth of the 50-60 Kt LLJ in conjunction with the rise/fall couplet, the stronger that feature becomes, then the better the potential will be for the development of a gravity wave. one must also have static stability present overtop of the stable layer. this would occur to the north of the warm frontal boundary...ahead of the main H5 trough axis and just to the north of the 500 hPa ridge invof sufficient upper lvl difluence.

the wave CISK theroy (particularly important in the past severe wx situation here in the Mid ATL) states that organized convection can develop due to the convergence associated with the wave its self, and heat release associated with the convection allows for the strengthening of the wave to occur.

[Stormsfury]

if a gravity wave is to develop it would do so at the mouth of the 50-60 Kt LLJ in conjunction with the rise/fall couplet, the stronger that feature becomes, then the better the potential will be for the development of a gravity wave. one must also have static stability present overtop of the stable layer.

That's right ... it usually develops at the leading edge of the dry slot punching through (behind the rain shield) ...



http://www.srh.noaa.gov/bmx/february_22 ... _loop.html

[Stormsfury]

[RNS]

Given that situation one would also like to see strong upper level divergence above low level convergence.

[Stormsfury]

This was the Birmingham, Alabama event ...

http://www.srh.noaa.gov/bmx/february_22 ... _1998.html

[RNS]

which would provide the best environement for UVM ahead of the cold front.