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Thanksgiving Week Severe Weather

msp

By msp,
in Central/Western States

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baroclinic_instability

baroclinic_instability

Posted
Posted

WHILE OVERALL SEVERE POTENTIAL SHOULD REMAIN LOW...AFOREMENTIONED

VERY STRONG FLOW FIELD SUPPORTS LOW-PROBABILITY POTENTIAL FOR WIND

AND/OR AN ISOLATED TORNADO OR TWO. IF A FEW STRONGER/ORGANIZED

CONVECTIVE FEATURES CAN OCCUR WITHIN THE LARGER-SCALE FRONTAL

CONVECTIVE BAND...SEVERE THREAT WOULD BECOME ENHANCED LOCALLY.

ATTM...DELINEATING ANY MORE LIKELY AREAS FOR SUCH LOCAL CONVECTIVE

ENHANCEMENT WOULD PROVE DIFFICULT...AND THUS WILL NOT INTRODUCE ANY

SLIGHT RISK AREAS. HOWEVER...A HIGHER-END SEVERE WEATHER REPORT OR

TWO IS POSSIBLE -- DESPITE THE LOW OVERALL SEVERE PROBABILITY...AS A

RESULT OF THE HIGHLY-FAVORABLE KINEMATIC CONDITIONS EXPECTED.

No slight risk yet.

Slight risk is a probability. You actually bring up an interesting point without really trying to do so, but even though the risk outlooks are probability based, they tend to slide to the high/mod for higher end severe threats where potential magnitude of the severe wx is increased. For instance, you rarely see a high risk outlook for a potential widespread wind event but with minimal potential for extreme damage if kinematic fields are marginal.

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Stebo

Stebo

Posted
Posted

1300Z outlook slight adjustment east in MI with the 2% Tor/5% wind risks into DTX's area, and shaved some of the southern Tor risks in AR. Still See Text

DAY 1 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0647 AM CST MON NOV 22 2010

VALID 221300Z - 231200Z

...NO SVR TSTM AREAS FORECAST...

A LARGE LOW AMPLITUDE UPPER TROUGH WILL PROGRESS RAPIDLY EASTWARD

ACROSS THE CENTRAL UNITED STATES TODAY...WHILE THE ASSOCIATED 80-90

KNOT MID LEVEL JET NOSES INTO THE GREAT LAKES REGION. STRONG

SOUTHWESTERLY LOW LEVEL WINDS AHEAD OF THE TROUGH HAVE BEEN

TRANSPORTING PARTIALLY MODIFIED GULF AIR MASS NORTHWARD WITH

DEWPOINTS IN THE UPPER 50S AS FAR NORTH AS PORTIONS OF IL/IND. AS A

COLD FRONT SAGS SOUTHWARD INTO THE MID MS VALLEY AND GREAT LAKES

THIS EVENING AND TONIGHT...THE POTENTIAL FOR ISOLATED STRONG/SEVERE

STORMS WILL INCREASE.

OPERATIONAL AND STORM-SCALE MODEL GUIDANCE IS IN FAIR AGREEMENT THAT

SCATTERED THUNDERSTORMS WILL AFFECT PORTIONS OF IL/WI/IND/LOWER MI

THIS MORNING THROUGH THE AFTERNOON...IN REGION OF STRONG LOW LEVEL

WARM ADVECTION. 12Z OBSERVED AND FORECAST SOUNDINGS SUGGEST RATHER

STEEP MID LEVEL LAPSE RATES BUT WEAK CAPE AND MINIMAL SURFACE-BASED

INSTABILITY. SMALL HAIL WILL BE POSSIBLE WITH THE STRONGEST

CELLS...BUT ORGANIZED SEVERE STORMS ARE NOT ANTICIPATED.

BY LATE AFTERNOON...THE PRIMARY COLD FRONT WILL EXTEND FROM A

SURFACE LOW OVER SOUTHERN WI INTO CENTRAL MO AND NORTHERN OK.

SCATTERED THUNDERSTORMS WILL BEGIN TO DEVELOP ALONG THE FRONT AND

SPREAD SOUTHEASTWARD ACROSS IL/IND. THERMODYNAMIC PARAMETERS WILL

REMAIN QUITE WEAK. HOWEVER...STRONG LOW/MID LEVEL WIND FIELDS AND

LINEAR NATURE OF CONVECTION WILL POSE A RISK OF GUSTY AND

OCCASIONALLY SEVERE WIND GUSTS. UNCERTAINTY REMAINS REGARDING

WHETHER SUFFICIENT INSTABILITY WILL DEVELOP FOR ORGANIZED SEVERE

STORMS...SO WILL MAINTAIN ONLY 5% PROBS AT THIS TIME.

THUNDERSTORMS WILL DEVELOP SOUTHWARD ALONG THE FRONT DURING THE

EVENING INTO PARTS OF AR. LOW LEVEL MOISTURE AND INSTABILITY WILL

BE SLIGHTLY STRONGER IN THIS AREA...BUT VEERED LOW LEVEL WINDS AND

WEAKER LARGE SCALE FORCING WILL BE OFFSETTING FACTORS FOR A MORE

ROBUST SEVERE THREAT.

..HART/HURLBUT.. 11/22/2010

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Stebo

Stebo

Posted
Posted

A couple things since I have arrived home, first off the wildcard of this line that's currently moving NE out of Chicago, I don't believe any model showed that. Question will be what effects it will have on this side of the lake for later on in the day, I think it might lay down some subsidence and allow us to have some sunshine (the pockets of sun currently behind it across IL/MO) and allow us to bubble up some with a cap that will break later on in the evening as the line comes in. Second thing is the uptick in instability in the NAM model for today/tonight if this were to verify plus the aforementioned point, I foresee an upgrade to a slight at 1630z outlook, probably for IL/NW IN and W MI, this side of the state the timing will hurt the chances but if a line can become cold pool dominant then things would certainly have a chance E of 127 in MI too.

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csnavywx

csnavywx

Posted
Posted

Yeah I'll be honest I was surprised how hard it was raining this morning over here, without storms we ended up with over .25 in an hour.

We got drenched, and the sun has been out off and on this morning already. New NAM has much better severe indices for this afternoon over Northern IL, especially around the 3-6pm timeframe.

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Stebo

Stebo

Posted
Posted

I'll be surprised if there isn't an upgrade to slight risk on the next outlook. Then again I thought it would've occurred by now so maybe take my post with a grain of salt.

Yeah I was kind of surprised the 1300Z wasn't upgraded, but then again, I'd be floored if it wasn't 1630Z.

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janetjanet998

janetjanet998

Posted
Posted

5% TOR probs

DAY 1 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

1007 AM CST MON NOV 22 2010

VALID 221630Z - 231200Z

...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON AND EVENING

ACROSS MID MS VALLEY INTO LOWER OH VALLEY...

..MID MS VALLEY

GIVEN THE BREAKS IN THE CLOUD COVER ACROSS THE MID MS VALLEY AHEAD

OF THE DEVELOPING SURFACE LOW NOW SERN IA AND THE COLD FRONT

ENTERING WRN MO...IT NOW APPEARS SUFFICIENT INSTABILITY WILL BE

AVAILABLE FOR SEVERE THUNDERSTORMS ACROSS MID MS VALLEY. WITH THE

S/WV TROUGH CURRENTLY MOVING NEWD FROM SD/NEB TO UPPER MS VALLEY BY

THIS EVENING...THE ASSOCIATED VERY STRONG DEEP LAYER SHEAR I.E.

500MB WIND MAX OF 90-100 AND 300MB WINDS TO 150KT ALONG WITH LARGE

SCALE ASCENT WILL SPREAD ACROSS THE WARM SECTOR E OF MS RIVER.

SINCE OBSERVED MID LEVEL LAPSE RATES ARE AROUND 7C/KM...AND WITH

SURFACE TEMPS RISING TO NEAR 70F AHEAD OF FRONT ACROSS IL...MLCAPES

WILL BE AOA 500 J/KG WITH LITTLE CINH BY MID AFTERNOON...MORE THAN

SUFFICIENT TO JUSTIFY A CONDITIONAL THREAT OF SEVERE THUNDERSTORMS

INCLUDING SUPERCELLS.

SURFACE LOW WILL MOVE NEWD ACROSS SRN/ERN WI LATER THIS AFTERNOON

AND THIS WILL ALLOW THE WARM FRONT TO SHIFT NWD POSSIBLY AS FAR AS

INTO SERN WI PRIOR TO ARRIVAL OF THE COLD FRONT. CURRENT ELEVATED

STORMS N OF WARM FRONT WILL BE FOLLOWED BY DEVELOPMENT OF SURFACE

BASED STORMS ASSOCIATED WITH FRONTAL CONVERGENCE BY MID AFTERNOON

VICINITY COLD FRONT AS IT CROSSES MS RIVER INTO IL.

PRIMARY THREAT WILL BE DAMAGING WINDS GIVEN THE STRONG SHEAR

PROFILES AND DRY MID LEVELS ENHANCING DOWNDRAFT POTENTIAL.

HOWEVER...SUPERCELLS INCLUDING TORNADO'S ARE POSSIBLE...PARTICULARLY

JUST AHEAD OF THE SURFACE LOW TRACK VICINITY THE WARM FRONT WHERE

LOW LEVEL SHEAR WILL BE ENHANCED AND THE GREATEST POTENTIAL OF ANY

DISCRETE CELLS WILL OCCUR.

BY EVENING STORMS WILL CONTINUED TO DEVELOP SWD ALONG THE COLD FRONT

INTO NRN AR AND EVENTUALLY LOWER OH/WRN TN VALLEY. EXTENT OF SEVERE

THREAT THIS FAR SOUTH STILL UNCERTAIN GIVEN THE UPPER SUPPORT MOVING

WELL TO THE NORTH AND MORE CINH TO OVER COME. HOWEVER AT LEAST SOME

THREAT OF DAMAGING WINDS WILL ACCOMPANY THE EXPECTED LINEAR

CONVECTIVE MODE THIS AREA GIVEN THE STRONG SHEAR.

..HALES/SMITH.. 11/22/2010

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