Severe Wx Discussion - November 5, 2005

[wxmann_91]

This will be my first attempt at a severe weather discussion on this board. Severe weather isn't the most popular here, but perhaps we can discuss severe weather days. I've contrived a system where every day a severe weather threat looks high enough, I'll start a discussion where we can look at models and make our forecasts, and then during the event, post warnings and reports, and then afterwards, maybe pictures of the event. Unfortunately, I probably won't be here most of the day due to school, but perhaps someone else can cover during that time. Does it seem redundant (since many storm chaser forums have better coverage) or does it seem like a good proposition? Please answer this question. If you say yes most likely by spring new threads will be popping up in this forum every day. If you say no then it is okay also.

Anyway, tomorrow looks to be an active day. Have made a quick glance at the models and a pretty good vort max is located in northern Indiana. Moisture looks meager at best, but that is to be expected this time of the year. The 8Z SWODY2 looks very promising for the prospect of severe weather tomorrow:

LATEST OBSERVATIONS SHOW LOWER 60S DEWPOINTS OVER THE NRN GULF. THE
BOUNDARY LAYER FLOW WILL REMAIN SLY THROUGH SATURDAY WITH FAVORABLE
TRAJECTORIES FOR PARTIALLY MODIFIED GULF AIR TO ADVECT NWD THROUGH
THE LOWER AND MID MS VALLEY AS WELL AS THE TN AND OH VALLEYS.
DEWPOINTS AROUND 60 ARE EXPECTED AS FAR N AS THE OH VALLEY BY
SATURDAY AFTERNOON. THE MOISTURE RETURN WILL BE COINCIDENT WITH
COOLING MID LEVEL PROFILES AND STEEPENING MID LEVEL LAPSE RATES
ASSOCIATED WITH THE AMPLIFYING UPPER TROUGH AND EWD ADVECTION OF THE
ELEVATED MIXED LAYER. BY LATE SATURDAY AFTERNOON MLCAPE SHOULD RANGE
FROM NEAR 1500 J/KG OVER THE MID/LOWER MS VALLEY TO AOB 1000 J/KG
OVER WRN PARTS OF THE OH VALLEY. THE ATMOSPHERE WILL LIKELY BE
CAPPED TO SURFACE BASED STORMS MUCH OF THE DAY. HOWEVER...LIFT WILL
INCREASE ALONG AND AHEAD OF THE FRONT OVER THE MID/LOWER MS VALLEY
AS SURFACE LOW DEEPENS AND THE SWLY LOW LEVEL JET STRENGTHENS IN
ASSOCIATION WITH THE AMPLIFYING SHORTWAVE TROUGH. STRONG VERTICAL
SHEAR WILL LIKELY SUPPORT SUPERCELL STRUCTURES...ESPECIALLY OVER THE
MS VALLEY REGION...BUT EVOLUTION INTO LINES IS ALSO PROBABLE.
INITIAL SEVERE THREAT SHOULD BE OVER THE MS VALLEY...SPREADING NEWD
INTO THE TN AND OH VALLEYS OVERNIGHT. AN UPGRADE TO HIGHER
PROBABILITIES AND POSSIBLY A SIGNIFICANT SEVERE AREA MAY BE
WARRANTED IN LATER OUTLOOKS ONCE UNCERTAINTIES REGARDING THE TIMING
AND EVOLUTION OF THE UPPER TROUGH HAVE BEEN MITIGATED.

This afternoon we should see a clearer picture of what will happen. Setups like these can be very easily either a boom or a bust, one thing goes wrong it's a bust, but should everything be together just right we could see an outbreak. The setup, in fact, looks eerily similar to the November 10, 2002 tornado outbreak, which has been one of the deadliest and biggest November outbreaks ever.

[Skywatch_NC]

And speaking of fall tornado outbreaks...there was a deadly tornado that hit an area of Raleigh in late November 1988.

Eric

[wxmann_91]

For those who are interested, the newest SWODY2 isn't as bullish. ST members are discussing the weaknesses in this setup. Moisture isn't going to be all that plentiful and the cap is expected to be strong (and there's a possibility a little too strong). However, too strong is only a possibility, as strong forcing ahead of the cold front, along with unidirectional shear, is expected to limit the threat of discrete supercells, but increase the chance of a strong squall line. If that happens, the chances of tornadoes happening drops considerably.

New update tomorrow morning.

[wxmann_91]

Thick clouds cover most of the area this morning. If it clears by this afternoon though the chances of severe will still be high.

Latest SWODY1 has a 5% chance of tornadoes across southern Illinois. Here are some snippets:

OVERALL SYNOPTIC SETUP WILL BECOME VERY FAVORABLE
FOR SEVERE THUNDERSTORMS LATE TODAY AND TONIGHT AS SYSTEM BECOMES
INCREASINGLY NEGATIVELY TILTED AND STRONGEST SHEAR OVERSPREADS THE
WARM SECTOR. HOWEVER...12Z SOUNDINGS AND OBSERVED MOISTURE FIELDS
INDICATE STRONG CAP AND RATHER DRY BOUNDARY LAYER MAY LIMIT RISK
FACTORS THROUGH MUCH OF THE AFTERNOON.

PRIMARY SEVERE THREAT WILL LIKELY WAIT UNTIL 22Z-00Z AS CAP WEAKENS
OVER PORTIONS OF CENTRAL/ERN MO INTO CENTRAL IL. INITIAL
DEVELOPMENT WILL LIKELY BE IN THE FORM OF SUPERCELLS WITH THE
POTENTIAL FOR DAMAGING WINDS AND TORNADOES SHOULD ACTIVITY REMAIN
SURFACE-BASED. THIS ACTIVITY WILL EITHER EVOLVE INTO OR BE OVERCOME
BY SQUALL LINE EXPECTED TO EVOLVE IMMEDIATELY AHEAD OF STRONG COLD
FRONT/LEADING EDGE OF STEEP ASCENT PLUME DURING THE EVENING. BROKEN
SQUALL LINE WITH EMBEDDED BOW ECHOES/LEWP STRUCTURES WILL SUSTAIN AT
LEAST A DAMAGING WIND THREAT AS IT RACES EWD INTO THE OH RIVER
VALLEY AND SRN GREAT LAKES OVERNIGHT. WIND DAMAGE COULD BECOME
WIDESPREAD GIVEN SIGNIFICANT WINDS /50+ KT/ JUST OFF THE SURFACE.
COLD MID LEVEL TEMPERATURES AND 1000 J/KG MUCAPE SHOULD SUSTAIN
ISOLATED LARGE HAIL WITH THIS LINE AS WELL. TORNADO THREAT AFTER
DARK MAY BE MITIGATED BY SHALLOW STABLE LAYER DUE TO NOCTURNAL
COOLING. HOWEVER...SIGNIFICANT LOW LEVEL SHEAR AND LOW LCLS WILL
LIKELY MAINTAIN AT LEAST A RISK OF AN ISOLATED TORNADO OVERNIGHT.

In summary...a very big severe weather outbreak had this occurred in April or May, but the mitigating factors in November will keep this from becoming a major outbreak. Nevertheless, an extremely good setup for November.

Note that by 21Z, the RUC places SRH values of >200 m2/s2 over western parts of the Slight Risk area.



By 0Z, much of the Slight Risk area is covered with SRH values over 250 m2s2. (note: data is not very good)



The clouds might be a problem, forecast to stick around through 0Z:



LCL heights look good:



However, CAPE is marginal:



For those who don't understand what I'm saying, here's a good chart:

[wxmann_91]

Latest mesoscale discussion is out:

http://www.storm2k.org/phpbb2/viewtopic.php?p=1129702#1129702

Today's threat may be more winds than anything else, but any supercell that develops may have a tornadic threat.

[wxmann_91]

Tornado watch about to be issued

http://www.storm2k.org/phpbb2/viewtopic.php?p=1129702#1129737

Though this thread is unpopular (and with good reason, all the members are gone), I want input on how I can make these discussions better. I hope to continue doing them but it won't be fun if there isn't a discussion.

Where's jkt and Sam Sagnella? I know there are some other chasers besides them on this forum (I know Nick Grillo and Ryan McGinnis is here and I don't really know if WxGuy1 is Jeff Snyder), so please provide input.

[wxmann_91]

New tornado watch issued for eastern MO and western IL.

http://www.storm2k.org/phpbb2/viewtopic.php?p=1129751#1129751

Looks like initiation will occur further west than expected.

[wxmann_91]

Well, convection fired rapidly after the watch was issued, but the convective mode turned linear, mitigating the tornado potential. Unfortunately for chasers, it probably means a grungefest and a bust. Oh well, there's always next time (which, according to the SPC, is probably around November 8-9).

There's also a prospect for severe weather tomorrow in New England. Depending on how promising it looks, I'll start a thread on that either later tonight or tomorrow, or I won't start it at all. But we'll see.

[jhamps10]

storms are about an hour out of Metro st. louis, torando warnings are in effect for the far outlying counties near STL.

I know that all of the st. louis mets are watching the storms, like I am, it could get to me by midnight, but I would like to commend Mike roberts at ch. 5, he came on BEFORE there was a tornado warning, and mentioned the rotation that was developing, nice job Mike.

[jhamps10]

Thick clouds cover most of the area this morning. If it clears by this afternoon though the chances of severe will still be high.

Latest SWODY1 has a 5% chance of tornadoes across southern Illinois. Here are some snippets:

OVERALL SYNOPTIC SETUP WILL BECOME VERY FAVORABLE
FOR SEVERE THUNDERSTORMS LATE TODAY AND TONIGHT AS SYSTEM BECOMES
INCREASINGLY NEGATIVELY TILTED AND STRONGEST SHEAR OVERSPREADS THE
WARM SECTOR. HOWEVER...12Z SOUNDINGS AND OBSERVED MOISTURE FIELDS
INDICATE STRONG CAP AND RATHER DRY BOUNDARY LAYER MAY LIMIT RISK
FACTORS THROUGH MUCH OF THE AFTERNOON.

PRIMARY SEVERE THREAT WILL LIKELY WAIT UNTIL 22Z-00Z AS CAP WEAKENS
OVER PORTIONS OF CENTRAL/ERN MO INTO CENTRAL IL. INITIAL
DEVELOPMENT WILL LIKELY BE IN THE FORM OF SUPERCELLS WITH THE
POTENTIAL FOR DAMAGING WINDS AND TORNADOES SHOULD ACTIVITY REMAIN
SURFACE-BASED. THIS ACTIVITY WILL EITHER EVOLVE INTO OR BE OVERCOME
BY SQUALL LINE EXPECTED TO EVOLVE IMMEDIATELY AHEAD OF STRONG COLD
FRONT/LEADING EDGE OF STEEP ASCENT PLUME DURING THE EVENING. BROKEN
SQUALL LINE WITH EMBEDDED BOW ECHOES/LEWP STRUCTURES WILL SUSTAIN AT
LEAST A DAMAGING WIND THREAT AS IT RACES EWD INTO THE OH RIVER
VALLEY AND SRN GREAT LAKES OVERNIGHT. WIND DAMAGE COULD BECOME
WIDESPREAD GIVEN SIGNIFICANT WINDS /50+ KT/ JUST OFF THE SURFACE.
COLD MID LEVEL TEMPERATURES AND 1000 J/KG MUCAPE SHOULD SUSTAIN
ISOLATED LARGE HAIL WITH THIS LINE AS WELL. TORNADO THREAT AFTER
DARK MAY BE MITIGATED BY SHALLOW STABLE LAYER DUE TO NOCTURNAL
COOLING. HOWEVER...SIGNIFICANT LOW LEVEL SHEAR AND LOW LCLS WILL
LIKELY MAINTAIN AT LEAST A RISK OF AN ISOLATED TORNADO OVERNIGHT.

In summary...a very big severe weather outbreak had this occurred in April or May, but the mitigating factors in November will keep this from becoming a major outbreak. Nevertheless, an extremely good setup for November.

Note that by 21Z, the RUC places SRH values of >200 m2/s2 over western parts of the Slight Risk area.



By 0Z, much of the Slight Risk area is covered with SRH values over 250 m2s2. (note: data is not very good)



The clouds might be a problem, forecast to stick around through 0Z:



LCL heights look good:



However, CAPE is marginal:



For those who don't understand what I'm saying, here's a good chart:

Grrreeaatt, 5%chance of twisters right over my house, we had a quiet storm season (Mar.-June), and now this is really scaring me out.