Sunday, November 28, 2010

Severe Weather Monday Night / Tuesday?


Significant Tornado Parameter >=1 at 3 a.m. Tuesday per the SREF


0-3 KM Helicity (shear) >=300m


CAPE 500 J/kg at 3 a.m. Tuesday


SPC Day Two Outlook

It looks like the models are showing a very small window during the early morning hours Tuesday when instability and shear may phase up and provide an opportunity for a slight risk of a tornado in Alabama. Instability will be very limited and it is still questionable if all ingredients will be in place at the same time. It is a situation that needs to be watched closely.

A few notes from official sources...

SPC Day Two Outlook:
THE ARRIVAL OF STRONGER FORCING FOR
ASCENT/HEIGHT FALLS AHEAD OF THE DIGGING SHORTWAVE TROUGH TOWARD
CENTRAL TX SUGGESTS STORMS SHOULD RAMP UP AGAIN LATE IN THE
EVENING/OVERNIGHT OVER THE LOWER MS VALLEY. THE INLAND INTRUSION OF
THE MOIST WARM SECTOR WILL AID IN SUFFICIENT DESTABILIZATION FOR
SURFACE BASED STORMS INTO THE SRN HALF OF MS AND SWRN AL OVERNIGHT.
FURTHER INCREASE IN MIDLEVEL WINDS ATOP THE LLJ WILL SUPPORT STRONG
DEEP LAYER SHEAR AND INCREASING LOW LEVEL HODOGRAPH CURVATURE FOR A
LATE EVENING AND OVERNIGHT TORNADO THREAT...SOME OF WHICH MAY BE
SIGNIFICANT. A THREAT FOR DAMAGING WINDS WILL ALSO BE POSSIBLE.

NWS Birmingham Hazardous Weather Outlook:
THERE IS A CHANCE OF SEVERE THUNDERSTORMS...INCLUDING THE THREAT OF
TORNADOES...ACROSS CENTRAL ALABAMA ON TUESDAY...ASSOCIATED WITH THE
PASSAGE OF A COLD FRONT. BECAUSE OF THE SMALL WINDOW OF OPPORTUNITY
DURING THE HEAT OF THE DAY...AND UNCERTAINTY AS TO THE TIMING OF THE
FRONT...THERE IS STILL A LOW DEGREE OF CONFIDENCE WITH THIS SEVERE
WEATHER THREAT.


NWS Birmingham Forecast Discussion:

ALTHOUGH CONFIDENCE IS LOW AND WINDOW IS SMALL...WILL CONTINUE TO HAVE A
SMALL WINDOW FOR SVR POSSIBLY EVEN TORNADIC ACTIVITY...MOST LIKELY
SE PORTIONS OF CWA IF ANY...DEPENDING ON TIMING OF FRONT.


NWS Huntsville Forecast Discussion:

THE END RESULT FOR US IS A SYSTEM
THAT WILL BE A LITTLE LESS POTENT IN TERMS OF INSTABILITY. HOWEVER...
HELICITY VALUES REMAIN IMPRESSIVE. OVERALL...BELIEVE THE SEVERE
THREAT WITH THE STORMS ALONG THE FRONT ARE RATHER LOW. HOWEVER...WITH
A 50-60 KT LOW LEVEL JET JUST OFF THE SURFACE...ANY MIXING DOWN OF
THOSE WINDS COULD CAUSE BRIEF DAMAGING WIND EVENTS.


...

2 comments:

Matt Graves said...

I appreciate you posting a good analysis of this. It does slightly concern me, but I have to wonder if we'll be warm enough to get any instability. Even Birmingham's discussion said the threat would probably be limited to southeast parts of its county warning area if it happened at all. It's hard to totally write off such a threat this time of year though. I hate overnight severe weather.

Mike Wilhelm said...

Thanks, Matt!