Feb 23rd-24th OV/GL Severe Weather, SPC Risk: Day 1 Slight Risk Options

[Southern Indiana]

Mostly a southern storm, but this consumes almost all of Kentucky and a small southern portion of Indiana




LMK AFD

.Short Term (Tonight through Thursday night)...
Updated at 300 PM EST Feb 22 2012

Main challenge in the short-term centers around potential for severe
weather late Thursday afternoon into Thursday night, as a vigorous
upper disturbance dives SE out of the Canadian Rockies, pushing a
cold front through the Ohio Valley. Limiting factor will be
instability, even with sfc temps pushing 70F on Thursday afternoon,
due to a warm nose near 850mb. There is a narrow window just before
sunset where we could realize marginal instability, if the mid-level
dry layer is eroded in time. Otherwise this is a very dynamic
system, with strong speed shear, and potentially enhanced
directional shear if the secondary sfc low develops over the
Mississippi Valley and moves ENE across Kentucky. All this adds up
to the slight risk advertised by SPC, and the main issue will be
damaging wind potential, with the best shot between 21Z Thursday and
03Z Friday. Will advertise this in the HWO, but with the marginal
nature of this event will keep the SVR mention out of the ZFP for
now.

PAH AFD

.SHORT TERM...(THIS EVENING THROUGH THURSDAY NIGHT)
ISSUED AT 245 PM CST WED FEB 22 2012

20Z SURFACE OBS REVEAL WARM FRONTAL BOUNDARY HAS SHEARED OUT.
HIGHER TDS BEHIND THE ONCE EXISTING BOUNDARY HAVE MADE THEIR WAY
INTO THE SRN FA...WITH TDS FROM THE U40S TO L50S THERE...AND STILL
LINGERING MID 30S ACROSS OUR NRN TIER. WEAK FRONT/TROF AXIS
ASSOCIATED WITH UPPER WAVE IS PERCHED JUST WEST OF FA. AS IT
SWEEPS THRU...IT MAY TAP THE LOW LEVEL MOISTURE POOLING OVER
WKY...RESULTING IN CONVECTION. NAM HAS BEEN MOST INSISTENT ON
THIS OCCURRENCE...AND WE CANT QUITE IGNORE IT...SO WE`LL LEAVE A
SLGT CHANCE EVENING MENTION GOING FOR MAINLY THE ERN 1/2 OF THE
FA.

AFTER THAT...THE NEXT SYSTEM TAKES SHAPE TO OUR NW...AND
REACTIVATES THE WARM FRONT. WE`LL SEE WAA SHOWERS/POPS NUDGING OUR
NRN TIER BY TOMORROW AM...BUT THE MAIN ACTION WILL COME LATE
PM/EARLY EVENING...WHEN THE COLD FRONT ENTERS THE FA. UPON SO
DOING...IT WILL HAVE AMPLE LOW LEVEL PARAMETERS IN PLACE ALONG
WITH NAM FORECAST 500-1000 J/KG SURFACE BASED CAPE. AS A RESULT WE
SEE WKY WITHIN SLGT RISK SVR FOR SWODY2...HOWEVER THE BEST CHANCE
WILL REMAIN TO OUR SOUTH AND EAST. THE WINDOW WILL BE
NARROW...FROM ABOUT 21-22Z..TO ABOUT 02-03Z..FOR CONVECTION/SVR
CHANCES. AFTER THAT THE COLD FRONT/PASSAGE SHUTS THOSE CHANCES
DOWN. MORE LIKELY THOSE CHANCES WILL BE/REMAIN BETTER TO OUR SOUTH
AND EAST.

again not alot, but the potential is there and shouldnt be ignored

This post has been edited by Southern Indiana: Feb 22 2012, 05:44 PM

[snowlover2]

New day 1 has slight risk up to I-70 in Ohio.


Tornado


Hail


Wind

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1154 PM CST WED FEB 22 2012

VALID 231200Z - 241200Z

...THERE IS A SLGT RISK OF SVR TSTMS FOR PARTS OF THE OH/TN VALLEYS
AND DEEP SOUTH...

...SYNOPSIS...
INTENSE MID-LEVEL JET FROM THE PACIFIC NW TO THE CNTRL ROCKIES WILL
PROGRESS EWD ON THU...AIDING IN AMPLIFICATION OF A SHORT WAVE
IMPULSE CURRENTLY OVER THE NRN HIGH PLAINS. THIS FEATURE SHOULD
REACH THE LOWER/MID-MO VALLEY BY EVENING AND REMAIN
POSITIVELY-TILTED AS IT EJECTS ACROSS THE MIDWEST TOWARDS THE LOWER
GREAT LAKES THROUGH FRI MORNING. PRIMARY SURFACE CYCLONE IS EXPECTED
TO BE INVOF IL/IND BORDER BY 00Z...WITH A W/E-ORIENTED WARM FRONT
SHIFTING NWD ACROSS THE OH VALLEY. THIS LOW SHOULD TRACK TOWARDS LK
ERIE...WHILE AN ATTENDANT COLD FRONT SWEEPS E/SEWD ACROSS THE MS/TN
VALLEYS AND WRN GULF COAST IN THE EVENING...BEFORE REACHING THE
CNTRL/SRN APPALACHIANS AND CNTRL GULF COAST BY 12Z/FRI.

...OH/TN VALLEYS TO THE CNTRL GULF COAST...
IN THE WAKE OF THE SHORT WAVE IMPULSE CURRENTLY OVER THE CNTRL/SRN
APPALACHIANS...STRONG LOW/MID-LEVEL WLYS HAVE ENVELOPED THE RESIDUAL
WARM SECTOR FROM THE TN VALLEY TO THE CNTRL GULF COAST. ALTHOUGH
MODEST BACKING TO SWLY LOW-LEVEL FLOW IS EXPECTED AS THE N-CNTRL
CONUS SHORT WAVE TROUGH AMPLIFIES...THIS TYPE OF REGIME SHOULD SERVE
TO LIMIT THE VERTICAL EXTENT OF RICHER GULF MOISTURE BENEATH AN
EXPANDING EML.

EVENING MODEL GUIDANCE VARY MARKEDLY WITH THEIR HANDLING OF THE
MOISTURE RETURN TOWARDS THE LOWER OH VALLEY. THE NAM AND
WRF-NMM/ETA-BASED MEMBERS OF THE SREF ARE MORE AGGRESSIVE THAN THE
GFS/ECMWF AND WRF-ARW/RSM MEMBERS OF THE SREF...WHICH RESULTS IN
SUBSTANTIAL DIFFERENCES IN BUOYANCY PROFILES.
NEVERTHELESS...VIGOROUS LARGE-SCALE ASCENT COUPLED WITH DAYTIME
HEATING SHOULD YIELD TSTM INITIATION INVOF SURFACE CYCLONE NEAR THE
LOWER OH VALLEY BY LATE AFTERNOON. HERE...VERY STRONG DEEP-LAYER
SHEAR AND AT LEAST MEAGER INSTABILITY WOULD PROMOTE A RISK FOR
ORGANIZED TSTM CLUSTERS AND EMBEDDED SUPERCELLS. BUT GIVEN THE
UNCERTAINTY IN THE QUALITY OF THE BOUNDARY LAYER MOISTURE...WILL
REFRAIN FROM INTRODUCING HIGHER SEVERE PROBABILITIES ATTM.

WITH SRN EXTENT...CONFIDENCE LESSENS ON TSTM INITIATION AS STRONGER
LARGE-SCALE ASCENT LARGELY REMAINS N OF THE OH VALLEY. BUT
CONVERGENCE ALONG THE COLD FRONT ALONG WITH WEAK MID-LEVEL HEIGHT
FALLS MAY RESULT IN TSTMS FORMING SWD ACROSS THE TN VALLEY INTO THE
DEEP SOUTH DURING THE EVENING. EVEN WITH ONLY WEAK
INSTABILITY...DEEP-LAYER SHEAR WILL BE QUITE FAVORABLE FOR ISOLATED
SUPERCELLS WITH ALL SEVERE THREATS POSSIBLE.

TOWARDS THE CNTRL GULF COAST...GUIDANCE IS LARGELY CONSISTENT IN
MAINTAINING AN EML THROUGH MOST OF THE PERIOD. SOME POTENTIAL FOR
TSTM DEVELOPMENT SHOULD EXIST OVERNIGHT ALONG THE COLD FRONT. BUT
MODEST INSTABILITY AND VEERING/WEAKENING LOW-LEVEL WINDS SHOULD
RESULT IN A MORE MARGINAL SEVERE RISK RELATIVE TO FARTHER N.

[HassayWx2306]

to far north here, but with the winter we have had, Just hearing thunder will be a sigh of relief. Snow might stay away but thunderstorms cant

[jdrenken]

Blog post that I found for Indiana

[WeatherMonger]

SPC has added a 10% tornado risk and 30% hatched wind threat

[Snow____]

Wow, this kind of blossomed. I'm actually a little excited about tonight. Going to be boomy. Hopefully they don't start until after I get home, which isn't until about 10.

[The Snowman]

I'm pretty worried about the tornado risk.
A 10% chance of a tornado by the SPC pretty much says a tornado is coming...

[snowrawrsnow]

Looks to be an interesting day, with it looking (in my opinion) likely a moderate risk will go up sometime today. The SPC mentions the reasons for NOT issuing a moderate risk yet as

QUESTIONS REGARDING THE QUALITY OF MOISTURE RETURN AND
DIABATIC HEATING ARE THE MAIN REASONS A MODERATE RISK WAS NOT
INSERTED AT THIS TIME.

[MichelleOH]

I'm assuming the moderate risk would be in the 10% tornado area? I'm not looking forward to this...

[OSUWx2]

Forecast high for today is 48F. It's already 49F+.

[WeatherMonger]

Looks like only real change with 1630Z update was removing 10% tornado and dropping the hatching in the 30% wind risk area

This post has been edited by WeatherMonger: Feb 23 2012, 11:42 AM

[Superstorm93]

Downgrade in tornado probs...

[snowrawrsnow]

Surprised the SPC took out the hatching from the 30% wind area, not as surprised they dropped the 10% Tornado area...

...LOWER OH VALLEY...
A BELT OF STRONG MID LEVEL FLOW IS IN PLACE ACROSS THE NRN HALF OF
THE CONUS WITH SEVERAL LOW AMPLITUDE SHORT WAVE IMPULSES EMBEDDED
WITHIN THIS STREAM. MOST SUBSTANTIAL DISTURBANCE APPEARS TO BE
MOVING ACROSS CNTRL HIGH PLAINS THIS MORNING AND WILL LEAD TO MODEST
TROUGH AMPLIFICATION OVER THE MIDWEST THROUGH THIS EVENING. AT THE
SURFACE...LOW PRESSURE MOVING INTO MO ATTM WILL CONTINUE TO DEEPEN
TODAY AS THE AFOREMENTIONED TROUGH LENDS LARGE SCALE SUPPORT FOR
DEEP-LAYER ASCENT. THE LOW IS FORECAST TO TRACK EAST ALONG A
WELL-DEFINED WARM FRONT TO NEAR WRN IND BY THIS EVENING...AND NEAR
LAKE ERIE BY EARLY FRIDAY. AS THIS OCCURS...ASSOCIATED SURFACE WARM
FRONT WILL MAKE ONLY SLOW NWD RETREAT...TO ALONG OR JUST NORTH OF
THE OH RIVER THROUGH LATE THIS AFTERNOON. ATTENDANT COLD FRONT WITH
THIS SYSTEM WILL SPREAD EAST OF THE MS RIVER THIS EVENING...AND BE
SITUATED FROM ERN OH TO SRN MS BY EARLY FRIDAY.

MODEL FORECASTS WITH THIS SYSTEM HAVE BEEN LESS THAN CONSISTENT FROM
ONE RUN TO THE NEXT. IN ADDITION...LATEST OBSERVATIONAL DATA
INDICATES THAT IT WILL BE DIFFICULT FOR A SUBSTANTIAL INCREASE IN
LOW LEVEL MOISTURE TO TAKE PLACE NEAR THE SURFACE LOW AND WARM FRONT
THROUGH LATE AFTERNOON AS LOW LEVEL TRAJECTORIES HAVE ORIGINS IN A
RELATIVELY DRY UPSTREAM AIRMASS. LATEST HIGH-RESOLUTION GUIDANCE IS
IN GENERALLY GOOD AGREEMENT THAT CONVECTION IS LIKELY TO INITIATE IN
A WEAKLY UNSTABLE AIRMASS NEAR THE SURFACE LOW AND WARM FRONT...OVER
WRN KY/SWRN IND...AROUND 20Z. IT ALSO APPEARS THAT THIS INITIAL
ACTIVITY WILL MOST LIKELY BE DECOUPLED AND ROOTED ABOVE THE BOUNDARY
LAYER. WITH TIME...HOWEVER...MAGNITUDE OF FORCING NEAR THE LOW AND
FRONTS SHOULD BE SUFFICIENT TO OVERCOME INHIBITION AND STORMS COULD
TAP TRULY SURFACE-BASED PARCELS. THIS SCENARIO IS FURTHER SUPPORTED
BY THE FACT THAT STRONG SURFACE HEATING IS UNDERWAY ACROSS THOSE
AREAS THAT ARE MOST LIKELY TO FAVOR STORM DEVELOPMENT LATER THIS
AFTERNOON.

OVER A RELATIVELY FOCUSED AREA NEAR THE SURFACE LOW AND IMMEDIATELY
EAST ALONG THE WARM FRONT...FORECAST LEVEL SHEAR PROFILES APPEAR
VERY SUPPORTIVE OF MESOCYCLONES/SUPERCELLS WITH PRONOUNCED AND
STRENGTHENING SPEED SHEAR IN THE STORM UPDRAFT LAYER. INITIAL
ACTIVITY ACROSS KY/IND AREAS COULD POSE A THREAT FOR LARGE HAIL.
TORNADO POTENTIAL WILL BE CONDITIONAL ON SURFACE-BASED STORM
DEVELOPMENT AND CURRENT INDICATIONS ARE THAT EVEN WITH SURFACE-BASED
DEVELOPMENT...LACK OF MORE SIGNIFICANT LOW LEVEL MOISTURE LENDS
UNCERTAINTY TO OVERALL TORNADO POTENTIAL AT THIS TIME.

STORMS SHOULD CONGEAL NEAR THE LOW AND ALONG ADVANCING COLD FRONT
THROUGH LATE EVENING WITH AN INCREASING CHANCE FOR SCATTERED
DAMAGING WIND EVENTS AS THIS EVOLUTION UNFOLDS.

...KY SOUTH TO THE TN VALLEY AND EVENTUALLY ACROSS THE APPALACHIAN
CREST...
BROKEN QUASI-LINEAR SQUALL LINE IS ANTICIPATED AHEAD OF THE COLD
FRONT MOVING ACROSS THESE AREAS LATE. WHILE MODEST FORCING ALONG THE
FRONT SHOULD FORCE THIS CONVECTION...TIME OF DAY AND LACK OF GREATER
INSTABILITY WOULD SUGGEST LIMITED SEVERE POTENTIAL WITH A FEW WIDELY
SCATTERED WIND/HAIL EVENTS POSSIBLE THROUGH THE REMAINDER OF THE
PERIOD.

..CARBIN/HURLBUT.. 02/23/2012

[Snow____]

Saddened by the lower probs but still excited overall.

[EverythingWX]

After looking over a few things, the best chance for any tornadoes will come this evening across extreme southern Indiana into parts of northern Kentucky. Surface dewpoints should approach the middle 50s with backed surface winds across this area.

Hodographs are forecast to be moderately curved across this area with a LLJ of 30-40 knots out of the SW or SSW. The current location and depth of the upper-level trough (via satellite imagery) appears to align well with the current model forecast.

Clear skies across this area will allow for sufficient heating and should lead to 500-1000 J/Kg of CAPE. While there does appear to be a somewhat elevated tornado threat across this area late this afternoon into this evening, I do not see a reason for the SPC to upgrade to a moderate risk at this time. However, if dewpoints can surge closer to 60F, then it may be necessary.

[KYweather2007]

My local mets in Louisville seem a lot more concerned than the SPC...we're only sitting at 51 here now and moisture return may be a problem with a 46 degree dewpoint right now but they are worried about individual supercells and a few of them think we should be in a moderate risk

[EverythingWX]

My local mets in Louisville seem a lot more concerned than the SPC...we're only sitting at 51 here now and moisture return may be a problem with a 46 degree dewpoint right now but they are worried about individual supercells and a few of them think we should be in a moderate risk

Even if there is a supercell or two, it would not classify as a moderate risk. Here is what needs to happen for a moderate risk according to the SPC...

"A MDT risk implies a greater concentration of severe thunderstorms, and in most situations, greater magnitude of severe weather and greater forecaster confidence compared to a SLGT risk. A MDT risk is usually reserved for days with substantial severe storm coverage, or an enhanced chance for a significant severe storm outbreak. Typical MDT risk days include multiple tornadic supercells with very large hail, or intense squall lines with widespread damaging winds."

[MichelleOH]

Local Dayton met says he's more concerned about the winds coming through with the front than the earlier storms. He thinks the storms will weaken before they get to our area.

[WeatherMonger]

MESOSCALE DISCUSSION 0145
NWS STORM PREDICTION CENTER NORMAN OK
0221 PM CST THU FEB 23 2012

AREAS AFFECTED...PORTIONS OF THE OH RIVER VALLEY

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 232021Z - 232145Z

CONVECTION IS EXPECTED TO INCREASE ACROSS PORTIONS OF THE OH RIVER
VALLEY OVER THE NEXT 2-4 HOURS. TORNADO WATCH MAY BE REQUIRED TO
ACCOUNT FOR THIS INCREASING THREAT.

SFC WARM FRONT CONTINUES ITS SLOW NWD RETREAT AS IT LIFTS ACROSS SRN
IND/IL...WWD INTO A WELL DEFINED SFC LOW ALONG I-70 OVER CNTRL MO.
OVER THE LAST FEW HOURS A RAPIDLY EXPANDING SHIELD OF LOW-MID CLOUDS
HAS DEVELOPED WITHIN WARM ADVECTION ZONE ACROSS SRN IL/SWRN IND INTO
WRN KY. THIS CERTAINLY REFLECTS THE MOISTENING/ASCENT PROCESS THAT
SHOULD SPREAD NEWD TOWARD THE WARM FRONT ACROSS THE OH VALLEY INTO
THE EVENING HOURS. LATEST OA FIELDS SUGGEST A NARROW AXIS OF
INSTABILITY...MUCAPE ON THE ORDER OF 500-1500 J/KG...HAS OVERSPREAD
WRN KY. IF THIS AIRMASS CAN ADVECT INTO THE WARM FRONTAL ZONE PRIOR
TO CONVECTIVE INITIATION THEN AN ENHANCED RISK OF ROBUST
UPDRAFTS...POSSIBLY SUPERCELLULAR IN NATURE...COULD EVOLVE. LATEST
VIS IMAGERY DOES NOT CURRENTLY SUGGEST INDIVIDUAL UPDRAFTS HAVE
DEEPENED APPRECIABLY BUT CONTINUED LARGE SCALE ASCENT SHOULD
ENCOURAGE STRONGER UPDRAFTS OVER THE NEXT FEW HOURS. WILL CONTINUE
TO MONITOR THIS REGION FOR POSSIBLE TORNADO WATCH.

..DARROW.. 02/23/2012


ATTN...WFO...ILN...LMK...IND...PAH...

LAT...LON 38258851 39118547 38918441 37848476 36778732 37018883
37798908 38258851

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