58 replies to this topic

[Hoosier]

This doesn't look like a big deal right now.




DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1129 AM CST WED FEB 22 2012

VALID 231200Z - 241200Z

...THERE IS A SLGT RISK OF SVR TSTMS LATE THURSDAY/THURSDAY NIGHT
ACROSS PARTS OF THE LOWER OHIO AND TENNESSEE VALLEYS INTO THE GULF
STATES...

...SYNOPSIS...
MODELS MAY BE COMING IN BETTER AGREEMENT CONCERNING A STRONG
MID-LEVEL JET STREAK NOW DIGGING INLAND ACROSS THE PACIFIC
NORTHWEST...AND ITS INFLUENCE ON A CLOSED LOW CURRENTLY CUT-OFF FROM
THE STRONGER WESTERLIES...NEAR THE BAJA SPUR. IT NOW APPEARS MOST
PROBABLE THAT AN INITIAL SHORT WAVE TROUGH WILL TURN EAST SOUTHEAST
OF THE NORTHERN ROCKIES BY 12Z THURSDAY...AND CONTRIBUTE TO STRONG
SURFACE CYCLOGENESIS EAST OF THE MIDDLE MISSOURI VALLEY THROUGH THE
LOWER GREAT LAKES REGION BY 12Z FRIDAY...AS AN UPSTREAM IMPULSE DIGS
THROUGH THE CENTRAL ROCKIES. IT IS THIS LATTER FEATURE THAT MIGHT
FINALLY CONTRIBUTE TO A MORE RAPID EASTWARD ACCELERATION OF THE BAJA
LOW...BUT THE LOW STILL MIGHT NOT PROGRESS EAST OF THE GULF OF
CALIFORNIA INTO THE MEXICAN PLATEAU UNTIL LATE IN THE PERIOD.

DESPITE SOME GREATER CERTAINTY CONCERNING THE PATTERN EVOLUTION
...THE SEVERE POTENTIAL FOR THURSDAY REMAINS RATHER UNCERTAIN. THE
MOISTENING BOUNDARY LAYER OVER THE GULF OF MEXICO /WITH UPPER
60S...LOWER 70S SURFACE DEW POINTS/ CONTINUES TO DEEPEN...BUT
LOW-LEVEL FLOW ACROSS MUCH OF THE SOUTH CENTRAL AND SOUTHEAST HAS
DEVELOPED A SIGNIFICANT WESTERLY COMPONENT...AND LITTLE SIGNIFICANT
BACKING IS EXPECTED TO OCCUR THROUGH THIS PERIOD. A GRADUAL
NORTHWARD RETURN OF MID 50S TO NEAR 60S SURFACE DEW POINTS...NOW
PRESENT ACROSS EAST TEXAS INTO THE LOWER MISSISSIPPI VALLEY...MAY
OCCUR...BUT GENERALLY NOT BEFORE CAPPING ELEVATED MIXED LAYERS
OVERSPREAD WHAT WILL BECOME THE WARM SECTOR OF THE DEVELOPING
CYCLONE. WITH THE PRIMARY MID-LEVEL COLD CORE AND FORCING FOR
UPWARD VERTICAL MOTION EXPECTED TO REMAIN DISPLACED TO THE NORTHWEST
OF THE WARM SECTOR...WEAK CAPE AND THE LACK OF STRONGER DEEP LAYER
LIFT SEEM LIKELY TO SUBSTANTIALLY REDUCE THE OVERALL SEVERE STORM
POTENTIAL FROM WHAT IT COULD BE IF A POTENTIALLY UNSTABLE AIR MASS
WAS ALREADY PRESENT OVER THE MID SOUTH AND GULF STATES. STILL...THE
PRESENCE OF A SHEARED AND STRONG DEEP LAYER MEAN FLOW FIELD...AREAS
WITH RATHER LARGE CLOCKWISE CURVED LOW-LEVEL HODOGRAPHS...AND
POCKETS OF AT LEAST WEAK DESTABILIZATION SHOULD BE CONDUCIVE TO SOME
STRONG/SEVERE STORM DEVELOPMENT.

...LOWER OH/TN VALLEYS INTO GULF STATES...
THE INITIATION OF VIGOROUS STORM DEVELOPMENT CURRENTLY SEEMS MOST
PROBABLE LATE THURSDAY AFTERNOON...FROM THE NORTHEAST
ARKANSAS/MISSOURI BOOTHEEL/WESTERN TENNESSEE REGION INTO THE LOWER
OHIO VALLEY. WITHIN AN AXIS OF STRONGER WARM SECTOR/PRE-COLD
FRONTAL HEATING...MIXED LAYER CAPE ON THE ORDER OF 500 J/KG APPEARS
POSSIBLE...AS LIFT INCREASES ON THE SOUTHERN FRINGE OF STRONGER
MID-LEVEL FORCING. AIDED BY INCREASING FRONTAL FORCING BENEATH
STRONGLY DIFLUENT HIGH LEVEL FLOW...UPSCALE CONVECTIVE GROWTH INTO A
SQUALL LINE IS POSSIBLE...AS CONVECTION ADVANCES SOUTHEASTWARD
TOWARD THE CENTRAL/SOUTHERN APPALACHIANS AND UPPER TENNESSEE VALLEY
THROUGH THURSDAY NIGHT. ISOLATED SUPERCELLS MAY NOT BE OUT OF THE
QUESTION WITHIN AND JUST AHEAD OF THE LINE...ACCOMPANIED BY
POTENTIAL FOR LARGE HAIL AND TORNADOES...IN ADDITION TO THE RISK FOR
STRONG DAMAGING WIND GUSTS. ADDITIONAL STRONG/SEVERE STORM
DEVELOPMENT IS POSSIBLE ALONG THE FRONT AS IT ADVANCES SOUTHWARD
INTO THE LOWER MISSISSIPPI VALLEY AND UPPER TEXAS COASTAL
AREAS...PERHAPS DEEP SOUTH TEXAS...THURSDAY NIGHT.

..KERR.. 02/22/2012

[Indystorm]

Indeed, even the hatched 30% svr probs for MS and AL have been removed from prior outlooks unless things ramp up again.

[andyhb]

00z NAM says Western Kentucky (Beau's region) may have something...

[Hoosier]

5% tor probs into southern IN/southwest OH




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.

..GRAMS/LEITMAN.. 02/23/2012

[Stebo48858]

Quite surprised how far north this risk is, although this low is really going to be strengthening as it moves ENE across IN/OH.

[foster]

WRF-NMM nearly void of any storms except for a line in Kentuckiana (if that is even the name)

[andyhb]

Stebo48858, on 23 February 2012 - 01:30 AM, said:

Quite surprised how far north this risk is, although this low is really going to be strengthening as it moves ENE across IN/OH.

NAM showed SBCAPES in excess of 1000 J/kg all the way into southern IN at 21z.

[Hoosier]

andyhb, on 23 February 2012 - 01:32 AM, said:

NAM showed SBCAPES in excess of 1000 J/kg all the way into southern IN at 21z.

We certainly have plenty of shear for organized storms so the question is the amount of instability.

[Stebo48858]

Hoosier, on 23 February 2012 - 01:47 AM, said:

We certainly have plenty of shear for organized storms so the question is the amount of instability.

If the NAM is correct IN might have tornadoes in the Southern half of the state and snow along I-80. Quite the contrast within a state.

[Hoosier]

Digging further into this setup, I'd go so far to say that a strong tornado can't be ruled out especially if the NAM instability happens. A lot of setups in this part of the country tend to have mainly unidirectional flow above 850 mb, but notice how there is decent turning above that level on this forecast sounding. This sounding exhibits very nice strengthening/veering winds with height.

Watch the temp/moisture trends closely tomorrow.


 lex.gif   25.7K   0 downloads

[Chicago Storm]

SPC WRF targets the Ohio River area, just ahead of the SLP...near the warm front.

[tornadotony]

Hoosier, on 23 February 2012 - 02:04 AM, said:

Digging further into this setup, I'd go so far to say that a strong tornado can't be ruled out especially if the NAM instability happens. A lot of setups in this part of the country tend to have mainly unidirectional flow above 850 mb, but notice how there is decent turning above that level on this forecast sounding. This sounding exhibits very nice strengthening/veering winds with height.

Watch the temp/moisture trends closely tomorrow.


lex.gif

I would completely agree. The issues with moisture that will plague the SE will have a hard time plaguing the OH Valley because of moisture pooling south of the boundary. Currently, the EMC WRF, WRF-NMM, and WRF-ARW all target the OH Valley pretty darn hard tomorrow, and with the kind of low-level instability and shear that should be there, I think this is a legitimate threat.

[andyhb]

Chicago Storm, on 23 February 2012 - 02:06 AM, said:

SPC WRF targets the Ohio River area, just ahead of the SLP...near the warm front.

Ouch, right near or over Louisville...

[Thundersnow12]

Chicago Storm, on 23 February 2012 - 02:06 AM, said:

SPC WRF targets the Ohio River area, just ahead of the SLP...near the warm front.

I usually am a severe wx magnet when I'm in Louisville..

[andyhb]

992 mb SLP (probably lower at the CoC) per current mesoanalysis:
 pmsl.gif   31.25K   0 downloads
LL shear is going to skyrocket as this thing approaches. 06z NAM has initialized, rather eager to see what it projects.

Edit: 0-3 km EHI values of 3-5 across portions of KY and Northern Middle TN by 21z per the 06z NAM.

[Bryan Wood]

RUC & NAM Hodographs for Seymour, IN area this evening. NAM seems to be overdoing it on the lower levels, but it's intriguing enough for me to consider chasing along the US 50 corridor/along the warm front. It's dependent on how the cloud cover moves today.

Attached Files

•  nam.jpg   56.2K   0 downloads
•  ruc.jpg   52.34K   0 downloads

[KokomoWX]

New SPC outlook...

Attached Files

•  day1.gif   12.98K   0 downloads
•  day1.tornado.gif   12.82K   0 downloads
•  day1.wind.gif   12.92K   0 downloads

[Bryan Wood]

SPC (on the IN/KY/OH area):

Quote

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

Amazing considering we were looking at a significant box in the MS/AL/GA area on Tuesday.

[OceanStWx]

Very sharp theta-e boundary depicted on the NAM in the latest runs, and compares pretty favorably to the GFS too. There will be some serious horizontal vorticity available along this feature.

[Bryan Wood]

OceanStWx, on 23 February 2012 - 09:19 AM, said:

Very sharp theta-e boundary depicted on the NAM in the latest runs, and compares pretty favorably to the GFS too. There will be some serious horizontal vorticity available along this feature.

That's the area I'm going to target. I'm going to start east of Louisville and adjust as necessary.

[OceanStWx]

Low 50s dewpoints already creeping into southern Illinois.

You can tell the kind of helicity that will be present along the front, gusty ever so slightly south of east winds north of the advancing warm front.

[TheWeatherPimp]

Back down to a 5% tornado risk.

[andyhb]

TheWeatherPimp, on 23 February 2012 - 11:41 AM, said:

Back down to a 5% tornado risk.

Moisture return going to be a problem.

[Bryan Wood]

Not liking the fact that the storms may initiate further west, may have trouble rooting in the boundary layer before sunset and may congeal into a squall line plus moisture return issues. Those are more than enough questions for me to call off the chase before it starts and save the money I would've spent on gas.

[OceanStWx]

TheWeatherPimp, on 23 February 2012 - 11:41 AM, said:

Back down to a 5% tornado risk.

Yeah, when I saw the graphics my first thought was moisture return. Lower 50s instead of middle.

Bryan Wood, on 23 February 2012 - 11:50 AM, said:

Not liking the fact that the storms may initiate further west, may have trouble rooting in the boundary layer before sunset and may congeal into a squall line plus moisture return issues. Those are more than enough questions for me to call off the chase before it starts and save the money I would've spent on gas.

I don't think the eventual squall line was ever really in doubt. It was the initial storms that posed a larger threat. Even so, there will be a strong boundary present, and squall line spins ups will be possible.

[TheWeatherPimp]

OceanStWx, on 23 February 2012 - 12:00 PM, said:

Yeah, when I saw the graphics my first thought was moisture return. Lower 50s instead of middle.



I don't think the eventual squall line was ever really in doubt. It was the initial storms that posed a larger threat. Even so, there will be a strong boundary present, and squall line spins ups will be possible.

With the helicity in place and the boundary present, spin ups will definitely be likely. It'll be interesting to watch the warning philosophy play out this afternoon as Louisville tends to tornado warn the whole line in these situations and Wilmington tends to try to warn based on individual couplets within the QLCS.

[PSUBlizzicane2007]

The sun has been out for the past 90+ minutes and temperatures are skyrocketing here in Louisville. One thing that I think the SPC might be underestimating wrt moisture is that the storms from last night/this morning left quite a bit of ground moisture here which the sun should now evaporate at an accelerated pace.

I don't know if I completely agree with the removal of the 10% chance since not a lot has changed since it was originally issued.

[Hoosier]

Temps are responding nicely. Can we get mid 50's dewpoints to the OH River by this evening?

[OceanStWx]

Strongest theta-e advection taking place in the Ohio Valley area. Also a ribbon of higher theta-e air is starting to make its way up the Mississippi Valley. It's going to be a tight race.

[Stebo48858]

OceanStWx, on 23 February 2012 - 01:43 PM, said:

Strongest theta-e advection taking place in the Ohio Valley area. Also a ribbon of higher theta-e air is starting to make its way up the Mississippi Valley. It's going to be a tight race.

It will be close but I think the moisture advection is winning so far. Especially with dews in the mid 50s in W KY/TN

[PSUBlizzicane2007]

Louisville is standing at 67 T, 47 Td, 49% RH with a SE wind at 15 G 20.

[Bryan Wood]

OceanStWx, on 23 February 2012 - 12:00 PM, said:

I don't think the eventual squall line was ever really in doubt. It was the initial storms that posed a larger threat. Even so, there will be a strong boundary present, and squall line spins ups will be possible.

There was no doubt in my mind that a squall line was inevitable as the cold front swings around...I just initially hedged that cells might have been able to be discreet further east (I was only going to go as far west as Louisville). Squall line spinups will be almost certain with the shear/helicity, but I don't chase squall line spin ups. I just watch those at home on GrLevel3.

[PSUBlizzicane2007]

68 T, 49 Td, 51% RH at Louisville now... low-level moisture is really advecting now

69 T, 53 Td, 56% RH at Fort Knox.


Newest SPC outlook is still very questionable considering what is going on. Not sure what their thoughts are behind what they've put out.

[Hoosier]

71/57 at Paducah

[TheWeatherPimp]

Hoosier, on 23 February 2012 - 03:12 PM, said:

71/57 at Paducah

Good chance temps across portions of Southern and Southeastern Indiana and Southwestern Ohio continue to rise even after the diurnal peak.