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July 26, 2012 Severe Weather Potential


earthlight

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I think Uptons call for storms this afternoon is not going to work out - everything should be pushed back a few hours till after 5 PM at least - I would suspect SPC issues a watch for the area as soon as they see the T-storms start developing out in PA and moving east I would think the watch is issued after 3PM some time and starts about 5 PM - 7PM and runs till about 11 PM - 1 AM what does everyone else think ?

That seems fairly reasonable.

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Mesoscale Discussion 1600

< Previous MD

MESOSCALE DISCUSSION 1600

NWS STORM PREDICTION CENTER NORMAN OK

1126 AM CDT THU JUL 26 2012

AREAS AFFECTED...PORTIONS CENTRAL/SRN INDIANA...OH...NRN KY...NRN

PANHANDLE OF WV...WRN/NRN PA...WRN NY.

CONCERNING...SEVERE POTENTIAL...WATCH LIKELY

VALID 261626Z - 261830Z

PROBABILITY OF WATCH ISSUANCE...95 PERCENT

SUMMARY...RAPID DEVELOPMENT...INTENSIFICATION AND UPSCALE GROWTH OF

TSTMS IS POSSIBLE THROUGH 20Z OVER WRN/NRN PARTS OF THIS DISCUSSION

AREA...INVOF ANY OF SEVERAL BOUNDARIES DESCRIBED BELOW. DAMAGING

GUSTS ARE PRIMARY THREAT...THOUGH OTHER SVR MODES ARE POSSIBLE.

DISCUSSION...15Z SFC MESOANALYSIS SHOWS THERMAL GRADIENT ASSOCIATED

WITH DIFFERENTIAL HEATING...AND CORRESPONDING TO DIFFUSE ERN FRINGE

OF THICKER CLOUD COVER ON VIS IMAGERY. THIS ZONE WAS LOCATED FROM

SRN IL AND SWRN INDIANA NEWD OVER W-CENTRAL/NRN OH...THEN ENEWD OVER

NWRN PA...WHERE IT INTERSECTED WARM FRONT EXTENDING ESEWD OVER

S-CENTRAL PA. WARM FRONT IS EXPECTED TO MOVE NEWD ACROSS

CENTRAL/ERN PA THROUGH MID-AFTERNOON. DIFFERENTIAL-HEATING ZONE

WILL MOVE LITTLE AS CLOUDS ERODE WITH EWD EXTENT BUT CONTINUE TO

ADVECT OVER AREA FROM W. VIS IMAGERY ALSO SHOWS MCV MOVING ENEWD

ABOUT 35 KT OVER W-CENTRAL IL...ON TRACK TO REACH NRN INDIANA AROUND

22Z...AND PRECEDED BY MESOSCALE ENHANCEMENTS TO DEEP-LAYER FLOW AND

MIDLEVEL ASCENT. GRAVITY WAVE WAS EVIDENT MOVING SEWD OVER SWRN

PA...OH/WV BORDER AND CENTRAL KY...BEHIND WHICH STRONGEST SFC

HEATING IS OCCURRING FROM NERN OH TO WRN KY.

IN LOW LEVELS...CINH EVIDENT IN 12Z PBZ/ILN RAOBS IS BEING REMOVED

QUICKLY BY STG DIABATIC HEATING AND BOUNDARY-LAYER MIXING...BELOW

PLUME OF ELEVATED MIXED-LAYER AIR THAT CONTRIBUTES STEEP LOW-MIDDLE

LEVEL LAPSE RATES. WITH SFC DEW POINTS COMMONLY 70S F...NET RESULT

WILL BE PRECONVECTIVE MLCAPE STRENGTHENING TO 3500-5000 J/KG RANGE

OVER BROAD SWATH OF WARM SECTOR...BETWEEN WARM FRONT AND

DIFFERENTIAL-HEATING ZONE. SUCH STG-EXTREME BUOYANCY ATOP

WELL-MIXED SUBCLOUD LAYERS...AMIDST NEARLY UNIDIRECTIONAL/WLY-WSWLY

DEEP-LAYER WINDS...SUGGEST POTENTIAL FOR ONE OR MORE

FORWARD-PROPAGATIONAL TSTM CLUSTERS WITH ORGANIZED/AGGREGATE COLD

POOLS ENHANCING SVR WIND RISK. THIS MAY OCCUR WITH DEVELOPMENT NOW

OVER LE AS IT ENCOUNTERS DESTABILIZING AIR MASS NEAR WARM FRONT AND

SRN-SHORE LAKE BREEZE...AS WELL AS SUBSEQUENT DEVELOPMENT INVOF

DIFFERENTIAL-HEATING ZONE AND AHEAD OF MCV OVER PORTIONS INDIANA/OH.

EFFECTIVE SHEAR INCREASES WITH NEWD EXTENT TOWARD AND OVER WARM

FRONT...VALUES REACHING 40-50 KT IN NWRN PA WHERE EFFECTIVE SRH ALSO

IS MAXIMIZED. THIS SUGGESTS RELATIVE MAX IN SUPERCELL/TORNADO RISK

ALSO MAY EXIST INVOF WARM FRONT...SHIFTING EWD/NEWD WITH THAT

BOUNDARY.

..EDWARDS/HART.. 07/26/2012

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There can be a silver lining on cooler temps, especially if near the effective warm front or an old outflow boundary, (within limits, of course) lower cloud bases. Storms a week ago near Boston got most active crossing the sea breeze boundary,

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Oh ok thanks.I would have thought, due to the severe portential, soundings would have been taken a bit more often.

Normally just at 0 and 12Z, but in the Plains, anyway, on expected active tornado days, one will see an 18Z or 19Z sounding.

The met department at Texas A&M will release a balloon at CLL, which is not a normal sounding location. Not shared with the public via the SPC website, but is shared with HGX forecast office.

Will sometimes see OUN/FWD and other Plains office's mention an extra balloon release. Might be worth checking local AFDs, I didn't see any mentioned, but it was a curosry check.

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Tornadoes

Probability of 2 or more tornadoes

Low (20%)

Probability of 1 or more strong (F2-F5) tornadoes

Low (5%)

Wind

Probability of 10 or more severe wind events

High (>95%)

Probability of 1 or more wind events > 65 knots

High (70%)

Hail

Probability of 10 or more severe hail events

Mod (40%)

Probability of 1 or more hailstones > 2 inches

Low (20%)

Combined Severe Hail/Wind

Probability of 6 or more combined severe hail/wind events

High (>95%)

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