SWODY2
SPC AC 071730
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1230 PM CDT TUE JUL 07 2009
VALID 081200Z - 091200Z
...THERE IS A SLGT RISK OF SVR TSTMS FOR MUCH OF THE NRN PLAINS...
...SYNOPSIS...
A LARGE-SCALE UPPER-LEVEL TROUGH CENTERED OVER SWRN CANADA/PACIFIC
NW SHOULD DEVOLVE INTO TWO DISTINCT SHORT WAVE TROUGHS THROUGH EARLY
THU...ONE OFF THE PACIFIC NW COAST AND THE OTHER ACROSS THE CANADIAN
PRAIRIE PROVINCES. THE LATTER WILL DEVELOP AS AN IMPULSE /ATTM
ROTATING AROUND THE BASE OF THE TROUGH OFF THE SWRN ORE/NWRN CA
COAST/ EJECTS NEWD WITH AN ATTENDANT STRONG TO INTENSE
MID/UPPER-LEVEL JET. UPPER-LEVEL TROUGH CENTERED OVER THE ERN GREAT
LAKES WILL GRADUALLY PROGRESS EWD ACROSS THE NORTHEAST. WEAK...SLOW
MOVING IMPULSES ARE ALSO EXPECTED TO MOVE ACROSS THE MID/LOWER MO
RIVER VALLEY INTO THE SOUTHEAST ALONG LEADING EDGE OF UPPER RIDGE
HOLDING OVER THE SRN ROCKIES/HIGH PLAINS.
...NRN PLAINS...
IN ADVANCE OF AN APPROACHING SHORT WAVE TROUGH...A PAIR OF SURFACE
CYCLONES WILL DEEPEN ACROSS SRN SASKATCHEWAN AND NERN WY.
COLD/OCCLUDED FRONT WILL STRETCH BETWEEN THESE LOWS AND TRACK EWD
INTO THE ERN DAKOTAS BY 09/12Z. WARM FRONT SHOULD BECOME DRAPED E OF
THE WY LOW AND LARGELY SERVE AS THE LEADING EDGE OF RICHER LOW-LEVEL
MOISTURE RETURNING FROM THE S. MODEL FORECASTS ARE REASONABLY
CONSISTENT WITH CONVECTIVE INITIATION OCCURRING ACROSS ERN MT DURING
THE MID-LATE AFTERNOON AS FORCED ASCENT INCREASES INVOF SURFACE COLD
FRONT. WITH 50S SURFACE DEW POINTS...STEEPENING MID-LEVEL LAPSE
RATES AND STRENGTHENING MID/UPPER-LEVEL FLOW...SUPERCELL DEVELOPMENT
IS QUITE LIKELY WITH LARGE HAIL AS THE PRIMARY INITIAL THREAT. AS
THE LLJ INCREASES INTO EARLY EVENING...LOW-LEVEL HODOGRAPHS WILL
BECOME FAVORABLY LARGE FOR POSSIBLE TORNADOES AS RICHER BOUNDARY
LAYER MOISTURE CONTINUES TO ADVECT NWD. HOWEVER...DISCRETE TSTMS MAY
QUICKLY GROW UPSCALE GIVEN THE STRONG FORCED ASCENT ASSOCIATED WITH
THE SHORT WAVE TROUGH/COLD FRONT AND THE RATHER STOUT LOWER-LEVEL
CAPPING INVERSION MITIGATING OPEN WARM SECTOR DEVELOPMENT.
ULTIMATELY...THE STRENGTH OF THE KINEMATIC FIELDS SUGGEST POTENTIAL
FOR WIDESPREAD/SIGNIFICANT WIND DAMAGE MAY DEVELOP WITH A
FAST-MOVING LINEAR MCS/BOW ECHO...IF STORMS CAN REMAIN ROOTED IN THE
BOUNDARY LAYER. GIVEN CONTINUED UNCERTAINTIES OVER THE DEGREE OF
CAPPING/LOW LEVEL MOISTURE RETURN AND OVERALL CONVECTIVE MODE...WILL
KEEP PROBABILITIES BELOW MDT RISK CATEGORY ATTM.
...MID-MS RIVER VALLEY...
ELEVATED TSTMS MAY BE ONGOING OVER THE SRN MN/IA AREA AT 08/12Z.
ALTHOUGH THE LLJ WILL WEAKEN DURING THE DAY...THIS ACTIVITY MAY
PERSIST INVOF RESIDUAL QUASI-STATIONARY FRONT. MODERATE INSTABILITY
S OF THIS BOUNDARY AND EFFECTIVE SHEAR OF 20-30 KT MAY BE SUFFICIENT
FOR A FEW ORGANIZED STORMS PRODUCING SEVERE HAIL/WIND. MID-LEVEL
HEIGHT RISES IN ADVANCE OF THE PACIFIC/NRN ROCKIES SHORT WAVE TROUGH
SHOULD HELP LIMIT THE OVERALL THREAT.
...CENTRAL GULF COAST INTO THE SOUTHEAST...
MODELS MAINTAIN A BELT OF MODERATE W/NWLY MID-LEVEL FLOW WITHIN BASE
OF LARGE-SCALE TROUGH OVER THE ERN STATES. THIS SHOULD SUPPORT
ISOLATED DOWNBURSTS AND PERHAPS MARGINAL SEVERE HAIL AS STORMS
DEVELOP ALONG STALLED/DIFFUSE FRONTAL BOUNDARY WED AFTERNOON.
...SRN NEW ENGLAND...
SEVERE THREAT WILL BE MUCH MORE MARGINAL WEDNESDAY AS COMPARED TO
TUESDAY. HOWEVER...VERY COLD MID LEVEL TEMPERATURES /-18C AT H5/
SHOULD SUSTAIN SHALLOW THUNDERSTORMS WITH DIURNAL HEATING AND
POSSIBILITY OF MARGINALLY SEVERE HAIL WITH A FEW CORES.
..GRAMS/DIAL.. 07/07/2009
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