SPC AC 270559
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1259 AM CDT MON JUL 27 2009
VALID 271200Z - 281200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE UPPER MISSISSIPPI
RIVER VALLEY...
...SYNOPSIS...
AS A BROAD UPPER RIDGE REMAINS OVER THE SOUTHWEST DESERTS/BAJA
VICINITY...LONGWAVE TROUGH WILL DOMINATE THE CONUS EAST OF THE
ROCKIES. WITH THE CORE OF THIS TROUGH CENTERED OVER
ONTARIO...MULTIPLE MID LEVEL SHORTWAVE TROUGHS WILL TRAVERSE THE
MIDWEST TO NORTHEAST STATES/NEW ENGLAND. ADDITIONAL DISTURBANCES
/SEVERAL CONVECTIVELY ENHANCED/ WILL BE EMBEDDED WITHIN
NORTHWESTERLY FLOW ALOFT FROM THE NORTHERN ROCKIES/HIGH PLAINS TO
THE SOUTHERN PLAINS/WESTERN GULF COAST STATES.
...UPPER MS VALLEY/MIDWEST...
WHILE PLACEMENT/TIMING IS DIFFICULT TO PINPOINT AT THIS
JUNCTURE...IT APPEARS THAT ONE OR MORE SUBTLE MID LEVEL
PERTURBATIONS /EMANATING FROM THE NORTHERN HIGH PLAINS/ MAY
OVERSPREAD THE REGION THIS AFTERNOON AHEAD OF A MORE APPRECIABLE
SHORTWAVE TROUGH DIGGING SOUTHEASTWARD TOWARD THE UPPER MIDWEST. IT
SEEMS PROBABLE THAT TSTMS SHOULD INCREASE IN COVERAGE/INTENSITY THIS
AFTERNOON AS A SURFACE TROUGH/WEAK COLD FRONT DEVELOPS
EAST-SOUTHEASTWARD ACROSS PORTIONS OF MN/IA/WI. WITH RESPECT TO THE
PREFRONTAL WARM SECTOR...SUITE OF 00Z NUMERICAL MODEL GUIDANCE IS
LIKELY AS MUCH AS 5-8 DEG F TOO MOIST WITH SURFACE DEWPOINTS...BUT
NEVERTHELESS...A WESTERLY MOISTURE INFLUX/EVAPOTRANSPIRATION SHOULD
BOOST DEWPOINTS THROUGH THE 60S F DURING THE DAY. THIS WOULD
POTENTIALLY YIELD MLCAPE OF 1000-1500 J/KG ACROSS PORTIONS OF
SOUTHERN/EASTERN MN INTO WI...WITH AS MUCH AS 2000-2500 J/KG OF
WEAKLY CAPPED MLCAPE ACROSS IA. STRENGTHENING FLOW ALOFT OVER MN/WI
WOULD SUPPORT ORGANIZED STORMS INCLUDING MULTICELLS/SOME
SUPERCELLS...WITH THE POSSIBILITY OF SEVERE HAIL/WIND AND PERHAPS
EVEN A TORNADO.
...NEW ENGLAND...
MID LEVEL TROUGH IN VICINITY OF THE LOWER GREAT LAKES OVERNIGHT
SHOULD PIVOT NORTHEASTWARD AND AT LEAST GRAZE PORTIONS OF NORTHERN
NEW ENGLAND BY EARLY/MID AFTERNOON. LARGE SCALE FORCING FOR ASCENT
ASSOCIATED WITH THIS FEATURE SHOULD CONTRIBUTE TO INCREASING TSTM
DEVELOPMENT BY LATE AFTERNOON ALONG/AHEAD OF AN APPROACHING COLD
FRONT. BENEATH 40 KT SOUTHWESTERLY MID LEVEL FLOW...ORGANIZED
MULTICELL STORMS/PERHAPS EVEN A FEW SUPERCELLS COULD DEVELOP...WITH
THE POTENTIAL FOR DAMAGING WINDS AND HAIL. A CATEGORICAL SLIGHT RISK
COULD ULTIMATELY BE WARRANTED /PRIMARILY FOR PORTIONS OF MAINE/ IN
SUBSEQUENT DAY 1 OUTLOOKS.
...MID ATLANTIC/SOUTHEAST STATES...
MID LEVEL TROUGH WILL SLOWLY SHIFT EASTWARD OVER THE SOUTHEAST
STATES TODAY...WITH A RESIDUALLY MOIST/POTENTIALLY UNSTABLE AIRMASS
REMAINING TO THE EAST OF A NEARLY STALLED SURFACE FRONT ALONG THE
APPALACHIANS. WHILE SLIGHTLY COOLER MID LEVEL TEMPERATURES WILL
OVERSPREAD THIS CORRIDOR TODAY...LARGE SCALE FORCING FOR ASCENT AND
VERTICAL SHEAR WILL OTHERWISE REMAIN LIMITED TODAY. WHILE A
PARTICULARLY ORGANIZED/APPRECIABLE SEVERE RISK IS NOT ANTICIPATED
ACROSS THIS CORRIDOR...ISOLATED DAMAGING WINDS/SOME HAIL WILL BE
POSSIBLE THIS AFTERNOON/EARLY EVENING VIA PULSE-TYPE/MULTICELLULAR
STORMS.
...WY TO CENTRAL/SOUTHERN HIGH PLAINS...
MULTIPLE FACTORS WILL CONTRIBUTE TO A BROAD CORRIDOR OF MAINLY
ISOLATED SEVERE HAIL/WIND POTENTIAL FOR PORTIONS OF WY/NORTHERN
GREAT DIVIDE VICINITY TO THE CENTRAL/SOUTHERN HIGH PLAINS. THE
SOUTHEASTWARD SHIFT OF THE PERSISTENT NORTHERN INTERMOUNTAIN WEST
UPPER LOW ACROSS THE NORTHERN GREAT DIVIDE...AND REINFORCING /NORTH
CENTRAL HIGH PLAINS/ AND/OR PERSISTENT UPSLOPE TRAJECTORIES /SOUTH
CENTRAL HIGH PLAINS/ WILL CONTRIBUTE TO A DIURNAL UPSWING IN TSTMS
THIS AFTERNOON. AS HAS BEEN THE CASE FOR THE PAST SEVERAL
DAYS...STRONGLY VEERING WIND PROFILES/MODERATE NORTHWESTERLY FLOW
ALOFT AND A MOIST AIRMASS WILL SUPPORT SOME STORMS CAPABLE OF SEVERE
HAIL/WIND THROUGH AROUND SUNSET.
...NORTH/EAST TX TO ARKLATEX/WESTERN GULF COAST...
SEVERE POTENTIAL IS DIFFICULT TO ASCERTAIN IN ADVANCE ACROSS THIS
REGION OWING TO EXTENSIVE EARLY MORNING TSTMS ACROSS TX. IT IS
PLAUSIBLE THAT ONE OR MORE EMBEDDED DISTURBANCES/POTENTIAL MCV/S
COULD ULTIMATELY FOCUS SEVERE WIND/HAIL POTENTIAL LATER TODAY ACROSS
EAST TX AND THE ADJACENT ARKLATEX/WESTERN GULF COAST IN VICINITY OF
A RESIDUAL/CONVECTIVELY MODIFIED FRONTAL ZONE. HOWEVER...ONLY LOW
SEVERE PROBABILITIES ARE WARRANTED AT THIS TIME GIVEN THE
UNCERTAINTY OF THE SCENARIO.
..GUYER/LEVIT.. 07/27/2009
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z
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