SPC Jul 26, 2012 1730 UTC Day 2 Convective Outlook

SPC 1730Z Day 2 Outlook

DAY 2 CONVECTIVE OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK
1231 PM CDT THU JUL 26 2012

VALID 271200Z - 281200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM THE OH/TN VALLEYS TO THE
LOWER MID-ATLANTIC...

...THERE IS A SLGT RISK OF SVR TSTMS FOR THE BLACK HILLS...

...SYNOPSIS...
SHORT WAVE TROUGH CENTERED ALONG THE MN/ONTARIO BORDER WILL DAMPEN
ON FRI AS IT TRACKS SEWD THEN EWD ACROSS THE GREAT LAKES.
MEANWHILE...AN IMPULSE AND ASSOCIATED SPEED MAX CRESTING THE
MID-LEVEL RIDGE IN THE NRN ROCKIES WILL RAPIDLY EJECT SEWD AND
LIKELY REACH THE MIDWEST BY EARLY SAT. THIS WILL EFFECTIVELY
MAINTAIN A LARGE-SCALE UPPER-LEVEL TROUGH FROM ONTARIO/QUEBEC
TOWARDS THE MID-MS/LOWER OH VALLEYS...WHILE THE MID-LEVEL
ANTICYCLONE DRIFTS FROM THE SOUTHWEST TO THE SRN PLAINS. AT THE
SURFACE...PRIMARY CYCLONE SHOULD BE CENTERED OVER PARTS OF IND/OH ON
FRI AFTERNOON WITH A COLD FRONT EXTENDING SWWD TOWARDS THE RED RIVER
VALLEY. A MYRIAD OF OUTFLOWS FROM D1 CONVECTION SHOULD BE PREVALENT
IN THE WARM SECTOR AHEAD OF THE FRONT. 

...OH/TN VALLEYS TO THE LOWER MID-ATLANTIC...
RELATIVELY NEBULOUS SURFACE PATTERN IS ANTICIPATED IN THE WAKE OF
WIDESPREAD TSTM DEVELOPMENT ON D1. ALTHOUGH THE INSTABILITY FIELD
WILL LIKELY BE FRACTURED...A BROAD CYCLONIC FLOW REGIME WILL PERSIST
BENEATH THE RIGHT ENTRANCE REGION OF AN UPPER-LEVEL JET CENTERED
FROM THE LOWER GREAT LAKES TO NEW ENGLAND. THIS BREEDS POTENTIAL FOR
ORGANIZED CLUSTERS GIVEN THE PRESENCE OF 25-45 KT WLYS AT 500 MB. 

THE MOST PROBABLE AREA FOR TSTM INITIATION ON FRI AFTERNOON APPEARS
TO BE ALONG AND AHEAD OF THE COLD FRONT IN THE MIDWEST/LOWER OH
VALLEY. LARGE-SCALE ASCENT SHOULD BE GREATEST IN THE FRONTAL ZONE
WITH THE SHORT WAVE IMPULSE CENTERED ACROSS LOWER MI AND AN UPSTREAM
IMPULSE APPROACHING FROM THE UPPER MIDWEST. HOWEVER...GUIDANCE
DIFFERS SUBSTANTIALLY WITH THE DEGREE OF INSTABILITY IN THE REGION
WHICH MAY BE RELATED TO OVERTURNING ON D1. SUSPECT WITH STRONG
HEATING...NAM-RELATED GUIDANCE MAY PROVE CLOSER TO REALITY. WITH
STEEPENING LAPSE RATES AND MODERATE EFFECTIVE SHEAR...PRIMARY
THREATS SHOULD BE BOTH SEVERE WIND/HAIL. 

FARTHER E...ANOTHER FOCUSED AREA OF TSTM DEVELOPMENT SHOULD BE ALONG
THE LEE TROUGH IN PARTS OF THE PIEDMONT/COASTAL PLAIN IN THE LOWER
MID-ATLANTIC. ALTHOUGH HIGHER-LEVEL LAPSE RATES MAY BE POOR...STRONG
HEATING AHEAD OF THE TROUGH AND MODERATE DEEP-LAYER SPEED SHEAR
SHOULD SUPPORT A FEW ORGANIZED CLUSTERS PRODUCING PRIMARILY DAMAGING
WIND.  
  
...NRN ROCKIES TO THE BLACK HILLS...
A BELT OF CONFLUENT MID-LEVEL FLOW /GENERALLY 25-40 KT AT 500 MB/
SHOULD PERSIST N OF THE MID-LEVEL ANTICYCLONE IN THE SOUTHWEST.
GUIDANCE SUGGESTS A WEAK MID-LEVEL IMPULSE MAY TOP THE RIDGE IN THE
SRN MT/NRN WY AREA ON FRI AFTERNOON. IN RESPONSE TO THIS WEAK
IMPULSE...THE LLJ WILL STRENGTHEN ACROSS WRN NEB/SD. ALTHOUGH
BUOYANCY SHOULD REMAIN MODEST...VERY STEEP LAPSE RATES AND
SUBSTANTIAL VEERING OF THE WIND PROFILE WITH HEIGHT WILL BE ADEQUATE
FOR ISOLATED SUPERCELLS IN THE LATE AFTERNOON/EARLY EVENING
PRODUCING LARGE HAIL AND SEVERE WIND. FARTHER W/NW...CONVECTIVE
COVERAGE APPEARS TO BE TOO ISOLATED TO WARRANT SLIGHT RISK
PROBABILITIES ATTM.

..GRAMS.. 07/26/2012

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