SWODY2
SPC AC 310536
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1236 AM CDT THU JUL 31 2008
VALID 011200Z - 021200Z
...THERE IS A SLGT RISK OF SVR TSTMS FRI/FRI EVENING ACROSS PARTS OF
THE UPPER MIDWEST INTO THE OH VALLEY....
...SYNOPSIS...
CONSIDERABLE AGREEMENT EXISTS AMONG THE MODELS CONCERNING THE
PROSPECTS FOR A STRENGTHING SUBTROPICAL HIGH OVER THE FOUR CORNERS
REGION TODAY...AND ITS SUBSEQUENT NORTHWARD/EASTWARD EXPANSION
THROUGH A LARGE PORTION OF THE CENTRAL STATES. A SEASONABLY STRONG
BELT OF WESTERLIES IS EXPECTED TO TOP THIS RIDGE...WITH A VERY WARM
ELEVATED MIXED LAYER ADVECTING OUT OF THE GREAT BASIN THROUGH MUCH
OF THE NORTHERN/CENTRAL PLAINS AND MIDDLE MISSISSIPPI VALLEY REGION
BY FRIDAY. LATEST GUIDANCE CONTINUES TO INDICATE THAT ONE
SIGNIFICANT SHORT WAVE IMPULSE EMBEDDED WITHIN THE STRONGER FLOW
WILL LIFT OUT OF THE WESTERN CANADIAN/PACIFIC NORTHWEST TROUGH
DURING THIS PERIOD...WHILE ANOTHER DIGS INTO THE TROUGH OVER THE
GREAT LAKES AND NORTHEAST. HOWEVER...IT IS NOW APPEARING MORE
PROBABLE THAT THE UPPER FLOW MAY REMAIN MORE AMPLIFIED THAN EARLIER
ANTICIPATED...WITH THE EASTERN IMPULSE CONSIDERABLY STRONGER...AND
THE WESTERN IMPULSE A BIT SLOWER TO SUPPRESS THE SHARP UPPER RIDGE
AXIS ACROSS THE NORTHERN PLAINS INTO SOUTH CENTRAL CANADIAN
PROVINCES. AND...THIS WILL IMPACT THE CONVECTIVE POTENTIAL FOR
FRIDAY/FRIDAY NIGHT.
...UPPER MIDWEST INTO THE SOUTHERN GREAT LAKES/OHIO VALLEY...
MODELS INDICATE A 50+ KT 500 MB JET STREAK WILL ACCOMPANY THE SHORT
WAVE IMPULSE DIGGING TO THE LEE OF THE PLAINS RIDGE. THIS FEATURE
IS EXPECTED TO ENHANCE FORCING FOR UPWARD VERTICAL MOTION SOUTHEAST
OF THE UPPER MISSISSIPPI VALLEY INTO THE OHIO VALLEY DURING THE DAY
FRIDAY. THERE ARE INDICATIONS THAT THIS MAY ALSO BE ACCOMPANIED BY
A CONVECTIVELY GENERATED OR ENHANCED IMPULSE...WHICH COULD PROVIDE
THE FOCUS FOR RENEWED CONVECTIVE DEVELOPMENT/INTENSIFICATION AS A
MOIST BOUNDARY LAYER CHARACTERIZED BY DEW POINTS NEAR 70F
DESTABILIZES WITH DAYTIME HEATING. WIND PROFILES LIKELY WILL BE
LARGELY UNIDIRECTIONAL... NORTHWESTERLY ON THE NORTHEASTERN
PERIPHERY OF THE UPPER RIDGE. BUT...COUPLED WITH A FAVORABLE
THERMODYNAMIC ENVIRONMENT...PROGGED SHEAR PROFILES APPEAR SUPPORTIVE
OF ONE OR MORE FORWARD PROPAGATING MESOSCALE CONVECTIVE SYSTEMS
CAPABLE OF PRODUCING DAMAGING WINDS AND HAIL. THIS THREAT SHOULD
PERSIST THROUGH MUCH OF THE DAY...INTO THE EVENING HOURS...BEFORE
GRADUALLY DIMINISHING AS THE BOUNDARY LAYER STABILIZES WITH THE LOSS
OF DAYTIME HEATING.
...NORTHERN PLAINS...
THE LIKELIHOOD OF A MORE AMPLIFIED UPPER PATTERN...WITH INITIALLY
DRY LOWER LEVELS/LATE MOISTURE RETURN...BENEATH A STRONGER CAPPING
MID-LEVEL THERMAL RIDGE...HAS INCREASED UNCERTAINTY WITH REGARD TO
THE CONVECTIVE POTENTIAL AND EXTENT OF THE SEVERE THREAT FOR THIS
PERIOD. A STRENGTHENING LOWER/MID TROPOSPHERIC WARM ADVECTION
REGIME AND RETURNING MOISTURE MAY STILL BECOME SUPPORTIVE OF
CONVECTIVE DEVELOPMENT ACROSS NORTH DAKOTA LATE FRIDAY NIGHT.
AND...IF THIS OCCURS...LOW SUB-CLOUD RELATIVE HUMIDITIES MAY PROMOTE
POTENTIAL FOR AT LEAST ISOLATED DAMAGING WINDS GUSTS...IN ADDITION
TO SOME HAIL IN THE PRESENCE OF FAVORABLE CLOUD BEARING LAYER SHEAR
AND STEEP LAPSE RATES.
..KERR.. 07/31/2008
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