[SWODY1] SWODY1

[Severe Weather Outlook Day 1]

ACUS01 KWNS 170547
SWODY1
SPC AC 170546

DAY 1 CONVECTIVE OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK
1246 AM CDT THU AUG 17 2006

VALID 171200Z - 181200Z

...THERE IS A SLGT RISK OF SVR TSTMS LATE THIS AFTN/TONIGHT ACROSS
PARTS OF THE NORTHERN PLAINS....

...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTN AND EVE ACROSS PARTS
OF THE CNTRL PLAINS/MID MS VLY....

SUBTROPICAL RIDGE ENCOMPASSING MUCH OF THE CENTRAL AND SOUTHERN TIER
OF THE U.S. WILL REMAIN STRONG THROUGH MUCH OF THIS FORECAST PERIOD.
 HOWEVER...WEAKENING OF THIS FEATURE MAY COMMENCE TOWARD THE END OF
THE PERIOD ...AS A SIGNIFICANT SHORT WAVE TROUGH... EMBEDDED WITHIN
A BELT OF STRONGER WESTERLIES ACROSS CANADA... FINALLY SHIFTS EAST
OF SASKATCHEWAN/MANITOBA.  THIS SYSTEM WILL BE TRAILED CLOSELY BY A
SHORT WAVE TROUGH IN A WEAKER SOUTHERN STREAM...ACROSS THE NORTHERN
INTERMOUNTAIN REGION/NORTHERN ROCKIES AND NORTHERN PLAINS.  

ADDITIONALLY...WEAK BROAD TROUGHING IN THE SUBTROPICAL WESTERLIES IS
FORECAST TO CONTINUE AROUND THE NORTHERN PERIPHERY OF THE UPPER
RIDGE...PROGRESSING EAST OF THE MID MISSOURI VALLEY THROUGH THE
SOUTHERN GREAT LAKES/OHIO VALLEY REGION.  SEVERAL OTHER IMPULSES
WILL MIGRATE THROUGH THE ANTICYCLONIC FLOW AROUND THE OZARK PLATEAU
SUBTROPICAL HIGH CENTER...FROM THE SOUTHERN ROCKIES INTO THE CENTRAL
PLAINS...AND ACROSS THE GULF STATES.

ALL OF THESE FEATURES...IN CONJUNCTION WITH SEASONABLE INSTABILITY
...WILL CONTRIBUTE TO SCATTERED THUNDERSTORM ACTIVITY TODAY/TONIGHT.
 MUCH OF THE COUNTRY WILL BE AFFECTED...WITH THE MOST NOTABLE
EXCEPTIONS THE NORTHEAST...STILL UNDER THE INFLUENCE OF RECENT
COOL/DRY INTRUSION...AND THE PACIFIC COAST STATES/GREAT
BASIN...ASSOCIATED WITH DRYING TO THE SOUTH/WEST OF NORTHERN
INTERMOUNTAIN TROUGH.

...CENTRAL PLAINS INTO MID MISSISSIPPI VALLEY...
IN THE WAKE OF THE SUBTROPICAL IMPULSE...A CONFLUENT LOW/MID-LEVEL
FLOW REGIME WITH A BELT OF 20 TO 30+ KT FLOW IS EXPECTED TO PERSIST
FROM PARTS OF NORTHERN KANSAS ACROSS THE MISSOURI/IOWA BORDER AREA
THROUGH MUCH OF THE DAY.  THIS WILL AID FORWARD PROPAGATION OF
CONVECTIVE DEVELOPMENT...WHICH IS EXPECTED TO INITIATE IN A WARM
ADVECTION REGIME ALONG/NORTH OF A LOW-LEVEL THERMAL RIDGE
AXIS...MOST LIKELY NEAR/SHORTLY AFTER PEAK AFTERNOON HEATING.  A
HOT...DEEP MIXED BOUNDARY LAYER ON THE SOUTHERN FRINGE OF A
SUBTROPICAL MOISTURE PLUME SHOULD PROVE FAVORABLE FOR
DOWNBURSTS...AND POTENTIALLY DAMAGING SURFACE GUSTS...WHICH COULD
BECOME FAIRLY NUMEROUS BEFORE STORMS WEAKEN WITH LOSS OF HEATING
THIS EVENING.

...NORTHERN PLAINS...
FAVORABLE OROGRAPHY NEAR THE BLACK HILLS MAY PROVIDE THE LONE/
PRIMARY FORCING TO SUPPORT CONVECTIVE PRIOR TO 22-23Z TODAY...AS
WARM MID-LEVEL TEMPERATURES PROVIDE SUBSTANTIAL CAP.  IF ACTIVITY
DOES DEVELOP...MODERATELY STRONG SOUTHWESTERLY MID-LEVEL FLOW WILL
CONTRIBUTE TO FAVORABLE SHEAR FOR ISOLATED SUPERCELLS IN AN
ENVIRONMENT WITH STEEP MID-LEVEL LAPSE RATES AND CAPE AROUND 2000
J/KG.  

THEREAFTER...INCREASING LARGE-SCALE ASCENT ASSOCIATED WITH THE
APPROACH OF UPPER TROUGH/STRENGTHENING SOUTHERLY LOW-LEVEL JET MAY
SUPPORT INCREASING CONVECTIVE DEVELOPMENT ALONG A SURFACE FRONT...
EXTENDING ACROSS NORTHERN SOUTH DAKOTA INTO VICINITY OF SURFACE LOW
TO THE LEE OF THE NORTH CENTRAL ROCKIES.  ACTIVITY PROBABLY WILL
INITIATE IN THE MOIST POST-FRONTAL UPSLOPE FLOW REGIME ACROSS
SOUTHEAST MONTANA/PARTS OF NORTHEAST WYOMING...AND COULD CONSOLIDATE
INTO AN ORGANIZED CONVECTIVE CLUSTER EASTWARD ALONG FRONT TONIGHT. 
IF THIS OCCURS...THERMODYNAMIC PROFILES FAVORABLE FOR EVAPORATIVE
COOLING NEAR HEAVY PRECIPITATION CORES...AND DOWNBURSTS/SURFACE COLD
POOL DEVELOPMENT...WILL SUPPORT POTENTIAL FOR DAMAGING WIND GUSTS. 
LARGE HAIL IS ALSO POSSIBLE.

..KERR/BOTHWELL.. 08/17/2006