Severe Thunderstorm Warning 233, NWS Hastings, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HASTINGS NE
222 PM CDT FRI SEP 15 2006

.SHORT TERM...THIS EVENING THROUGH SUNDAY NIGHT. PRIMARY FORECAST
CONCERN WILL REVOLVE AROUND THE CHANCE FOR STRONG TO SEVERE
THUNDERSTORMS THIS EVENING AND POSSIBLE REDEVELOPMENT OVER FAR
EASTERN ZONES TOMORROW AFTERNOON. WATER VAPOR IMAGERY SHOWS A LARGE
TROUGH DIGGING OVER THE WESTERN CONUS WITH UPPER AIR OBSERVATIONS
DEPICTING A 90 TO 100 KT JET LEVEL SPEED MAX OVER THE DESERT
SOUTHWEST. FAVORABLE LEFT EXIT REGION OF THE JET IS LOCATED OVER
NEBRASKA. A 994 MB SFC LOW IS POSITIONED OVER THE WESTERN DAKOTAS
EARLY THIS AFTERNOON WITH A 1020MB HIGH SITUATED OVER SOUTHEAST
MISSOURI. THE SUBSEQUENT TIGHT PRESSURE GRADIENT ACROSS THE PLAINS...
AND AMPLE MIXING UNDER PARTLY TO MOSTLY SUNNY SKIES...HAS DRIVEN
SOUTH WINDS UP INTO THE 20 TO 30MPH RANGE THIS AFTERNOON.  THE STRONG
SOUTHERLY FLOW HAS ALSO HELPED TO DRIVE DEWPOINTS OUT OF THE LOWER
50S THIS MORNING TO AROUND 60 THIS AFTERNOON.

THE INITIAL CONCERN FOR LATE THIS AFTERNOON AND EARLY THIS EVENING
REVOLVES AROUND THE POSSIBILITY OF SFC BASED CONVECTION ACROSS OUR
WESTERN CWA.  SFC HEATING UNDER MOSTLY SUNNY SKIES...ALONG WITH
ENHANCED SFC CONVERGENCE ACROSS SOUTHWEST NEBRASKA IS NOW RESULTING
IN THE DEVELOPMENT OF A CUMULUS FIELD EXTENDING FROM MCK TO LBF TO
TIF.  THIS AREA OF ENHANCED CONVERGENCE WILL SLOWLY SHIFT EAST INTO
OUR CWA LATER THIS AFTERNOON AND THIS EVENING ACTING AS A FOCAL
POINT FOR CONVECTIVE DEVELOPMENT. THE RUC AND GFS ARE STILL
FORECASTING HIGH CIN VALUES FOR THIS EVENING WHICH WOULD MAKE SFC
BASED CONVECTION MORE DIFFICULT TO ACHIEVE.  THE NAM WOULD BE MORE
SUPPORTIVE OF SEEING A FEW SFC BASED STORMS.  OVERALL FEELING IS
THAT MOST OF THE THUNDERSTORMS THIS AFTERNOON AND EVENING WILL
REMAIN ELEVATED ESPECIALLY OVER EASTERN AND CENTRAL ZONES...MAKING
DAMAGING WINDS AND LARGE HAIL THE PRIMARY THREATS.  DEEP LAYER SHEAR
OF CLOSE TO 40KTS WITH MLCAPE VALUES OF 1500 J/KG WILL SUPPORT THE
POSSIBILITY OF SEVERE THUNDERSTORMS. A STRONG 50 TO 60KT LOW LEVEL
JET WILL CONTINUE TO FEED THUNDERSTORMS AFTER DARK WITH STORMS
TRACKING NORTHEAST ACROSS OUR CWA.

THUNDERSTORMS SHOULD EXIT OUR CWA AFTER MIDNIGHT TONIGHT WITH
DECREASING CLOUDS FROM WEST TO EAST BY DAYBREAK.  A PREFRONTAL
SFC TROUGH AND COLD FRONT WILL BOTH TRACK ACROSS OUR CWA DURING THE
DAY ON SATURDAY.  TEMPERATURES WILL STILL RISE INTO THE 80S AS THE
COLD AIR WILL TAKE A WHILE TO FILTER INTO THE REGION.  SEVERE
THUNDERSTORMS WILL LIKELY REDEVELOP ALONG THE PREFRONTAL TROUGH
SATURDAY AFTERNOON...BUT THIS WILL LIKELY NOT OCCUR UNTIL THE
TROUGH IS EAST OF OUR CWA OR JUST EXITING OUR EASTERN MOST
COUNTIES.  SFC COLD FRONT WILL QUICKLY FOLLOW BEHIND THE INITIAL
TROUGH WITH EVERYTHING THROUGH OUR CWA BY TOMORROW EVENING.  GIVEN
THIS TIMING...MOST OF OUR CWA WILL REMAIN DRY ON SATURDAY WITH JUST
A SLIGHT CHANCE OF THUNDERSTORMS OVER OUR FAR EASTERN CWA.  ANY
THUNDERSTORMS THAT DEVELOP ALONG OUR EASTERN CWA FROM YORK TO
HEBRON WILL STAND THE CHANCE OF BECOMING SEVERE THANKS TO STRONG
WIND SHEAR AND MODERATE INSTABILITY. NOTICEABLY COOLER AIR THEN
FILTERS INTO THE REGION ON SUNDAY AS SFC HIGH PRESSURE BUILDS IN
MAKING FOR A DRY BUT COOL DAY.

.LONG TERM...MONDAY THROUGH FRIDAY.  THE BEGINNING OF THE EXTENDED
PERIOD WILL BE UNDER THE INFLUENCE OF THE UPPER TROUGH OF LOW
PRESSURE WHICH WILL HAVE JUST PASSED TO OUR EAST SUNDAY NIGHT.
HEIGHTS WILL BEGIN TO RISE BEHIND THE DEPARTING SYSTEM...BUT THE
AIRMASS WILL REMAIN RATHER COOL FOR MUCH OF THE WEEK.  READINGS
MODERATE JUST SLIGHTLY ON TUESDAY...THEN MODELS DIVERGE IN HANDLING
OF PATTERN FROM MID WEEK ON.  THE 06Z GFS SUGGESTED NEXT CLOSED LOW
WILL SLIP SOUTHEAST THRU OUR CWA TUESDAY NIGHT OR WEDNESDAY BRINGING
ANOTHER CHANCE OF PCPN.  THE 12Z GFS TAKES PART OF THIS NEXT PIECE
OF ENERGY TO OUR NORTH...BUT STILL DIGS A TROUGH OVER THE
ROCKIES...THEN SWINGS A WEAKER TROUGH THRU THURS NIGHT OR
FRIDAY...WITH MAIN PCPN SETTING UP TO OUR SOUTH.  THE ECMWF ALSO
SUGGESTS A TROUGH OVER THE MOUNTAINS...BUT MAIN DEEPER CLOSED LOW
REMAINING TO OUR NORTH.  THE 12Z GFS IS MORE SIMILAR TO THE
ECMWF...AND THE CANADIAN FALLS IN BETWEEN THIS.  GIVEN THE
DIFFERENCES IN TIMING AND PLACEMENT OF THIS NEXT SYSTEM...HAVE LEFT
THE EXTENDED FORECAST DRY.  TEMPERATURES OVERALL WILL GENERALLY BE
BELOW SEASONAL NORMALS.

&&

.GID WATCHES/WARNINGS/ADVISORIES...
NE...NONE.
KS...NONE.
&&

WESELY

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