Severe Thunderstorm Warning 268, NWS North Platte, NE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
258 PM CDT MON AUG 20 2001

MAIN FORECAST CHALLENGE WILL BE PRECIP CHANCES NEXT SEVERAL DAYS.

MODELS VARYING QUITE A BIT ON HEIGHT FIELDS ACROSS SOUTHWEST CONUS
THIS PAST MORNING AS A RESULT OF SHORT WAVE SITTING ACROSS AZ.  AVN
AND NGM INITIALIZED TOO HIGH ACROSS AZ WITH THE ETA DOING THE BEST.
IT COMES AS NO SURPRISE THAT THE AVN IS MUCH QUICKER AT PUSHING WAVE
ACROSS AREA BY TOMORROW AFTERNOON VERSUS THE ETA.  WITH WATER VAPOR
IMAGERY SHOWING ONLY A SLOW DRIFT OF WAVE TO NORTHEAST...WILL FAVOR
THE ETA FOR THIS FORECAST.

WEAK WARM FRONT WILL EXTEND FROM NORTHEAST COLORADO INTO NORTHERN
KANSAS THIS EVENING WITH LEE TROUGH EXTENDING ACROSS WESTERN
PANHANDLE.  STRONG MOISTURE CONVERGENCE IN PANHANDLE ALONG WITH GOOD
UPPER SUPPORT FROM SHORT WAVE CURRENTLY SEEN EXITING CENTRAL ROCKIES
WILL PRODUCE SCATTERED CONVECTION ACROSS WESTERN FA BY EARLY
EVENING.  FORCING WILL THEN SHIFT EAST INTO CENTRAL AND EASTERN CWA
AS 45-50 KNOT LLJ NOSES INTO AREA DURING OVERNIGHT HOURS AND LIFTS
FRONT INTO CENTRAL NEBRASKA BY SUNRISE.  EXPECT CONVECTION TO FOLLOW
BEST LOW-LEVEL FORCING AND WILL THEREFORE MENTION SCATTERED
PRECIPITATION ACROSS ALL OF CWA TONIGHT.

ANTICIPATE SURFACE LOW TO DEVELOP ACROSS NORTHEAST NEBRASKA BY
AFTERNOON ON TUESDAY WITH SURFACE TROUGH/WEAK FRONT ALIGNED FROM
NORTHEAST TO WEST CENTRAL CWA.  MOISTURE SHOULD REMAIN DECENT ON
BACK SIDE OF TROUGH/WEAK FRONT INTO THE AFTERNOON AS NEXT WAVE MOVES
INTO AREA.  BEST SUPPORT WOULD FAVOR A CHANCE OF TSRA ACROSS WESTERN
HALF OF CWA BY AFTERNOON.  EXPECT CHANCE ACROSS ALL OF AREA TUESDAY
NIGHT AS WAVE SHIFTS SLOWLY FROM WEST TO EAST ACROSS CWA.  FOR THIS
REASON WILL BLANKET CWA WITH 30-40 POPS.  HIGH TEMPERATURES WILL BE
TRICKY ON TUESDAY AS 850 MB TEMPS SUGGESTING UPPER 80S NORTH TO
MIDDLE 90S SOUTH DESPITE THICKNESS FIELDS DROPPING ACROSS NORTHERN
AND CENTRAL ZONES.

LOW-LEVEL PATTERN CHANGES LITTLE INTO WEDNESDAY AS NEXT WAVE MOVES
INTO CENTRAL HIGH PLAINS.  THIS SHOULD SET THE STAGE FOR ANOTHER
ROUND OF SHOWERS AND THUNDERSTORMS STARTING BY LATE AFTERNOON IN THE
WEST AND SHIFTING INTO THE EAST BY EARLY EVENING.  WILL BLANKET AREA
WITH 30-40 POPS ONCE AGAIN.  TEMPERATURES SHOULD BE A FEW DEGREES
COOLER FOR HIGHS AS LOW-LEVEL TEMPERATURE AND THICKNESS FIELDS
LOWER.  MIDDLE 80S NORTH TO AROUND 90 SOUTH LOOK GOOD AT THIS TIME.

EXTENDED...MODELS AGREE ON SHIFTING UPPER LOW/TROUGH ACROSS SOUTHERN
CANADA AND NORTHERN CONUS.  HOWEVER...MAJOR TIMING DIFFERENCES EXIST
BETWEEN THE MRF...UKMET AND ECMWF.  THE MRF IS MUCH QUICKER AT
EJECTING THIS SYSTEM WITH WEAK RIDGING THEN TAKING PLACE BEHIND WAVE
ON DAYS 5 THROUGH 7.  THE ECMWF AND UKMET ARE AROUND 24 HOURS SLOWER
WITH THIS SYSTEM EVOLUTION.  ENSEMBLE MEAN HEIGHT FIELDS ARE IN THE
MIDDLE OF THESE TWO SOLUTIONS AND WILL LEAN TOWARDS THIS COMPROMISE
FOR EXTENDED.  CONDITIONS STILL LOOKING GOOD FOR PRECIP
THURSDAY...BUT THEN DRY FRIDAY AND SATURDAY UNDER WEAK RIDGING.
RETURN FLOW SHOULD BEGIN TO SETUP SUNDAY AND MONDAY BRINGING A
CHANCE FOR RAIN BOTH DAYS AS LEE TROUGH DEEPENS ALONG FRONT RANGE
REGION AND PULLS FRONT BACK NORTH ACROSS FA.

.LBF...NONE.

AWJ