Severe Thunderstorm Warning 63, NWS Cheyenne, WY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
143 PM MDT SAT AUG 31 2002

ISOLATED SHOWERS AND THUNDERSTORMS ARE STILL POSSIBLE THROUGH THE
EVENING HOURS OVER MAINLY THE WESTERN NEBRASKA PANHANDLE...THAT PART
OF THE CWA WILL BE AHEAD OF A SURFACE LOW PRESSURE TROUGH ALLOWING
FOR BETTER BOUNDARY LAYER MOISTURE AND STEEPER LAPSE RATES.  THAT
SURFACE LOW PRESSURE TROUGH WILL MOVE EAST OF THE CWA THIS EVENING
AHEAD OF A WEAK COLD FRONT WHICH MOVES THROUGH THE CWA LATE TONIGHT
AND SUNDAY MORNING.  THE RESULTING WESTERLY SURFACE WINDS WILL KEEP
MOST OF THE LOWER CLOUDS AND FOG OUT OF THE CWA LATER TONIGHT.
A SHORTWAVE TROUGH WHICH WAS LOCATED FROM NORTH CENTRAL MONTANA TO
NORTHERN NEVADA AT MIDDAY WILL MOVE OVER THE CWA BY SUNDAY
AFTERNOON...WITH MOST OF ITS ENERGY MOVING OVER WESTERN SOUTH DAKOTA
AND POSSIBLY INTO THE NORTHERN PANHANDLE.  THE AVN CONTINUES TO BE
WETTEST AND MOST UNSTABLE OF THE MODELS OVER THAT AREA SUNDAY
AFTERNOON BUT HAS BACKED OFF ON ITS QPF FROM THE 06Z RUN.  FOR NOW
WILL KEEP THE MENTION OF LOW POPS IN THE FORECAST FOR SUNDAY AFTERNOON
AND EARLY EVENING IN THE NORTHERN NEBRASKA PANHANDLE.  AS THE UPPER
LOW CYRRENTLY OVER BRITISH COLUMBIA MOVES EAST THROUGH MONDAY...
THE FLOW ALOFT BECOMES MORE NORTHWESTERLY AND ANOTHER SURFACE COLD
FRONT MOVES ACROSS THE CWA LATE SUNDAY NIGHT AND MONDAY MORNING.
WITH A MORE STABLE AND DRIER AIR MASS IN PLACE OVER THE CWA MONDAY
BEHIND THE FRONT WILL LEAVE OUT POPS AND GO WITH COOLER READINGS.  A
BOUNDARY LAYER SOUTHEAST WIND FLOW RETURNS OVER THE EAST PART OF THE
CWA TUESDAY AHEAD OF ANOTHER SURFACE LOW PRESSURE TROUGH.  THE
AVN SHOWS LOWER LIFTED INDICES AND AN INCREASE IN MOISTURE OVER THE
WESTERN NEBRASKA PANHANDLE FOR TUESDAY AFTERNOON.  EVEN THOUGH THERE
IS NOT MUCH IN THE WAY OF DYNAMICS...SURFACE FORCING ALONG THE LOW
PRESSURE TROUGH SHOULD BE ENOUGH FOR WIDELY SCATTERED SHOWERS AND
THUNDERSTORMS TO DEVELOP...EVEN THOUGH THE AVN HAS NO QPF.  FOR
NOW WILL LEAN MORE TOWARDS THE ETA WITH SLIGHTLY LOWER MEAN LAYER
RELATIVE HUMIDITIES AND A DEEPER UPPER LOW MOVING ACROSS CANADA.
FWC AND MAV GUIDANCE LOOKS CLOSE FOR THE TEMPERATURES THROUGH
TUESDAY.  THE ETA SEEMS TO BE TOO WARM AND EVEN SHOWS WARMING IN
SOME AREAS IN THE COOLER AIR MASS ON MONDAY.

.EXTENDED...
SOUTHWEST FLOW WILL CONTINUE ALOFT OVER THE CWA THROUGH THE EXTENDED
PERIOD AS AN UPPER LEVEL TROUGH MOVES ACROSS THE PACIFIC NORTHWEST.
A SHORT WAVE MOVES ACROSS THE AREA WEDNESDAY WITH UPPER
LEVEL DIVERGENCE. DUE TO THE LIMITED AMOUNT OF MOISTURE AVAILABLE...
ONLY A SLIGHT CHANCE OF PRECIP IS EXPECTED OUTSIDE THE MOUNTAINS.
BETTER MOISTURE WILL BE AVAILABLE THURSDAY FOR A BETTER CHANCE OF
PRECIP.  A COLD FRONT WILL MOVE ACROSS THE FORECAST AREA ON FRIDAY...
WITH UPSLOPE FLOW DEVELOPING AFTER FRONTAL PASSAGE.  THIS WILL
RESULT IN A CHANCE OF PRECIP AGAIN ON FRIDAY ALONG WITH COOLER
TEMPERATURES.  SATURDAY LOOKS DRY AND COOL AS A FLAT RIDGE OF
HIGH PRESSURE BEGINS TO BUILD INTO THE AREA.  TEMPERATURES WILL BE
ABOUT NORMAL THROUGH FRIDAY AND THEN COOL TO 5 TO 10 DEGREES BELOW
NORMAL.

.CYS...
WY...NONE.
NE...NONE.

WEILAND/DAUGHERTY