Severe Thunderstorm Warning 34, NWS Cheyenne, WY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
215 PM MDT THU AUG 22 2002

.SHORT TERM...CLOSED UPR LOW OVR NW U.S. DURING THE NEXT 36 HOURS
WITH SVRL WAVES EJECTING OUT OF THE LOW IN WSW FLOW ALF OVR CWA.
UPR RDG OVR ERN WY/WRN NEB THRU PD WITH WAVES MOVG THRU THE RDG.
FIRST VORT CURRENTLY MOVG THRU ERN WY WITH SOME TSTMS DVLPG OVR
CARBON AND ALBANY COUNTIES. LAPS ANALYSIS SHOWING GREATEST
INSTABILITY AND CAPE OVR EAST CENTRAL WY INTO THE NW NEB PANHANDLE.
AS THE VORT SHIFTS EAST THIS AFT AND EVENING...ERN WY UNDER
INFLUENCE OF WEAK RDG AXIS AND NVA. CONVECTION SHOULD SHIFT INTO THE
PANHANDLE THIS EVENING. CLOUDS DECREASE OVERNIGHT WITH WINDS
BECOMING LIGHT DOWNSLOPE MOST AREAS. LOW LVL MOISTURE FLUSHES OUT SO
DO NOT EXPECT ANY LOW CLOUDS THIS EVENING. ON FRIDAY...NEXT FEATURE
MOVES THRU CWA AT THE PEAK OF AFT HEATING WITH BETTER SURFACE
CONVERGENCE ALONG QUASI-STATIONARY BOUNDARY IN ERN WY.  BETTER LOW
LVL UPSLOPE FLOW. DAY TWO OUTLOOK HAS EASTERN WY AND WRN NEB IN
SLIGHT RISK AND I AGREE WITH THIS PLACEMENT. HOWEVER...LATEST MODEL
RUNS SHOWING WEAKLY UNSTABLE AMS AND LOW LVL MSTR SLOW TO RETURN.
LATER SHIFTS WILL HAVE TO MONITOR THESE TRENDS. H7 TEMPS WARM 2-4
DEGREES C FRI AND THICKNESSES INCREASE. LATER START TO CLOUD
DEVELOPMENT WILL HELP TEMPS CLIMB INTO THE 80S AT THE LOWER
ELEVATIONS. FOLLOWING THE PASSAGE OF THE UPR TROF...BOUNDARY SINKS
SOUTH THRU ERN WY. LOW LVL MSTR INCREASES WITH E-SELY UPSLOPE FLOW
ERN AREAS WITH LOW CLOUDS AND AREAS OF FOG POSSIBLE SAT AM.

.EXTENDED...
EXTENDED MODELS SUPPORT A TROF DEVELOPING IN SOUTHWEST OF ALASKA WITH
SOME RIDGING PERSISTING OVER THE WESTERN US AND THE INTER-MOUNTAIN
REGION. THE 0-5 WAVE SUPPORTS THIS ASSESSMENT WITH A MEAN RIDGE
POSITION OVER THE WESTERN US. THE ECMWF DEVIATES FROM THE
MRF AND UKMO MODELS SOMEWHAT SUGGESTING THAT THE PERSISTENT RIDGING
IS LIKELY TO ERODE GIVING WAY TO TRANSITIONAL WEATHER CONSISTENT WITH
LATE AUGUST CLIMATOLOGY.

ALOFT...A SHORT WAVE TROF IS EXPECTED TO MOVE SLOWLY THROUGH THE MEAN
RIDGE POSITION THIS WEEKEND BUT THE RIDGE SHOULD BECOME THE DOMINATE
FEATURE BY MID WEEK ONCE AGAIN. LOW LEVEL MOISTURE WITH SCATTERED
SHOWERS AND LATE DAY THUNDERSTORMS SHOULD MOVE EAST BY SATURDAY WITH
DRYER CONDITIONS ACROSS THE CWA ON SUNDAY AND MONDAY. TEMPERATURES
WILL BE AT OR SLIGHTLY BELOW NORMAL OVER THE WEEKEND. TUESDAY SHOULD
AGAIN SEE A RETURN OF SOME MOISTURE WITH WEAK UPSLOPE FLOW FOR
SCATTERED LATE DAY SHOWERS AND THUNDERSTORMS. WEDNESDAY AND
THURSDAY WILL AGAIN SEE WEAK RIDGING OVER THE AREA AND THIS SHOULD
YIELD DRYER CONDITIONS. TEMPERATURES WILL REMAIN ABOUT NORMAL OR
SLIGHTLY BELOW NORMAL INTO LATE WEEK ACROSS THE CWA.

&&

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

JLS/WTP