Damaging Wind in Wyoming, May 21, 2002

SOUTH CENTRAL AND SOUTHEAST MONTANA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
209 PM MDT TUE MAY 21 2002

.SHORT TERM...VALID FOR WED...THU...FRI...

COMPLICATED PATTERN SETTING UP FOR TONIGHT THROUGH THURSDAY MORNING AS
UPPER LEVEL SYSTEM MOVES INTO MONTANA. AVN AND ETA BOTH HANDLING THE
SYNOPTIC PATTERN SIMILARLY WITH THE AVN BEING ABOUT 200 MILES FARTHER
NORTH WITH LOW LEVEL FEATURES THAN THE ETA. LIKE THE ETA/META
SOLUTION WITH A BIT SLOWER TIMING AND MORE SOUTHERLY TRACK PER 15Z
ANALYSIS WITH SURFACE LOW PRESSURE CENTERED IN SOUTHWEST WYOMING WITH
A SECONDARY LOW DEVELOPING IN SOUTH CENTRAL MONTANA. ETA IS PUTTING OUT
VERY HIGH QPF OVER THE WESTERN HALF OF MY CWA OVER THE NEXT 24 TO 36
HOURS WITH SOME VALUES OVER TWO INCHES FOR THE STORM TOTALS. AS
PRECIPITATION TURNS TO SNOW EARLY WEDNESDAY MORNING HEAVY SNOW
ACCUMULATIONS CAN BE EXPECTED ABOVE 6000 FEET SO WILL ISSUE A WINTER
STORM WARNING FOR THE AREAS CURRENTLY UNDER A WATCH. PRECIPITATION MAY
CHANGE OVER TO SNOW AT LOWER ELEVATIONS AROUND SUNRISE IN THE WARNED
LOCATIONS BUT 850 MB TEMPS AROUND +2C SHOULD PREVENT ADVISORY
ACCUMULATIONS. STRONG WRAP AROUND WILL DRIVE COLD FRONT INTO THE AREA
EARLY WEDNESDAY...MODELS INDICATING 12 MB PRESSURE RISES BEHIND
THIS FEATURE WITH WINDS APPROACHING WARNING CRITERIA FOR THE
WESTERN 2/3 OF MY CWA...THINK STRONG UPWARD MOTION WILL LIMIT TRANSFER
OF 60KT WINDS FROM 800-700MB LAYER TO SURFACE SO WILL HOLD OFF ON
ISSUING A WARNING.

SYSTEM BEGINS TO EXIT THE STATE THURSDAY MORNING WITH SOME WRAP AROUND
PRECIPITATION HOLDING ON IN THE EAST UNTIL LATE AFTERNOON. TEMPERATURES
WILL GET CLOSE TO RECORD LEVELS FOR THURSDAY AND FRIDAY WITH RECORD LOWS
AROUND 31 DEGREES...ESPECIALLY FRIDAY MORNING AS CANADIAN HIGH PRESSURE
BUILDS IN AND SKIES CLEAR OUT. SKIES CONTINUE TO CLEAR OUT FRIDAY BUT
TEMPS WILL BE SLOW TO WARM WITH GENERAL ZONAL FLOW ALOFT WARM WITH A FEW
INSTABILITY SHOWERS IN THE AFTERNOON. CHAMBERS

.LONG TERM...VALID FOR SAT...SUN...MON...TUE...
LONG RANGE MODELS IN GOOD AGREEMENT WITH A BROAD RIDGE AND NEARLY ZONAL
FLOW ACROSS THE AREA SATURDAY. ECMWF THEN BECOMES THE OUTLIER AS UKMET
AND AVN/MRF BOTH TURN FLOW SOUTHWEST WITH ANOTHER UPPER LEVEL LOW OFF
THE SOUTHERN BRITISH COLUMBIA COAST. MRF HAS A SURFACE TROUGH AND
PACIFIC COLD FRONT MOVING ACROSS MONTANA SATURDAY AND SUNDAY WITH COOLER
TEMPERATURES TRAILING BEHIND. WILL MODERATE GUIDANCE TEMPERATURE FALLS
WITH THIS SYSTEM TO INDICATE SLIGHT COOLING TREND THROUGH SUNDAY...AND
INSERT SLIGHT CHANCE POPS FOR SATURDAY/SATURDAY NIGHT IN THE WEST...AND
SATURDAY NIGHT/SUNDAY IN THE EAST. SURFACE HIGH MOVES INTO THE AREA
BEHIND THE FRONT BEGINNING MONDAY...WHILE UPPER FLOW BECOMES MORE ZONAL
BY MONDAY/NIGHT TUESDAY. TEMPERATURES SLOWLY REBOUND TO NEAR NORMAL
VALUES FOR DAYS 6 AND 7. CARPENTER

    WED     THU     FRI     SAT     SUN     MON     TUE
-----------------------------------------------------------
BIL 045/051 034/054 033/060 044/065 046/064 045/068 045/071
    8+/R    42/W    22/W    02/B    20/E    00/B    00/B
LVM 041/045 029/052 028/060 038/065 044/064 041/067 043/071
    ++/0    62/0    22/W    02/B    20/E    00/B    00/B
HDN 045/052 035/055 034/061 043/066 045/065 044/069 044/072
    88/R    42/W    22/W    02/B    20/E    00/B    00/B
MLS 050/055 037/056 035/060 045/065 047/064 046/068 046/071
    66/W    64/W    22/W    02/B    20/E    00/B    00/B
4BQ 048/055 038/057 035/060 042/065 045/064 044/068 045/071
    66/W    64/W    22/W    00/B    22/E    00/B    00/B
BHK 049/054 038/055 035/061 042/066 045/065 044/069 045/071
    64/W    64/W    22/W    00/B    22/E    00/B    00/B
SHR 046/055 037/055 034/058 040/064 045/063 044/066 044/069
    67/W    64/W    22/W    00/B    22/E    00/B    00/B

.BYZ...WINTER STORM WARNING FOR LATE TONIGHT AND WEDNESDAY FOR MOUNTAIN
ZONES...