Heavy Snow in Wyoming, January 22, 2003

SOUTH CENTRAL AND SOUTHEAST MONTANA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
215 PM MST WED JAN 22 2003

.SHORT TERM...VALID FOR THU AND FRI...

MAIN FORECAST PROBLEM WILL BE HOW FAST ARCTIC AIR ERODES OUT OVER THE
FORECAST AREA ON THURSDAY.

TONIGHT...NORTHWEST FLOW CONTINUING OVER THE AREA TONIGHT AS HIGH
PRESSURE RIDGE MOVES IN OVER THE AREA. RIDGE WILL FLATTEN OVERNIGHT AS
SHORT WAVE MOVES THROUGH FROM THE PACIFIC NORTHWEST COAST. ETA
INDICATING 700MB FRONTOGENESIS TO SETUP AGAIN OVER THE WESTERN AREAS
AROUND 06Z TONIGHT. ETA PROVIDING GOOD INSTABILITY IN THE MID LEVELS
ALONG WITH GOOD 700MB WARM ADVECTION. MOISTURE NOT AS IMPRESSIVE AS LAST
NIGHTS SNOW EVENT BUT ENOUGH REMAINS FOR SOME ADDITIONAL SNOW
ACCUMULATIONS IN THE WESTERN ZONES. 700 MB WARM AIR ADVECTION WILL MAKE
ITS WAY INTO EASTERN MONTANA AFTER 06Z...BRINGING A CHANCE OF SNOW.
TEMPERATURES WILL DROP OFF FAST OVER THE SOUTHEAST TONIGHT BUT SHOULD
RECOVER SOME AS CLOUDS MOVE IN.

THURSDAY...SHORT WAVE MOVES THROUGH QUICKLY AND SHOULD BE OUT OF THE
EASTERN ZONES BY 18Z. MODELS TRY TO PUSH ARCTIC AIR OUT THURSDAY BUT
FEEL THIS WILL BE TOUGH TO DO...ESPECIALLY WITH RECENT AMOUNT OF
SNOWFALL. STRONG TEMPERATURE INVERSION SETS UP OVER THE AREA AND STRONG
WINDS ALOFT WILL NOT BE ABLE TO MIX DOWN TO THE SURFACE. WILL CONTINUE
TO UNDERCUT TEMPERATURE GUIDANCE BY AT LEAST 10 TO 15 DEGREES.

THURSDAY NIGHT AND FRIDAY...SHORT WAVE TO MOVE THROUGH THURSDAY NIGHT
INTO FRIDAY MORNING. MOISTURE IS LIMITED WITH THIS WAVE AND WILL KEEP
DRY FORECAST GOING. LITTLE BETTER MIXING TO TAKE PLACE ON FRIDAY AND
HAVE RAISED TEMPERATURES. WILL STILL STAY BELOW GUIDANCE AS SNOW COVER
WILL INHIBIT TEMPERATURES FROM REACHING MAXIMUM POTENTIAL. RICHMOND

.LONG TERM...VALID FOR SAT...SUN...MON...TUE...WED...

THE FLOW ALOFT BECOMES ZONAL FOR A TIME...BEFORE UPPER RIDGING AGAIN
COMES INTO PLAY LATER IN THE PERIOD. ECMWF...CANADA...OLDER MRF AND
NEWER AVN SHOW AGREEMENT FOR THE MOST PART UNTIL LATER ON IN THE
PERIOD WHEN AVN AND MRF DIFFER IN PLACEMENT OF FRONTAL BOUNDARY WITH
AVN KEEPING THIS FEATURE FARTHER NORTH THAN DOES THE MRF. AM INCLINED
TO CONSIDER THE NEWER AVN RUN THIS TIME WITH HAVING BOTH TUESDAY AND
WEDNESDAY DRY. CONCEIVABLY...THE FRONTAL BOUNDARY MAY BACK DOOR INTO
NORTHEAST MONTANA...BUT WILL HOLD OFF ON THAT FOR THE NOW. AM NOT THAT
ENTHUSED ABOUT MODERATING TEMPERATURES TO THE EXTENT THAT GUIDANCE
HAS.  EVEN MIXING FROM THE NEW AVN SOUNDINGS INDICATES WARMER
TEMPERATURES. THE COLD AIR DOME IS FAIRLY THICK AND SNOW COVER ALSO
WILL IMPEDE ITS MOVING OUT. HAVE BACKED DOWN ON TEMPERATURES AND KEPT
THEM MORE IN TUNE WITH CONTINUITY. THE BEST RIPPLES TO CAUSE
PRECIPITATION IN THE FLOW OCCUR DURING SATURDAY AND ALSO DURING MONDAY.
AT THIS TIME...WILL ONLY CONSIDER SCATTERED POPS. ANOTHER THING TO
CONSIDER IS SOME WINDY CONDITIONS OVER THE UPPER YELLOWSTONE VALLEY
ESPECIALLY DURING SUNDAY. CHB

    THU     FRI     SAT     SUN     MON     TUE     WED
-----------------------------------------------------------
BIL 905/023 014/035 018/030 021/040 025/044 026/044 024/043
    63/S    00/E    03/S    30/E    03/O    30/B    00/B
LVM 909/026 018/038 015/031 019/043 023/045 025/045 022/040
    64/S    00/E    03/S    30/N    03/S    30/B    00/B
HDN 910/024 013/036 015/031 018/041 022/046 022/045 021/045
    64/S    00/E    03/S    30/E    03/O    30/B    00/B
MLS 915/020 010/029 011/023 008/034 018/039 021/038 017/035
    43/S    00/E    33/S    30/E    03/S    30/B    00/B
4BQ 909/027 014/036 015/026 011/033 017/039 020/037 016/036
    44/S    00/E    03/S    30/E    03/S    30/B    00/B
BHK 918/016 009/027 008/019 005/031 014/035 017/034 013/031
    34/S    00/E    33/S    30/E    03/S    30/B    00/B
SHR 005/022 014/035 017/031 016/036 019/042 021/042 020/040
    64/S    00/E    03/S    30/E    03/O    30/B    00/B

.BYZ...
MT...NONE.

WY...NONE.

MTZ028>042-056>058-WYZ098-099-231200-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE BILLINGS MT
254 PM MST WED JAN 22 2003

THIS HAZARDOUS WEATHER OUTLOOK IS FOR SOUTH CENTRAL...SOUTHEAST
MONTANA AND NORTH CENTRAL WYOMING.

.DAY ONE...
NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.
SNOW WILL BE LIKELY ACROSS THE AREA THIS EVENING WITH ACCUMULATIONS
REACHING AN ADDITIONAL TWO INCHES. THE SNOW WILL BE DIMINISHING TO
SHOWERS TOWARD MIDNIGHT.

.DAYS TWO THROUGH SEVEN...
NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.
SOME SNOW IS ANTICIPATED FOR THE AREA ON SATURDAY...AND THERE WILL
BE THE POSSIBILITY OF RAIN OR SNOW DURING MONDAY. NONE OF THESE
EVENTS ARE ANTICIPATED TO CREATE HAZARDOUS CONDITIONS AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...
WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER
CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES.

WCJIN-WYNW-WYNE