High Wind in Montana, December 14, 2001

SOUTH CENTRAL AND SOUTHEAST MONTANA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
200 PM MST FRI DEC 14 2001

.SHORT TERM...VALID FOR SAT...SUN...MON...
THERE ARE SOME DIFFERENCES IN THE MODELS TODAY...MAINLY WITH TIMING
EARLY ON. ANOTHER DIFFERENCE SHOWS UP AT ABOUT 24 HOURS OUT WITH
APPROACH OF ANOTHER SHORTWAVE ONTO THE BRITISH COLUMBIA SHORE. THE NEXT
UPSTREAM WAVE IS MUCH STRONGER ON THE AVN AND THEREFORE A MUCH DEEPER
SURFACE LOW MOVES INTO SOUTHWEST CANADA EARLY SUNDAY. THE AVN WOULD
SUPPORT MORE WIND OVER THE UPPER YELLOWSTONE VALLEY ON SUNDAY. PREFER
THE SLOWER ETA IN THE SHORT TERM. WILL SIDE WITH THE AVN FOR SUNDAY AS
AVN GRIDS DO PICK UP SHORTWAVE IN QUESTION (AND SEEM TO BE HANDLING IT
FAIRLY WELL)...WHILE THE ETA GRIDS DO NOT GO OUT THAT FAR.

COLD FRONT TO PUSH THROUGH THE FORECAST AREA THIS EVENING. THIS FRONT
WILL INTERACT WITH POTENTIAL INSTABILITY UP TO ABOUT 400MB. MOISTURE
MAINLY AT MID LEVEL AT THE MOMENT...AND WILL HAVE TO FIGHT SOME INITIAL
DOWNSLOPE. LIKE THE IDEA OF KEEPING POPS SCATTERED. EXCEPTION WILL BE AT
SHERIDAN WHERE STRONG DIVERGENCE/CONVERGENCE COUPLET EXITS. MODELS HAVE
BEEN VERY CONSISTENT ON THIS FEATURE. OMEGA OF 8 MB/S THERE DURING THE
EVENING. SHOULD BE A QUICK SHOT OF PRECIPITATION TONIGHT. THE SOUTHEAST
WILL HAVE FRONTAL LIFT FOR SCATTERED POPS. WILL CARRY THE POPS IN THE
SOUTHEAST EARLY SATURDAY AS THE UPPER TROUGH MOVES INTO THE DAKOTAS
SATURDAY AFTERNOON. WINDS WILL BE GUSTY WITH FRONTAL PASSAGE TONIGHT.
THE PRESSURE GRADIENT SLACKENS UP QUICKLY LATE TONIGHT. DRIER AIR TO
WORK IN BEHIND THE TROUGH TO SQUELCH ANY FURTHER PRECIPITATION CHANCES.

A FAIRLY FLAT FLOW DEVELOPS FOR SATURDAY NIGHT AND SUNDAY. A SHORTWAVE
SWINGS ACROSS SOUTHERN CANADA SUNDAY AFTERNOON FOR LEE TROUGHING.
SURFACE PRESSURE GRADIENT BECOMES PRETTY TIGHT ALONG THE EAST SLOPES.
MID LEVEL WINDS MORE OF A WEST TO NORTHWEST FLOW. WILL NOT GO WITH ANY
HIGHLIGHTS FOR THE UPPER YELLOWSTONE VALLEY...BUT HIT WINDS HARD FOR
SUNDAY. A FLAT RIDGE THEN HOLDS OVER THE AREA SUNDAY NIGHT AND MONDAY
FOR DRY AND MILD WEATHER. HUMPHREY

.LONG TERM...VALID FOR TUE...WED...THU...FRI...
PER MRF...COOL UNSETTLED WEATHER RETURNING TO THE REGION WITH A SERIES
OF WEAK UPPER LEVEL DISTURBANCES MOVING THROUGH FLOW ALOFT FOLLOWED BY
A COLD FRONTAL PASSAGE LATE TUE. FRONT WILL ALLOW TEMPS TO DROP BACK TO
SEASONAL READINGS WITH ISOLD SNOW SHOWERS AT BEST AS 500MB HEIGHTS DROP
TO AROUND 534DM AND 1000-500MB THICKNESS VALUES FALL TO NEAR 525 BY 12Z
FRI ACROSS THE REGION. AVN MODEL AT 12Z TUE TENDS TO BE A BIT WARMER
LEADING INTO THE EXTENDED THAN WHAT THE MRF IS SUGGESTING AND SHOWS THE
DISTURBANCES CROSSING THE REGION TO BE SLIGHTLY STRONGER. OVERALL
PATTERN SIMILAR BUT DIFFERENT WITH TIMING AND RIDGE/TROUGH PLACEMENT.
AVN/ECMWF TENDS TO BE MORE IN LINE WITH ONE ANOTHER LEADING INTO THE
EXTENDED WHILE THE MRF SEEMS TO BE ODD MODEL OUT AND WILL GO MORE WITH
THE ECWMF SOLUTION...WARMER FIRST PART OF EXTENDED AND THEN COOLING BUT
NOT AS MUCH/FAST AS WHAT MRF SUGGESTS.  SPRINGER

    SAT     SUN     MON     TUE     WED     THU     FRI
-----------------------------------------------------------
BIL 023/033 019/045 027/049 024/039 020/032 018/032 018/032
    30/B    00/B    00/B    22/B    22/E    22/E    22/E
LVM 019/032 022/045 027/049 023/038 017/030 014/030 014/030
    30/J    00/N    00/N    22/E    22/E    22/E    22/E
HDN 022/034 015/047 025/051 023/039 018/031 015/031 015/031
    30/B    00/B    00/B    22/E    22/E    22/E    22/E
MLS 023/033 012/041 023/045 020/038 016/030 013/030 013/030
    42/J    00/B    00/B    22/E    22/E    22/E    22/E
4BQ 023/033 012/041 023/045 020/038 016/032 013/030 013/030
    42/J    00/B    00/B    22/E    22/E    22/E    22/E
BHK 022/032 010/039 021/043 018/034 013/028 011/028 011/028
    42/J    00/B    00/B    22/E    22/E    22/E    22/E
SHR 021/031 009/040 020/045 019/040 016/034 012/032 012/030
    62/J    00/B    00/B    22/E    22/E    22/E    22/E

.BYZ...NONE.