High Wind in Montana, March 12, 2002

SOUTH CENTRAL AND SOUTHEAST MONTANA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
225 PM MST TUE MAR 12 2002

.SHORT TERM...VALID FOR WED...THU...FRI...
ZONAL FLOW OVER THE STATE. COLD FRONT HAS PUSHED INTO NORTHERN WYOMING
THIS AFTERNOON. SHORTWAVE ENERGY WAS RIDING ACROSS SOUTHERN MONTANA AT
THE MOMENT. AXIS OF INSTABILITY EVIDENT ON INFRARED SATELLITE ALONG AND
NORTH OF THE BOUNDARY. ALL THESE THINGS HAVE COMBINED TO PRODUCE SHOWERS
ACROSS THE BILLINGS FORECAST AREA. INSTABILITY AXIS PROGGED TO SLIP
SOUTH TONIGHT AS THE COLD FRONT PENETRATES INTO CENTRAL WYOMING. WILL
KEEP SCATTERED POPS GOING TONIGHT. WILL KEEP THE LIKELY EVENING POPS
GOING ALONG THE EAST SLOPES. FORECAST THEN GETS INTERESTING.

AVN AND ETA CONFLICTING WITH SPEED OF NEXT UPSTREAM WAVE FORECAST OVER
THE INTERMOUNTAIN WEST. THE AVN IS MUCH QUICKER WITH IT INTO WYOMING
WEDNESDAY. THE ETA BARELY GETS IT INTO NORTHWEST WYOMING BY WEDNESDAY
AFTERNOON. THIS WILL AFFECT THE SPEED OF DEVELOPING 700MB LOW PROGGED TO
SHIFT ACROSS CENTRAL WYOMING. WILL SIDE TOWARD THE AVN AS IT APPEARS TO
HAVE THE STRENGTH AND MORE EASTWARD MOVEMENT OF WAVE ENERGY MOVING INTO
THE NORTHERN CALIFORNIA SHORE BETTER. AS THE SHORTWAVE RIPS ACROSS
WYOMING...THIS WILL SET UP AN AREA OF 700MB CONVERGENCE OVER NORTHERN
WYOMING. THIS WILL COMBINE WITH POTENTIAL INSTABILITY UP TO 500MB AND
SURFACE CONVERGENCE WITH THE COLD FRONTAL BOUNDARY STILL IN THE AREA TO
CREATE A CHANCE OF SNOW SHOWERS. THE ONE CONCERN I HAVE WITH THE AVN
SOLUTION IS THAT OFTEN TIMES...ENERGY STILL DIGGING ON THE BACK SIDE OF
A DEVELOPING TROUGH...KEEPS DYNAMICS FARTHER SOUTH. THIS IS WHAT THE ETA
INDICATES AND I SEE MERIT IN IT BASED ON PAST EXPERIENCE. WILL KEEP THE
MENTION OF CHANCE POPS IN SHERIDAN WEDNESDAY AND WEDNESDAY NIGHT.
HOPEFULLY ANOTHER MODEL RUN WILL GIVE US A MORE DEFINITIVE ANSWER ON THE
DIRECTION TO GO.

OTHERWISE...WILL LINGER LOW POPS OVER SOUTHERN MONTANA AS MODELS
INCREASE THE POTENTIAL INSTABILITY WEDNESDAY AFTERNOON. THERE IS SOME
WEAK SHORTWAVE ENERGY THAT IS PROGGED TO SLIP THROUGH THE AREA AS WELL.
THE NORTHERN PART OF SOUTHEAST MONTANA CAN GET AWAY WITH NO POPS AS THE
AIRMASS SHOULD BE DRIER THERE AND ALSO WILL BE FARTHER AWAY FROM THE
SURFACE FRONT. WILL INTRODUCE LOW POPS FOR LIVINGSTON ON FRIDAY. UPPER
LOW OVER THE GULF OF ALASKA IS FORECAST TO DROP INTO BRITISH COLUMBIA ON
FRIDAY. THIS WILL SET UP A SOUTHWEST FLOW OVER THE STATE. DESPITE THE
SOUTHWEST FLOW...HEIGHTS LOWER AS MAIN TROUGH SHIFTS EAST FROM THE EAST
PACIFIC. THE AVN BRINGS A WEAK SHORTWAVE ACROSS THE WEST. THIS WITH SOME
MOISTURE AND INSTABILITY MAY BE ENOUGH FOR THE MENTION OF SHOWERS. MOST
OF THE ACTIVITY WILL FOCUS ON THE MOUNTAINS...BUT FEET IT IS WORTH A LOW
POP AT LIVINGSTON. HUMPHREY

.LONG TERM...VALID FOR SAT...SUN...MON...TUE...
EXTENDED MODELS IN BETTER AGREEMENT TODAY THAN YESTERDAY...BUT STILL A
LOT OF UNCERTAINTY AS LATEST AVN DIVERGES FROM 00Z MRF.  BOTH THE MRF
AND ECMWF DIG AN UPPER TROUGH OVER THE WESTERN THIRD OF THE US AND
DEVELOP A CLOSED LOW OVER SOUTHERN BC ON SATURDAY...AVN DEVELOPS A
STRONGER LOW FURTHER SOUTHEAST INTO NORTHERN IDAHO. ON SUNDAY ECMWF/MRF
DIVERGE A BIT AS THE MRF LEANS TO A MORE PROGRESSIVE PATTERN IN THE
NORTHERN STREAM...WHILE THE ECMWF IS LESS PROGRESSIVE WITH SYSTEMS
ROTATING AROUND POLAR VORTEX. THE MAJORITY OF THE UPPER LEVEL ENERGY
WITH THE MRF/ECMWF LOOKS TO SLIDE DOWN THE WEST COAST AND GET CAUGHT UP
IN THE SOUTHERN STREAM MOVING INTO OK/TX ON SUNDAY BYPASSING OUR CWA.
THE AVN WRAPS MOST OF THE ENERGY AROUND THE UPPER LOW KEEPING IT IN THE
NORTHERN STREAM WHICH IS A MORE ACTIVE PATTERN FOR OUR AREA. A SERIES OF
DISTURBANCES THEN MOVE ACROSS THE AREA SUNDAY NIGHT THROUGH TUESDAY
ALLOWING COLDER CANADIAN AIR TO SLOWLY ADVANCE INTO THE AREA BY SUNDAY.
WITH THE UNCERTAINTY ON TIMING AND STRENGTH OF UPPER WAVES WILL BUMP UP
POPS TO 30 PERCENT MONDAY...AND WILL BUMP UP TEMPS A BIT FOR SATURDAY
AND SATURDAY NIGHT AS LATEST AVN SHOWS BEST LOW LEVEL CAA HOLDS OFF
UNTIL SUNDAY...OTHERWISE TEMPERATURE TREND FROM PREVIOUS SHIFT LOOKS
REASONABLE AT THIS POINT WITH COLDER AIR MOVING IN ON SUNDAY AND MONDAY
THEN SLOWLY MODERATING ON TUESDAY. MAY NEED TO ADJUST FRIDAY POPS AND
TEMPS IF AVN SOLUTION VERIFIES SINCE LOW CONFIDENCE IN ANY GIVEN MODEL
AT THIS TIME. CHAMBERS

    WED     THU     FRI     SAT     SUN     MON     TUE
-----------------------------------------------------------
BIL 028/042 025/040 023/040 018/030 017/026 012/023 014/029
    32/W    00/E    00/E    33/J    33/J    33/J    22/E
LVM 025/040 023/037 021/037 016/032 015/027 010/024 012/029
    42/J    00/E    02/E    33/J    33/J    33/J    22/E
HDN 026/044 023/042 021/042 018/031 017/025 012/022 014/029
    32/W    00/E    00/E    33/J    33/J    33/J    22/E
MLS 025/044 024/041 022/041 020/030 019/025 010/022 012/027
    20/E    00/E    00/E    33/J    33/J    33/J    22/E
4BQ 025/044 024/041 022/041 020/032 019/026 010/023 012/027
    22/W    20/W    00/E    33/J    33/J    33/J    22/E
BHK 024/042 022/039 020/039 019/030 019/025 009/022 011/026
    20/E    00/E    00/E    33/J    33/J    33/J    22/E
SHR 026/038 021/036 019/038 018/033 016/025 011/022 014/027
    44/J    40/J    00/E    33/J    33/J    33/J    22/E

.BYZ...NONE.