Heavy Snow in Montana, March 8, 2002

SOUTH CENTRAL AND SOUTHEAST MONTANA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
230 AM MST FRI MAR 8 2002

.SHORT TERM...VALID FOR TDY...SAT...SUN...
UPPER TROUGH SHIFTING EAST THIS HOUR INTO IDAHO AND WESTERN NEVADA.
STRONG SHORTWAVE ENERGY WAS DRIVING EAST AT THE BASE OF THE TROUGH IN
CENTRAL NEVADA. THIS ENERGY ONLY SHOWING MINOR MOVEMENT SOUTHEAST.
MODELS TAKE THIS INTO SOUTHERN UTAH THIS MORNING...THEN INTO SOUTHEAST
COLORADO BY 00Z SATURDAY. CURRENT TRACK MAY BE A BIT TOO FAR NORTH...
WHICH WOULD HELP THE CHANCE OF HEAVY SNOW. STRONG UPPER DIVERGENCE AND
Q-VECTOR FORCING WAS LINED UP FROM NORTH CENTRAL MONTANA INTO SOUTHEAST
IDAHO. VERY IMPRESSIVE ENHANCEMENT SHOWING UP ON THE INFRARED SATELLITE
LOOP WITH -63C OVER YELLOWSTONE PARK. RADAR INCREASING...BUT NOT
LIGHTING UP AS MUCH AS I WOULD LIKE WITH ENHANCEMENT SPREADING
NORTHEAST. DIVERGENT PATTERN PROGGED OVER SOUTH CENTRAL MONTANA THIS
MORNING WITH STRONGEST LIFT AROUND 12Z. PROBLEM IS...THE STRONGEST
FORECAST LIFT IS PROJECTED TO BE IN A LAYER OF -18C TO -24C...WHICH IS
NOT IDEAL FOR ICE CRYSTAL GROWTH. THAT IS WORKING AGAINST HEAVY SNOW.
SNOW WATER EQUIVALENT WOULD BE AROUND 25 TO 1...WHICH COULD ACCUMULATE A
QUICK 2 TO 4 ADDITIONAL INCHES THIS MORNING. ADVISORY MAY BE BETTER FOR
THE NON MOUNTAINOUS AREAS THIS MORNING AS VISIBILITIES HAVE NOT BEEN
LOWERED TO HEAVY SNOW CRITERIA YET. WILL LEAVE THE WARNING GOING RIGHT
NOW FOR SOUTH CENTRAL MONTANA...BUT MAY DROP IT DOWN TO AN ADVISORY AT
THE LAST MINUTE AFTER WATCHING THE RADAR AND CHECKING OBSERVATIONS.

SAME DYNAMICS MORE INTO THE SOUTHEAST EARLY THIS MORNING AND SWING OUT
BY LATE AFTERNOON. SHORTWAVE OVER SOUTHWEST WYOMING PUSHES INTO THE
SOUTHEAST THIS MORNING. SURFACE LOW PROGGED BY THE AVN INTO NORTHEAST
COLORADO BY 18Z THEN QUICKLY INTO KANSAS 00Z SATURDAY. IMPRESSIVE
DYNAMICS MOVE OVER THE REGION...BUT AGAIN STRONGEST OMEGA HIGHER IN THE
COLDER AIR. PLUS THE SYSTEM MOVES SO QUICKLY...THIS SHOULD KEEP SNOW
AMOUNTS UNDER CONTROL. LIFT IN THE AREA OF BEST INSTABILITY BETWEEN AND
12Z AND 18Z. CURRENTLY HAVE WINTER WEATHER ADVISORY GOING AND WILL LEAVE
THIS UP. WILL LEAVE ISOLATED POPS IN THE EAST THIS EVENING AS THE TROUGH
AXIS CLEARS THE STATE.

COLD AIR WILL REMAIN ENTRENCHED TODAY AS STRONG LOW PRESSURE SOUTH OF
THE AREAS KEEP THE AIR IN PLACE. UPPER RIDGE BUILDS IN TONIGHT AND
CONTINUES THIS TREND SATURDAY. WARM AIR ADVECTION AND DOWNSLOPE SHOULD
SCOUR THE ARCTIC OUT LATE TONIGHT AND SATURDAY. WILL KEEP LOWS DOWN
TONIGHT TO ACCOUNT FOR A QUICK DROP THIS EVENING BEFORE READINGS STEADY
OUT. SHORTWAVE ENERGY RIDES OVER THE TOP OF THE RIDGE SATURDAY NIGHT AND
SUNDAY...SO WILL KEEP IT DRY. TEMPERATURES WILL BE TRICKY AS WE ARE
EXPERIENCING A HIGHER SUN ANGLE NOW IN MARCH...ALONG WITH DOWNSLOPE AND
WARMING ALOFT. WILL TRIM THINGS BACK A FEW DEGREES WITH FRESH SNOW
COVER AND SOME CLOUDS. HUMPHREY

.LONG TERM...VALID FOR MON...TUE...WED...THU...
MODELS ADVERTISING MONDAY SHORT WAVE ENERGY BREAKING DOWN RIDGE AND
LEAVING ZONAL FLOW IN ITS WAKE. NEW MODELS SHOWING ENERGY FROM MONDAY
WAVE SPLITTING. NEW AVN SENDS SOUTHERN ENERGY FROM THIS WAVE FURTHER
SOUTH INTO FOUR CORNERS REGION AND SLOWS ITS PROGRESSION. THIS TREND IS
ALSO SHOWN IN THE MRF. HOWEVER...THIS WOULD NOT MEAN SIGNIFICANT CHANGES
TO OUR WEATHER...SO WILL KEEP GOING DAY 4 FORECAST. LATE TUESDAY CLIPPER
SYSTEM STILL ADVERTISED TO HEAD NORTH OF MONTANA...KEEPING US IN WARM
SECTOR. NEW RUN OF THE MRF SHOWING MORE OF A LONGWAVE TROUGH ACROSS AREA
WEDNESDAY AND THURSDAY WITH COLDER AIR...WHILE NEW ECMWF SHOWING SYSTEM
DRAGGING COLDER AIR INTO AREA ADVERTISED BY PREVIOUS MRF FOR THURSDAY.
IF EITHER OF THESE SCENARIOS PLAY OUT...FORECAST TEMPERATURES MAY BE
MUCH TO WARM WEDNESDAY AND THURSDAY. WILL ADVISE DAY SHIFT OF THESE
ISSUES. NO CHANGES AT THIS TIME. JZ

    TDY SAT     SUN     MON     TUE     WED     THU
-------------------------------------------------------
BIL 009 003/030 016/040 026/044 023/045 023/040 029/040
    +/S 00/B    00/E    11/E    22/E    22/E    22/E
LVM 012 004/030 016/040 025/041 022/042 021/039 028/038
    +/S 20/B    00/E    11/E    22/E    22/E    22/E
HDN 009 001/030 014/040 026/045 021/046 021/042 028/041
    +/S 00/B    00/E    11/E    22/E    22/E    22/E
MLS 008 904/025 007/036 025/039 024/045 020/042 030/044
    +/S 20/B    00/E    11/E    22/E    22/E    22/E
4BQ 008 904/025 007/036 026/040 024/043 020/041 025/040
    +/S 20/B    00/E    11/E    22/E    22/E    22/E
BHK 006 906/022 002/034 024/038 023/042 019/040 031/043
    +/S 20/B    00/E    11/E    22/E    22/E    22/E
SHR 011 902/031 013/040 027/046 025/047 022/041 032/044
    +/S 00/B    00/E    11/E    22/E    22/E    22/E

.BYZ...HEAVY SNOW WARNING FOR SOUTH CENTRAL MONTANA THIS MORNING
       WINTER WEATHER ADVISORY FOR SOUTHEAST MONTANA AND THE SHERIDAN
       FOOTHILLS TODAY.