Winter Storm in Montana, December 6 to 7, 2003

SOUTHWEST AND NORTH CENTRAL MONTANA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
855 PM MST SAT DEC 6 2003

.DISCUSSION...

UPDATED DISCUSSION FOR TONIGHT...PREVIOUS MESOETA PAINTED CENTRAL MT
WITH DECENT QPF AND LATEST RUN DOES SAME BUT SHIFTS HIGHER QPF A
LITTLE FARTHER N. LOOKS LIKE THERE WILL BE A COUPLE OF SHORTWAVES
MOVING OVER OUR SRN AND CNTRL ZONES LATER TONIGHT INTO SUN. LATEST
GFS HAS COME IN AND IT IS A LITTLE FARTHER S THAN THE MESOETA WITH
HIGHER QPF VALUES. HAVE DECIDED TO EXTEND SNOW ADVISORY FARTHER N
INTO SRN PTNS OF LEWIS AND CLARK AND CASCADE COUNTIES AS WELL AS ALL
OF FERGUS AND JUDITH BASIN COUNTIES. IN LINE WITH THIS WILL SPREAD
HIGH POPS N TO MATCH UP WITH HIGHLIGHTS. OTHERWISE WILL RAISE LOWS
AT BZN AND HVR. BLANK

TONIGHT THROUGH TUESDAY...DEEP LOW PRESSURE CENTER OVER THE EASTERN
PACIFIC AND HIGH PRESSURE OVER THE MIDWEST. THIS CREATES MOIST SW
FLOW ALOFT OVER THE CWA...HIGH LEVELS OF MOISTURE REMAIN OVER THE
SOUTHWEST THRU 18Z SUN.  BROAD TROF MOVES OVER THE PAC NW WILL
SLOWLY MOVE EAST OVER THE AREA. A SMALLER SHORTWAVE MOVING THROUGH
THE TROF WILL ADD SOME DYNAMICS. UVV WILL NOT BE STRONG...BUT
INCREASES NEAR 12Z AS LOW LEVEL LOW PRESSURE MOVES OVER THE
SOUTHWEST AND BEST CHANCE FOR HEAVY SNOW IS IN THIS PERIOD. TEMPS
ARE STILL VERY MILD ACROSS THE AREA...MOST SNOW GROWTH SHOULD BE
ABOVE THE MAX RH LEVEL...AND THE HEAVY SNOW EVENTS SHOULD BE LIMITED
TO THE HIGHER ELEVATIONS. ON MONDAY A SHORTWAVE MOVES ACROSS
ALTA/SASK DURING THE MORNING AND AN ASSOCIATED COLDFRONT CROSSES THE
CAN BORDER. CHANCE OF PRECIP WILL BE LOW BUT THIS WILL CONTINUE THE
COOLING TREND. ZELZER

TUESDAY NIGHT THROUGH WEDNESDAY NIGHT...GFS/ECMWF ARE IN GOOD
AGREEMENT WITH SOLUTION DURING THIS PERIOD. AN UPPER LEVEL TROUGH
WILL MOVE INTO THE PACIFIC NORTHWEST TUESDAY NIGHT...CAUSING AN
INCREASINGLY MOIST SOUTHWEST FLOW ALOFT OVER THE TFX CWA. WEAK
EMBEDDED DISTURBANCES WILL BRING A CHANCE OF SNOW TO THE WESTERN
MOUNTAIN AREAS. A SURFACE BOUNDARY WILL ALSO MOVE INTO SOUTHWEST
MONTANA FROM THE SOUTHWEST. THIS SETS UP A DIVIDING LINE BETWEEN THE
WARMER AIR AND SOUTHWEST WINDS OVER SOUTHWEST MONTANA AND THE COOLER
AIR WITH MORE EASTERLY WINDS ACROSS NORTH CENTRAL MONTANA. THE UPPER
TROUGH WILL MOVE SLOWLY TO THE EAST AND BRING A COUPLE OF SHORTWAVES
THROUGH THE AREA WEDNESDAY AND WEDNESDAY NIGHT...SPREADING A CHANCE
OF SNOW ACROSS THE TFX CWA DURING THIS TIME...ESPECIALLY OVER THE
WESTERN MOUNTAINS. TEMPERATURES ACROSS THE AREA WILL BE BELOW
SEASONAL AVERAGES DURING THIS TIME...WITH TEMPERATURES TO THE NORTH
AND EAST OF THE BOUNDARY BEING MUCH BELOW NORMAL AND ONLY REACHING
INTO THE TEENS ON WEDNESDAY.  COULSTON

THURSDAY THROUGH SATURDAY...AN ARCTIC AIRMASS WILL MOVE THROUGH THE
AREA THURSDAY AND THURSDAY NIGHT WITH GOOD UPSLOPE FLOW ACROSS NORTH
CENTRAL MONTANA. MODELS INDICATE AN UPPER LEVEL TROUGH TO SWING
ACROSS NORTHERN MONTANA THURSDAY AND THURSDAY NIGHT...BRINGING A
CHANCE OF SNOW TO THE AREA. WEAK UPPER LEVEL RIDGING WILL THEN BUILD
INTO THE AREA FROM THE WEST FRIDAY THROUGH SATURDAY FOR GENERALLY
DRY CONDITIONS. TEMPERATURES WILL MODERATE FRIDAY NIGHT AND SATURDAY
AS DOWNSLOPE FLOW RETURNS. THE SOUTHWEST VALLEYS WILL REMAIN
COLD...ESPECIALLY IF THERE IS GOOD SNOW COVER. WILLIAMSON DC

.CCF NUMBERS
GTF BE 028/037 017/029 012 13360
    BEEBB 024/013 019/009 014/904 022/013 034 31014330000
CTB EE 022/034 017/025 007 13--0
    BEEBB 018/009 014/004 008/909 019/013 032 310-4330000
HLN SC 027/037 020/030 015 13992
    BEEBB 026/014 029/011 022/004 022/007 031 31014441000
BZN SC 030/033 015/031 011 13+93
    BEEBB 026/015 026/013 026/901 022/000 029 31014332000
WEY SE 022/029 008/021 005 13+94
    BEEBB 021/012 032/010 030/901 027/904 030 32024332000
DLN SC 029/035 020/030 012 13972
    BSEBB 027/018 028/016 026/011 026/010 032 22125332-00
HVR EE 024/034 011/026 007 130-0
    BEEBB 022/008 012/002 008/908 014/009 027 11003330000
LWT SE 029/031 018/030 011 138+0
    BEEBB 023/012 016/008 015/902 020/017 029 31003440000

.TFX...HEAVY SNOW WARNING FOR ZONES 8 15 55 IN SOUTHWEST MONTANA
       TONIGHT THROUGH SUNDAY MORNING
    ...WINTER WEATHER ADVISORY FOR SNOW FOR ZONES 52 53 54 12 14 50
       AND 51 (CENTRAL AND NRN PORTION OF SW MT TONIGHT INTO SUNDAY

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE GREAT FALLS MT
530 PM MST SAT DEC 6 2003

MTZ008>015-044>055-071245-
BEAVERHEAD-NORTHERN ROCKY MOUNTAIN FRONT-GLACIER-HILL-CASCADE-
CHOUTEAU-CENTRAL AND SOUTHERN LEWIS AND CLARK-MADISON-TOOLE-
LIBERTY-EASTERN PONDERA-BLAINE-SOUTHERN ROCKY MOUNTAIN FRONT-
EASTERN TETON-JUDITH BASIN-FERGUS-JEFFERSON-BROADWATER-MEAGHER-
GALLATIN-
530 PM MST SAT DEC 6 2003

THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTH CENTRAL AND SOUTHWEST
MONTANA

.DAY ONE...TODAY

AREAS OF SNOW WILL DEVELOP TONIGHT OVER CENTRAL AND SOUTHWEST
MONTANA...AS A CANADIAN COLD FRONT PUSHES SOUTH THROUGH THE REGION.
AS A RESULT...A WINTER STORM WARNING HAS BEEN ISSUED FOR FAR
SOUTHWEST MONTANA...AND A WINTER WEATHER ADVISORY IS IN EFFECT FOR
AREAS SOUTH AND EAST OF THE HELENA VALLEY. PLEASE REFER TO GTFWSWTFX
FOR FURTHER DETAILS.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

AREAS OF SNOW WILL CONTINUE TO FALL OVER SOUTHWEST MONTANA THROUGH
MID DAY SUNDAY. THE SNOW WILL BE HEAVY AT TIMES DURING THE MORNING
HOURS.