Winter Storm and Heavy Snow in Montana, December 26 to 27, 2002

WESTERN MONTANA AND NORTH CENTRAL IDAHO FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
155 PM MST THU DEC 26 2002

.SHORT TERM...VERY COMPLEX FORECAST TODAY. SOME MINOR MODEL
DIFFERENCES TODAY BUT SHOULD NOT POSE MUCH PROBLEM FOR THE
FORECAST. ONE WAVE MOVING THROUGH SRN CANADA THIS AFTERNOON...THE
TAIL END OF WHICH IS PRODUCING PRECIP OVER MAINLY MOUNTAINOUS
PORTIONS OF WESTERN MSO CWA. HAVE NOT SEEN ANY REPORTS OF MUCH MORE
THAN A FEW HUNDREDTHS OF PRECIP FROM THIS WAVE IN THE VALLEYS BUT
THE MOUNTAINS CERTAINLY FARED BETTER AS KMLP HAS PICKED UP A
COUPLE INCHES OF SNOW. STRONG OROGRAPHIC FLOW IS DEVELOPING BEHIND
THE WAVE SO PRECIP LIKELY TO CONTINUE IN THE MOUNTAINS INTO TONIGHT.
SINCE WAVE IS MOVING AWAY...DONT EXPECT MUCH MORE FROM IT OVER THE
VALLEYS. NOT TO WORRY THOUGH...SINCE THE CLOUDS FROM THE NEXT
HEADACHE CAN BE SEEN MOVING ONSHORE ALONG THE WEST COAST NOW.

WARM FRONT IS FORECAST TO DEVELOP OVER ERN WA/OR AND AFFECT THE
ENTIRE CWA LATER TONIGHT INTO TOMORROW. QPF LOOKS TO BE HEAVY OVER
THE MTNS OF ID AND FAR WEST MT WITH AS MUCH AS ONE INCH LIQUID IN
SOME SPOTS BY 00Z SAT. MORE IMPRESSIVE THOUGH...IS THE JET DYNAMICS
THAT SETS UP OVER THE AREA. MODELS SHOW A 120KT JET ALOFT WITH AS
HIGHS AS 75KTS AS LOW AS 700 MBS BY TOMORROW AFTERNOON. EVEN THE
850 WINDS ARE FORECAST IN THE 35-40KT RANGE. INITIALLY IT LOOKS COLD
ENOUGH FOR SNOW OVER NW MT BUT SNOW LEVELS WILL BE RISING TO 4500
FT OR SO BY AFTERNOON SO EXPECT A MIX IN THE AFTERNOON OVER THE
VALLEYS. WILL GO WITH AN ADVISORY FOR THE VALLEYS AND UPGRADE THE
MTNS TO A WARNING. FURTHER SOUTH...THE SNOW LEVELS WILL RANGE FROM
5000 FT OVER WC MT TO 6000 FT OVER LEMHI COUNTY BY AFTERNOON. WILL
HAVE WARNINGS FOR THE MTNS THERE AS WELL...BUT IT SHOULD WARM UP
FAST ENOUGH IN THE VALLEYS TO AVOID HEADLINES.

WE STAY IN A WARM ADVECTION PATTERN THROUGH SAT BUT PRECIP BACKS
DOWN A BIT AS STRONGEST LOW LEVEL JET DYNAMICS MOVE EAST. WILL
CONTINUE TO COVER THAT PERIOD WITH CHC POPS. COLD FRONT FINALLY
GOES THROUGH SAT NIGHT. MODELS FORECAST A WAVE TO FORM ALONG THE
FRONT SAT NGT/SUN WHICH AFFECTS SOUTHWEST MT AND LEMHI CNTY. THE
AVN IS THE MOST AGGRESSIVE WITH THIS FEATURE BUT BOTH MODELS SHOW
GOOD QPF OVER THE AREA SAT NGT THROUGH SUN. WILL BE COVERING THE
FROPA WITH CHC POPS MOST AREAS BUT GOING LIKELY OVER SW MT AND
LEMHI CNTY. HAVE ALSO ISSUED A WATCH SINCE FCST QPF AMOUNTS ARE
EXCESSIVE (6/10THS AT LEAST). PRECIP DIMINISHES FROM WEST TO
EAST DURING THE DAY SUNDAY. WRIGHT

.LONG TERM...SOME DISCREPANCIES BETWEEN THE MODELS TODAY. THE MRF
HAS THE LOW IN THE NORTH PACIFIC STAYING TO THE NORTH AND KEEPING A
MORE SOUTHWEST TO ZONAL FLOW THROUGH THE PERIOD. THE GFS ON THE
OTHER HAND BRINGS THE SURFACE LOW INTO EASTERN WASHINGTON EARLY
NEW YEARS DAY AND THEN BUILDS A RIDGE ALONG THE COAST WITH
NORTHWEST FLOW. EITHER WAY MONDAY WILL BE THE COLDEST DAY WITH COLD
ARCTIC AIR IN PLACE...AND THEN SLOWLY WARM THROUGH THE EXTENDED
PERIOD AS WARM AIR ADVECTION TAKES PLACE. WILL BE KEEPING CHANCE POPS
FOR THE EXTENDED.   KOCH

.MSO...WINTER STORM WARNING LATE TONIGHT THROUGH FRIDAY ABOVE 4500
        FEET MTZ001>004-043
       WINTER STORM WARNING LATE TONIGHT THROUGH FRIDAY ABOVE 5000
        FEET IDZ005-006 AND MTZ006
       WINTER STORM WARNING LATE TONIGHT THROUGH FRIDAY ABOVE 6000
        FEET IDZ009-010
       WINTER WEATHER ADVISORY FOR SNOW LATE TONIGHT THROUGH FRIDAY
        BELOW 4500 FEET MTZ001>004-043
       WINTER STORM WATCH SATURDAY NIGHT AND SUNDAY FOR MTZ007 AND
        IDZ009-010

...7-DAY SPOT TEMPS AND POPS...
LIB SEE 029/037 030/035 023/027 32797452
     EEEE 017/027 018/030 018/029 020/032 3634343433
FCA SEE 026/036 028/033 021/026 32685452
     EEEE 015/026 018/029 017/029 019/032 3633443343
POL SEE 028/037 028/037 024/027 32465453
     EEEE 015/028 019/030 018/030 018/033 3633443343
MSO SEE 025/037 029/036 023/027 32355553
     EEEE 016/026 017/030 017/029 018/030 3623343343
HMM OEE 024/041 028/038 024/026 32455553
     EEEE 018/027 018/029 017/030 019/032 3623443343
BTM SES 019/040 023/039 017/021 32464575
     EEEE 005/021 009/025 012/027 012/028 3623343333
ORO REE 039/051 036/043 031/034 32674452
     EEEE 025/036 027/037 028/037 028/038 3624334354
GRV REE 033/046 033/035 027/031 32564452
     EEEE 021/030 023/032 024/033 023/034 3624444454
SMN SJS 018/036 026/033 020/023 32775675
     EEEE 008/020 011/024 011/025 011/027 3623443343

MTZ001>007-043-IDZ005>010-271300-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE MISSOULA MT
600 AM MST THU DEC 26 2002

THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN MONTANA AND NORTH
CENTRAL IDAHO

.DAY ONE... TODAY

SCATTERED SNOW SHOWERS WILL DEVELOP IN NORTHWEST MONTANA THIS
MORNING AND INCREASE THIS AFTERNOON...ACCUMULATING 1 TO 3 INCHES IN
THE VALLEYS AND 3 TO 6 INCHES IN THE MOUNTAINS BY TONIGHT.
SOUTHWEST WINDS WILL INCREASE TO 15 TO 25 MPH IN NORTHWEST MONTANA.
OTHERWISE NO HAZARDOUS WEATHER IS EXPECTED EXCEPT IN NORTHWEST
MONTANA TODAY.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

A SERIES OF STORM SYSTEMS WILL MOVE ACROSS THE REGION FRIDAY
THROUGH WEDNESDAY. THE STRONGEST SYSTEM WILL MOVE THROUGH FRIDAY
THROUGH SATURDAY NIGHT. SEE THE LATEST WINTER STORM WATCH
(GTFWSWMSO) FOR DETAILS. A STRONG JET STREAM WILL BE ASSOCIATED WITH
THESE STORMS...CREATING STRONG WEST TO SOUTHWEST WINDS...ESPECIALLY
AT HIGHER ELEVATIONS.

SUBSEQUENT STORM SYSTEMS WILL MOVE THROUGH MONDAY THROUGH
WEDNESDAY...AND WILL CONTAIN ABUNDANT MOISTURE AIDED BY A STRONG JET
STREAM. THESE WINDS AND ABUNDANT MOISTURE WILL PRODUCE STRONG
OROGRAPHICS IN THE MOUNTAINS OF CENTRAL IDAHO AND NORTHWEST
MONTANA...BRINGING THE POSSIBILITY OF SNOWFALL WITH SIGNIFICANT
ACCUMULATIONS...MAINLY IN THE MOUNTAINS. A MIX OF RAIN AND SNOW IS
LIKELY IN THE SOUTHERN VALLEYS ON FRIDAY AND SATURDAY...WITH
PRECIPITATION FALLING AS ALL SNOW MONDAY THROUGH WEDNESDAY AS A COLD
FRONT PASSES THROUGH THE REGION SUNDAY.

.SPOTTER INFORMATION STATEMENT...

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