Heavy Snow and High Wind in Montana, December 1 to 3, 2012

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1050 PM MST FRI NOV 30 2012

UPDATE TO AVIATION

.UPDATE...
CURRENT SATELLITE IMAGERY SHOWS MOISTURE ASSOCIATED WITH WEAK
SHORTWAVE TROF OVER SOUTHWEST MT IS STEADILY DISSIPATING AND MOVING
EAST. RADAR AND SURFACE OBSERVATIONS INDICATE THERE IS SOME SPOTTY
LIGHT VALLEY RAIN/MTN SNOW OVER PORTIONS OF BEAVERHEAD/MADISON/
GALLATIN COUNTIES WHILE REST OF FORECAST AREA IS DRY. LATEST
SHORT-TERM MODEL RUNS CONTINUE THE MOSTLY DRY CONDITIONS OVER
CENTRAL AND HILINE COUNTIES OVERNIGHT SO HAVE REMOVED MENTION OF
PRECIPITATION NORTH AND EAST OF A CUT BANK-GREAT FALLS-LEWISTOWN
LINE THROUGH SATURDAY MORNING.  HOWEVER...LIKE PAST FEW NIGHTS...THE
SHALLOW POOL OF COLDER TEMPERATURES IS LEADING TO PATCHY AREAS OF
FREEZING FOG ALONG THE HILINE SO HAVE ADDED MENTION OF THAT INTO THE
OVERNIGHT FORECAST.  FINALLY...NO CHANGES TO CURRENTLY POSTED HIGH
WIND AND WINTER STORM HEADLINES.
WARANAUSKAS

&&

.DISCUSSION...

TONIGHT THROUGH SUNDAY...COPIOUS AMOUNTS OF PACIFIC MOISTURE
CONTINUE TO STREAM OVER MONTANA WITH RAIN AND SNOW OVER THE
MOUNTAINS THIS AFTERNOON AND OVERCAST SKIES ELSEWHERE THOUGH SOME
SHOWERS HAVE ALSO BEEN OCCURRING NEAR LEWISTOWN. UPGRADED THE
WINTER STORM WATCH TO A WINTER STORM WARNING FOR FAR SOUTHWEST
MONTANA AS PERIODS OF WET SNOW AND RAIN WERE BEGINNING TO IMPACT
AREA ROADWAYS. THIS WARNING WILL CONTINUE THROUGH SUNDAY NIGHT.
SHOWERS ARE ALSO OCCURRING IN THE VICINITY OF HAVRE AND WITH
TEMPERATURES NEAR FREEZING AND WEAK OVERRUNNING THERE IS A SMALL
POSSIBILITY FOR LIGHT FREEZING RAIN OR DRIZZLE. DOWNSLOPING WINDS
SHOULD KEEP MOST OF NORTH- CENTRAL MONTANA DRY THOUGH THERE WILL BE
SOME PRECIPITATION NOT REACHING THE GROUND. TEMPERATURES REMAIN ABOVE
SEASONAL AVERAGES TODAY AND WILL CONTINUE THROUGH AT LEAST SUNDAY
BEFORE A COLD FRONTAL PASSAGE. MUCH OF THE SHOWER ACTIVITY TODAY IS
OCCURRING WITH AN UPPER-LEVEL SHORTWAVE AND SNOW HAS BEEN REPORTED
ABOVE ELEVATIONS OF 6000 FEET. HEAVIER SNOW WAS REPORTED OVER CHIEF
JOSEPH PASS EARLIER THIS AFTERNOON WITH ROADWAYS SNOW-COVERED AND
SLICK SO ISSUED A WINTER WEATHER ADVISORY FOR SNOW AND BLOWING SNOW
THAT WILL BE IN EFFECT THROUGH 7 PM MST THIS EVENING. SNOW
ACCUMULATIONS UP TO 6 INCHES ARE POSSIBLE FOR CHIEF JOSEPH PASS AND
SURROUNDING AREAS. THIS FIRST SHORTWAVE WILL EXIT LATE TONIGHT AND
PRECIPITATION WILL TAPER. ANOTHER SHORTWAVE TROUGH WILL MOVE ACROSS
THE FORECAST AREA ON SATURDAY AND BRING ANOTHER SURGE OF
MOISTURE...HOWEVER BEST PRECIPITATION CHANCES WILL ONCE AGAIN BE
CONFINED TO THE MOUNTAINS ACROSS SOUTHWEST MONTANA INCLUDING WEST
YELLOWSTONE AS WELL AS FOR AREAS ALONG THE CONTINENTAL DIVIDE.
DOWNSLOPING WILL LIMIT PRECIPITATION OVER THE PLAINS AND MID-LEVEL
WINDS WILL START TO INCREASE ALONG THE ROCKY MOUNTAIN FRONT AND A
HIGH WIND WATCH REMAINS IN EFFECT.

A MORE SIGNIFICANT STORM SYSTEM WILL MOVE INTO THE AREA LATE
SATURDAY NIGHT THROUGH SUNDAY NIGHT AS A TROUGH OF LOW PRESSURE
AND ASSOCIATED SURFACE COLD FRONT MOVE THROUGH THE AREA. THIS
SYSTEM WILL BE A VERY FAST-MOVING SYSTEM WITH WIDESPREAD STRONG
WINDS ANTICIPATED AND A HIGH WIND WATCH IS IN EFFECT FOR THE
ENTIRE FORECAST AREA BEGINNING LATE SATURDAY NIGHT THROUGH SUNDAY
NIGHT. WIND GUSTS UP TO 60 MPH ARE POSSIBLE. DURING THE DAY ON
SUNDAY...SURFACE TEMPERATURES WILL REMAIN ABOVE AVERAGE OVER THE
PLAINS AND SOME VALLEYS ACROSS SOUTHWEST MONTANA SO PRECIPITATION
SHOULD BE MAINLY RAIN...HOWEVER BY SUNDAY EVENING TEMPERATURES
WILL QUICKLY FALL AND CHANGE PRECIPITATION OVER TO SNOW THOUGH
LITTLE SNOW ACCUMULATIONS ARE EXPECTED IN THIS AREA AS
PRECIPITATION SHOULD BE TAPERING BY THAT TIME. THERE IS HOWEVER
THE POSSIBILITY FOR ROADWAYS TO FREEZE AS THE TEMPERATURES FALL
BELOW FREEZING. ACROSS THE MOUNTAINS ACROSS SOUTHWEST MONTANA
INCLUDING WEST YELLOWSTONE...HEAVY SNOW WITH ACCUMULATIONS OF ONE
TO TWO FEET ARE POSSIBLE. THE COMBINATION OF HEAVY SNOW AND STRONG
WINDS MAY ALSO CAUSE NEAR BLIZZARD CONDITIONS. THERE IS THE
POTENTIAL FOR HEAVY SNOW ALONG THE ROCKY MOUNTAIN FRONT AS WELL SO
HAVE ADDED A WINTER STORM WATCH FOR THESE AREAS DUE TO THE
COMBINATION OF FORECASTED SNOW AND STRONG WINDS. SIGNIFICANT
IMPACTS TO TRAVEL...ESPECIALLY OVER MOUNTAIN PASSES AS WELL AS
OUTDOOR RECREATION ARE EXPECTED ALONG THE CONTINENTAL DIVIDE AND
MOUNTAINS ACROSS FAR SOUTHWEST MONTANA. WILL CONTINUE TO MONITOR
AND UPDATE AS NECESSARY. MLV

SUNDAY NIGHT THROUGH FRIDAY...MEDIUM RANGE MODELS ARE IN REASONABLE
AGREEMENT THROUGH THE MIDDLE OF NEXT WEEK WITH THE USUAL SPREAD IN
TIMING/AMPLITUDE DEVELOPING LATER NEXT WEEK AS A PROGRESSIVE
WESTERLY FLOW ALOFT CONTINUES OVER THE REGION. THE LONGWAVE UPPER
LEVEL TROUGH CURRENTLY OFF THE WEST COAST OPENS UP WITH A STRONGER
WAVE AND UPPER LEVELS JET MAXIMUM MOVING QUICKLY NE ACROSS THE
NORTHERN ROCKIES SUNDAY NIGHT. MODELS ARE IN RELATIVELY CLOSE
AGREEMENT NOW DEPICTING THE TRACK OF THE SURFACE LOW ASSOCIATED WITH
THIS ENERGY TRACKING EAST ALONG THE CANADIAN BORDER WITH THE MID
LEVEL CIRCULATION FURTHER NORTH IN ALBERTA AND STRONG WEST TO
SOUTHWEST FLOW TO THE SOUTH OVER NORTH CENTRAL AND SW MT LATE SUNDAY
THROUGH SUNDAY NIGHT. A WIDESPREAD HIGH WIND EVENT APPEARS LIKELY
LATE SUNDAY THOUGH SUNDAY EVENING AS THE PACIFIC FRONT MOVES ACROSS
THE AREA. ANY SIGNIFICANT PRECIPITATION WILL GENERALLY BE CONFINED
TO THE MTNS SUNDAY NIGHT...WITH STRONG WEST FLOW LIMITING
PRECIPITATION EAST OF THE ROCKIES TO SHOWERS. A SLIGHTLY COOLER
AIRMASS MOVES IN BEHIND THE FRONT ON MONDAY...BUT AFTERNOON
TEMPERATURES WILL STILL BE ABOVE AVERAGE FOR EARLY DECEMBER. WEAK
UPPER LEVEL RIDGING MONDAY THROUGH TUES NIGHT WILL KEEP MUCH OF THE
AREA DRY WITH PRECIPITATION MAINLY LIMITED TO OCCASIONAL SNOW
SHOWERS ALONG AND WEST OF THE CONTINENTAL DIVIDE. TEMPERATURES WILL
WARM BACK TO WELL ABOVE AVERAGE LEVELS BY TUESDAY AND REMAIN MILD
TUESDAY NIGHT AS WINDS INCREASE AGAIN AHEAD OF THE NEXT PACIFIC
UPPER LEVEL TROUGH...WHICH SHOULD MOVE INLAND DURING THE
WEDNESDAY/THURSDAY PERIOD. ANOTHER PERIOD OF STRONG WINDS AND MTN
SNOW IS POSSIBLE AS THIS SYSTEM MOVES ACROSS THE AREA LATE
WEDNESDAY. AS THE UPPER LEVEL TROUGH PROGRESSES INLAND THURSDAY AND
FRIDAY MODELS DIFFER SOME WITH THE AMPLITUDE OF THE TROUGH...HOWEVER
TEMPERATURES SHOULD COOL BACK CLOSER TO SEASONAL AVERAGES WITH ANY
PRECIPITATION APPEARING LIGHT. HOENISCH

&&

.AVIATION...
UPDATED 0550Z.
MOSTLY VFR CONDITIONS EXPECTED AT TERMINALS ACROSS THE AREA UNLESS
OTHERWISE MENTIONED...BUT MOUNTAIN TOPS WILL GENERALLY BE OBSCURED
BY PRECIPITATION/CLOUDS. THE MOIST SOUTHWESTERLY FLOW ALOFT WILL
KEEP MAINLY MID/HIGH LEVEL CLOUDINESS OVER THE AREA. A COLD FRONTAL
BOUNDARY DRAPED ACROSS NORTH CENTRAL MONTANA WILL CONTINUE THE LOW
(IFR) CLOUDS AND PATCHY FOG ALONG THE HI-LINE AREA (KCTB KHVR). THE
BOUNDARY WILL MOVE NORTHEAST AGAIN AFTER 10Z...ALLOWING WINDS TO
SHIFT MORE SOUTHERLY AND BRING IMPROVING CONDITIONS. ANOTHER
DISTURBANCE WILL MOVE SLOWLY THROUGH THE AREA THROUGH 18Z...WHICH
WILL KEEP PRECIPITATION IN THE MOUNTAIN AREAS (INCLUDING KHLN AND
KBZN) THROUGH AROUND 14Z...AND BRING ISOLATED PRECIPITATION TO THE
AREA NORTH OF KGTF/KLWT BETWEEN 10Z AND 18Z AS THE BOUNDARY
RETREATS. BREEZY SOUTHWESTERLY DOWNSLOPE WINDS OVER THE PLAINS WILL
KEEP THOSE AREAS DRY THROUGH MOST OF THE DAY ON SATURDAY.
HOWEVER...ANOTHER DISTURBANCE WILL BRING ANOTHER CHANCE FOR LOWER
ELEVATION PRECIPITATION TO THE VALLEYS OF SOUTHWEST MONTANA AFTER
20Z.  COULSTON

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  37  52  36  50 /  20  10  10  50
CTB  29  47  31  43 /  20  20  20  50
HLN  31  46  32  48 /  30  40  40  70
BZN  30  46  30  49 /  40  40  40  60
WEY  31  36  31  37 / 100 100 100 100
DLN  32  45  33  47 /  60  60  60  70
HVR  25  44  28  45 /  20  10  10  40
LWT  32  49  33  50 /  20  20  20  50

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WATCH FROM LATE SATURDAY NIGHT THROUGH SUNDAY EVENING
BROADWATER...CASCADE...CENTRAL AND SOUTHERN LEWIS AND CLARK...
CHOUTEAU...EASTERN GLACIER...EASTERN PONDERA...EASTERN TETON...
FERGUS...JEFFERSON...JUDITH BASIN...LIBERTY...MEAGHER...TOOLE.

WINTER STORM WATCH FROM SATURDAY EVENING THROUGH SUNDAY EVENING
FOR ELEVATIONS ABOVE 5000 FEET FOR CENTRAL AND SOUTHERN LEWIS
AND CLARK...NORTHERN ROCKY MOUNTAIN FRONT...SOUTHERN ROCKY
MOUNTAIN FRONT.

WINTER STORM WARNING UNTIL 5 AM MST MONDAY BEAVERHEAD...
GALLATIN...MADISON.

HIGH WIND WATCH FROM SATURDAY EVENING THROUGH SUNDAY AFTERNOON
BEAVERHEAD...GALLATIN...MADISON.

HIGH WIND WATCH FROM LATE TONIGHT THROUGH MONDAY MORNING
NORTHERN ROCKY MOUNTAIN FRONT...SOUTHERN ROCKY MOUNTAIN FRONT.

&&

WEATHER.GOV/GREATFALLS

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE GREAT FALLS MT
523 PM MST FRI NOV 30 2012

MTZ009-048-020030-
NORTHERN ROCKY MOUNTAIN FRONT-SOUTHERN ROCKY MOUNTAIN FRONT-
523 PM MST FRI NOV 30 2012

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTH CENTRAL
MONTANA.

.DAY ONE...TONIGHT

THERE IS A LOW PROBABILITY OF WIDESPREAD HAZARDOUS WEATHER.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

A HIGH WIND WATCH IS IN EFFECT FROM EARLY SATURDAY MORNING THROUGH
MONDAY MORNING.

ALSO...A WINTER STORM WATCH IS IN EFFECT FROM SATURDAY EVENING
THROUGH SUNDAY EVENING FOR ELEVATIONS ABOVE 5000 FEET...WITH 8 TO
15 INCHES OF SNOWFALL EXPECTED.

.SPOTTER INFORMATION STATEMENT...

PLEASE FORWARD ANY WIND SPEED OR SNOWFALL REPORTS...AND ANY
WEATHER RELATED IMPACT INFORMATION...TO THE NATIONAL WEATHER
SERVICE OFFICE IN GREAT FALLS.

MTZ008-015-055-020030-
BEAVERHEAD-MADISON-GALLATIN-
523 PM MST FRI NOV 30 2012

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTHWEST
MONTANA.

.DAY ONE...TONIGHT

THERE IS A LOW PROBABILITY OF WIDESPREAD HAZARDOUS WEATHER.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

A WINTER STORM WARNING IS IN EFFECT FOR FAR SOUTHERN PORTIONS OF
BEAVERHEAD AND MADISON COUNTIES AND THE SOUTHERN HALF OF GALLATIN
COUNTY THROUGH LATE SUNDAY NIGHT.

A HIGH WIND WATCH IS IN EFFECT FROM SATURDAY EVENING THROUGH
SUNDAY AFTERNOON.

.SPOTTER INFORMATION STATEMENT...

PLEASE FORWARD ANY WIND SPEED OR SNOWFALL REPORTS...AND ANY
WEATHER RELATED IMPACT INFORMATION...TO THE NATIONAL WEATHER
SERVICE OFFICE IN GREAT FALLS.

MTZ010>014-044>047-049>054-020030-
EASTERN GLACIER-HILL-CASCADE-CHOUTEAU-
CENTRAL AND SOUTHERN LEWIS AND CLARK-TOOLE-LIBERTY-
EASTERN PONDERA-BLAINE-EASTERN TETON-JUDITH BASIN-FERGUS-
JEFFERSON-BROADWATER-MEAGHER-
523 PM MST FRI NOV 30 2012

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL
MONTANA...NORTH CENTRAL MONTANA AND SOUTHWEST MONTANA.

.DAY ONE...TONIGHT

THERE IS A LOW PROBABILITY OF WIDESPREAD HAZARDOUS WEATHER.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

A HIGH WIND WATCH IS IN EFFECT FROM EARLY SUNDAY MORNING THROUGH
SUNDAY NIGHT.

A WINTER STORM WATCH IS IN EFFECT FOR SOUTHERN LEWIS AND CLARK
COUNTY FROM SATURDAY EVENING THROUGH SUNDAY EVENING FOR
ELEVATIONS ABOVE 5000 FEET...WITH 8 TO 15 INCHES OF SNOWFALL
EXPECTED.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME.