Winter Storm in Montana, February 22 to 24, 2011

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1030 PM MST MON FEB 21 2011

...UPDATE TO AVIATION...

.DISCUSSION...
UPDATE FORTHCOMING. HAVE UPDATED POP AND WEATHER GRIDS THIS EVENING.
DROPPED THE HIGH WIND WARNING FOR THE NORTHERN ROCKY MOUNTAIN FRONT
AS WINDS SLOWLY DECREASING. HOWEVER...SURFACE WINDS STILL GUSTY AND
WILL ALLOW THE BLOWING SNOW ADVISORY TO REMAIN IN PLACE. UPPER TROF
CONTINUES TO APPROACH FROM THE WEST WITH CONDITIONS GENERALLY
DETERIORATING TUESDAY. EMANUEL

&&

.AVIATION...
UPDATED 0530Z.
AN UPPER LEVEL TROUGH OF LOW PRESSURE WILL GRADUALLY MOVE SOUTHEAST
INTO MONTANA TONIGHT AND TUESDAY. VFR CONDITIONS WILL MOSTLY PERSIST
ACROSS THE AREA...BUT CONDITIONS WILL WORSEN FROM THE NORTHWEST
AFTER 15Z AS A CANADIAN COLD FRONT MOVES INTO THE AREA. MID AND HIGH
LEVEL CLOUDINESS AHEAD OF THE TROUGH WILL INCREASE TONIGHT...WHILE
BREEZY SOUTHWEST WINDS WILL DECREASE. SCATTERED SNOW SHOWERS WILL
ALSO OBSCURE THE TOPS OF THE WESTERN MONTANA MOUNTAINS. ON
TUESDAY...THE TROUGH WILL MOVE INTO THE STATE...BRINGING THE COLD
FRONT SOUTH THROUGH THE AREA AND INCREASING THE CHANCE FOR SNOW.
SNOW WILL GENERALLY OBSCURE THE MOUNTAINS AFTER 15Z. OVER THE PLAINS
AND IN THE VALLEYS...OCCASIONAL MVFR CONDITIONS ARE POSSIBLE WITH
SNOW SHOWERS INITIALLY...BUT THEY WILL BECOME MORE WIDESPREAD FROM
NORTHWEST TO SOUTHEAST AFTER 15Z (WITH POSSIBLE IFR CONDITIONS AT
TIMES) AS WINDS SHIFT MORE NORTHERLY AND UPSLOPE BEHIND THE COLD
FRONT.  COULSTON

&&

.PREVIOUS DISCUSSION...ISSUED 241 PM MST MON FEB 21 2011

TONIGHT THROUGH WEDNESDAY...GUSTY WEST-SOUTHWESTERLY WINDS HAVE
DEVELOPED OVER NORTH-CENTRAL AND CENTRAL MONTANA WHICH ALLOWED
TEMPERATURES TO RAPIDLY WARM INTO THE 20S TO AROUND 30 DEGREES
THIS AFTERNOON. THESE WINDS COMBINED WITH THE RECENT SNOWFALL HAVE
CAUSED WIDESPREAD BLOWING/DRIFTING SNOW ALONG THE NORTHERN ROCKY
MOUNTAIN FRONT AND EASTERN GLACIER COUNTY...WHILE LOCALIZED AREAS
OF BLOWING SNOW ARE EXPECTED ELSEWHERE. THUS...HAVE CONTINUED
BLOWING SNOW ADVISORY. NEXT PACIFIC TROUGH OF LOW PRESSURE WILL
MOVE INTO THE INTER-MOUNTAIN WEST ON TUESDAY AND CROSS THE
CONTINENTAL DIVIDE BY TUESDAY AFTERNOON/EVENING BRINGING ANOTHER
ARCTIC COLD FRONT OVER THE AREA. WIDESPREAD LIGHT SNOW WILL
DEVELOP ALONG AND BEHIND THE FRONT WITH GUSTY WINDS WITH FRONTAL
PASSAGE. MODELS ARE INDICATING LOWER QPF AMOUNTS SO AM EXPECTING
WIDESPREAD LIGHT SNOWFALL AND ISOLATED AREAS OF HEAVIER SNOW
MAINLY IN THE HIGHER ELEVATIONS. FOR NOW AM EXPECTING SNOW AMOUNTS
OF 1 TO 3 INCHES IN THE PLAINS/VALLEYS AND 3 TO 6 INCHES IN THE
MOUNTAINS. TEMPERATURES WILL FLUCTUATE THROUGH THE PERIOD WITH
WARMER TEMPERATURES AROUND SEASONAL AVERAGES ON TUESDAY BEFORE THE
ARCTIC AIRMASS RETURNS BY WEDNESDAY WITH DAYTIME HIGHS FALLING
INTO THE TEENS. MLS

WEDNESDAY NIGHT THROUGH MONDAY...ANOTHER PERIOD OF VERY COLD
TEMPERATURES IS EXPECTED TO AFFECT THE REGION FROM WEDNESDAY THROUGH
FRIDAY. AS A NOW...FRIDAY MORNING LOOKS TO BE THE COLDEST
MORNING...ESPECIALLY IN THE CUT BANK AND HAVRE AREAS...WHERE MORNING
TEMPERATURES WILL BE AROUND 30 DEGREES BELOW ZERO. THERE WILL
CONTINUE TO BE A CHANCE FOR SNOW WEDNESDAY NIGHT THROUGH
THURSDAY...WITH SOME SNOW ACCUMULATIONS LIKELY...ESPECIALLY OVER
CENTRAL AND SOUTHWEST MONTANA. DAYTIME HIGHS WILL ALSO BE COLD OVER
NORTH CENTRAL MONTANA LATER THIS WEEK...WITH MOST AREAS STAYING
BELOW ZERO FOR DAY TIME HIGHS. THE GOOD NEWS...THIS COLD SNAP WILL
BE SHORT-LIVED...AND THE ROLLER-COASTER TEMPERATURE PATTERN WILL
CONTINUE. EXPECT TEMPERATURES TO START TO WARM ON SATURDAY...AND BY
SUNDAY...AFTERNOON HIGHS WILL RANGE FROM THE MID 20S TO NEAR 30
DEGREES. TEMPERATURES WILL CONTINUE THE WARMING TREND INTO
MONDAY...WITH MOST AREAS A FEW DEGREES WARMER THAN SUNDAY. THERE
WILL BE A FEW PASSING SNOW SHOWERS AFFECTING THE REGION SUNDAY AND
MONDAY...BUT MOST OF THE SNOWFALL ACTIVITY WILL BE CONFINED MAINLY
TO THE MOUNTAINS. BRUSDA

&&

.HYDROLOGY...
ICE JAM FLOODING ON THE JEFFERSON RIVER CONTINUES NEAR
SILVER STAR IN NORTHWEST MADISON COUNTY. ADDITIONAL STREAM RISES
SHOULD BE SLOW AND FLASH FLOODING IS NOT EXPECTED.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  17  30   5   8 /  10  50  70  70
CTB  17  23  -1   3 /  10  40  60  60
HLN  19  33  13  17 /  10  50  50  80
BZN  16  31   9  21 /  20  40  50  60
WEY   7  23   5  22 /  20  70  60  60
DLN  18  28   9  23 /  20  40  40  60
HVR  15  25   2   5 /   0  30  50  40
LWT  16  31   5  10 /  10  30  70  70

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL 5 AM MST TUESDAY EASTERN GLACIER...
NORTHERN ROCKY MOUNTAIN FRONT.

FLOOD WARNING IN EFFECT UNTIL AT LEAST 10 AM MST WEDNESDAY FOR THE
JEFFERSON RIVER IN MADISON COUNTY NEAR THE TOWN OF SILVER STAR.

&&

WEATHER.GOV/GREATFALLS

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE GREAT FALLS MT
955 PM MST MON FEB 21 2011

MTZ009-010-221400-
NORTHERN ROCKY MOUNTAIN FRONT-EASTERN GLACIER-
955 PM MST MON FEB 21 2011

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

.DAY ONE...TONIGHT

A WINTER WEATHER ADVISORY FOR BLOWING SNOW IS IN EFFECT FOR THE
NORTHERN ROCKY MOUNTAIN FRONT AND EASTERN GLACIER
COUNTY...INCLUDING THE CUT BANK AREA...THROUGH TONIGHT.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

AN UPPER LEVEL WEATHER SYSTEM WILL MOVE INTO MONTANA ON TUESDAY.
PERIODS OF LIGHT SNOW ARE EXPECTED FROM TUESDAY AFTERNOON THROUGH
THURSDAY...PRODUCING ACCUMULATIONS OF 2 TO 3 INCHES IN THE VALLEYS
AND OVER THE PLAINS...WITH 4 TO 8 INCHES OF SNOW EXPECTED IN THE
MOUNTAINS. THUS WINTER WEATHER HIGHLIGHTS COULD BE ISSUED LATER
THIS WEEK.

ANOTHER ROUND OF ARCTIC AIR WILL MOVE INTO THE REGION BEGINNING
ON WEDNESDAY...AND CONTINUE TO RESIDE OVER THE AREA INTO THE
WEEKEND. ANYONE WHO HAS OUTDOOR ACTIVITIES PLANNED FOR LATER THIS
WEEK SHOULD BE PREPARED FOR ANOTHER ROUND OF VERY COLD
TEMPERATURES AND LOW WIND CHILL VALUES.

.SPOTTER INFORMATION STATEMENT...

WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER
CONDITIONS AND IMPACTS TO THE NATIONAL WEATHER SERVICE OFFICE IN
GREAT FALLS.

MTZ015-221400-
MADISON-
955 PM MST MON FEB 21 2011

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTHWEST
MONTANA.

.DAY ONE...TONIGHT

A FLOOD WARNING IS IN EFFECT FOR THE JEFFERSON RIVER SOUTH OF THE
TOWN OF SILVER STAR DUE TO ICE JAM CONDITIONS.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

THE FLOOD WARNING FOR THE JEFFERSON RIVER NEAR SILVER STAR
CONTINUES UNTIL AT LEAST WEDNESDAY MORNING.

AN UPPER LEVEL WEATHER SYSTEM WILL MOVE INTO MONTANA ON TUESDAY.
PERIODS OF LIGHT SNOW ARE EXPECTED FROM TUESDAY AFTERNOON THROUGH
THURSDAY...PRODUCING ACCUMULATIONS OF 2 TO 3 INCHES IN THE VALLEYS
AND OVER THE PLAINS...WITH 4 TO 8 INCHES OF SNOW EXPECTED IN THE
MOUNTAINS. THUS WINTER WEATHER HIGHLIGHTS COULD BE ISSUED LATER
THIS WEEK.

ANOTHER ROUND OF ARCTIC AIR WILL MOVE INTO THE REGION BEGINNING
ON WEDNESDAY...AND CONTINUE TO RESIDE OVER THE AREA INTO THE
WEEKEND. ANYONE WHO HAS OUTDOOR ACTIVITIES PLANNED FOR LATER THIS
WEEK SHOULD BE PREPARED FOR ANOTHER ROUND OF VERY COLD
TEMPERATURES AND LOW WIND CHILL VALUES.

.SPOTTER INFORMATION STATEMENT...

WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER
CONDITIONS AND IMPACTS TO THE NATIONAL WEATHER SERVICE OFFICE IN
GREAT FALLS.

MTZ008-011>014-044>055-221400-
BEAVERHEAD-HILL-CASCADE-CHOUTEAU-
CENTRAL AND SOUTHERN LEWIS AND CLARK-TOOLE-LIBERTY-
EASTERN PONDERA-BLAINE-SOUTHERN ROCKY MOUNTAIN FRONT-
EASTERN TETON-JUDITH BASIN-FERGUS-JEFFERSON-BROADWATER-MEAGHER-
GALLATIN-
955 PM MST MON FEB 21 2011

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

.DAY ONE...TONIGHT

THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER THROUGH TONIGHT
IS LOW.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

AN UPPER LEVEL WEATHER SYSTEM WILL MOVE INTO MONTANA ON TUESDAY.
PERIODS OF LIGHT SNOW ARE EXPECTED FROM TUESDAY AFTERNOON THROUGH
THURSDAY...PRODUCING ACCUMULATIONS OF 2 TO 3 INCHES IN THE VALLEYS
AND OVER THE PLAINS...WITH 4 TO 8 INCHES OF SNOW EXPECTED IN THE
MOUNTAINS. THUS WINTER WEATHER HIGHLIGHTS COULD BE ISSUED LATER
THIS WEEK.

ANOTHER ROUND OF ARCTIC AIR WILL MOVE INTO THE REGION BEGINNING
ON WEDNESDAY...AND CONTINUE TO RESIDE OVER THE AREA INTO THE
WEEKEND. ANYONE WHO HAS OUTDOOR ACTIVITIES PLANNED FOR LATER THIS
WEEK SHOULD BE PREPARED FOR ANOTHER ROUND OF VERY COLD
TEMPERATURES AND LOW WIND CHILL VALUES.

.SPOTTER INFORMATION STATEMENT...

WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER
CONDITIONS AND IMPACTS TO THE NATIONAL WEATHER SERVICE OFFICE IN
GREAT FALLS.