Winter Weather Advisory 40, NWS Missoula, MT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
210 PM MDT FRI MAY 4 2012

...SPRING SNOW STORM TO CAUSE IMPACTS TONIGHT THROUGH SATURDAY...

.DISCUSSION...THERE IS HIGH CONFIDENCE IN THE SPRING SNOW STORM
EXPECTED TO IMPACT THE NORTHERN ROCKIES BEGINNING THIS EVENING.
PRECIPITATION WILL IMPACT CENTRAL IDAHO FIRST...THEN SPREAD INTO
WEST CENTRAL AND SOUTHWEST MONTANA LATER THIS EVENING. AS IT DOES
SO: RAIN WILL MIX WITH SNOW IN VALLEYS AND COULD FALL AT A
MODERATE TO HEAVY RATE AT TIMES. BY TONIGHT...SNOW LEVELS WILL
DRAMATICALLY DROP AND CAUSE RAINFALL TO TURN TO SNOW. THE
PRECIPITATION WILL BE MOST FOCUSED OVER WEST CENTRAL
MONTANA...INCLUDING THE BITTERROOT AND MISSOULA VALLEYS, AS WELL
AS ACROSS SOUTHWEST MONTANA...INCLUDING GEORGETOWN LAKE THROUGH
BUTTE.

THIS WEATHER SYSTEM WILL CREATE SEVERAL IMPACTS: THE FIRST WILL
BE SLICK, SNOW COVERED MOUNTAIN PASSES AND ROADWAYS THAT
ACCUMULATE A COATING OF SNOW OVERNIGHT. THE SECOND IMPACT WILL BE
DAMAGE TO NEWLY BLOOMED TREES, SHRUBS, AND FLOWERS FROM WET HEAVY
SNOWFALL. DAMAGE COULD RESULT FROM THE ADDITIONAL WEIGHT PLACED
ON THEM BY THE SNOW. POWER LINES MAY ALSO SUFFER...WITH DOWNED
POWER LINES AND/OR POWER OUTAGES POSSIBLE.

BY SATURDAY MORNING THE PRECIPITATION WILL SLOWLY SHIFT NORTH AND CREATE
A RAIN/SNOW MIX ONCE AGAIN ACROSS VALLEYS OF WEST CENTRAL MONTANA
INTO NORTHWEST MONTANA. HOWEVER...THE BEST FOCUS OF PRECIP WILL
REMAIN ALONG THE DIVIDE. ROADWAYS SHOULD BE RELIEVED OF ANY
IMPACTS FROM SNOWFALL BY SATURDAY AFTERNOON.

CONDITIONS WILL REMAIN SHOWERY BUT STEADILY IMPROVE
SUNDAY...MARKING THE BEGINNING TO A DRIER AND WARMER PATTERN.

A RIDGE OF HIGH PRESSURE WILL BUILD INTO THE REGION LATE SUNDAY
NIGHT CREATING DRIER AND MUCH WARMER TEMPERATURES. TEMPERATURES
WILL BE IN THE UPPER 60S MONDAY WITH THE WARMER DAYS EXPECTED TO BE
TUESDAY AND WEDNESDAY WITH HIGHS IN THE MID TO UPPER 70S.
NORTHWESTERN MONTANA WILL LIKELY SEE COOLER TEMPERATURES THAN THE
MISSOULA/BITTERROOT VALLEYS WEDNESDAY DUE TO THE NEXT STORM
SYSTEM. A COLD FRONT IS EXPECTED TO PUSH THROUGH WESTERN MONTANA
WEDNESDAY NIGHT AND THURSDAY MORNING. BRIEF HEAVY RAIN AND
POSSIBLY SOME THUNDER ALONG WITH GUSTY WINDS WILL ACCOMPANY THE
FRONT. GUST COULD BE AS HIGH AS 25-30MPH. GUSTY WEST NORTH WEST
WINDS WILL ALSO BE BEHIND THE FRONT THURSDAY AFTERNOON, GUSTS
COULD ONCE AGAIN REACH 25-30MPH.

&&

.AVIATION...AFTERNOON WINDS HAVE PICKED UP AND SHOULD CONTINUE TO
BE PRESENT THROUGH LATER THIS EVENING. AS A RIGOROUS WEATHER
SYSTEM TREKS ACROSS CENTRAL IDAHO AND WESTERN MONTANA...A MIX
OF RAIN AND SNOW WILL OCCUR...BEFORE PRECIPITATION CHANGES TO ALL
SNOW TONIGHT. LOWERED VISIBILITIES AND CLOUD DECKS ARE LIKELY
BEYOND 05/0300Z FOR KSMN, KBTM, AND KMSO. SHOWERS CAN BE EXPECTED
AT KGPI AND OTHER NORTHWEST MONTANA LOCATIONS...HOWEVER THEY WILL
SEE THE LEAST EFFECTS FROM THIS SYSTEM. EXPECT DETERIORATED
CONDITIONS THROUGH 05/1500Z AT THE VERY LEAST.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...WINTER WEATHER ADVISORY FROM 8 PM THIS EVENING TO NOON MDT
     SATURDAY BUTTE/BLACKFOOT REGION.

     WINTER WEATHER ADVISORY FROM 8 PM THIS EVENING TO NOON MDT
     SATURDAY BITTERROOT/SAPPHIRE MOUNTAINS.

     WINTER WEATHER ADVISORY FROM 8 PM THIS EVENING TO NOON MDT
     SATURDAY POTOMAC/SEELEY LAKE REGION.

ID...WINTER WEATHER ADVISORY FROM 8 PM THIS EVENING TO NOON MDT
     SATURDAY EASTERN LEMHI COUNTY...WESTERN LEMHI COUNTY.

&&

SHORT TERM...ALLEGRETTO
LONG TERM....ROBINSON/PALLISTER
AVIATION...ALLEGRETTO