Areal Flood Warning 7, NWS Missoula, MT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
356 AM MDT WED APR 25 2012

...ANOTHER WARM DAY WITH THUNDERSTORMS FOLLOWED BY A BIG CHANGE TO
END THE WEEK...

...RIVERS AND STREAMS WILL CONTINUE TO SEE STEADY RISES THROUGH
WEEKS END...

.DISCUSSION...ANOTHER ROUND OF NOCTURNAL CONVECTION OCCURRED
DURING THE NIGHT AND A FEW ROGUE STORMS COULD CONTINUE ACROSS WEST
CENTRAL MONTANA THROUGH MID MORNING. BEYOND THAT...CONDITIONS
TODAY WILL BE QUITE SIMILAR TO THAT OF YESTERDAY: PERSISTENT CLOUD
COVER WITH THE POSSIBILITY OF A RUMBLE OF THUNDER IN THE AFTERNOON
AND EVENING HOURS. MOST DEVELOPMENT SHOULD REMAIN CONFINED TO WEST
CENTRAL/SOUTHWEST MONTANA AND CENTRAL IDAHO. NORTHWEST MONTANA
SHOULD SEE THE LEAST ACTION TODAY.

ALL MODELS ARE SHOWING A LARGE SWATH OF NOCTURNAL CONVECTION
MOVING NORTH THROUGH IDAHO AND INTO THE PANHANDLE/NORTHWEST
MONTANA BY EARLY THURSDAY MORNING. THE BIGGEST THREAT WITH THESE
STORMS WILL BE VERY INTENSE RAINFALL GIVEN THAT THE OVERNIGHT
HOURS DURING THESE SPRING MONTHS DO NOT TYPICALLY SUPPORT
SUFFICIENT INSTABILITY FOR HAIL OR STRONG WINDS. WIDESPREAD
SHOWERS WITH A CHANCE FOR THUNDERSTORMS WILL CONTINUE ELSEWHERE
THROUGHOUT THE DAY THURSDAY AHEAD OF A VERY STRONG COLD FRONT
WHICH IS CURRENTLY FORECAST TO PASS ACROSS CENTRAL IDAHO AND
WESTERN MONTANA THURSDAY EVENING.

A BURST OF HEAVY PRECIPITATION ALONG WITH BRIEF GUSTY AND
POTENTIALLY DAMAGING WINDS ARE EXPECTED DURING THE FRONTAL
PASSAGE. ADDITIONALLY...THE SNOW LEVEL IS EXPECTED TO DROP VERY
QUICKLY AS THE FRONT PASSES WITH SNOW BEING POSSIBLE ABOVE
4000 FEET THROUGH FRIDAY. THE HIGHER TERRAIN...INCLUDING MOUNTAIN
PASSES...CAN EXPECT TO RECEIVE PERHAPS 1 TO 4 INCHES OF SNOWFALL
WITH THE HIGHEST TERRAIN POTENTIALLY ACCUMULATING 6 TO 8 INCHES
THROUGH FRIDAY. THOSE WITH EARLY SEASON TRAVEL PLANS INTO THE
BACK COUNTRY SHOULD BE PREPARED TO ENCOUNTER WINTER WEATHER AND
COLD TEMPERATURES THURSDAY NIGHT THROUGH SATURDAY MORNING. TRAVEL
OVER MOUNTAIN PASSES MAY BE SLIGHTLY AFFECTED BY REDUCED
VISIBILITY AND PERHAPS SLUSHY CONDITIONS ON THE ROAD. HOWEVER
MAJOR IMPACTS ARE NOT EXPECTED MAINLY BECAUSE ROAD SURFACE
TEMPERATURES SHOULD REMAIN QUITE WARM DESPITE THE DRAMATICALLY
COOLER AIR TEMPERATURES.

TEMPERATURES ON FRIDAY WILL BE SOME 35 DEGREES COLDER THAN THE
RECORD BREAKING READINGS WHICH OCCURRED TO BEGIN THE WEEK. ABUNDANT
AFTERNOON RAIN/SNOW/GRAUPEL SHOWERS SEEM LIKELY GIVEN THE STRONG
INSTABILITY PROVIDED BY THE COLD UPPER LEVEL LOW PRESSURE SYSTEM
PARKED DIRECTLY OVER WESTERN MONTANA. SATURDAY'S WEATHER WILL BE
LARGELY DEPENDENT UPON THE TRAJECTORY AND SPEED OF THE UPPER LOW
AS IT EXITS THE REGION. AT THIS TIME WEATHER MODELS ARE STRUGGLING
TO FIND CONSISTENCY WITH THESE FACTORS AND HAVE THUS MAINTAINED AN
UNSEASONABLY COLD BUT SHOWERY FORECAST FOR SATURDAY.

THE EXITING LOW PRESSURE SYSTEM WILL HEAD INTO EASTERN
MONTANA ON SUNDAY...BUT THE NORTHERN ROCKIES WILL REMAIN UNDER
UNSETTLED NORTHWEST FLOW. THIS TYPE OF PATTERN IS HISTORICALLY
CONDUCIVE TO KEEPING SHOWERS AROUND...SO HAVE LEFT IN MENTIONING
OF CHANCE FOR CONTINUED RAIN SHOWERS THROUGH MONDAY.

BY MID TO LATE NEXT WEEK...A DRYING AND WARMING PATTERN CHANGE
COULD RESULT...BUT CONFIDENCE IS LOW AT THIS TIME. WILL NEED TO WAIT
A FEW MORE FORECAST MODEL RUNS BEFORE DRYING OUT ANY PART OF NEXT
WEEK'S FORECAST JUST YET.

&&

.AVIATION...A FEW RUMBLES OF THUNDER HAVE BEEN EXPERIENCED
OVERNIGHT AT KMSO BUT THESE THUNDERSHOWERS SHOULD DIMINISH THROUGH
THE REMAINDER OF THE MORNING. A BREAK DURING THE REST OF THE
MORNING AND EARLY AFTERNOON WILL OCCUR FOR THE ENTIRE NORTHERN
ROCKIES...HOWEVER THE ATMOSPHERE WILL ONCE AGAIN DESTABILIZE THIS
AFTERNOON AND RESULT IN THE POTENTIAL FOR ANOTHER LATE AFTERNOON
ROUND OF CONVECTION. BE PREPARED FOR THE CHANCE OF INCREASED
THUNDERSTORM ACTIVITY...PARTICULARLY AT KMSO...KBTM...AND KSMN
THROUGH THIS EVENING. BEYOND THAT: A RATHER ROBUST WEATHER SYSTEM
WILL BRING A MUCH WETTER AND COOLER PATTERN SHIFT...WHICH WILL
LIKELY HAVE AN IMPACT ON AVIATION OPERATIONS THURSDAY-FRIDAY.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...NONE.
ID...NONE.

&&

DISCUSSION...DICKERSON/ALLEGRETTO
AVIATION....ALLEGRETTO