Lake Wind Advisory 2, NWS Missoula, MT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
1237 PM MDT TUE APR 27 2010

.DISCUSSION...GRANGEVILLE WINDS ARE STILL BREEZY BUT HAVE REMAINED
BELOW ADVISORY CRITERIA AFTER THE INITIAL BURST OF WIND THIS
MORNING. SALMON AREA IS NOW GETTING THE STRONG SOUTHERLY
FLOW...AND HAVE ISSUED AN ADVISORY FOR THAT AREA. GUSTS WILL
LIKELY REMAIN CLOSE TO 40 MPH IN THAT AREA THROUGH MID EVENING.

&&

.AVIATION...SOUTHWEST FLOW AHEAD OF AN APPROACHING STORM SYSTEM
WILL BRING INCREASING AND LOWERING CLOUDS TO THE REGION TODAY. THE
CHANCE FOR SHOWERS WILL ALSO INCREASE TODAY AND ESPECIALLY TONIGHT
AS A COLD FRONT IS FORECAST TO MOVE THROUGH THE REGION. GUSTY
WINDS ARE EXPECTED AT MOST AIRFIELDS TODAY WITH OCCASIONAL GUSTS
IN EXCESS OF 30KTS POSSIBLE AT KMSO...KSMN AND KBTM. THERE WILL
ALSO BE A SLIGHT CHANCE FOR SOME THUNDERSTORMS IN VICINITY OF
KMSO...KBTM AND KSMN LATE THIS AFTERNOON AND DURING THE OVERNIGHT
HOURS. WIDESPREAD VISUAL OBSCURATION OF MOUNTAINS AND PASSES ARE
EXPECTED THROUGH AT LEAST THE NEXT 24 HOURS REGION WIDE.

&&

.PREV DISCUSSION... /ISSUED 629 AM MDT TUE APR 27 2010/

UPDATE...UPON FURTHER REVIEW WE HAVE DECIDED TO ISSUE A WIND
ADVISORY FOR THE CAMAS PRAIRIE AND GRANGEVILLE AREAS OF WEST-
CENTRAL IDAHO THROUGH THIS AFTERNOON.

DISCUSSION...RECENT OBSERVATIONS AND MODEL DATA CONFIRM LITTLE
STABILITY IN THE PROFILE OVER WEST-CENTRAL IDAHO THIS MORNING.
GIVEN MODELS ARE CONSISTENTLY SHOWING WINDS ALOFT INCREASING WITH
TIME THIS MORNING AND OBSERVATIONS OVER SOUTHERN IDAHO/EASTERN
OREGON CONFIRM THE PRESENCE OF VERY GUST WINDS...HAVE DECIDED TO
ISSUE A WIND ADVISORY IN ANTICIPATION OF CONTINUED GUSTS TO 45
MPH OVER THE CAMAS PRAIRIE AND GRANGEVILLE AREAS.

AVIATION...SOUTHWEST FLOW AHEAD OF AN APPROACHING STORM SYSTEM
WILL BRING INCREASING AND LOWERING CLOUDS TO THE REGION TODAY. THE
CHANCE FOR SHOWERS WILL ALSO INCREASE TODAY AND ESPECIALLY TONIGHT
AS A COLD FRONT IS FORECAST TO MOVE THROUGH THE REGION. GUSTY
WINDS ARE EXPECTED AT MOST AIRFIELDS TODAY WITH OCCASIONAL GUSTS
IN EXCESS OF 30KTS POSSIBLE AT KMSO...KSMN AND KBTM. THERE WILL
ALSO BE A SLIGHT CHANCE FOR SOME THUNDERSTORMS IN VICINITY OF
KMSO...KBTM AND KSMN LATE THIS AFTERNOON AND DURING THE OVERNIGHT
HOURS. WIDESPREAD VISUAL OBSCURATION OF MOUNTAINS AND PASSES ARE
EXPECTED THROUGH AT LEAST THE NEXT 24 HOURS REGION WIDE.

PREV DISCUSSION... /ISSUED 403 AM MDT TUE APR 27 2010/

DISCUSSION...A DEEPENING UPPER LEVEL TROUGH OF LOW PRESSURE WILL
MOVE INTO THE NORTHERN ROCKIES REGION TODAY BRINGING GUSTY WINDS AND
AN INCREASING CHANCE FOR SHOWERS. THE UPPER LEVEL JET STREAM IS
FORECAST TO PASS OVER THE AREA TODAY AS THE TROUGH APPROACHES
WHICH WILL LEAD TO INCREASING WINDS THROUGHOUT THE ENTIRE
ATMOSPHERE AND THUS WINDY CONDITIONS AT THE SURFACE. HIGHEST WIND
GUSTS ARE EXPECTED OVER CENTRAL IDAHO AND SOUTHWEST MONTANA TODAY
AND ALTHOUGH GUSTS MAY APPROACH 40 MPH IN SOME LOCATIONS...BELIEVE
AT THIS TIME THESE GUSTS WILL BE OCCASIONAL AND GENERALLY BELOW
ADVISORY CRITERIA (GUSTS > 40MPH).

VERY LIGHT PRECIPITATION IN THE WARM SECTOR OF THIS SYSTEM HAS
ALREADY SPREAD ACROSS THE COLUMBIA BASIN AND EASTERN WASHINGTON.
THIS PRECIPITATION WILL SLOWLY SPREAD EAST TODAY AS THE SURFACE
COLD FRONT MOVES INLAND...BUT LITTLE IN THE WAY OF MEASURABLE
RAINFALL IS EXPECTED UNTIL LATER TODAY WHEN THE FRONT DRAWS NEAR.
FORECAST MODELS ARE ALL IN AGREEMENT THAT THE COLD FRONTAL PASSAGE
WILL BE ABOUT 6 HOURS SLOWER THAN PREVIOUSLY FORECAST. THIS WILL
HELP INCREASE THE POSSIBILITY OF THUNDERSTORMS THIS AFTERNOON DUE
TO BETTER AFTERNOON HEATING...DESPITE THE CLOUD COVER. BUT OVERALL
THE INSTABILITY IN ADVANCE OF THE COLD FRONT IS MARGINAL AND THUS
ONLY A SLIGHT CHANCE OF THUNDERSTORMS WAS INCLUDED IN THE
FORECAST. ALL MODELS SUGGEST INTENSE DYNAMICS AND FAVORABLE UPPER
LEVEL JET SUPPORT ALONG THE COLD FRONT AS IT PASSES OVER CENTRAL
IDAHO BETWEEN 9PM AND MIDNIGHT AND WESTERN MONTANA BETWEEN
MIDNIGHT AND 3AM/WEDNESDAY MORNING. THESE FACTORS SHOULD AID IN
PRODUCING GUSTY WINDS AND BRIEF HEAVY PRECIPITATION AS THE FRONT
PASSES TO THE EAST. HEAVIER PRECIPITATION APPEARS POSSIBLE OVER
NORTHWEST MONTANA OVERNIGHT AS THESE LOCATIONS WILL BE IN CLOSER
PROXIMITY TO THE SURFACE A MID LEVEL AREAS OF LOW PRESSURE AND
THUS IN A FAVORABLE REGION FOR SYNOPTIC LIFTING. SHOWERS WILL
CONTINUE THROUGH WEDNESDAY AND WEDNESDAY NIGHT IN THE POST FRONTAL
REGIME UNDER MOIST NORTHWESTERLY FLOW ALOFT. SNOW LEVELS WILL
FALL TO 4000-4500 FEET AND THUS LIGHT ACCUMULATIONS ARE EXPECTED
OVER MOUNTAIN PASSES.

THURSDAY THROUGH SATURDAY...THE MODELS CONTINUE TO BE IN AGREEMENT
ABOUT A BROAD TROUGH COVERING A GOOD PORTION OF THE UNITED STATES.
THE MAIN LOW PRESSURE CENTER APPEARS TO BE OVER SOUTHERN
SASKATCHEWAN AND ROTATING INTO NORTHERN MINNESOTA BY SATURDAY. THIS
LOW PRESSURE IS EXPECTED TO KEEP PLENTY OF MOISTURE BEING WRAPPED
INTO MONTANA...ESPECIALLY ALONG THE CONTINENTAL DIVIDE. THE NORTHERN
ROCKIES SHOULD EXPECT WIDESPREAD PRECIPITATION WITH THE DIVIDE
RECEIVING A SIGNIFICANT AMOUNT OF SNOW IN THE HIGHER TERRAIN AND
RAIN IN THE VALLEYS. THIS TROUGH WILL ALSO KEEP TEMPERATURES WELL
BELOW SEASON NORMALS. THE LATEST RUNS OF THE MODELS ARE TRENDING
TO A MORE PROGRESSIVE FLOW FOR THE END OF THE WEEKEND INTO NEXT
WEEK. THE UPPER LEVEL FLOW APPEARS TO BECOME WESTERLY AS A
DISTURBANCE DROPS OUT OF ALASKA. THIS FLOW PATTERN WILL CAUSE
MOISTURE TO STREAM INTO THE NORTHERN ROCKIES WITH JUST A SLIGHT
WARMING TREND.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...NONE.
ID...WIND ADVISORY UNTIL 8 PM MDT THIS EVENING EASTERN LEMHI COUNTY.

&&

UPDATE...WHITMORE
PREVIOUS DISCUSSION...DICKERSON/SMITH