537
FXUS65 KGGW 210418 AAA
AFDGGW
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE GLASGOW MT
918 PM MST FRI NOV 20 2009
SHORT TERM...FOR NORTHEAST MONTANA...TONIGHT THROUGH SUNDAY
THE UPPER LEVEL TROUGH...CURRENTLY SLAMMING INTO THE NORTHWEST
COAST...CONTINUES TO EJECT MOISTURE INTO THE SOUTHWEST FLOW OVER
THE DIVIDE WHICH IS PRODUCING OPAQUE HIGH CLOUDS ABOVE
NORTHEASTERN MONTANA THIS EVENING. ADJUSTED SKY COVER FARTHER TO
THE EAST.
A LEE SURFACE TROUGH WILL SLIDE EAST OVER THE ZONES TONIGHT WHICH
WILL BACK SOUTHERLY WINDS TO THE WEST BY MORNING. A SURFACE
GRADIENT OF INCREASING STRENGTH WILL MAINTAIN WINDS TONIGHT AT
10KT-15KT OVER FAVORED AREAS. MADE A FEW TWEAKS TO THE WIND GRIDS
BASED ON CURRENT OBSERVATIONS AND UPDATED GUIDANCE.
OTHERWISE CONDITIONS WILL STAY DRY SO FEW GRID CORRECTIONS ARE
NEEDED. SCT
PREVIOUS DISCUSSION...
AN UPPER TROUGH IS MOVING OVER THE WEST COAST THIS AFTERNOON WITH
AN UPPER RIDGE REMAINING OVER THE NORTHERN HIGH PLAINS. A COPIOUS
AMOUNT OF UPPER LEVEL PACIFIC MOISTURE IS SPILLING OVER THE
CONTINENTAL DIVIDE RESULTING IN AN EXTENSIVE AREA OF DENSE CIRRUS
CLOUDS. THE OPAQUENESS OF THIS CIRRUS HAS GENERALLY HELD
TEMPERATURES BELOW FORECAST VALUES...BUT NEVERTHELESS STILL VERY
MILD FOR THE LATER HALF OF NOVEMBER.
THE TROUGH WILL CONTINUE ITS PROGRESSION EAST TONIGHT WITH HIGH
CLOUDS CONTINUING TO STREAM OVERHEAD. LOW TEMPERATURES WILL BE ON
THE MILD SIDE...WITH A FEW OF THE LOW LYING AREAS EXPERIENCING
COLD AIR DRAINAGE AS THE WIND BECOMES LIGHT. A PACIFIC COLD FRONT
ASSOCIATED WITH THE TROUGH WILL MOVE THROUGH SATURDAY MORNING WITH
A STRONG WEST WIND DEVELOPING DURING THE LATE MORNING AND
CONTINUING THROUGH THE AFTERNOON. COLD AIR ADVECTION AND
SUBSIDENCE SHOULD SUSTAIN THE SURFACE WIND ALONG WITH STRONGER
GUSTS AS 850MB WIND SPEEDS REACH NEAR 35KT. AFTERNOON RELATIVE
HUMIDITY VALUES COULD BE RATHER LOW WITH A DOWNSLOPING WESTERLY
WIND. A SHORT PERIOD OF NEAR CRITICAL FIRE WEATHER CONDITIONS ARE
POSSIBLE. SEE THE FIRE WEATHER DISCUSSION BELOW FOR MORE
INFORMATION. THE WIND SPEED WILL EASILY MEET LAKE WIND ADVISORY
CRITERIA...SO ONE WILL BE ISSUED FOR FORT PECK LAKE.
A SHORTWAVE RIDGE CROSSES THE NORTHERN PRAIRIE SATURDAY NIGHT AND
EARLY SUNDAY BRINGING AN END TO THE WIND AND LESS CLOUD COVER. LOW
TEMPERATURES SATURDAY NIGHT COULD APPROACH SEASONAL AVERAGES UNDER
A MOSTLY CLEAR SKY. A SHORTWAVE TROUGH QUICKLY ARRIVES SUNDAY
AFTERNOON. A FEW AREAS OF LIGHT RAIN ARE POSSIBLE IN THE
AFTERNOON. SURFACE TEMPERATURES APPEAR TOO WARM FOR ANY SNOW
DURING THE AFTERNOON. AJZ
LONG TERM...SUNDAY NIGHT THROUGH FRIDAY
NO SIGNIFICANT CHANGES IN THE LONG TERM PERIOD. SEVERAL WEAK
SHORTWAVE TROFS MOVE THROUGH THE REGION...ONE SUNDAY NIGHT WITH
ANOTHER ON TUESDAY. SOME POTENTIAL FOR PRECIPITATION WITH EITHER
OF THE WAVES SO KEPT THE LOW POPS FOR THOSE PERIODS. OTHERWISE
WITH THE MORE PROGRESSIVE FLOW TEMPERATURES WILL BE CLOSER TO
NORMAL BUT STILL WARM FOR LATE NOVEMBER.
PREVIOUS LONG TERM DISCUSSION....AN UPPER SHORT-WAVE TROUGH
SWINGS THROUGH EASTERN MONTANA SUNDAY NIGHT BUT APPEARS TO KEEP
MOST ENERGY TO OUR SOUTH. THE COLD FRONT IS RATHER SUBTLE SO DO
NOT EXPECT MUCH IN THE WAY OF QPF...BUT CANNOT RULE IT OUT EITHER.
WITH 850MB TEMPERATURES AT -2*C TO -4*C ANY PRECIPITATION THAT
DOES DEVELOP WILL LIKELY BE SNOW. THE GFS AND EC DO NOT BEGIN IN
PHASE...WITH THE GFS AROUND 6-HOURS AHEAD OF THE EC. SO WILL KEEP
12-HOURS POP/WX GRIDS. THE GEM ALSO FAVORS KEEPING MOST QPF TO OUR
SOUTH BUT SUPPORTS LOW POPS FOR OUR AREA. THE PHASE DIFFERENCE
BETWEEN GFS AND EC BECOMES MORE PRONOUNCED DURING THE REMAINDER OF
THE EXTENDED PERIOD AS THE MODELS BECOME MORE PROGRESSIVE.
MONDAY/MONDAY NIGHT...THE TROUGH MOVES TO THE EAST AS AN UPPER
RIDGE/WARM FRONT MOVES OVER THE WEST. THE RIDGE WILL LIKELY BE
SHORT LIVED SINCE MODELS SHOW ANOTHER SHORT WAVE TROUGH
APPROACHING. THE GEM IS SLOWER TO EXIT ANY PRECIPITATION SO WILL
MODIFY POPS BASED ON THE UNCERTAINTY.
TUESDAY/TUESDAY NIGHT...THE 00Z GFS AND 12Z EC AGREE WITH THE
SHORT-WAVE AFFECTING THE AREA BUT DIFFER QUITE A BIT ON LOCATION
AND TIMING. THE GFS BRINGS IN THE MOISTURE DURING THE DAY WHILE
THE EC PREFERS TUESDAY NIGHT. THE 00Z EC WHICH CAME IN DURING THE
SHIFT KEPT THE MOISTURE SOUTH OF THE AREA. THE GEM BY NOW APPEARS
TO BE ON A DIFFERENT PLANET...SO WILL DISREGARD. AGAIN ANY
PRECIPITATION THAT DEVELOPS WILL LIKELY BE LIGHT AND IN THE FORM
OF SNOW OR A MIX WITH MOST 850MB TEMPERATURES NEAR OR BELOW 0*C.
SURFACE TEMPERATURES WILL LIKELY DROP MUCH CLOSER TO NORMAL.
WEDNESDAY AND BEYOND...UPPER RIDGING APPEARS TO FOLLOW...ALTHOUGH
ENSEMBLE AND OPERATIONAL PHASING AND AMPLITUDE VARY GREATLY
BETWEEN GFS AND EC. SURFACE TEMPERATURES ARE EXPECTED TO ONCE
AGAIN RISE ABOVE NORMAL...BY AROUND 10*F TO 15*F. THE NEXT SHORT
WAVE TROUGH CRASHES INTO THE NORTHWEST COAST AROUND THURSDAY...BUT
THERE CONTINUES TO BE NO CONSENSUS AS TO HOW THE TROUGH DEVELOPS
AND AFFECTS NORTHEAST MONTANA. SCT
AVIATION
VFR CONDITIONS. SCATTERED TO BROKEN HIGH CLOUDS WILL GIVE WAY TO
INCREASING MID-LEVEL CLOUDS LATE TONIGHT AS A COLD FRONT
APPROACHES THE AREA. EAST TO SOUTHEAST WINDS OVERNIGHT WILL TURN
NORTHWEST AND INCREASE BEHIND THE FRONTAL PASSAGE DURING THE LATE
MORNING. RAE
FIRE WEATHER
A STRONG WEST WIND WILL DEVELOP SATURDAY BEHIND A COLD FRONT.
WIND SPEEDS ARE EXPECTED TO REACH 20 TO 30 MPH...WITH GUSTS TO 40
MPH DURING THE LATE MORNING AND AFTERNOON HOURS. AFTERNOON
MINIMUM RELATIVE HUMIDITY VALUES ARE EXPECTED TO BRIEFLY DROP INTO
THE 20 TO 30 PERCENT RANGE BEFORE BEGINNING A STEADY RECOVERY NEAR
SUNSET. THEREFORE...A BRIEF PERIOD OF CRITICAL FIRE WEATHER
CONDITIONS ARE POSSIBLE SATURDAY AFTERNOON...BUT HIGHLIGHTS ARE
NOT EXPECTED AT THIS TIME DUE TO THE SHORT DURATION OF LOW
RELATIVE HUMIDITY. THE MOST SUSCEPTIBLE AREAS WILL BE THE LITTLE
ROCKY MOUNTAINS AND THE MISSOURI BREAKS REGION OF ZONES 119 AND
121...WHICH WILL EXPERIENCE A RATHER POOR RELATIVE HUMIDITY
RECOVERY TONIGHT. AJZ
GLASGOW WATCHES/WARNINGS/ADVISORIES
LAKE WIND ADVISORY FROM 10 AM TO 5 PM MST SATURDAY FOR FORT PECK
LAKE.
WEATHER.GOV/GLASGOW
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