FXUS65 KBYZ 092239
AFDBYZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
339 PM MST WED DEC 9 2009
.SHORT TERM...VALID FOR THU AND FRI...
UPPER LEVEL PATTERN TO BE CHANGING DURING THE SHORT TERM FORECAST
AS AN UPPER LEVEL RIDGE OVER THE EASTERN PACIFIC RETROGRADES A
BIT WESTWARD. THIS ALLOWS A NORTH NORTHWESTERLY FLOW TONIGHT AND
THURSDAY TO BECOME WEST NORTHWESTERLY BY LATE ON FRIDAY NIGHT.
OVERALL THIS WILL KEEP TWO PRIMARY WEATHER FEATURES IN PLAY ACROSS
MONTANA AND NORTH CENTRAL WYOMING...A GENERAL DOWNSLOPE WIND
PATTERN AND MID LEVEL MOISTURE STREAMING ACROSS THE AREA. FIRST FORECAST
CONCERN WILL BE WIND CHILLS OVERNIGHT AND THURSDAY MORNING AS
PRESSURE GRADIENTS ARE MAINTAINED OR TIGHTEN ACROSS THE AREA.
TEMPERATURES ONLY WARMED TO THE SINGLE DIGITS TODAY AND A FEW
AREAS REMAINED BELOW ZERO. SATELLITE SHOWS A FEW BREAKS IN CLOUD
COVER COMING INTO SOUTHERN MONTANA SO EVENING DIURNAL COOLING
SHOULD PUSH TEMPERATURES TO BELOW ZERO IN MOST AREAS. COMBINED
WITH THE STRONGER WINDS THIS WILL AGAIN YIELD WIND CHILL VALUES
BELOW 20 BELOW ZERO OVERNIGHT AND CONCERNED THAT IT MAY BE A MORE
DECEPTIVE WINDCHILL WITH THERMOMETER READINGS NOT INDICATING TRUE
MEASURE OF WIND CHILL. HAVE ISSUED WIND CHILL ADVISORY UNTIL 9
A.M. FOR THE ENTIRE REGION AGAIN. MOISTURE STREAMING ACROSS THE
AREA IN NORTHWEST FLOW ALOFT WILL DRIVE SOME MOUNTAIN SNOW AND
FLURRIES OVER THE PLAINS BUT ACCUMULATIONS ARE NOT EXPECTED TO BE
SIGNIFICANT. WINDS MAY CAUSE LOCAL BLOWING SNOW BUT STILL NOT
SEEING SIGNIFICANT IMPACTS SO WILL ONLY HAVE A MENTION IN ZONES.
TOMORROW WINDS WILL SLACKEN A BIT AS ONE SURFACE TROUGH MOVES EAST
AWAY FROM THE AREA WHILE ANOTHER ONE FORMS OVER ALBERTA. WITH A
WARMER START EXPECT TEMPERATURES TO HAVE A BETTER CHANCE OF
CLIMBING INTO THE TEENS. STILL MOISTURE STREAMING ACROSS THE AREA
WITH WEAK RIPPLES IN THE FLOW AND WITH MID LEVEL WINDS
NORTHWESTERLY DO NOT THINK THERE IS ENOUGH DOWNSLOPING INFLUENCE
TO LIMIT SNOW SHOWER OR FLURRY THREAT. WINDS WILL RESTRENGTHEN
THURSDAY NIGHT AND PRESSURE GRADIENT WILL BECOME VERY FAVORABLE
FOR GAP FLOW WIND AREAS. HAVE ELEVATED WINDS TO NEAR CRITERIA FOR
NYE AND LIVINGSTON AREAS AND WINDS BEING MAINTAINED OVER THE
REGION WILL SUPPORT WARMER TEMPERATURES ESPECIALLY FOR THE WESTERN
ZONES. FRIDAY THE POLAR VORTEX THAT HAS BEEN DRIVING THE COLD
EPISODE BEGINS TO MOVE WESTWARD ACROSS SASKATCHEWAN AND INDUCES
PRESSURES FALLS ALONG THE CANADIAN ROCKY MOUNTAIN FRONT WITH
SURFACE LOW PRESSURE DIGGING FURTHER SOUTH INTO MONTANA. WILL BE
DRIER FRIDAY WITH THE BACKING FLOW CAUSING A BIT MORE DOWNSLOPE
AND ELIMINATED LOW ELEVATION FLURRIES. BORSUM
.LONG TERM...VALID FOR SAT...SUN...MON...TUE...WED...
INTRODUCED EXTENSIVE COOL DOWN TO THE EXTENDED PERIOD...THINKING
THAT THE COLD FRINGES OF ARCTIC AIR WILL HAVE GREATER IMPACT INTO
WESTERN ZONES THAN WOULD NORMALLY BE EXPECTED WITH THE MAIN BRUNT
OF THE ARCTIC AIRMASS SLIPPING OFF TO THE EAST THROUGH THE WEEK
NEXT WEEK.
ALTHOUGH UPPER LEVEL FLOW TURNS MORE WESTERLY FOR THE WEEKEND.
THE SWITCH TO A MORE ZONAL TYPE FLOW LASTS ONLY A SHORT
TIME...TRANSITIONING BACK TO A MORE NORTHERLY FLOW WITH NEXT
ARCTIC SWEEPING THROUGH THE REGION SUNDAY NIGHT AND MONDAY.
FURTHERMORE...MODELS FAVOR PRECIP POTENTIAL ACROSS MUCH OF THE
REGION AS PIECES OF ENERGY ROTATE THROUGH THE AREA...WHICH SHOULD
LIMIT SIGNIFICANT IMPACT OF DIURNAL HEATING THROUGH THE WEEKEND.
DOWNSLOPE FLOW WILL LIKELY CAUSE SOME WARMING...MAINLY
WEST...APPEARING TO GET NEAR FREEZING AT BEST. MODELS BOTH SUPPORT
TIMING OF THE ARCTIC INTO THE AREA...BUT GFS IS MUCH
STRONGER...AND TAKES A MUCH DEEPER CUT INTO THE CWA. GFS ALSO
KEEPS THE COLD NORTHWESTERLY FLOW INTACT ACROSS THE REGION
THROUGH THE REMAINDER OF THE PERIOD. DID KEEP THE GENERAL TREND
OF SLOW WARMING FROM WEST TO EAST THROUGH THE PERIOD...BUT COOLED
EVERYTHING SIGNIFICANTLY. ALSO KEPT CHANCE POPS INTACT...WITH
ADJUSTMENT MAINLY FOR COLLABORATION. GILSTAD
&&
.AVIATION...
MAINLY VFR TO BORDERLINE MVFR FLIGHT CONDITIONS ARE EXPECTED
THROUGH THE EVENING AND OVERNIGHT...AS A WEAK DISTURBANCE MOVES
ACROSS THE REGION...BRINGING A CHANCE FOR LOCALIZED LIGHT SNOW TO
MUCH OF THE REGION...ESPECIALLY WEST.
INCREASING WINDS ARE EXPECTED THROUGH THE EVENING AND OVERNIGHT FROM KBIL
WEST....ESPECIALLY AROUND KLVM AND K3HT AREAS...INCLUDING THE
BEARTOOTH FOOTHILLS AND JUDITH GAP. WEST WINDS OF 25 TO 35
KTS...AND PEAK GUSTS TO 45 KTS WILL BE POSSIBLE THROUGH THE NIGHT.
BLOWING SNOW WILL BE POSSIBLE IN THESE REGIONS. GILSTAD
&&
.PRELIMINARY POINT TEMP/POPS...
THU FRI SAT SUN MON TUE WED
-----------------------------------------------------------
BIL 902/013 002/016 006/017 011/021 007/018 009/024 015/028
11/M 10/N 12/S 22/S 22/S 21/B 00/B
LVM 903/014 007/023 012/024 011/027 014/024 013/031 020/033
22/J 10/N 22/S 22/S 22/S 23/S 22/S
HDN 903/017 902/022 000/020 006/019 902/018 002/022 007/025
11/M 10/B 12/S 22/S 22/S 20/B 00/B
MLS 905/012 907/013 905/012 903/013 904/011 901/016 000/017
22/J 10/B 22/S 22/S 22/S 21/B 00/B
4BQ 904/015 903/020 003/020 005/020 002/017 004/018 007/024
21/M 10/B 12/S 22/S 22/S 21/B 00/B
BHK 905/010 906/013 901/011 000/012 903/010 904/014 003/015
22/J 10/B 22/S 22/S 22/S 20/B 00/U
SHR 909/013 905/024 002/025 006/027 006/023 006/025 011/030
21/M 10/B 12/S 22/S 22/S 21/B 00/B
&&
.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...WIND CHILL ADVISORY IN EFFECT UNTIL 9 AM MST THURSDAY FOR
ZONES 28>42-56>58-63>66.
WY...WIND CHILL ADVISORY IN EFFECT UNTIL 9 AM MST THURSDAY FOR
ZONE 99.
&&
$$
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