FXUS65 KBYZ 301650
AFDBYZ
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BILLINGS MT
950 AM MST MON NOV 30 2009
.SHORT TERM...VALID FOR TDY AND TUE...
ISSUED A WIND ADVISORY FOR THE UPPER YELLOWSTONE AND UPPER
STILLWATER RIVER VALLEYS THROUGH LATE TONIGHT. PRESSURE GRADIENT
IS ABOUT 16 MB ACROSS THE BEARTOOTH MOUNTAINS AND AN AREA OF
PRESSURE FALLS IS TRACKING SOUTHEAST OUT OF NORTHWEST MONTANA THIS
MORNING IN ADVANCE OF THE NEXT UPPER SYSTEM EXPECTED TO MOVE
THROUGH THE AREA LATE TONIGHT. THIS SHOULD KEEP THE PRESSURE
GRADIENT TIGHT THROUGH LATE TONIGHT BEFORE A COLD FRONT MOVES
THROUGH EARLY TUESDAY MORNING ALLOWING WINDS TO RELAX. STILL SOME
CONCERN THAT WINDS LATE IN THE DAY INTO THIS EVENING WILL REACH
WARNING LEVELS FROM BIG TIMBER TO HARLOWTON. CROSS SECTIONS NOT
SUPER IMPRESSIVE AS WINDS JUST OFF THE SURFACE ARE IN THE 40 KT
RANGE AND WOULD PREFER 50 KTS OR BETTER. HOWEVER WITH PRESSURE
FALLS CONTINUING TODAY AND THE FRONTAL PASSAGE OVERNIGHT MAY BE
ENOUGH IMPETUS TO PUSH WINDS OVER THE THRESHOLD IN THESE AREAS.
WILL EVALUATE THE POTENTIAL FURTHER FOR THE AFTERNOON
PACKAGE...BUT CURRENTLY HAVE WINDS UP TO JUST UNDER WARNING LEVELS
FOR THIS AREA.
OTHER ADJUSTMENTS...TWEAKED CLOUD COVER DOWNWARD OVER WESTERN AND
CENTRAL AREAS WITH AN AREA OF SUBSIDENCE OVER THESE
AREAS...SPREADING EAST THIS AFTERNOON. CLOUD COVER WILL INCREASE
FROM NORTHWEST TO SOUTHEAST TONIGHT AS THE NEXT SYSTEM MOVES IN.
REST OF THE FORECAST ON TRACK. TEMPERATURES LOOK TO BE IN THE LOW
TO MID 50S MOST LOCATIONS THIS AFTERNOON WITH BREEZY WESTERLY
WINDS CENTRAL AND EAST. CHAMBERS
.LONG TERM...VALID FOR WED...THU...FRI...SAT...SUN...
EXTENDED FORECAST HAS A SOLID POTENTIAL FOR COLDER WEATHER BY THE
WEEKEND BUT THERE DOES NOT APPEAR TO BE A CLEAR PATH TO THIS
TRANSITION. MODELS SHOW DRY NORTHERLY FLOW IN PLACE WITH COOL
SURFACE HIGH PRESSURE IN PLACE ON WEDNESDAY WITH AN UPSTREAM RIDGE
OVER THE PACIFIC NORTHWEST. MOISTURE BEGINS STREAMING OVER THIS
RIDGE INTO THE WESTERN ZONES AND HAVE MOUNTAIN SHOWERS WITH DRY
PLAINS. ECMWF AND GFS DISAGREE ON THE PATTERN FOR THURSDAY AS THE
GFS PUSHES A WEAKENING RIDGE AXIS INTO THE AREA WHILE THE ECMWF
KEEPS A STRONGER CLOSED SYSTEM OVER THE NORTHEAST PACIFIC. GFS
SHOWS DOWNSLOPNIG AND WARMER TEMPERATURES WHILE THE ECMWF WOULD
KEEP THE COLDER TEMPERATURES. STILL MAINLY DRY EXCEPT FOR MOUNTAIN
SHOWER ACTIVITY AND HAVE TEMPERATURES WARMER THAN WEDNESDAY. FRIDAY
REALLY BECOMES DIFFICULT AS THE GFS PUSHES THE RIDGE EAST OF THE
AREA AND BEGINS DEVELOPING AN UPPER LEVEL WAVE OVER NORTHWEST
MONTANA WHILE THE ECMWF CONTINUES TO LAG THE PACIFIC SYSTEM
FURTHER BEHIND AND NUDGES THE RIDGE INTO THE AREA. HAVE STUCK WITH
A GFS SOLUTION AND KEPT FRIDAY A FAIRLY WELL MIXED DAY AND
INCREASED POPS ESPECIALLY FOR THE SOUTHWESTERN ZONES...AND BOOSTED
WINDS TO REFLECT DOWNSLOPE. SUSPECT THAT THE BEST SOLUTION WILL BE
BETWEEN THE TWO EXTENDED MODELS WITH THE WAVE NOT PROGRESSING INTO
MONTANA QUITE AS QUICKLY AND SUPPORTING A SECOND DAY OF DOWNSLOPE
WITH WARMER MINIMUMS SUPPORTING HIGHER TEMPERATURES. FOLLOWING
THIS BLENDED SOLUTIONS...AREA SHOULD SEE A FIRST SURGE OF COOLER
AIR INTO THE AREA ON SATURDAY WITH POTENTIAL FOR PRECIP ALONG AND
BEHIND THE FRONT DUE TO UPSLOPE BUT MAIN UPPER LEVEL DYNAMICS
SOUTH OF THE AREA. SUNDAY AND MONDAY ARE CLEARLY COLDER WITH 850
MB TEMPERATURES PROGGED TO BE -10C OR LESS ON BOTH MODELS AND HAVE
REDUCED TEMPERATURES ACCORDINGLY. DOES NOT LOOK TO BE A LOT OF
SNOW POTENTIAL EXCEPT FOR SOME UPSLOPE AS REAL ACTION LOOKS TO BE
OVER THE NORTHERN GREAT BASIN. THERE IS COLD AIR IN PLACE OVER
ALASKA AND EARLY DECEMBER IS A TYPICAL TIME OF YEAR FOR A SHOT OF
THIS AIRMASS TO REACH MONTANA. MAIN MESSAGE IS THAT WHILE
THURSDAY AND FRIDAY WEATHER AND TEMPERATURES ARE NOT CLEAR CUT...A
DRAMATIC TURN TO MUCH COLDER IS EXPECTED THIS WEEKEND. BORSUM
&&
.AVIATION...
EXPECTING WINDS TO REMAIN SOUTHWESTERLY INTO THIS EVENING...UNTIL
A COLD FRONTAL PASSAGE OVERNIGHT SHIFTS WINDS SLIGHTLY MORE TO THE
NORTH AND WEST. WIND SPEEDS SHOULD DECREASE AFTER THE FRONTAL
PASSAGE...HOWEVER...THERE IS A CHANCE FOR SOME MOUNTAIN SNOW
SHOWERS NEAR KLVM MONDAY NIGHT...WHICH COULD PRODUCE VISIBILITY
PROBLEMS AND MVFR CONDITIONS. SINGER
&&
.PRELIMINARY POINT TEMP/POPS...
TDY TUE WED THU FRI SAT SUN
-------------------------------------------------------
BIL 053 035/035 015/027 018/035 020/039 020/032 020/022
0/N 04/S 11/B 01/B 11/B 11/B 11/B
LVM 052 034/034 011/025 008/033 011/037 017/030 013/019
0/N 26/S 21/B 11/N 11/B 12/J 22/J
HDN 057 034/034 014/029 017/037 018/041 019/035 018/024
0/U 03/S 21/B 01/B 11/B 11/B 11/B
MLS 054 030/030 015/029 014/034 016/038 018/032 017/021
0/U 02/S 21/B 11/B 11/B 11/B 11/B
4BQ 057 031/031 014/028 013/031 015/038 017/032 016/028
0/U 02/S 21/B 11/B 11/B 11/B 11/B
BHK 051 028/034 015/027 010/030 012/034 012/030 012/021
0/B 02/S 21/B 11/B 11/B 11/B 11/B
SHR 055 028/028 012/027 014/035 018/039 019/032 018/027
0/U 07/S 21/B 11/B 11/B 22/J 22/J
&&
.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...WIND ADVISORY IN EFFECT UNTIL 5 AM MST TUESDAY FOR ZONES
65-66.
WY...NONE.
&&
$$
WEATHER.GOV/BILLINGS
