FXUS65 KBYZ 031019
AFDBYZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
319 AM MST THU DEC 3 2009
.SHORT TERM...VALID FOR TDY AND FRI...
LIGHT SNOW CONTINUING OVER EASTERN MONTANA AND PORTIONS OF CENTRAL
MONTANA AS NORTHERLY FLOW ALOFT REMAINS CYCLONIC. UPPER LEVEL LOW
OVER THE DAKOTAS IS SHIFTING EASTWARD WHILE A RIDGE OVER THE
PACIFIC MOVES EASTWARD. THIS BRINGS DRY AIR INTO THE WESTERN ZONES
TODAY AS THE MOISTURE STILL CONTINUES TO STREAM ACROSS THE EAST.
THIS WILL ALLOW THE LIGHT SNOW TO CONTINUE BUT AS SURFACE HIGH
OVER CENTRAL MONTANA DIGS SOUTHWARD THIS ALLOWS THE LOW LEVEL FLOW
TO BACK A BIT AND SHOULD START SHIFTING SOME DRIER AIR INTO THE
EASTERN ZONES. KEPT TREND OF LOWER POPS FOR THE DAYTIME PERIOD
TODAY SINCE CLOUD TOPS ARE GENERALLY WARMING AND SNOWFALL BY
SUNRISE COULD BE MORE LIKE FLURRIES. TEMPERATURES WILL BE COLD AS
MIXING SHOULD BE LIMITED AND A BIT MORE SNOW COVER OVER THE AREA
WILL LIMIT ANY IMPACTS OF INSOLATION. TONIGHT THE WESTERN RIDGE
BEGINS TO BREAKDOWN AND POSITIVELY TILT INTO THE AREA WHILE
LEESIDE TROFFING BEGINS TO DEVELOP ALONG THE CANADIAN ROCKIES.
THIS WILL ALLOW DOWNSLOPE WINDS TO DEVELOP OVER THE WESTERN ZONES
AND BRING WARMER TEMPERATURES. AIRMASS DOES DRY OUT OVERNIGHT AND
HAVE NO PRECIP MENTIONED TONIGHT OR FRIDAY. FORECAST PROBLEM
BECOMES HOW STRONG TO MAKE GAP FLOW WINDS...ESPECIALLY FRIDAY
MORNING AS THE LEESIDE TROF DIGS A BIT DEEPER INTO NORTH CENTRAL
MONTANA. CURRENTLY HAVE WINDS IN THE GAP FLOW AREAS AT JUST BELOW
WIND ADVISORY CRITERIA WHICH LOOKS GOOD AND WILL LET DAY SHIFT
DECIDE IF IT NEEDS TO BE UPGRADED. WARMING TEMPERATURES ACROSS THE
AREA UP 10 DEGREES ON FRIDAY LOOKS REASONABLE AS MODELS ARE
PROGGING SOME WARMING AT 700MB TO BE AVAILABLE TO MIX DOWN. UPPER
LEVEL WAVE DIGGING TOWARDS THE AREA ON FRIDAY NIGHT SPREADS SOME
INCREASING MOISTURE INTO SOUTHWEST MONTANA...BUT SHOULD BE
COMPETING WITH DRY AIR OVER THE PLAINS. THIS SHOULD ALLOW SOME
MOUNTAIN SNOW SHOWERS TO DEVELOP BUT PLAINS WILL HAVE TO WAIT
UNTIL SATURDAY TO SEE SNOW SHOWER ACTIVITY. TEMPERATURES WILL BE
MILD FRIDAY NIGHT...AND PROBABLY THE WARMEST LOW TEMPERATURES WE
WILL SEE FOR A WEEK. BORSUM
.LONG TERM...VALID FOR SAT...SUN...MON...TUE...WED...
DID MAKE SOME CHANGES TO THE EXTENDED FORECAST. THE CHANGES
INVOLVED BEING MORE AGGRESSIVE ON COLD AND THE CHANCE OF SNOW.
THE NEXT ARCTIC SURGE...WHICH WILL BE THE BIGGEST OF THE SEASON
SO FAR...WILL INVADE SATURDAY AFTERNOON. THE MAIN SURGE OF COLD
AIR WILL BE SATURDAY NIGHT AND SUNDAY. 850MB TEMPERATURES OF -22C
GET INTO MONTANA WITH AS COLD AS -20C MOVING INTO THE FORECAST
AREA. WITH FULL SUNSHINE THAT WOULD PROVIDE A HIGH IN THE UPPER
SINGLE DIGITS. THIS AIR WILL COME DOWN WITH CLOUDS AND LIGHT
SNOW...SO WILL GO WITH MID SINGLE DIGITS FOR HIGHS BOTH SUNDAY
AND MONDAY. THE COLDEST DAY SHOULD BE MONDAY. UPSLOPE FLOW SHOULD
PROVIDE LIGHT SNOW BEGINNING SATURDAY AND CONTINUING THROUGH
MONDAY NIGHT. THE UPSLOPE WEAKENS SUNDAY NIGHT...SO WILL TAPER
BACK POPS THEN. DYNAMIC FORCING WAS FAIRLY WEAK SO AM NOT
EXPECTING A HUGE SNOW EVENT. THE AIRMASS SHOULD BE COLD ENOUGH TO
LIMIT THE FLAKE SIZE TOO BUT SHOULD STILL GET A COUPLE OF INCHES
OF NEW SNOW SUNDAY THROUGH MONDAY. SATURDAY HAS THE BEST CHANCE
OF ACCUMULATING SNOW TO A FEW INCHES WITH STRONG Q VECTOR FORCING
OVER THE STATE. WILL BUMP POPS UP FOR ALL PERIODS SATURDAY
THROUGH MONDAY NIGHT. VERY SLOW MODERATION IS EXPECTING TUESDAY
AND WEDNESDAY WITH NORTHERLY FLOW GRADUALLY BACKING. HUMPHREY
&&
.AVIATION...
OCCASIONAL MVFR TO IFR CONDITIONS CAN BE EXPECTED TODAY WITH LOW
CLOUDS AND LIGHT SNOW. CONDITIONS WILL GRADUALLY IMPROVE THIS
AFTERNOON. THE MOUNTAINS WILL BE FREQUENTLY OBSCURED THROUGH THE
DAY. SOUTHWEST WINDS WILL INCREASE AT KVLM LATE TONIGHT TOWARD
TOWARD FRIDAY MORNING WITH GUSTS TO 50 MPH.HUMPHREY
&&
.PRELIMINARY POINT TEMP/POPS...
TDY FRI SAT SUN MON TUE WED
-------------------------------------------------------
BIL 022 009/034 016/023 005/006 904/005 901/013 006/020
1/M 00/N 15/S 54/S 32/S 22/S 21/B
LVM 022 006/031 009/021 905/006 912/004 909/016 005/025
0/U 00/N 25/S 54/S 32/S 22/S 22/S
HDN 025 003/035 013/027 004/011 901/012 906/018 005/024
1/M 00/B 04/S 44/S 32/S 22/S 21/B
MLS 022 004/032 012/024 002/012 903/009 905/012 901/018
1/M 00/U 12/S 22/S 21/B 22/S 21/B
4BQ 020 002/032 012/028 004/013 000/013 902/020 004/023
2/J 00/B 12/S 23/S 22/S 22/S 21/B
BHK 018 901/027 010/024 002/014 901/014 901/015 002/020
4/J 00/B 11/B 22/S 21/E 22/S 21/B
SHR 022 901/036 013/027 002/011 904/011 906/017 000/023
2/J 00/B 03/S 44/S 32/S 22/S 22/S
&&
.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...NONE.
WY...NONE.
&&
$$
WEATHER.GOV/BILLINGS
