FXUS65 KBYZ 111351
AFDBYZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
651 AM MST FRI DEC 11 2009
.SHORT TERM...VALID FOR TDY AND SAT...
PRESSURE GRADIENT TIGHTENING ACROSS OUR WESTERN SECTIONS AS
ANTICIPATED. LOOKS LIKE IT SHOULD BE ENOUGH TO HIT CRITERIA IN GAP
FLOW AREAS. HAVE ISSUED A WIND ADVISORY FOR THESE AREAS THROUGH
18Z. BT
PREVIOUS DISCUSSION...
TEMPORARY WARM UP EXPECTED THE NEXT COUPLE OF DAYS. FORECAST
PROBLEMS FOR THIS PACKAGE INCLUDE WINDS IN THE GAP FLOW AREAS OF
LIVINGSTON AND THE BEARTOOTH FOOTHILLS...AND POSSIBLE INFILTRATION
OF COOLER AIR LATE SATURDAY/SATURDAY NIGHT BEFORE MAIN ARCTIC
SURGE OCCURS SUNDAY.
AT THIS HOUR LIVINGSTON WINDS ARE SUSTAINED JUST A LITTLE OVER 30
MPH AND THE MINE AT NYE 25 TO 30 MPH...BUT GUSTS RATHER AVERAGE.
SOME STRENGTHENING OF THE PRESSURE GRADIENT STILL POSSIBLE THROUGH
15Z ACCORDING TO CROSS SECTIONS AND SURFACE PRESSURE PROGS. GFS
THOUGH IS NOT THAT IMPRESSIVE WITH DOWNWARD FORCING ALONG FRONT
RANGE. PROGS OF THE VERTICAL PROFILE SUGGEST WINDS WILL BACK OFF
SOME BY 18Z. WE MAY STILL HIT ADVISORY LEVEL SPEEDS IN THE
LIVINGSTON AREA BRIEFLY AN HOUR OR TWO AFTER SUNRISE...BUT
PROBABILITY OF THIS SEEMS A BIT TO LOW FOR HIGHLIGHT AT THIS TIME.
WILL KEEP FORECASTS WINDS JUST UNDER HIGHLIGHT CRITERIA.
FLOW ALOFT TODAY WILL BECOME A BIT MORE ZONAL WITH LESS ENERGY
INVOLVED. THEREFORE HAVE REMOVED ANY REMAINING POPS ACROSS THE
AREA. A MODEST AND GRADUAL ADVECTION OF WARMER AIR EXPECTED TO
OCCUR IN LOW TO MID LEVELS AS FLOW BACKS AND THIS SHOULD CONTINUE
THROUGH TONIGHT AND INTO SATURDAY. HAVE TRENDED TEMPS A LITTLE
WARMER INTO THE EAST...ESPECIALLY SATURDAY. CONFIDENCE GOOD THAT
WE CAN EXPECT WARMER TEMPS THAN THE LAST FEW DAYS...AND IF WE
MANAGE DECENT MIXING SATURDAY WE COULD BREAK ABOVE THE FREEZING
MARK IN MANY AREAS. CLOUD COVER WILL BE A LIMITING FACTOR AND A
LITTLE WARY OF SOME SHALLOW COLD AIR SNEAKING INTO THE NORTHERN
ZONES LATE SATURDAY OR SATURDAY NIGHT BEFORE THE MAIN SURGE SUNDAY
AS WE ANTICIPATE PRESSURE FALLS TO OUR SOUTHWEST WITH TROUGH
MOVING THROUGH GREAT BASIN. HAVE RAISED POPS A BIT OVER THE
NORTHERN ZONES SATURDAY NIGHT AND KEPT OVERNIGHT LOWS BELOW
GUIDANCE OVER NORTHERN SECTIONS TO ACCOUNT FOR THIS POSSIBILITY.
BT
.LONG TERM...VALID FOR SUN...MON...TUE...WED...THU...
MAIN FORECAST ISSUE IN THE EXTENDED CONTINUES TO BE SURGE OF
ARCTIC AIR WHICH SEEMS TO BE A CERTAINTY NOW IN THE SUN/MON TIME
FRAME. MODELS COMING TOGETHER NOW BUT STILL DEPICT SOME SLIGHT
TIMING ISSUES. CONSENSUS IS FOR STRONG COLD ADVECTION BEHIND
ARCTIC FRONT TO KICK IN NO LATER THAN EARLY SUNDAY. AS FOR
POPS...BEST FORCING/OVERRUNNING AND POTENTIAL FOR SNOWFALL APPEARS
TO BE LATE SUNDAY INTO MONDAY AS UPPER WAVE SWINGS THROUGH THE
AREA. THIS ARCTIC WILL BE MUCH SHALLOWER THAN THE LAST EPISODE...
AND FORECAST SOUNDINGS SHOW AN ELEVATED DENDRITIC LAYER SHOULD BE
PRESENT DURING TIME OF PCPN. THUS WOULD EXPECT MANY PLACES TO GET
A QUICK INCH OR TWO OR SNOWFALL...PERHAPS A BIT MORE IN UPSLOPE
AREAS...SOMEWHAT TYPICAL WITH AN ARCTIC. HAVE RAISED POPS TO
LIKELY ACROSS A LARGE PORTION OF THE FORECAST AREA SUNDAY NIGHT
AND MONDAY. PCPN SHOULD TAPER OFF MONDAY AFTERNOON OR EVENING AS
DESCENT WORKS IN FROM THE NW. AS FOR TEMPS THIS IS SHAPING UP TO
BE AN EVEN COLDER AIRMASS THAN THE ONE THAT JUST EXITED. COLD AIR
CURRENTLY ASSOCIATED WITH DEEP UPPER LOW IN THE NORTHWEST
TERRITORIES IS ON THE ORDER OF -30F TO -40F...AND THIS IS THE
AIRMASS WE WILL BE TAPPING INTO...ALBEIT BRIEFLY. MAIN ISSUE WITH
TEMPERATURE FORECASTS IS TIMING. SUNDAY HIGHS SHOULD BE EARLY IN
THE DAY...WITH TEMPS FALLING THROUGHOUT...AND BELOW ZERO READINGS
A GOOD BET BY SUNDAY NIGHT IF NOT SOONER. MONDAY SHOULD BE COLDEST
DAY WITH HIGHS LIKELY BELOW ZERO ACROSS OUR CENTRAL AND EAST...AND
THIS MAY EVEN BE TOO OPTIMISTIC IF GFS FORECAST OF -26C AT 850MB
HOLDS TRUE. OTHER MODELS ARE A BIT WARMER THAN THIS. WITH THE
INCREASED CONFIDENCE HAVE LOWERED TEMPS EACH PERIOD SUNDAY THROUGH
MONDAY NIGHT. MONDAY NIGHT COULD BE PARTICULARLY COLD IN OUR EAST
AS SFC RIDGE SETTLES IN...AND AT THIS POINT WOULD EXPECT LOWS NEAR
20 BELOW AT LEAST FROM MILES CITY TO BAKER AND EKALAKA. GUSTY NW
WINDS ON MONDAY WILL LIKELY LEAD TO BITTER WIND CHILLS AS WELL.
WIND CHILLS COULD DROP TO NEAR 40 BELOW ON MONDAY. BRRR.
THIS ARCTIC WILL BE SHORT-LIVED AS RIDGING AND INCREASED DOWNSLOPE
FLOW BEGIN ON TUESDAY AND WILL LEAD TO A RAPID WARM UP. WEDNESDAY
AND THURSDAY SHOULD BE MOSTLY DRY AND WARMER WITH HIGHS ABOVE
FREEZING AND POSSIBLY INTO THE 40S. MODELS IN GOOD AGREEMENT HERE.
WILL PROBABLY HAVE GAP WIND CONCERNS THESE DAYS WITH THE FLOW
GENERALLY WESTERLY. THOUGH THIS IS SEVERAL DAYS OFF YET HAVE
PAINTED FAIRLY STRONG WINDS AT LIVINGSTON AND NYE ACCORDINGLY.
JKL
&&
.AVIATION...
MAIN AVIATION HAZARD CONTINUES TO BE WIND ALONG THE EASTERN SLOPES
OF THE CRAZY AND BEARTOOTH/ABSAROKA MOUNTAINS. LOOK FOR GUSTS OF
35-45 KTS AT KLVM...STRONGEST BETWEEN 12-18Z THIS MORNING...AND
20-30 KTS AT K3HT. OTHERWISE VFR WILL PREVAIL OVER THE NEXT 24
HOURS UNDER SCATTERED TO BROKEN MID AND HIGH CLOUD. THERE IS A
SLIGHT CHANCE OF SNOW OVER THE BEARTOOTH/ABSAROKAS LATE TONIGHT...
AND OBSCURATIONS ARE POSSIBLE ONCE THE SNOW DEVELOPS. JKL
&&
.PRELIMINARY POINT TEMP/POPS...
TDY SAT SUN MON TUE WED THU
-------------------------------------------------------
BIL 026 012/030 012/019 903/000 907/024 020/035 026/042
0/N 01/E 25/S 66/S 11/B 11/B 11/N
LVM 028 015/034 018/024 004/010 007/031 024/037 027/042
0/N 02/J 25/S 66/S 21/E 11/N 11/N
HDN 025 005/028 009/020 903/000 908/022 009/035 014/040
0/B 01/B 24/S 65/S 11/B 11/B 11/B
MLS 021 901/023 002/015 908/903 916/015 005/028 012/033
0/B 11/E 33/S 53/S 11/B 11/B 11/B
4BQ 025 003/027 006/020 904/000 916/018 006/032 015/037
0/B 01/B 22/S 55/S 11/B 11/B 11/B
BHK 019 902/022 001/013 908/903 920/013 003/026 010/030
0/B 12/J 22/S 43/S 11/B 11/B 11/B
SHR 026 007/033 012/028 001/008 908/025 010/037 015/040
0/B 01/B 23/S 66/S 21/B 11/B 11/B
&&
.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...WIND ADVISORY IN EFFECT UNTIL 11 AM MST THIS MORNING FOR
ZONES 65-66.
WY...NONE.
&&
$$
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