FXUS65 KBYZ 120047
AFDBYZ
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BILLINGS MT
547 PM MST FRI DEC 11 2009
.SHORT TERM...VALID FOR SAT AND SUN...
UPDATED FORECAST TO ISSUE A WIND ADVISORY FOR THE UPPER
YELLOWSTONE AND UPPER STILLWATER RIVER VALLEYS THROUGH SATURDAY
MORNING. WINDS IN LIVINGSTON AND NEAR NYE ARE VERY CLOSE TO
ADVISORY LEVELS ALREADY THIS EVENING. LATEST MODEL PROGS SHOW
PRESSURE GRADIENT WILL STRENGTHEN LATE TONIGHT...AND THE MODELS
ARE ALREADY UNDER DOING THE CURRENT GRADIENT. WARM ADVECTION IN
THE 850-700MB LAYER OVERNIGHT WILL STRENGTHEN THE INVERSION IN THE
RIVER VALLEYS OF THE NORTHERN BEARTOOTH MOUNTAINS. AS A RESULT
EXPECT TO SEE SOME STRENGTHENING OF WINDS OVERNIGHT INTO TOMORROW
MORNING. SOUTHWEST WINDS WILL BE 30 TO 45 MPH WITH OCCASIONAL
GUSTS OF 60 TO 65 MPH. WINDS HAVE BEEN STRONG FOR A FEW DAYS NOW
IN THESE AREAS SO DO NOT EXPECT BLOWING SNOW TO BE A MAJOR ISSUE
AND ONLY MENTIONED LOCAL IMPACTS ASSOCIATED WITH IT. SNOW DRIFTING
ACROSS ROADWAYS MAY LEAD TO SOME SLICK SPOTS. CHAMBERS
PREVIOUS DISCUSSION...MAJOR WEATHER CHANGE THIS WEEKEND AS A
MILDER SATURDAY WILL BE RUDELY REPLACED BY ANOTHER BLAST OF
ARCTIC AIR INTO MONTANA AND NORTH CENTRAL WYOMING. SURFACE TROUGH
LAYING ACROSS SOUTHEASTERN MONTANA WITH FLOW ALOFT CONTINUING TO
BACK IN RESPONSE TO AN UPPER LOW OVER NORTHERN CANADA ELONGATING
WESTWARD. RELATIVELY WARMER WEATHER TO CONTINUE TONIGHT AS MIXING
AND DOWNSLOPE FLOW KEEPS BREEZY WINDS OVER THE WESTERN
ZONES...AND EVEN SOUTHEASTERLY FLOW OVER THE EASTERN ZONES WILL
KEEP TEMPERATURES FROM FALLING TOO FAR. MOISTURE SPREADING INTO
SOUTHWEST MONTANA FROM A SYSTEM OVER CALIFORNIA WILL START
GENERATING INCREASED MOUNTAIN PRECIPITATION. SATURDAY THE SURFACE
TROUGH BEGINS TO SHIFT SOUTHWARD AS PRESSURE FALLS OCCUR OVER
WYOMING AND THIS WILL SHIFT THE WARMER AIR A BIT WESTWARD BUT
STILL WELL INTO THE 20S FOR MOST AREAS. PRECIPITATION CONTINUES
TO BE MAINLY OROGRAPHICALLY DRIVEN INTO THE MOUNTAINS AS THE
WESTERLY FLOW ALOFT WILL BE MAINLY DOWNSLOPISH FOR THE PLAINS.
SATURDAY NIGHT AN ARCTIC SURGE MOVES THROUGH NORTHERN MONTANA
HEADING TOWARDS THE AREA WITH SURFACE PRESSURE FALLS CONTINUING
OVER WYOMING. DOWNSLOPE WILL BEGIN TO LOOSE ITS INFLUENCE
SATURDAY NIGHT AND A FEW MORE SHOWERS WILL REACH THE PLAINS WITH
A CHANCE FOR THE NORTHERN ZONES TO FEEL THE INFLUENCE OF THE
ARCTIC FRONT BY EARLY SUNDAY MORNING. BY SUNDAY MORNING A WINTER
WEATHER EPISODE IS IN PLACE AS THE ARCTIC FRONT WILL SURGE
THROUGH THE AREA WHILE THE AIRMASS HAS BECOME FAIRLY MOIST.
MODELS PROGGING HIGHER THETA E VALUES ALONG AN AXIS TO THE LEE OF
THE BIG HORNS TO AROUND THE NORTH SIDE OF THE CRAZY MOUNTAINS.
WHILE NOT CONFIDENT WHERE SNOWFALL ACCUMULATIONS WILL BE
GREATEST...MODELS ARE HINTING AT BETTER BANDS OF PRECIPITATION
DEVELOPING...WITH SOME UPSLOPE AREAS BEING FAVORED AND OTHERS
FAVORED AS UPPER LEVEL SUPPORT EXISTS FROM WEAK WAVE CROSSING THE
AREA. MAIN THINKING THAT THIS SYSTEM WILL HAVE A CHANCE TO CAUSE
MORE DIFFICULTY THAN PREVIOUS ARCTIC STEM FROM THREE IDEAS...1.
ITS A SHALLOWER ARCTIC SO FAVORED SNOW GROWTH REGION WILL REMAIN
OVER THE AREA LONGER. 2. PRESSURE GRADIENT LINGERING OVER THE
AREA WILL CAUSE STRONGER WINDS TO PERSIST CAUSING BLOWING AND
DRIFTING AND DRIVING WIND CHILLS. 3. THE AIRMASS KEEPS DEEPER
MOISTURE OVER THE AREA SO PRECIPITATION SHOULD BE HEAVIER THAN
PREVIOUS ARCTIC. ONE IMPORTANT DIFFERENCE IS THAT ROAD
TEMPERATURES SHOULD BE BELOW FREEZING THROUGH THE EPISODE AND
SNOW SHOULD STAY SNOW AND NOT MELT INTO ICE. HAVE ISSUED A WINTER
STORM WATCH TO COVER THESE THREATS AND LATER SHIFTS WILL CLARIFY
THE THREATS FOR SPECIFIC AREAS AS DETAILS BECOME CLEARER. DO
THINK THE DRAMATIC CHANGE FROM A PLEASANT SATURDAY TO A HAZARDOUS
WEATHER SUNDAY IS WORTH HIGHLIGHTING GIVEN THAT TRAVEL IS
BEGINNING AN UPSWING IN ADVANCE OF THE HOLIDAYS. SUNDAY NIGHT THE
WINTRY WEATHER WILL CONTINUE AS TEMPERATURES PLUNGE BELOW ZERO.
BORSUM
.LONG TERM...VALID FOR MON...TUE...WED...THU...FRI...
MODELS WERE VERY CONSISTENT ON HAVING MONDAY BEING THE COLDEST
DAY WITH THE NEXT ARCTIC INVASION. THE MODELS WERE SETTING UP A
BAROCLINIC ZONE OVER NORTHERN LOCATIONS. KEPT THE IDEA OF LIKELY
POPS FOR MONDAY. RAISED POPS SOME FOR MONDAY NIGHT AS UPSLOPE
FLOW AND MOISTURE OVER RUNNING THE ARCTIC BOUNDARY CONTINUES. THE
ARCTIC LIFTS OUT VERY QUICKLY ON TUESDAY. TUESDAY WILL BE A VERY
TRICKY DAY FOR TEMPERATURES AS FRESH SNOW COVER WILL BE
COUNTERACTED BY STRONG WARM AIR ADVECTION. SHOULD BE ABLE TO
REACH INTO THE 20S OVER WESTERN AND CENTRAL ZONES...AND MAY EVEN
BE A BIT WARMER. THE EAST WILL BE SLOWER TO REBOUND WITH HIGHS
HELD IN THE TEENS. RIDGING TAKES OVER FOR WEDNESDAY THROUGH
SATURDAY AND THIS WILL PROVIDE A PERIOD OF MILD AND MAINLY DRY
WEATHER. HUMPHREY
&&
.AVIATION...
STRONG SOUTHWEST WINDS AT LIVINGSTON WILL GUST TO 40KTS EARLY
THIS EVENING BEFORE DECREASING BY LATE EVENING. VFR FLYING
WEATHER CAN BE EXPECTED TONIGHT AND AGAIN SATURDAY. SOME MID
LEVEL MOISTURE WILL WORK INTO THE MOUNTAINS THROUGH THE PERIOD
AND CREATE SCATTERED SNOW SHOWERS. MOUNTAIN TOPS WILL
OCCASIONALLY BE OBSCURED IN THE SNOW SHOWERS. HUMPHREY
&&
.PRELIMINARY POINT TEMP/POPS...
SAT SUN MON TUE WED THU FRI
-----------------------------------------------------------
BIL 014/031 012/014 905/000 907/024 020/035 026/042 027/044
01/E 37/S 66/S 31/B 11/B 11/N 11/B
LVM 017/034 017/022 002/010 007/031 024/037 027/042 031/042
02/J 37/S 66/S 31/E 11/N 11/N 11/N
HDN 007/029 006/016 905/000 908/022 009/035 014/040 017/045
01/B 26/S 66/S 31/B 11/B 11/B 11/B
MLS 001/026 902/007 910/903 916/015 005/028 012/033 016/041
11/E 35/S 53/S 21/B 11/B 11/B 11/B
4BQ 005/029 003/010 906/000 916/018 006/032 015/037 016/045
01/B 24/S 65/S 21/B 11/B 11/B 11/B
BHK 000/025 902/008 910/903 920/013 003/026 010/030 012/039
12/J 24/S 43/S 11/B 11/B 11/B 11/B
SHR 009/034 013/020 901/008 908/025 010/037 015/040 016/044
01/B 24/S 66/S 31/B 11/B 11/B 11/B
&&
.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...WINTER STORM WATCH IN EFFECT FROM LATE SATURDAY NIGHT THROUGH
MONDAY AFTERNOON FOR ZONES 28>42-56>58-63>66.
WIND ADVISORY IN EFFECT UNTIL NOON MST SATURDAY FOR ZONES
65-66.
WY...WINTER STORM WATCH IN EFFECT FROM LATE SATURDAY NIGHT THROUGH
MONDAY AFTERNOON FOR ZONE 99.
&&
$$
WEATHER.GOV/BILLINGS
