Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 290615
AFDBYZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
1115 PM MST FRI NOV 28 2014

.UPDATE...
STRONG PREFRONTAL DOWNSLOPE SW-W WINDS HAVE DEVELOPED ACROSS MUCH
OF SHERIDAN COUNTY FROM RANCHESTER TO SHERIDAN AND BIG HORN...WITH
A PEAK GUST OF 66 MPH AT THE SHERIDAN AIRPORT SO FAR. HAVE ISSUED
A HIGH WIND WARNING TO COVER THE EAST SLOPES OF THE BIGHORNS
THROUGH 12Z...BUT IN REALITY THE WINDS WILL END WITH THE COLD
FRONTAL PASSAGE WHICH IS WITHIN A COUPLE HOURS FROM OCCURRING.
ARCTIC FRONT IS MUCH FASTER THAN PREVIOUSLY THOUGHT SO HAVE
DROPPED FORECAST LOW TEMPS MANY DEGREES ACROSS THE CWA. IT IS
ALREADY 5 ABOVE AT JUDITH GAP AS OF 11 PM. JKL

&&

.SHORT TERM...VALID FOR SAT AND SUN...

ARCTIC FRONT WAS SEEN ENTERING EXTREME N MT THIS AFTERNOON AND
WAS THROUGH KHVR AS OF 20Z. THERE WAS A 40 DEGREE TEMPERATURE
DIFFERENCE ACROSS THIS BOUNDARY. THIS FRONT WILL BRING MUCH COLDER
WEATHER AND SNOW TO THE FORECAST AREA THROUGH EARLY SUN.

CHECKING MOUNTAIN WAVE SITUATION FOR TONIGHT SHOWED THAT THERE
WILL NOT BE A CRITICAL LAYER AND SURFACE LOOKED STABLE SO WILL NOT
ISSUE ANY ADDITIONAL WIND HIGHLIGHTS. WILL CONTINUE THE KLVM...NYE
AND BIG TIMBER ADVISORIES THROUGH NOON MST SAT.

FOR TONIGHT...WILL CONTINUE POPS OVER THE WESTERN MOUNTAINS AND
LEFT LOW EVENING POPS OVER THE E BASED ON RADAR TRENDS.
OTHERWISE...SOME JET SUPPORT WILL REMAIN OVER THE REGION THROUGH
SAT NIGHT DUE TO THE COUPLED JET ALOFT. WEAK SHORTWAVES WILL MOVE
ACROSS THE AREA IN ZONAL FLOW THROUGH SAT. A MUCH STRONGER
WAVE...SEEN IN WATER VAPOR ALONG THE BC COAST THIS AFTERNOON WILL
MOVE INTO THE AREA SAT NIGHT AND EXIT THE REGION SUN MORNING. THIS
WAVE WILL PUSH THE ARCTIC FRONT INTO THE AREA SAT MORNING. STRONG
FRONTOGENESIS WILL ACCOMPANY THE FRONT...ESPECIALLY OVER AND NEAR
THE FOOTHILLS. THE FRONTOGENESIS EXITS THE AREA AROUND 12Z SUN.
LOW-LEVEL NE UPSLOPE FLOW WILL ALSO ACCOMPANY THE
SYSTEM...CREATING ADDITIONAL LIFT.

TIME-HEIGHT CROSS SECTIONS DEPICTED A SEVERAL HOUR PERIOD OF
STRONG LIFT...INSTABILITY...AND GOOD DENDRITIC GROWTH OVER THE
AREA AS THE FRONT MOVES S. THE STRONGEST LIFT WILL BE FROM KBIL TO
KSHR W...WHERE SNOW AMOUNTS WILL BE 2 TO 5 INCHES...WITH THE
HIGHEST AMOUNTS OVER AND NEAR THE FOOTHILLS. FURTHER E...EXPECT 1
TO 2 INCHES. NOTE THAT W FLOW ALOFT WILL NOT FAVOR HIGH SNOW
AMOUNTS IN THE NE BIG HORNS. WEST-FACING SLOPES WILL BE MORE
FAVORED FOR BETTER ACCUMULATIONS IN THE BEARTOOTHS/ABSAROKAS...BUT
NOT EXPECTING A LONG ENOUGH EVENT FOR A WARNING THERE. PLAN ON
ISSUING SNOW ADVISORIES OVER THE LOW-ELEVATIONS FOR A COMBINATION
OF SNOW...AREAS OF BLOWING SNOW AND COLD WIND CHILLS. GUSTY N TO
NE WINDS ACCOMPANIED BY FALLING TEMPERATURES WILL CREATE LOW WIND
CHILLS INTO EARLY SUN.

SOME LINGERING VORTICITY WILL REMAIN OVER THE AREA SUN AND SUN
NIGHT...BUT THE AIRMASS WILL BE DRYING OUT. HAVE LOWERED POPS ON
SUN AND KEPT SUN NIGHT DRY.

TEMPERATURES WERE IN GOOD SHAPE...WITH HIGHS OCCURRING EARLY SAT
MORNING...THEN TEMPERATURES FALLING THROUGH THE DAY. TEMPERATURES
ON SUN WILL STAY IN THE TEENS AND SINGLE DIGITS. ARTHUR

.LONG TERM...VALID FOR MON...TUE...WED...THU...FRI...

MEDIUM RANGE MODELS IN GOOD AGREEMENT WITH SOME MINOR CONTINUITY
ISSUES SHOWING UP IN THE LONG RANGE MODELS.

MODELS ARE ALL IN GOOD AGREEMENT IN ERODING ARCTIC AIR OUT OF THE
REGION WITH A FAST ZONAL FLOW ALOFT SETTING UP MONDAY. THIS WILL
ALLOW TEMPERATURES TO MODERATE WITH A WARMUP TO NEAR SEASONAL
VALUES. VORTICITY MAXIMUM MOVING ACROSS SOUTHERN CANADA WILL BRING
AN INCREASING MID LEVEL WINDS ALONG WITH A DEEPENING LEE SIDE
TROUGH. GFS INDICATING 700 MB WIND SPEEDS OF 70 KTS BY LATE MONDAY
AFTERNOON THROUGH TUESDAY MORNING. HAVE INCREASED SURFACE WIND
SPEEDS TO SUB ADVISORY FOR THIS TIME PERIOD FOR THE GAP FLOW
AREAS. WEAK CYCLONIC FLOW OVER THE AREA TUESDAY NIGHT AND
WEDNESDAY WILL ALLOW A COLD FRONT TO BACK DOOR INTO OUR AREA. THIS
WILL BRING A SLIGHT CHANCE OF SNOW SHOWERS BUT SNOW ACCUMULATIONS
WILL BE LIGHT WITH AMOUNTS LESS THAN AN INCH. FAIRLY BENIGN
WEATHER PATTERN SETTING UP FOR THE REMAINDER OF THE WEEK AS THE
OVERALL FLOW ALOFT WILL REMAIN ZONAL. THIS WILL RESULT IN NEAR
SEASONAL TEMPERATURES AND OCCASIONAL MOUNTAIN SNOW SHOWERS.
RICHMOND

&&

.AVIATION...

STRONG WEST TO SOUTHWEST WINDS WILL CONTINUE ALONG THE FOOTHILLS
FROM LIVINGSTON TO NYE TO RED LODGE TO SHERIDAN. GUSTS TO 55KTS
CAN BE EXPECTED AT LIVINGSTON AND SHERIDAN THROUGH AROUND 10Z. A
STRONG COLD FRONT WILL BLAST THROUGH THE AREA AND DECREASE THE
WINDS IN THESE LOCATIONS AFTER 10Z. CEILINGS WILL LOWER AS THE
COLD FRONT MOVES THROUGH WITH MVFR CONDITIONS DEVELOPING. SNOW
WILL DEVELOP LATE THIS MORNING AND EARLY THIS AFTERNOON AND LOWER
CONDITIONS TO IFR. MOUNTAINS WILL BE OBSCURED. TWH

&&

.PRELIMINARY POINT TEMP/POPS...

    SAT     SUN     MON     TUE     WED     THU     FRI
-----------------------------------------------------------
BIL 010/012 903/013 003/031 022/033 018/034 022/041 027/041
    08/S    +0/B    01/B    22/J    11/B    21/B    11/B
LVM 032/037 902/016 005/033 026/036 021/037 028/042 028/041
    29/O    +0/B    01/B    22/W    12/J    22/W    11/B
HDN 013/015 902/014 901/032 018/034 015/034 019/041 022/042
    06/S    +1/B    01/B    22/J    11/B    21/B    11/B
MLS 015/016 905/010 902/027 016/028 011/031 015/036 020/037
    17/S    60/B    00/U    22/J    11/B    11/B    10/B
4BQ 018/025 000/013 000/032 018/033 015/036 019/040 021/040
    03/S    61/B    01/U    12/J    12/J    21/B    11/B
BHK 017/019 904/008 902/026 015/025 010/028 015/035 018/036
    14/S    50/B    00/U    12/J    11/B    11/B    10/B
SHR 019/024 000/013 000/034 020/035 017/035 021/043 023/042
    04/O    +2/S    00/B    22/J    12/J    21/B    11/B

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...WINTER WEATHER ADVISORY IN EFFECT FROM 7 AM SATURDAY TO 11 AM
      MST SUNDAY FOR ZONES 28-29-42-63.
     WINTER WEATHER ADVISORY IN EFFECT FROM NOON SATURDAY TO 11 AM
      MST SUNDAY FOR ZONES 30>41-56>58-64>66.
     WIND ADVISORY IN EFFECT UNTIL NOON MST SATURDAY FOR ZONES
      65-66.
WY...WINTER WEATHER ADVISORY IN EFFECT FROM NOON SATURDAY TO 11 AM
      MST SUNDAY FOR ZONE 99.
     HIGH WIND WARNING IN EFFECT UNTIL 5 AM MST SATURDAY FOR ZONE
      99.

&&

$$
WEATHER.GOV/BILLINGS


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