Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 270327
AFDBYZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
827 PM MST FRI DEC 26 2014

.UPDATE...
MADE A FEW ADJUSTMENTS TO TONIGHTS FORECAST BASED ON RADAR AND
SATELLITE TRENDS. WEAK SHORT WAVE MOVING ACROSS THE REGION TONIGHT
BUT IS ONLY BRINGING SOME MID TO HIGH LEVEL CLOUDS TO THE AREA.
RADAR NOT PICKING UP ANY RETURNS AND IR SATELLITE SHOWING WAVE HAS
JUST ABOUT CLEARED THE AREA. HAVE REMOVED POPS FOR THIS EVENING AS
THIS SYSTEM CONTINUES TO WEAKEN AS IT MOVES SOUTHEAST ACROSS THE
AREA. LOWERED TEMPS A FEW DEGREES OVER OUR FAR EASTERN ZONES
TONIGHT AS LOWS ARE NEAR FORECASTED VALUES. PRESSURE FALLS
OCCURRING EAST OF THE DIVIDE THIS EVENING AS MORE ENERGY ALOFT
MOVES INTO MONTANA. THIS WILL BRING GUSTY WINDS TO OUR GAP FLOW
AREAS OF LIVINGSTON AND NEAR NYE BY SUNRISE. WINDS STILL LOOK
TO STAY BELOW ADVISORY CRITERIA BUT AN OCCASIONAL GUSTS TO 50 MPH
LOOKS REASONABLE. RICHMOND

&&

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

WEAK SHORTWAVE TROUGH AXIS WAS WORKING INTO THE FORECAST AREA
THIS AFTERNOON. THIS ENERGY WAS GENERATING A FEW LIGHT SNOW
SHOWERS OVER SOUTH CENTRAL ZONES. MAIN FORCING WILL WORK INTO THE
EASTERN HALF OF THE AREA LATE THIS AFTERNOON AND THIS EVENING...SO
LINED UP POPS WITH THAT THINKING. LOWERING MID LEVEL HEIGHTS OVER
BRITISH COLUMBIA WILL LEAD TO A TIGHTENING SURFACE PRESSURE
GRADIENT LATE TONIGHT ALONG THE EAST SLOPES. THIS WILL CAUSE WINDS
TO INCREASE AT LIVINGSTON AND NYE...BUT GRADIENT DOES NOT LOOK
TIGHT ENOUGH TO SUPPORT ADVISORY LEVELS WINDS. SATURDAY SHOULD BE
A LITTLE WARMER DAY WITH LOW LEVEL DOWNSLOPE INCREASING.

STRONG ENERGY WILL DROP INTO THE GREAT BASIN LATE SATURDAY
NIGHT AND SUNDAY. THIS WILL OPEN THE DOOR FOR AN ARCTIC BOUNDARY
TO SLIDE INTO THE AREA. 850MB TEMPERATURES FALL TO AROUND -15C
SUNDAY AFTERNOON FOR FALLING TEMPERATURES THROUGH THE DAY. HIGHS
WILL BE EARLY IN THE DAY. MODEST QG FORCING DUE TO FRONTOGENESIS
WILL PRODUCE SNOWFALL AFTER THE FRONT MOVES. THE SNOW WILL START
OVER THE WEST LATE SATURDAY NIGHT WITH SOME JET INDUCED
ASCENT...BUT SPREAD EAST THROUGH THE DAY SUNDAY AND LINGER INTO
EARLY. THE ECMWF WAS SLOWER WITH TIMING OF STRONGEST LIFT...AS IT
HOLDS IT BACK UNTIL LATE SUNDAY AFTERNOO AND SUNDAY EVENING. THE
GFS PUTS THE STRONGEST LIFT SUNDAY AFTERNOON WITH WEAKENING ASCENT
SUNDAY NIGHT.

OVERALL...LOOKS LIKE A LONGER DURATION SNOW EVENT WITH LESS WATER
AVAILABLE FOR QPF. THAT BEING SAID...THE DENDRITE GROWTH ZONE
LOOKS TO BE IN THE BEST TIME OF FORCING SUNDAY AFTERNOON...SO SNOW
COULD BE BRIEFLY HEAVY SUNDAY AFTERNOON AND POTENTIALLY SUNDAY
EVENING. SNOW RATIOS WILL BE HIGHER WITH THIS EVENT...WITH A MUCH
COLDER ATMOSPHERE. LOOKS TO BE MAINLY AN ADVISORY TYPE OF EVENT AT
THE MOMENT WITH GENERALLY 3-6 INCHES EXPECTED OVER SOUTH CENTRAL
MONTANA AND 1-3 INCHES OVER SOUTHEAST MONTANA. THE BEARTOOTH AND
RED LODGE FOOTHILLS ARE AT RISK TO RECEIVE HIGHS SNOW AMOUNTS WITH
STRONG LOW LEVEL UPSLOPE SLOW...WHICH LOOKS TO BE 4-8 INCHES
THROUGH EARLY MONDAY. THE NORTH AND NORTHEAST FACING SLOPES OF THE
MOUNTAINS WILL FARE BETTER IN SNOW ACCUMULATION COMPARED TO WEST
FACING SLOPES...BUT DOES NOT LOOK HEAVY ENOUGH FOR A WARNING AT
THE MOMENT.

GIVEN THE LACK OF STRONG UPPER LEVEL FORCING...WILL NOT ISSUE A
WINTER STORM WATCH AT THIS TIME. THE MOUNTAINS AND FOOTHILLS COULD
APPROACH WARNING AMOUNTS...BUT SHOULD BE A LONGER DURATION EVENT
PROVIDING THOSE TOTALS. WILL LIKELY NEED TO ISSUE ADVISORIES IN
THE NEAR FUTURE IF THE MODELS CONSISTENCY TO STAY CONSISTENT. TWH

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

MADE A FEW MINOR CHANGES TO THE EXTENDED FORECAST...FOR THE
PERIOD BEGINNING MONDAY. THE ARCTIC AIRMASS CONTINUES TO DOMINATE
THE WEATHER PATTERN THROUGH THE DAY MONDAY AND TUESDAY...RESULTING
IN TEMPERATURES WELL BELOW SEASONAL AVERAGE. THIS WILL BE THE
COLDEST OF DECEMBER AND BELOW ZERO TEMPERATURES ARE
EXPECTED...ESPECIALLY MONDAY NIGHT AS SKIES CLEAR. SNOW WITH THIS
SYSTEM LOOKS LIKE IT PERSIST ACROSS THE REGION THROUGH
MONDAY...ESPECIALLY FOR SOUTHERN AND WESTERN MOST ZONES. INCREASED
EXISTING POPS FOR MONDAY AND ADDED LINGERED POPS INTO MONDAY
EVENING.

A SFC HIGH IS PUSHED INTO THEN REGION TUESDAY.. WEAK DOWNSLOPE
FLOW APPEARS TO DEVELOP LATER IN THE DAY...AND BEGINS TO MODERATE
TEMPERATURES ACROSS THE REGION. THIS BRINGS A PERIOD OF DRY AND
COOL WEATHER THROUGH THURSDAY. ON THE BRIGHT SIDE...TEMPS WILL BE
20 DEGREES WARMER THAN DURING THE COLD SNAP OF SUNDAY NIGHT
THROUGH TUESDAY.

ANOTHER ARCTIC BEGINS MOVING INTO NORTHERN ALBERTA ON
THURSDAY...AND IS CURRENTLY PROGGED INTO MONTANA AND WYOMING FRIDAY.
TRAJECTORY AND DEVELOPMENT OF THIS SYSTEM APPEARS SIMILAR TO THE
SUNDAY SYSTEM...WITH MARGINAL DYNAMICS BUT GOOD MOISTURE
AVAILABILITY TO SUPPORT LIGHT SNOW. HAVE INCREASED POPS
SLIGHTLY BASED ON CONSISTENCY. AAG

&&

.AVIATION...

EXPECT MOSTLY VFR CONDITIONS OVERNIGHT. WINDS WILL INCREASE
TONIGHT AROUND LIVINGSTON. GUSTS OVER 30 KTS WILL BE POSSIBLE
THROUGH MUCH OF THE DAYS. WINDS WILL INCREASE A LITTLE DURING THE
DAY TOMORROW ACROSS THE REST OF THE AREA...GENERALLY 15 TO 20
KTS...WITH GUSTS 20 TO 30 KTS. HIGH CLOUDS WILL INCREASE DURING
THE DAY AS THE NEXT SYSTEM APPROACHES THE AREA. REIMER
&&

.PRELIMINARY POINT TEMP/POPS...

    SAT     SUN     MON     TUE     WED     THU     FRI
-----------------------------------------------------------
BIL 010/027 015/022 904/002 915/006 000/029 015/030 016/029
    11/N    48/S    73/J    21/N    00/N    11/N    23/J
LVM 005/026 013/023 904/010 919/011 902/029 015/035 018/032
    11/Q    69/S    63/J    21/B    00/N    11/N    22/J
HDN 007/028 012/024 903/004 917/006 904/027 013/029 013/029
    11/B    28/S    73/J    21/B    00/N    11/B    23/J
MLS 011/028 015/021 906/005 907/009 003/026 014/028 012/025
    11/B    26/S    42/J    10/U    00/B    11/B    23/J
4BQ 009/029 012/025 904/006 912/006 902/026 014/029 013/027
    10/B    17/S    63/J    21/B    00/U    11/B    23/J
BHK 007/026 011/017 909/003 908/007 002/024 013/026 010/023
    11/B    15/S    42/J    00/U    00/B    11/B    22/J
SHR 002/027 009/024 902/008 916/010 902/030 015/034 015/031
    10/B    18/S    74/J    21/B    00/U    11/B    23/J

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...NONE.
WY...NONE.

&&

$$
WEATHER.GOV/BILLINGS



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