Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 211026
AFDBYZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
326 AM MST SUN DEC 21 2014

.SHORT TERM...VALID FOR TDY AND MON...

ACTIVE WEATHER WILL CONTINUE THROUGH THE SHORT TERM AS AN
UNSETTLED NORTHWEST FLOW ALOFT MOVES ACROSS THE FORECAST AREA. A
NORTHWEST FLOW ALOFT WITH NUMEROUS PIECES OF VORTICITY WITHIN IT
WILL MOVE FROM NORTHWEST TO SOUTHEAST ACROSS OUR AREA TODAY INTO
MONDAY. WATER VAPOR SATELLITE SHOWING A STEADY STREAM OF MOISTURE
MOVING OFF THE PACIFIC AND ACROSS THE PACIFIC NORTHWEST INTO IDAHO
AND WESTERN MONTANA. THERE HAVE EVEN BEEN A FEW LIGHTNING STRIKES
IN WASHINGTON EARLY THIS MORNING. THE BULK OF THIS MOISTURE WILL
BE IMPACTING MAINLY OUR SOUTHWEST MOUNTAINS. TIME HEIGHTS FOR THE
COOKE CITY AREA CONTINUE SHOW UNSTABLE CONDITIONS INTO MONDAY
MORNING. THE STRONGEST LIFT AND INSTABILITY WILL BE DURING THE DAY
TODAY AND THIS IS WHEN THE HEAVIEST SNOW ACCUMULATIONS ARE
EXPECTED. IR SATELLITE HAS BEEN SHOWING THE COLDEST CLOUD TOPS
STAYING SOUTHWEST OF THE MOUNTAINS BUT THERE STILL REMAINS QUITE A
BIT OF LOW-LEVEL MOISTURE HITTING THE MOUNTAINS. AS A
RESULT...SNOWFALL AMOUNTS MAY BE LESS THAN PREVIOUSLY THOUGHT BUT
STILL LOOKING AT TOTAL AMOUNTS IN THE 15-20 INCH RANGE FOR THE
BEARTOOTH/ABSAROKAS.

MODELS CONTINUE TO SHOW A DISTURBANCE MOVING ACROSS OUR FORECAST
AREA THIS MORNING INTO THIS AFTERNOON...MAINLY AFFECTING OUR
CENTRAL AND EASTERN LOCATIONS. I DID LOWER POPS THROUGH 9AM INTO
JUST THE SLIGHT CHANCE TO CHANCE CATEGORY ACROSS THE EAST.
HOWEVER...MODELS CONTINUE TO SHOW QUITE A BIT OF LIFT AND DYNAMICS
OVER THE AREA BY MID TO LATE MORNING SO WILL KEEP LIKELY POPS
GOING FROM ABOUT ROSEBUD COUNTY EASTWARD FOR LATE THIS MORNING
INTO THE AFTERNOON. TEMPERATURES REMAIN BELOW FREEZING OUT EAST
AND GIVEN SOME WARM AIR JUST ABOVE THE SURFACE CAN`T RULE OUT SOME
AREAS OF FREEZING RAIN THIS MORNING. WILL HOLD OFF FOR NOW ON AN
ADVISORY AND SEE HOW THINGS UNFOLD THIS MORNING AS TEMPERATURES
SHOULD WARM ABOVE FREEZING BY LATE MORNING.

MAIN IMPACT TODAY FOR MOST AREAS ACROSS THE LOWER ELEVATIONS WILL
BE WIND. GAP FLOW WINDS WILL CONTINUE AS A STRONG SURFACE LOW
MOVES FROM SOUTHWESTERN CANADA SOUTHEAST INTO EASTERN MONTANA AND
THE WESTERN DAKOTAS. LEE-SIDE TROUGHING WILL BE IN PLACE AND THIS
IS VERIFYING IN THE LIVINGSTON AREA AND ADJACENT FOOTHILLS WHERE
WINDS ARE NOW IN THE 30-35 MPH SUSTAINED RANGE. GAP WINDS WILL
CONTINUE UNTIL THE LOW MOVES EAST SWINGING A COLD FRONT ACROSS THE
WESTERN AREAS THIS AFTERNOON. ALTHOUGH COLD AIR ADVECTION WILL
ALLOW THE GAP EFFECT TO END...STRONG WINDS WILL CONTINUE FOR THE
GAP AREAS AS PRESSURE GRADIENTS WILL REMAIN VERY TIGHT INTO
TONIGHT. AS THE LOW MOVES EAST...A TIGHT EAST/WEST PRESSURE
GRADIENT WILL BE ACROSS OUR WESTERN AND CENTRAL AREAS TODAY
RESULTING IN VERY WINDY CONDITIONS. IN ADDITION...SOUNDINGS SHOW
60-75KT WINDS JUST ABOVE THE SURFACE. ALTHOUGH PLENTY OF LIFT WILL
ACCOMPANY THE PREVIOUSLY MENTIONED DISTURBANCE...ANY SHOWER
ACTIVITY WILL HAVE THE POTENTIAL TO MIX SOME OF THESE VERY STRONG
WINDS DOWN TO THE SURFACE SO WE CAN`T RULE OUT A 60-70 MPH GUST
FOR SOME LOCATIONS ACROSS THE PLAINS. CONFIDENCE IS HIGH THAT HIGH
WINDS WILL BE LIKELY FOR WHEATLAND AND GOLDEN VALLEY COUNTIES SO
WILL BE UPGRADING THE HIGH WIND WATCH TO A WARNING.
HOWEVER...CONFIDENCE IS LOW FOR A WIDESPREAD HIGH WIND EVENT
FURTHER EAST SO WILL NOT ISSUE ANY WARNINGS BUT WILL HIGHLIGHT THE
POTENTIAL FOR THE POSSIBILITY OF A DAMAGING WIND GUST IN THE HWO
AND SPS.

AS THE UPPER LOW PULLS EAST INTO THE DAKOTAS LATE TONIGHT INTO
MONDAY...MODELS BRING WRAP AROUND MOISTURE INTO OUR EASTERN ZONES
WITH CONTINUED TIGHT PRESSURE GRADIENTS RESULTING IN GUSTY
NORTHWEST WINDS. HAVE INCREASED POPS TO LIKELY ACROSS THE
EAST...AS WELL AS BUMPED SNOW AMOUNTS UP INTO THE 1-2 INCH RANGE.
WILL NEED TO MONITOR THIS LATER TODAY FOR POSSIBLE HIGHLIGHTS.
HOOLEY

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

LONG TERM MODEL SOLUTIONS HAVE COME INTO GOOD AGREEMENT THROUGH
FRIDAY LENDING BETTER CONFIDENCE FOR A SNOW EVENT CHRISTMAS EVE
INTO CHRISTMAS DAY.

NORTHERLY JET STREAM OVER THE AREA MONDAY SHIFTS EAST OF THE AREA
TUESDAY WITH LONGITUDINAL RIDGING BUILDING IN FROM THE WEST AS
PACIFIC JET AXIS SHIFTS NORTHWARD INTO SOUTH WEST CANADA. THIS
SOLUTION IS SIMILAR TO THE GFS SOLUTION FROM YESTERDAY WITH THE
ECMWF SHIFTING NORTH TO MATCH THAT SOLUTION TODAY AS THE GFS HAS
HELD ITS SOLUTION STEADY OVER THE PAST 24 HOURS. THIS SHIFT NORTH
AND RESULTING RIDGING WILL BRING WARMER TEMPERATURES AND GUSTY
DOWNSLOPE WINDS TO THE AREA TUESDAY AND WEDNESDAY. EXPECT A PERIOD
OF ADVISORY OR STRONGER WINDS FOR THE WESTERN FOOTHILLS TUESDAY
NIGHT INTO WEDNESDAY WITH THIS PATTERN. COULD SEE A FEW SHOWERS
AROUND BUT THESE WILL BE MAINLY CONFINED TO THE MOUNTAINS.

CHRISTMAS EVE/CHRISTMAS DAY...ZONAL JET SAGS SOUTH DURING THE DAY
WEDNESDAY AS A PACIFIC SYSTEM PUSHES INTO THE PACIFIC NORTHWEST
DIGGING A TROF INTO OREGON. THIS WILL KEEP WINDY AND DRY
CONDITIONS IN PLACE MOST OF THE DAY WEDNESDAY. BY LATE AFTERNOON
THE RIGHT REAR QUAD OF THE JET SHIFTS OVER THE AREA. THIS WILL
DRAG COLDER CANADIAN AIR SOUTHWARD INTO THE AREA AND ENHANCE UPPER
LEVEL DIVERGENCE. THIS PATTERN WILL GENERATE SIGNIFICANT LIFT AS
THE DIVERGENCE ALOFT COMBINES WITH QG FORCING FROM THE APPROACHING
PACIFIC WAVE ALL OVER RUNNING THE DEEPENING COLD SURFACE AIRMASS.
EXPECT PRECIPITATION TO BEGIN TO DEVELOP SOMETIME LATE AFTERNOON
OVER NORTHERN ZONES AND INCREASE IN COVERAGE AND INTENSITY THROUGH
THE EVENING HOURS. OPERATIONAL GFS GENERATES OVER HALF AN INCH OF
QPF WITH THIS SYSTEM OVER THE WESTERN 2/3 OF THE FORECAST AREA
FROM LATE WEDNESDAY NIGHT THROUGH CHRISTMAS DAY...WITH THE ECMWF
NOT FAR BEHIND AT AROUND FOUR TENTHS OF AN INCH ALONG WITH THE
CONSALL. PROGGED SNOW RATIOS RESULT IN A 3 TO 6 INCH ADVISORY TYPE
SNOW FOR AREAS WEST OF A ROUNDUP TO BROADUS LINE...WITH POTENTIAL
FOR HEAVIER SNOWFALL IN THE FAVORED UPSLOPE AREAS INCLUDING RED
LODGE AND SHERIDAN. TO THE EAST OF THIS LINE SNOWFALL TAPERS OFF
PRETTY QUICKLY BUT AN INCH OR TWO STILL LOOKS POSSIBLE BY
CHRISTMAS MORNING. AS A RESULT OF THIS INCREASED CONSISTENCY
SHIFTED BEST PRECIPITATION CHANCES INTO THE MIDNIGHT TO NOON TIME
FRAME CHRISTMAS DAY AND INCREASED POPS ESPECIALLY OVER UPSLOPE
AREAS. STILL PLENTY OF TIME FOR MODELS TO CHANGE COURSE BUT
ENCOURAGED BY THE CONSISTENCY IMPROVEMENT TODAY. THOSE WITH TRAVEL
PLANS CHRISTMAS EVE/DAY SHOULD BE PREPARED FOR WINTER TRAVEL
CONDITIONS AND MAY WANT TO MOVE UP TRAVEL PLANS TO TUESDAY/EARLY
WEDNESDAY TO AVOID THIS POTENTIAL SNOWFALL.

FRIDAY INTO NEXT WEEKEND...AFTER A DRY DAY FRIDAY UNFORTUNATELY
IMPROVED CONSISTENCY QUICKLY DIMINISHES GOING INTO THE WEEKEND AS
THE GFS BRINGS IN A SIMILAR SYSTEM TO THURSDAYS FOR THE WEEKEND.
THE EUROPEAN SOLUTION SPLITS THIS SYSTEM INTO TWO PIECES AND
ESSENTIALLY GOES AROUND OUR AREA WITH IT KEEPING WARM AND MAINLY
DRY CONDITIONS OVER US. FOR NOW WENT A BIT COLDER THAT AVERAGE
FOR TEMPERATURES AND NEAR CLIMATOLOGY FOR PRECIPITATION CHANCES
FOR THIS PERIOD. CHAMBERS
&&

.AVIATION...

AN ACTIVE WEATHER DAY TODAY WITH SEVERAL HAZARDS TO AVIATION
INTERESTS EXPECTED. SOME HAZARDS WILL CONTINUE INTO TONIGHT.

THIS MORNING A WARM ADVECTION PATTERN WITH INCREASING
PRECIPITATION CHANCES WILL SPREAD ACROSS THE AREA FROM WEST TO
EAST. MORNING TEMPERATURES ARE COLD ENOUGH THAT PRECIPITATION MAY
BE IN THE FORM OF FREEZING RAIN EAST OF A ROUNDUP TO SHERIDAN
LINE. IN ADDITION TO THE FREEZING RAIN POTENTIAL OCCASIONAL MVFR
CONDITIONS CAN BE EXPECTED IN THESE AREAS. TO THE WEST OF THIS
LINE EXPECT MAINLY RAIN THIS MORNING. BY THIS AFTERNOON ALL LOWER
ELEVATION PRECIPITATION WILL BE RAIN. PRECIPITATION CHANCES WILL
DIMINISH FROM WEST TO EAST LATE IN THE DAY.

FOR THE MOUNTAINS...HEAVY SNOW IS EXPECTED RESULTING IN MOUNTAIN
AND PASS OBSCURATION...DESCENDING INTO THE ADJACENT VALLEYS AND
FOOTHILLS AT TIMES.

STRONG WINDS WILL DEVELOP OVER WESTERN FOOTHILLS THIS MORNING AND
SPREAD INTO THE PLAINS THIS AFTERNOON AND TONIGHT. FOOTHILLS WINDS
WILL GUST OVER 50KTS AT TIMES TODAY THROUGH TONIGHT...WHILE
AFTERNOON WINDS IN THE PLAINS WILL BE IN THE 30 TO 40KT RANGE.
JUST OFF THE SURFACE WESTERLY WINDS WILL RANGE FROM 50 TO 75KTS
AROUND 2KFT AGL. THIS WILL RESULT IN LOW LEVEL WIND SHEAR ISSUES
THIS AFTERNOON THROUGH TONIGHT ACROSS THE AREA AS WELL AS STRONG
MOUNTAIN WAVE TURBULENCE LEE OF AREA MOUNTAINS. SHOWER ACTIVITY
TODAY INTO TONIGHT MAY AT TIMES PUSH THESE STRONGER WINDS TO THE
SURFACE FOR LOCALIZED GUSTS OVER 50KTS. CHAMBERS
&&

.PRELIMINARY POINT TEMP/POPS...

    TDY MON     TUE     WED     THU     FRI     SAT
-------------------------------------------------------
BIL 047 034/041 024/038 025/039 023/029 015/027 013/029
    3/W 34/W    20/B    12/O    66/S    31/B    11/B
LVM 045 031/037 016/034 021/037 023/030 010/024 010/028
    4/W 44/W    21/N    23/S    77/S    41/B    12/S
HDN 049 031/039 021/036 019/037 022/029 011/024 011/028
    5/W 34/W    31/B    13/O    66/S    31/B    11/B
MLS 044 028/034 022/034 020/037 020/025 011/023 012/026
    6/W 36/J    21/B    03/O    43/S    21/E    12/S
4BQ 045 031/035 024/035 018/038 021/027 014/023 011/027
    6/W 46/W    31/B    11/B    45/S    21/E    11/B
BHK 040 026/031 020/030 016/036 017/023 009/022 010/025
    7/W 67/J    32/S    12/S    33/S    21/E    12/S
SHR 045 030/036 021/034 018/039 022/028 010/025 009/031
    4/W 44/W    41/B    12/O    66/S    31/B    11/B

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...HIGH WIND WARNING IN EFFECT FROM 8 AM THIS MORNING TO NOON
      MST MONDAY FOR ZONES 28-42-63.
     WIND ADVISORY IN EFFECT UNTIL NOON MST MONDAY FOR ZONES
      41-65-66.
     WINTER STORM WARNING IN EFFECT UNTIL NOON MST MONDAY FOR ZONE
      67.
WY...NONE.

&&

$$
WEATHER.GOV/BILLINGS


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