Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 270409
AFDBYZ

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BILLINGS MT
909 PM MST THU FEB 26 2015

.UPDATE...
EASTERLY UPSLOPE FLOW OVER WESTERN PORTIONS OF THE FORECAST AREA
WAS CAUSING THE STRATUS TO REMAIN ANCHORED IN PLACE PER SURFACE
OBSERVATIONS AND SATELLITE IMAGERY. MODELS SHOWED THE UPSLOPE
WEAKENING OVERNIGHT WHICH SHOULD ALLOW THE CLOUDS TO BREAK UP.
ADJUSTED SKY COVER BASED ON THE ABOVE. TEMPERATURES ACROSS THE
PLAINS WERE MOSTLY IN THE SINGLE DIGITS ABOVE ZERO AT 04Z.
ADJUSTED A FEW MIN TEMPERATURES TO REFLECT LATEST TRENDS.
CHALLENGING FORECAST UNDER THE STRATUS AS LOWS WILL DEPEND ON HOW
MUCH THE CLOUD COVER BREAKS UP. WITH FRESH SNOW COVER...850 MB
TEMPERATURES -12 TO -16 DEGREES C...AND GENERALLY LIGHT WINDS...THE
ADDITION OF CLEAR SKIES WOULD CAUSE TEMPERATURES TO FALL QUITE A
BIT. WINDS WERE GENERALLY LIGHT ACROSS THE AREA WITH A FEW
LOCATIONS ABOVE 10 MPH. THE WINDS WILL REMAIN LIGHT
OVERNIGHT...WITH SPOTTY AREAS POSSIBLY MEETING WIND CHILL
CRITERIA. NOT EXPECTING A WIDESPREAD ENOUGH AREA WITH 10 MPH WINDS
FOR A LONG ENOUGH TIME PERIOD TO SUPPORT ISSUING A WIND CHILL
ADVISORY.

OTHERWISE...VORTICITY SEEN SPINNING OFF THE BC COAST ON WATER
VAPOR IMAGERY THIS EVENING WILL BROADEN INTO A SPLIT TROUGH AS IT
SHIFTS SE THROUGH SAT. SOME Q-VECTOR CONVERGENCE WILL MOVE ACROSS
THE AREA DURING THIS TIME AND ANOTHER FRONT WITH FRONTOGENESIS
WILL MOVE INTO THE AREA AND THE FLOW WILL BECOME UPSLOPE AGAIN.
MODELS SHOWED LIGHT QPF FOR THIS SYSTEM WHICH WILL MAINLY AFFECT
AREAS W OF KBIL. ARTHUR

&&

.SHORT TERM...VALID FOR FRI AND SAT...

THE OVERALL FORECAST REMAINS CONSISTENT...WITH GOOD AGREEMENT
AMONGST MODELS...POINTING TOWARD HIGH TEMPS 15 TO 25 DEGREES
BELOW SEASONAL AVERAGE THROUGH THE SHORT TERM PERIOD.
THEREFORE...MINIMAL CHANGES THROUGH THE SHORT TERM
PERIOD...FOLLOWING THE MORNING UPDATE.

HIGHS TODAY REMAIN QUITE COOL...WITH READINGS ONLY INTO MID TEENS
SO FAR. CLOUD COVER HAS HUNG IN THROUGH MUCH OF THE DAY...BUT IS
BREAKING UP AS A SHORT WAVE RIDGE SLIDES INTO THE REGION FROM THE
NORTHWEST. THIS CONTINUES TO POINT TO CLEAR SKIES
TONIGHT...ALLOWING THE TEMPS TO PLUMMET BELOW ZERO ACROSS THE
REGION. HAVE COOLED OVERNIGHT LOWS BELOW GUIDANCE IN MOST
AREAS...BUT MAY NOT BE ENOUGH WITH CLEAR SKIES AND LIGHT WINDS.
MAINLY CLEAR SKIES SHOULD PERSIST MUCH OF THE DAY
FRIDAY...ALLOWING FOR MORE SIGNIFICANT WARM UP...BUT STILL WELL
BELOW SEASONAL AVERAGE.

A WEAK DISTURBANCE WILL MOVE INTO THE WESTERN MOUNTAINS LATE
FRIDAY EVENING...AND SPREAD SNOW TOWARDS KBIL AND KSHR...WHILE
BEST ENERGY REMAINS TO THE WEST...DROPPING FROM THE PACIFIC NW
INTO THE GREAT BASIN. SNOW IS EXPECTED TO CONTINUE...MAINLY WEST
OF A LINE FROM KBIL TO KSHR...THROUGH SATURDAY...WITH BEST
POTENTIAL IN THE HIGH TERRAIN AND EASTERLY SLOPES. ALTHOUGH THIS
DOES NOT APPEAR TO BE A BIG SNOW EVENT AT THIS TIME...IT MAY NOT
TAKE MUCH IN THE WAY OF A STRENGTHENING OF THE DISTURBANCE TO MAKE
FOR A MORE SIGNIFICANT EVENT. EASTERLY FLOW DOES PREVAIL FOR AN
EXTENDED PERIOD OF TIME...WITH RESPECTABLY MOIST AND DEEP
DENDRITIC LAYER TO AID OROGRAPHIC LIFT. ECMWF AND NAM STILL
PRODUCE VERY LITTLE IN THE WAY OF QPF OVER OUR AREA...BUT WOULD BE
SURPRISED IF FO NOT SEE AT LEAST SOME LIGHT SNOW OR FLURRIES
DEVELOP IN UPSLOPE. AAG

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

QUIET WEATHER WITH A WARMING TREND EXPECTED SUNDAY AND MONDAY...AS
DEEP LOW IMPACTS THE SW CONUS AND WE AWAIT ENERGY FROM NW CANADA.
SUNDAY SHOULD BE A LIGHT WIND DAY BUT ON MONDAY THERE IS POTENTIAL
FOR SOME ENHANCED DOWNSLOPE/PREFRONTAL WINDS...IE MONDAY SHOULD BE
THE WARMEST OF THE NEXT SEVERAL DAYS. GIVEN WE REALLY DO NOT HAVE
MUCH LOWER ELEVATION SNOW COVER HAVE RAISED EXPECTED TEMPS A
LITTLE...CLOSER TO ANTICIPATED 850MB MIX DOWNS. THINGS THEN GET
INTERESTING IN A HURRY.

MODELS COMING TOGETHER IN BOTH TIMING AND STRENGTH OF STRONG
CANADIAN CLIPPER AND FROPA WHICH WILL IMPACT OUR AREA MONDAY NIGHT
THROUGH TUESDAY NIGHT. IN FACT...THE GFS/ECMWF/UKMET/CANADIAN ARE
IN REMARKABLE AGREEMENT IN TERMS OF 500MB HEIGHTS AT 144 HRS. SO
THERE IS SOME CONFIDENCE TO BE HAD...THOUGH WOULD EXPECT SOME
MODEL SHIFTS YET TO OCCUR OVER THE COMING DAYS GIVEN THE NATURE
OF SUCH HIGH AMPLITUDE WX PATTERNS.

STRONG CANADIAN COLD FRONT EXPECTED TO ARRIVE MONDAY NIGHT
USHERING IN PERHAPS THE COLDEST AIR WE HAVE SEEN SINCE EARLY
JANUARY...WITH 850MB TEMPS TO -20C OR COLDER TUESDAY AND TUESDAY
NIGHT. IT SHOULD BE NOTED THAT THIS AIRMASS WILL BE IN ARCTIC
REGIONS NORTH OF ALASKA/YUKON BEFORE ITS RAPID SOUTHWARD PLUNGE.
HAVE LOWERED FORECAST TEMPS MONDAY NIGHT THROUGH TUESDAY NIGHT
AND AM AT THIS TIME EXPECTING SOME BELOW ZERO READINGS TO OCCUR...
NOT AN EASY FEAT FOR EARLY MARCH. AS FOR PCPN...OUR WESTERN
FOOTHILLS WILL BE MOST FAVORED FOR SNOWFALL BY THE TRACK OF THIS
TROF AND UPSLOPE WINDS. THIS DOES NOT LOOK TO BE JUST AN
OROGRAPHIC EVENT THOUGH AS LATEST MODEL TRENDS SUGGEST A WEAK
700MB LOW TRACKING TO OUR SW AND FAIRLY STRONG UPPER LEVEL QG
FORCING. SOMETHING TO THINK ABOUT. FOR NOW HAVE RAISED POPS
ANOTHER NOTCH ACROSS OUR WEST AND SOUTH CENTRAL PARTS WHERE THERE
IS POTENTIAL FOR SEVERAL INCHES OF SNOW. MAIN IMPACT FOR OUR EAST
WILL LIKELY BE WINDS AND COLD TEMPS RATHER THAN SNOWFALL.

CURRENT INDICATIONS ARE THAT WE WILL SEE RISING HEIGHTS...DRY WX
AND A WARMING TREND FOR THE END OF NEXT WEEK.

JKL
&&

.AVIATION...

MOSTLY CLEAR SKIES AND VFR CONDITIONS WILL PREVAIL THIS EVENING.
THE EXCEPTION WILL BE SOME LOWER STRATUS ACROSS THE
BEARTOOTH/ABSAROKA FOOTHILLS AREAS INCLUDING KLVM...ALTHOUGH THIS
SHOULD BREAK UP LATE THIS EVENING. AFTER 06Z...SOME MID AND HIGH
LEVEL CLOUDS WILL GRADUALLY MOVE INTO THE AREA FROM WEST TO
EAST...BUT VFR CONDITIONS WILL CONTINUE TO PREVAIL. HOOLEY
&&

.PRELIMINARY POINT TEMP/POPS...

    FRI     SAT     SUN     MON     TUE     WED     THU
-----------------------------------------------------------
BIL 903/023 008/021 004/033 018/041 010/014 902/023 012/037
    00/B    22/S    00/U    01/U    55/S    21/B    11/N
LVM 901/025 003/020 904/032 013/039 007/016 911/023 006/037
    02/J    56/S    20/U    01/B    66/S    21/B    11/N
HDN 903/026 009/024 004/033 011/042 011/016 904/021 007/038
    00/B    22/S    00/U    00/U    45/S    21/B    11/B
MLS 905/024 007/022 006/030 013/040 010/015 901/022 008/036
    00/U    11/E    01/U    00/U    22/S    11/B    11/B
4BQ 905/024 008/024 003/031 009/042 012/017 901/018 004/037
    00/U    11/E    00/U    00/U    24/S    21/B    11/B
BHK 908/023 004/022 004/029 011/040 009/015 902/018 004/033
    00/U    00/B    11/B    00/U    22/S    11/B    11/B
SHR 911/021 006/018 902/026 005/037 010/014 904/016 001/033
    00/U    13/S    00/U    00/U    36/S    31/B    11/B

&&

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

&&

$$
WEATHER.GOV/BILLINGS


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