Area Forecast Discussion
Issued by NWS Billings, MT

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000
FXUS65 KBYZ 270244
AFDBYZ

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BILLINGS MT
844 PM MDT FRI SEP 26 2014

.UPDATE...

COLD FRONT HAS PUSHED THROUGH THE FORECAST AREA THIS EVENING AND
IS LOCATED FROM THE WESTERN DAKOTAS SOUTHWEST INTO CENTRAL WYOMING
AT 8 PM. COOLER AIR AND NORTHEASTERLY WINDS HAVE DEEPENED UP TO
AROUND 5000 FEET OVER THE PAST FEW HOURS. OVER THE TOP OF THIS
FRONTAL BOUNDARY JET DYNAMICS COMBINED WITH THE FRONTAL
CONVERGENCE ARE PRODUCING ISOLATED TO SCATTERED SHOWERS AND
THUNDERSTORMS WEST OF A ROUNDUP TO BILLINGS LINE. THESE CELLS ARE
MOVING TO THE NORTH AT 20 TO 30 MPH. ANOTHER AREA OF STRONGER JET
DYNAMICS IS LOCATED OVER EASTERN IDAHO AT THIS TIME AND THIS WILL
PUSH INTO THE WESTERN HALF OF THE FORECAST AREA OVERNIGHT INTO
TOMORROW MORNING. HI-RES MODELS HINTING AT A GOOD AREA OF SHOWER
ACTIVITY ALONG THE WESTERN FOOTHILLS AND MOUNTAINS...AS WELL AS A
PERSISTENT NORTH/SOUTH ORIENTED BAND OF SHOWERS SETTING UP
SOMEWHERE BETWEEN BILLINGS AND BIG TIMBER AROUND SUNRISE.
INCREASED POPS 10 TO 20 PERCENT FROM ROUNDUP AND BILLINGS WEST TO
THE FOOTHILLS TO ACCOUNT FOR THIS EXPECTED ACTIVITY. LATEST MODELS
PUSH JET FORCING A BIT FURTHER EAST IN THE MORNING AND LATE
AFTERNOON TOMORROW. ADDED SOME LOW POPS AS FAR EAST AS ROSEBUD
COUNTY TO ACCOUNT FOR THIS VARIABILITY AND SPREAD LIKELY POPS AS
FAR EAST AS A ROUNDUP TO NYE LINE. BUMPED CLOUD COVER SOME TO
ACCOUNT FOR INCREASE IN PRECIPITATION POTENTIAL AND COVERAGE. REST
OF THE FORECAST IS IN GOOD SHAPE. CHAMBERS

&&

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

COLD FRONT HAS OOZED THROUGH MOST OF THE AREA BUT WITH STRONGER
COLD ADVECTION NOT OCCURRING UNTIL TONIGHT. TEMPS HAVE WARMED INTO
THE 80S AND LOWER 90S THIS AFTERNOON...WITH 2PM TEMP OF 93F AT
SHERIDAN TYING A RECORD FOR THE DAY. BILLINGS WINDS HAVE SHIFTED
TO THE NE AND LOW LEVEL CONVERGENT AREA LONG WITH WEAK ENERGY FROM
THE SW ALLOWING FOR A CU FIELD TO FORM FROM BILLINGS WEST...WITH
LATEST RADAR SHOWING WEAK ECHOES IN PARK AND SWEET GRASS
COUNTIES. AREAS FROM BILLINGS WEST CAN EXPECT ISOLATED SHOWERS/
TSTMS THROUGH THE EARLY EVENING HOURS...THIS REMAINS CONSISTENT
WITH RECENT HRRR RUNS...WITH THE EAST REMAINING DRY/CLEAR. MAIN
FORECAST ISSUE CONTINUES TO REVOLVE AROUND DEEP PACIFIC TROF WHICH
IS PUSHING SLOWLY INLAND AND WILL BEGIN TO IMPACT OUR WEST LATER
TONIGHT.

OVERALL THEME OF FORECAST REMAINS UNCHANGED TODAY. PCPN CHANCES
WILL INCREASE WEST OF BILLINGS LATER TONIGHT...WITH RAIN LIKELY
WEST OF BILLINGS SATURDAY...THEN BECOMING LIKELY ACROSS THE CWA
SATURDAY NIGHT THROUGH SUNDAY NIGHT AS UPPER LOW SHIFTS TO OUR
SOUTH LEAVING OUR REGION IN A FAVORABLE DIFFLUENT REGION ALOFT.
HAVE ADJUSTED POPS A BIT...WITH THE MAIN CHANGE BEING TO DRY OUT
BILLINGS ON SATURDAY. STRONGER FORCING SHOULD STAY TO OUR WEST...
WITH COOLER LOW LEVEL NE WINDS KEEPING OUR AIRMASS STABLE WITH
WITH A 5-6KFT CLOUD DECK. THIS MAY SUPPORT A FEW SPRINKLES BUT
SHOULD NOT BE ANYTHING MORE THAN THAT IF YOU ARE PLANNING TO BE
OUTDOORS IN BILLINGS ON SATURDAY. OTHER CHANGE WAS TO RAISE POPS
NEAR SHERIDAN AND LAME DEER SUNDAY NIGHT AS ALL MODELS SHOW
STRONGER PIECE OF ENERGY LIFTING OUT OF WYOMING. COULD ALSO BE
SOME TSTMS WITH ELEVATED INSTABILITY IN OUR SOUTHEAST.

IMPACTS WITH THIS SYSTEM WILL NOT BE GREAT. COULD SEE SOME WET
SNOW OVER THE HIGHEST PEAKS INCLUDING BEARTOOTH PASS BY SATURDAY
NIGHT...BUT SNOW LEVELS LOOK TO STAY UP NEAR 10KFT. OTHERWISE WE
ARE TALKING ABOUT A COUPLE DAYS OF MUCH COOLER AND OCCASIONALLY
WET WEATHER...WITH PCPN TOTALS NEAR AN INCH IN PLACES BY SUNDAY
NIGHT ESPECIALLY IN OUR WESTERN UPSLOPE AREAS...ALONG WITH A
HEALTHY NE WIND. THOUGH IT WILL BE A COLD RAIN...DO NOT THINK
FOOTHILL LOCATIONS SUCH AS RED LODGE AND STORY WILL SEE SNOW THIS
TIME.

AFTER NEAR RECORD HEAT AGAIN TODAY WE WILL SEE TEMPS DROP
SIGNIFICANTLY FOR SATURDAY AND CLOSER TO LATE SEPTEMBER NORMALS.
SUNDAY WILL BE EVEN COOLER WITH HIGHS ONLY IN THE UPPER 40S AND
50S ACROSS MOST LOWER ELEVATIONS.

JKL

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

LARGE UPPER TROUGH WILL BE TRACKING THROUGH THE NORTHERN AND
CENTRAL ROCKIES TO START THE EXTENDED. MODELS HAVE COME INTO GOOD
AGREEMENT THROUGH MONDAY NIGHT...BUT HAVE SOME SIGNIFICANT AND
CRITICAL DIFFERENCES THROUGH TUESDAY EVENING.

A STRONG SHORT WAVE WILL LIFT ACROSS THE FORECAST AREA FROM THE
SOUTH ON THE FRONT SIDE OF THE TROUGH MONDAY. MODELS VERY MUCH IN
AGREEMENT SO ADJUSTED POPS FOR THIS FEATURE WHICH HITS MAINLY
EASTERN ZONES. GFS THEN HAS UPPER CLOSED LOW THAT LIFTS THROUGH SE
MONTANA MONDAY NIGHT INTO TUESDAY WHILE ECMWF KEEPS SYSTEM OPEN
AND TRACKS IT FURTHER SOUTH. THE GFS SOLUTION IS THUS MUCH MORE
BULLISH WITH SIGNIFICANT QPF OVER OUR EAST TUESDAY DUE TO TROWAL
TYPE DEVELOPMENT...BUT THE ECMWF SCENARIO KEEPS THE FORCING IN
THE DAKOTAS. GEM ALSO KEEPS WAVE OPEN SIMILAR TO THE ECMWF. I HAVE
THEREFORE USED A BLEND WHILE LEANING TOWARD THE LESS AGGRESSIVE
ECMWF SOLUTION.

THE LONG WAVE PATTERN REMAINS CYCLONIC THE REST OF THE WORK WEEK
WITH THE MODELS HAVING DIFFERENCES TRYING TO TIME SOME SHORT WAVES
WITHIN THE MEAN FLOW. SO SOME UNSETTLED WEATHER IS EXPECTED WITH
SEASONABLE TEMPERATURES. BT


&&

.AVIATION...

VFR CONDITIONS WILL GENERALLY PREVAIL THROUGH THIS EVENING.
HOWEVER...LOCAL MVFR CONDITIONS ARE POSSIBLE TONIGHT DUE TO
LOWERED VISIBILITY IN SHOWERS AND THUNDERSTORMS...MAINLY ALONG AND
WEST OF A ROUNDUP TO BILLINGS LINE. GUSTY NORTHEASTERLY WINDS
WILL CONTINUE THROUGH THE DAY SATURDAY. CHAMBERS

&&

.PRELIMINARY POINT TEMP/POPS...

    SAT     SUN     MON     TUE     WED     THU     FRI
-----------------------------------------------------------
BIL 055/065 045/054 043/064 049/066 045/060 042/057 042/064
    23/T    66/W    63/W    22/W    22/W    02/W    20/U
LVM 050/059 045/055 040/064 044/064 037/058 035/057 036/065
    67/T    87/W    63/W    33/W    32/W    12/W    21/B
HDN 051/070 047/057 043/066 048/068 044/061 041/060 040/066
    12/T    66/W    63/W    22/W    22/W    02/W    20/U
MLS 055/073 047/057 043/064 050/066 046/062 041/059 041/065
    00/B    35/W    55/T    33/W    22/W    12/W    21/B
4BQ 055/076 049/060 044/065 051/064 044/059 039/058 039/063
    00/U    24/T    64/T    33/T    22/W    12/W    21/U
BHK 055/077 048/058 041/061 050/064 044/060 039/057 037/060
    00/U    24/W    55/T    74/T    22/W    12/W    21/B
SHR 052/073 048/057 042/066 046/065 042/056 037/057 036/064
    00/B    35/T    73/W    23/W    22/W    02/W    20/U

&&

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

&&

$$
WEATHER.GOV/BILLINGS


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