Area Forecast Discussion
Issued by NWS Billings, MT

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000
FXUS65 KBYZ 052117
AFDBYZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
317 PM MDT THU MAY 5 2016

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

RIDGE THAT HAS DOMINATED THE WEATHER THIS WEEK WILL BREAK DOWN
TONIGHT AS A SHORTWAVE PUSHES SOUTHEAST ACROSS SOUTHERN CANADA AND
DEEPENING LOW OVER CALIFORNIA PUSHES INTO THE GREAT BASIN. COLD
FRONT CURRENTLY OVER NORTH CENTRAL MONTANA WILL SLIDE SOUTHWARD
TONIGHT AND MOVE THROUGH THE AREA FROM THE EARLY MORNING HOURS
INTO MID DAY FRIDAY. AHEAD OF THE FRONT MAY STILL SEE AN ISOLATED
EVENING THUNDERSTORM FOR AREAS WEST OF BILLINGS. OVERNIGHT SHOWERS
WILL LIKELY DEVELOP ALONG THE COLD FRONT AS IT PUSHES SOUTHWARD
INTO THE AREA. BETTER CHANCE OF RAIN DEVELOPS DURING THE DAY
FRIDAY AS NORTHERLY UPSLOPE WINDS BEHIND THE COLD FRONT COMBINE
WITH DEEPENING DIVERGENCE ALOFT BROUGHT BY THE GREAT BASIN UPPER
LOW...CONTINUING FRIDAY NIGHT INTO SATURDAY.

MODELS SHOWING A DEEP EASTERLY FLOW INTO THE SOUTHERN MOUNTAINS
PROVIDING AMPLE LIFT FOR PRECIPITATION WITH THE BEST AREA FOR
PRECIPITATION FRIDAY INTO SUNDAY SOUTH OF A HARLOWTON TO BILLINGS
TO BROADUS LINE. HAVE KEPT LIKELY POPS FOR THE FOOTHILLS AND
CATEGORICAL FOR THE MOUNTAINS WITH CURRENT PRECIPITATION FORECAST
PROVIDING UP TO AN INCH OF PRECIPITATION THROUGH SUNDAY
MOUNTAINS...UP TO THREE QUARTERS OF AN INCH FOR THE FOOTHILLS
AROUND SHERIDAN AND RED LODGE...AND AND A QUARTER INCH FOR THE
LOWER ELEVATIONS.

WHILE THE CURRENT PRECIPITATION BULLSEYE WITH THIS SYSTEM IS
FOCUSED JUST SOUTH OF THE AREA OVER CENTRAL WYOMING...THERE HAVE
BEEN MODEL RUNS OVER THE PAST 24 HOURS THAT SNEAK THIS BULLSEYE
NORTHWARD AND HIT SOUTHERN ZONES WITH SIGNIFICANTLY MORE
PRECIPITATION THAN IS CURRENTLY IN THE FORECAST...ESPECIALLY OVER
SHERIDAN COUNTY AND THE BIGHORN MOUNTAINS. ONE OF THESE RUNS PUT
OVER 3 INCHES OF PRECIPITATION IN THE MOUNTAINS ABOVE SHERIDAN AND
AN INCH AND A HALF OR MORE IN THE LOWER FOOTHILLS. THOUGH
CURRENTLY LOOKING UNLIKELY SHOULD THIS SCENARIO DEVELOP COMBINED
WITH THE ONGOING SNOW MELT...RIVERS AND STREAMS IN THIS AREA WOULD
SWELL QUICKLY. WILL HAVE TO KEEP A CLOSE EYE ON THE POTENTIAL FOR
THE SYSTEM TO JUMP FURTHER NORTH OVER THE NEXT 24 HOURS...AS IT
WON`T TAKE MUCH OF A SHIFT TO DRAMATICALLY INCREASE PRECIPITATION
POTENTIAL OVER THE SOUTHERN HALF OF THE FORECAST AREA.

TEMPERATURES BEHIND THE COLD FRONT WILL DROP INTO THE 60S AND
LOWER 70S FOR FRIDAY AND SATURDAY. SOUTHERN ZONES MAY BE COOLER
DEPENDING ON INTENSITY AND COVERAGE OF PRECIPITATION. CHAMBERS

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

AN UPPER LEVEL LOW PRESSURE SYSTEM WILL DEVELOP AND SLIDE
EASTWARD OVER SOUTHERN WYOMING ON SUNDAY MORNING. THE 12Z GFS IS
KEEPING MORE RIDGING OVER EASTERN MONTANA AND THE CLOSED LOW
FURTHER SOUTH THEN WAS PREVIOUSLY FORECAST. WITH THIS SOLUTION
SUNDAY LOOKS TO BE A BREAK BETWEEN THE RAIN CHANCES ON FRI/SAT AND
THE NEXT SYSTEM THAT APPROACHES EARLY NEXT WEEK.

SUNDAY AFTERNOON...SOUTHEASTERLY FLOW WILL BEGIN TO BRING A
LITTLE MORE LOW LEVEL MOISTURE OUT AHEAD OF THE NEXT SYSTEM
APPROACHING FROM THE NORTHWEST ON MONDAY. THE MODEL TREND HAS BEEN
FOR A SLOWER AND MORE NORTHERLY PROGRESSION OF THIS SYSTEM WITH
THE CLOSED UPPER LOW SITUATED OVER CENTRAL MONTANA BY WEDNESDAY.

THEREFORE...POP CHANCES WILL INCREASE MONDAY MORNING FROM WEST TO
EAST THROUGH THE DAY. GOOD CONFIDENCE IN RAIN WITH OVERCAST SKIES
UNTIL WE GET TO WEDNESDAY. AT THAT POINT MODEL SOLUTIONS BEGIN TO
DIFFER WITH THE EURO CLEARING OUT THE LOW AND ASSOCIATED PRECIP
QUICKLY WHILE THE GFS KEEPS THE LOW IN PLACE WITH WRAP AROUND
MOISTURE AND COOLER TEMPERATURES FILTERING IN FROM THE NORTHWEST.
FOR NOW..KEEPING CHANCE POPS THROUGH THE END OF THE PERIOD UNTIL
THE MODELS SHOW BETTER AGREEMENT. WALSH

&&

.AVIATION...

MAINLY VFR CONDITIONS THROUGH THE PERIOD. WIND SHIFT BEHIND THE
FRONTAL PASSAGE AROUND 06-07Z FOR BIL/LVM AND 10-12Z FOR MLS/SHR.
TOMORROW VCSH CONCERNS AND MVFR CIGS FOR SHR..BIL..LVM. FOR NOW
WENT WITH MVFR BUT MAY NEED TO LOWER TO IFR IN SUBSEQUENT FORECAST
PACKAGES. WALSH

&&

.PRELIMINARY POINT TEMP/POPS...

    FRI     SAT     SUN     MON     TUE     WED     THU
-----------------------------------------------------------
BIL 055/064 045/065 042/074 049/061 041/054 040/057 041/062
    24/T    32/T    11/B    45/T    55/W    44/W    32/W
LVM 048/058 042/061 038/074 043/059 037/052 035/056 036/060
    26/T    63/T    22/T    66/T    55/W    43/W    22/W
HDN 047/067 045/066 041/074 042/064 039/056 038/058 039/063
    14/T    32/T    11/B    34/T    55/W    44/W    33/W
MLS 056/072 044/070 044/075 048/070 045/059 043/060 043/064
    12/W    21/U    10/U    24/T    55/W    32/W    22/W
4BQ 052/074 045/067 041/069 042/067 041/056 039/058 039/062
    12/T    32/T    11/B    35/T    55/W    43/W    33/W
BHK 052/073 043/070 041/070 043/068 043/059 039/058 038/061
    01/N    11/U    00/U    23/T    44/W    32/W    33/W
SHR 045/064 040/057 039/067 039/060 038/053 037/054 036/060
    14/T    66/T    32/T    35/T    55/W    33/W    32/W

&&

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

&&

$$
WEATHER.GOV/BILLINGS


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