Area Forecast Discussion
Issued by NWS Billings, MT

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000
FXUS65 KBYZ 190248
AFDBYZ

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BILLINGS MT
848 PM MDT THU SEP 18 2014

.UPDATE...
LOW AMPLITUDE TROUGH AND ASSOCIATED SHORT WAVE ACTIVITY RIDING
ALONG A PLUME OF PACIFIC/SUBTROPICAL MOISTURE HAS RESULTED IN A
RAINY EVENING ACROSS MUCH OF OUR FORECAST AREA THIS EVENING. STILL
LIGHTNING UPSTREAM IN NW WYOMING AND SOUTHERN IDAHO. TRAJECTORY
MOVES MUCH OF THIS ACROSS OUR SOUTH AND EAST OVERNIGHT. I HAVE
ADJUSTED POPS TO ACCOUNT FOR THESE EXPECTATIONS...KEEPING HIGHEST
POPS MAINLY EAST OF A RED LODGE TO HYSHAM LINE OVERNIGHT.
BILLINGS STILL HAS A CHANCE OF ANOTHER SURGE...BUT GENERALLY
LOOKS LIKE IT WILL STAY SOUTH OF CITY OVERNIGHT. BT

&&

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

SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS WILL OCCUR TONIGHT
AND ISOLATED STRONG OR EVEN SEVERE STORMS ARE POSSIBLE THROUGH THE
EARLY EVENING HOURS.

AS OF MID AFTERNOON...THERE HAVE BEEN ENOUGH BREAKS IN CLOUD COVER
TO ENABLE TEMPERATURES IN THE 70S F BEHIND THE EARLIER SHOWERS AND
THUS MLCAPE VALUES HAVE RISEN TO 500-1000 J/KG IN SOUTHWESTERN AND
SOUTH CENTRAL MT PER RAP-BASED SPC MESOANALYSIS DATA. HEIGHT FALLS
HAVE CONTRIBUTED TO SEVERAL STORMS FROM THE ID PANHANDLE TO AROUND
LIVINGSTON AS OF 21 UTC. WE EXPECT FURTHER EXPANSION OF THAT STORM
ACTIVITY AS IT PROPAGATES EAST-NORTHEAST ACROSS THE AREA AND SO WE
ARE CARRYING LIKELY POPS ACROSS SOUTH CENTRAL MT AND NORTH CENTRAL
WY THIS EVENING. RECENT HRRR RUNS APPEAR TO MATCH THIS IDEA AND SO
WE LEANED TOWARD ITS SOLUTIONS TO BUILD THE EVENING FORECAST. SOME
RISK OF STRONG OR EVEN MARGINALLY SEVERE STORMS EXISTS WITH 0-6-KM
BULK SHEAR AROUND 40 KT. WELL-ORGANIZED...PERSISTENT CELLS WITH 50
DBZ HEIGHTS OVER 25 THOUSAND FEET AGL AND/OR BASE VELOCITIES OF 50
KT OR BETTER AT HEIGHTS UNDER 2000 FT AGL MAY NEED SEVERE THUNDER-
STORM WARNINGS...THOUGH WE NEED TO STRESS THAT WILL BE AN ISOLATED
OCCURRENCE AT MOST. A CHANCE OF SHOWERS AND WEAK STORMS WILL EXIST
OVER THE AREA AFTER MIDNIGHT TOO...BUT MAINLY IN SOUTHEASTERN MT.

A DRIER NORTHWEST FLOW ALOFT WILL TAKE OVER FRI AND BY SAT HEIGHTS
ALOFT WILL BE RISING STEADILY AS A RIDGE DEVELOPS OVER THE REGION.
WE ARE NOW ADVERTISING A DRY FORECAST IN MOST AREAS FRI EXCEPT FOR
THE MOUNTAINS AND IN FAR SOUTHEASTERN MT IN THE MORNING AS NONE OF
THE 12 UTC GUIDANCE SIMULATED ANY PRECIPITATION AND SOUNDINGS FROM
THOSE MODELS SHOWED STABLE PROFILES WITH A MID-LEVEL INVERSION. WE
EXPECT HIGHS NEAR 80 F FRI IN A WELL-MIXED AIR MASS AND IN THE 70S
F SAT WITH LIGHTER WINDS IN A MORE SHALLOW BOUNDARY LAYER. SCHULTZ

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

RELATIVELY WARM...LOW-KEY WEATHER IS EXPECTED FOR MUCH OF THE LONG
TERM FORECAST PERIOD AND WE ACCORDINGLY LEANED ON THE CONSENSUS OF
12 UTC GUIDANCE TO BUILD THE GRIDDED FORECAST DATABASE. WE DO HAVE
A CHANCE OF SHOWERS AND STORMS IN PLAY ACROSS NORTH CENTRAL WY AND
PARTS OF SOUTHERN MT SUN NIGHT THROUGH TUE IN RESPECT TO POTENTIAL
FOR A WEAK UPPER-LEVEL LOW MEANDERING ACROSS WY. GUIDANCE HAS BEEN
TRENDING A BIT NORTH WITH THAT FEATURE AND AN IN-HOUSE SET OF MOS-
BASED POP DATA SUPPORTED LOW-END PRECIPITATION CHANCES DURING THAT
TIME FRAME. HOWEVER...THE TRACK OF THE LOW IS QUESTIONABLE BECAUSE
IT WILL BE UNDERCUTTING MEAN RIDGING ALOFT WHICH ITSELF LOOKS LIKE
IT WILL MOVE EASTWARD WITH TIME AS A TROUGH BECOMES ESTABLISHED IN
THE PACIFIC NORTHWEST BY LATE IN THE WEEK. A WARMING TREND WILL BE
IN PLACE WITH WARM AIR ADVECTION AHEAD OF THAT TROUGH. SCHULTZ

&&

.AVIATION...

SCATTERED SHOWERS AND THUNDERSTORMS CONTINUE ACROSS MUCH OF THE
REGION THIS EVENING...AND WILL CONTINUE INTO TONIGHT...WITH MVFR
TO IFR CONDITIONS EXPECTED WITH THE THUNDERSTORMS. OBSCURATION
OVER AREA MOUNTAINS WILL CLEAR OVERNIGHT. SHOWERS AND
THUNDERSTORMS ARE EXPECTED TO CLEAR FROM WEST TO EAST EARLY FRIDAY
MORNING. AAG

&&

.PRELIMINARY POINT TEMP/POPS...

    FRI     SAT     SUN     MON     TUE     WED     THU
-----------------------------------------------------------
BIL 059/080 052/075 049/076 053/075 054/077 054/078 054/079
    41/B    10/U    00/U    12/T    22/T    11/U    12/T
LVM 051/078 043/077 043/076 047/077 049/078 048/079 049/079
    31/N    10/U    00/U    12/T    22/T    21/B    22/T
HDN 058/082 050/077 045/078 052/078 052/078 052/080 052/081
    71/B    10/U    00/U    12/T    22/T    11/U    12/T
MLS 061/082 051/075 045/076 052/078 054/076 053/079 053/081
    82/T    00/U    00/U    01/U    12/T    21/U    11/B
4BQ 061/082 051/076 046/076 053/076 054/075 052/079 052/082
    62/T    10/U    00/U    12/T    22/T    21/U    11/U
BHK 060/080 049/074 041/073 047/076 051/072 049/076 050/078
    62/T    10/U    00/U    01/U    12/T    21/U    11/B
SHR 058/080 048/076 045/077 051/073 049/075 049/078 050/080
    52/T    20/U    00/U    22/T    22/T    21/U    11/B

&&

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

&&

$$
WEATHER.GOV/BILLINGS



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