Area Forecast Discussion
Issued by NWS Billings, MT

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000
FXUS65 KBYZ 040929
AFDBYZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
329 AM MDT FRI SEP 4 2015

.SHORT TERM...VALID FOR TDY AND SAT...

A DEEP UPPER TROUGH WAS POSITIONED OVER THE PACIFIC NORTHWEST
THIS MORNING. THIS TROUGH WILL BE THE WEATHER MAKER FOR THE
NORTHERN ROCKIES THE NEXT SEVERAL DAYS. SOUTHWEST FLOW ON THE
FRONT SIDE OF THE TROUGH HAS SENT SEVERAL DISTURBANCES INTO THE
FORECAST AREA OVERNIGHT FOR ROUNDS OF SHOWERS AND THUNDERSTORMS.
THE LAST OF THE STRONGER WAVES WAS MOVING THROUGH SOUTH CENTRAL
MONTANA THIS HOUR. WEAKER WAVES WERE PRESENT OVER NORTHERN
UTAH...BUT STRENGTH OF THIS WAVE DOES NOT APPEAR TO BE ENOUGH TO
OVERCOME CAPPING DUE TO LOW LEVEL NORTHEAST FLOW. THIS WILL LEAD
TO A DRY DAY FOR MOST OF THE DAY TODAY. A STRONGER WAVE DOES ROUND
THE TROUGH AND MOVE IN THIS EVENING AND THIS WILL GENERATE
SCATTERED SHOWERS AND THUNDERSTORMS.

THE UPPER TROUGH THEN KICKS NORTHEAST INTO NORTHERN MONTANA ON
SATURDAY. THIS WAS FARTHER NORTH THAN PREVIOUS RUNS AND THUS NOT
EXPECTING TREMENDOUSLY COOL WEATHER FOR SATURDAY. A POTENT
SHORTWAVE DOES RIP ACROSS THE FORECAST AREA SATURDAY AFTERNOON AND
EVENING FOR DYNAMIC ASCENT. CAP IN PLACE WITH COOL UPSLOPE LOW
LEVEL FLOW...BUT SHOULD SHOULD HAVE NO PROBLEM LIFTING THE
ATMOSPHERE ABOVE THE BOUNDARY LAYER AND TAPING INTO ELEVATED
INSTABILITY. MU CAPE GETS TO AROUND 1000J/KG FOR MOST OF THE
FORECAST AREA. EFFECTIVE BULK SHEAR WILL BE AROUND 45KTS...SO SOME
INGREDIENTS WILL BE IN PLACE FOR STRONG TO POSSIBLY SEVERE
THUNDERSTORMS. BOTH THE HI RES ARW AND NAM IGNITE STRONG STORMS
SOUTH TO SOUTHWEST OF BILLINGS LATE SATURDAY AFTERNOON. WILL KEEP
THE MENTION IN THE HWO. PRECIPITABLE WATERS OF AROUND 1 INCH WOULD
LEAD TO HEAVY RAIN. STORMS SHOULD BE MOVING AT A GOOD PACE WITH
500MB WINDS AT 50KTS...WHICH WOULD LIMIT THE FLASH FLOODING
THREAT. THAT BEING SAID...STORMS WILL PRODUCE VERY HEAVY RAIN AS
THEY MOVE THROUGH AND COULD PRODUCE WATER ISSUES FOR A BRIEF
PERIOD OF TIME.

THE SYSTEM KICKS NORTHEAST QUICKLY AND ENDS UP IN NORTH CENTRAL
MONTANA BY 12Z SUNDAY. THIS DRIES THE AREA IN SHORT ORDER...SO
LOWERED POPS OVERNIGHT SATURDAY NIGHT. WINDS WILL INCREASE AND
BECOME QUITE GUSTY SATURDAY NIGHT AS THE LOW DEEPENS OVER SOUTHERN
CANADA. 850-700MB WINDS WERE NOT AS STRONG THIS MODEL RUN WITH THE
SYSTEM MOVING FARTHER NORTH. 700MB TEMPERATURES WERE NOT AS COLD
THIS MODEL RUNS...SINCE THE UPPER TROUGH WAS FARTHER NORTH...BUT
STILL COLD ENOUGH FOR SNOW POTENTIAL OVER THE HIGHER PEAKS. THIS
SNOW CHANCE LOOKS LIMITED THOUGH AS THE LOW KICKS NORTHEAST SO
QUICKLY AND DRIES THE AREA OUT. TWH

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

THE LABOR DAY WEEKEND WILL END ON A COOLER...BUT LIKELY DRY TUNE.
THE 00 UTC GFS...ECMWF...AND GEM ALL AGREED ON A STRONG WESTERLY
/DOWNSLOPE/ FLOW DEVELOPING SUNDAY ON THE SOUTHERN FLANK OF THE
DEEP UPPER-LEVEL LOW THAT WILL BE SITUATED ACROSS SOUTHERN CANADA
BY THAT TIME. WE THEREFORE REDUCED POPS SIGNIFICANTLY SUNDAY AND
WENT WITH A DRY FORECAST IN MOST PLACES BY AFTERNOON. SUNDAY WILL
BE WINDY WITH SUSTAINED SPEEDS NEAR 30 MPH AND GUSTS AROUND 40 MPH
LIKELY BASED ON MEAN BOUNDARY LAYER WINDS OF 30 KT IN THE 00 UTC
MODEL GUIDANCE. THE WINDS WILL SETTLE DOWN CONSIDERABLY FOR LABOR
DAY AS THE GRADIENT RELAXES...BUT HIGHS ON BOTH SUNDAY AND MONDAY
WILL ONLY BE IN THE 60S F IN MOST LOWER-ELEVATION LOCATIONS.

HEADING INTO NEXT WEEK...IT APPEARS THAT WEAK 500-MB TROUGHING IS
GOING TO PREVAIL TUESDAY AND WEDNESDAY BEFORE HEIGHTS ALOFT BEGIN
TO MORE STEADILY REBOUND THURSDAY AND FRIDAY. THE RESULT WILL BE A
DISTINCT WARMING TREND WITH HIGHS INCREASING FROM AROUND 70 F ON
TUESDAY TO NEAR 80 F BY THURSDAY. THAT SCENARIO WAS WELL-CAPTURED
BY THE 00 UTC MULTI-MODEL CONSENSUS THAT WE USED TO BUILD THE
LONG TERM FORECAST. THAT GUIDANCE LED US TO A DRY FORECAST FOR
MOST PLACES AND DAYS NEXT WEEK AS WELL...THOUGH IF WEAK SHORTWAVE
IMPULSES ARRIVE IN THE MEAN TROUGH TUESDAY OR WEDNESDAY THERE MAY
BE SOME ISOLATED SHOWER ACTIVITY IN SPOTS THOSE DAYS. SCHULTZ

&&

.AVIATION...

SOME LOW CLOUDS WITH MVFR OR EVEN IFR CEILINGS COULD DEVELOP OVER
PARTS OF SOUTHERN MT THIS MORNING...ESPECIALLY IN THE KMLS TO KBHK
CORRIDOR...BUT OUR CONFIDENCE IN THAT IS LOW. VFR CONDITIONS WILL
OTHERWISE PREVAIL TODAY WITH ONLY A LOW-END CHANCE OF A SHOWER OR
THUNDERSTORM. THE PROBABILITY OF SHOWERS AND THUNDERSTORMS WITH
LOCAL MVFR CONDITIONS WILL INCREASE SOMEWHAT AFTER 00 UTC. SCHULTZ

&&

.PRELIMINARY POINT TEMP/POPS...

    TDY SAT     SUN     MON     TUE     WED     THU
-------------------------------------------------------
BIL 073 053/071 050/065 043/068 042/072 047/075 047/075
    2/T 33/T    77/T    21/B    11/B    11/B    11/U
LVM 072 046/072 043/062 036/067 035/073 041/074 042/076
    3/T 46/T    86/T    21/B    11/B    11/B    22/W
HDN 078 053/077 049/068 042/071 041/074 045/077 045/075
    2/T 33/T    66/T    21/U    11/U    11/B    11/U
MLS 081 059/080 053/066 044/070 043/071 046/077 047/073
    2/T 44/T    66/T    31/B    11/U    11/B    11/B
4BQ 082 060/084 054/069 046/071 046/071 049/077 049/073
    1/B 33/T    43/T    11/U    11/U    11/B    11/U
BHK 084 060/082 054/068 043/069 043/069 044/076 047/070
    2/T 44/T    53/T    11/U    11/B    11/B    11/B
SHR 082 052/081 047/069 039/071 038/073 042/076 043/074
    2/T 33/T    53/T    11/U    11/U    11/B    11/U

&&

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

&&

$$
WEATHER.GOV/BILLINGS



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