Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 062059
AFDBYZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
259 PM MDT WED MAY 6 2015

.SHORT TERM...VALID FOR THU AND FRI...

COOL WEATHER WILL CONTINUE THE NEXT FEW DAYS WITH OPPORTUNITIES
FOR ADDITIONAL MOISTURE...ESPECIALLY BY FRIDAY NIGHT.

TONIGHT...SHOWERS OVER SOUTHEASTERN MT ASSOCIATED WITH A SHORTWAVE
TROUGH LIFTING OUT OF NEBRASKA INTO THE DAKOTAS WILL CONTINUE INTO
THE EVENING...MAINLY AROUND BAKER AND EKALAKA...BUT GRADUALLY END
OVERNIGHT. RADAR TRENDS THIS AFTERNOON SUGGEST THE END OF SHOWERS
MAY BE A BIT SLOWER THAN THE 12 UTC GLOBAL MODELS AND MORE RECENT
RAP SIMULATIONS SUGGEST...SO WE DID HANG ONTO SOME MODEST /CHANCE-
STYLE/ POPS THERE EVEN AFTER MIDNIGHT. MEANWHILE...ANOTHER MIDDLE-
AND UPPER-LEVEL SHORTWAVE WHICH CAN BE SEEN OVER UTAH ON AFTERNOON
MOISTURE CHANNEL IMAGERY WILL APPROACH SOUTHWEST MT BY LATE NIGHT.
WE ARE THEREFORE ADVERTISING INCREASING POPS AROUND LIVINGSTON BY
LATE NIGHT...THOUGH THE BETTER FORCING LIKELY WON/T ARRIVE UNTIL
THURSDAY MORNING. BETWEEN THESE WAVES...LIKE IN BILLINGS...THERE
ISN/T APT TO BE TOO MUCH GOING ON OVERNIGHT.

THURSDAY...SHOWERS ARE LIKELY ACROSS THE WESTERN SECTIONS OF SOUTH
CENTRAL MT LIKE AT LIVINGSTON AND ACROSS THE MOUNTAINS AS MODERATE
QG-FORCING CROSSES THE AREA WITH THE SHORTWAVE TROUGH ORIGINATING
ACROSS UTAH TODAY. THERE IS SIGNIFICANT CONVECTION ONGOING WITH
THAT WAVE AS OF MID AFTERNOON...WHICH INCREASES OUR CONFIDENCE IN
GETTING MOISTURE ON THURSDAY OVER PARTS OF SOUTH CENTRAL MT AS THE
REMNANTS OF THAT CONVECTION WILL LIKELY MAKE IT INTO THE AREA. THE
REST OF THE AREA WILL HAVE COOL AND CLOUDY BUT DRY WEATHER...WITH
HIGHS MAINLY IN THE 50S F PER THE 12 UTC MULTI-MODEL CONSENSUS WE
USED TO BUILD MOST OF THE SHORT TERM FORECAST.

FRIDAY...LOW-LEVEL FLOW WILL TURN MORE EASTERLY AND DIFFLUENCE IS
LIKELY TO INCREASE DURING THE DAY...SO WE HAVE INCREASING POPS IN
SOUTH CENTRAL MT AND NORTH CENTRAL WY BY AFTERNOON. HIGHS WILL BE
EVEN COOLER THAN THURSDAY WITH THE MORE EASTERLY WIND COMPONENT.

FRIDAY NIGHT...PRECIPITATION WILL LIKELY BECOME MORE WIDESPREAD AS
DIFFLUENCE ALOFT FURTHER INTENSIFIES WITH THE EASTWARD ADVANCEMENT
OF A 500-MB LOW TOWARD THE FOUR CORNERS REGION. THE 12 UTC ECMWF
AND GFS GENERALLY AGREE ON THIS IDEA AND SO WE HAVE LIKELY POPS IN
PLACE FOR ALL OF SOUTH CENTRAL MT AND NORTH CENTRAL WY. WE HAVE A
RAIN/SNOW MIX IN THE FORECAST OVERNIGHT IN MANY AREAS BASED ON
850-MB TEMPERATURES OF 0 TO +2 C. FOOTHILLS LOCATIONS MAY GET SOME
ACCUMULATIONS BY DAYBREAK SATURDAY. HOWEVER...AT THIS POINT WE
CHOSE TO ADVERTISE ONLY RAIN IN THE FORECAST FOR BILLINGS PROPER
AS FORECAST SOUNDINGS SUGGEST NEAR-SURFACE WET BULB TEMPERATURES
WILL REMAIN JUST ABOVE 0 C WITH THE FREEZING LEVEL NEAR 1400 FT
AGL. WE WILL CERTAINLY REVISIT THAT WITH LATER FORECAST CYCLES
THOUGH...AND WE DO HAVE A MIX OF RAIN AND SNOW IN THE FORECAST FOR
THE HIGHER HILLS AROUND BILLINGS LATE FRIDAY NIGHT. SCHULTZ

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

COOL AND WET WEATHER EARLY IN THE EXTENDED PERIOD WILL GIVE WAY TO
A MODEST WARMING TREND NEXT WEEK.

UPPER LOW OVER THE CENTRAL ROCKIES SATURDAY WILL KICK INTO THE
HIGH PLAINS SUNDAY...INDUCING A STRONG SFC LOW OVER THE CENTRAL
PLAINS. THIS IS NOT AN IDEAL TRACK FOR US AND HEAVIEST PCPN WITH
THIS SYSTEM WILL OCCUR OUTSIDE OF OUR CWA FROM EASTERN WY INTO
SD...BUT WE WILL SEE SOME RAIN/SNOW NONETHELESS. ENERGY OUT OF
CANADA WILL DROP THROUGH WESTERN MT INTO SOUTHEAST ID BEFORE
PHASING WITH LOW TO OUR SOUTH. MODELS ARE IN SOME DISAGREEMENT
HERE...WITH THE GFS SHOWING DEEPER SOUTHERLY MOISTURE ADVECTION
SATURDAY INTO SATURDAY NIGHT THAN ANY OTHER MODEL...BUT THE GFS
SEEMS TO BE MOST REASONABLE GIVEN THE TRACK OF THIS NORTHERN
STREAM VORTICITY MAX AND DIFFLUENT FLOW ALOFT. SO IN ALL HAVE
LEANED TOWARD THE WETTER GFS TODAY BUT WITH CAUTION DUE TO SOME
UNCERTAINTY.

SATURDAY SHOULD BE A WET DAY ACROSS MOST OF OUR AREA BUT
ESPECIALLY THE UPSLOPE AREAS OF OUR WEST AND SOUTH. PCPN SHOULD
THEN TURN LIGHTER SATURDAY NIGHT AND FOR THE MOST PART TAPER OFF
LATE SATURDAY NIGHT INTO SUNDAY AS MAIN FORCING BECOMES ASSOCIATED
WITH STRONG LOW IN THE CENTRAL HIGH PLAINS AND WE DRAW DRIER AIR
FROM THE NE. EXPECT PCPN AMOUNTS FROM A QUARTER TO HALF INCH WITH
PERHAPS A BIT MORE IN UPSLOPE AREAS. 700MB TEMPS NEAR -8C
CERTAINTY INDICATE SNOW FOR THE HIGH TERRAIN AND WE WILL SEE
SEVERAL INCHES ALONG NE SLOPES. IT APPEARS ELEVATIONS DOWN TO
MAYBE 4500 FEET WILL ALSO SEE SOME WET SNOWFALL AS 850MB TEMPS
FALL TO NEAR ZERO BY EARLY SATURDAY IN OUR WEST...THEN SLIGHTLY
BELOW ZERO IN OUR SOUTHEAST SATURDAY NIGHT. COULD SEE SEVERAL
INCHES OF SNOW AT NOTORIOUSLY SNOWY SPRING LOCATIONS SUCH AS RED
LODGE AND STORY...BUT AGAIN MUST STRESS THE UNCERTAINTY IN THE
DURATION OF THE MOISTURE ADVECTION AND PCPN.

AS FOR BILLINGS...BELIEVE IT OR NOT WE COULD SEE A MIX WITH WET
SNOW EITHER EARLY SATURDAY MORNING OR SATURDAY NIGHT...BUT WARM
GROUND TEMPS WILL KEEP US FROM ACCUMULATING EXCEPT PERHAPS A BIT
OVER THE HIGHER HILLS. IF THE GFS VERIFIES...WE WILL SEE AN ALL-
DAY RAIN WITH TEMPS NO WARMER THAN THE LOWER 40S.

TEMPS SATURDAY WILL STRUGGLE TO GO ANYWHERE AND HIGHS WILL RANGE
FROM THE 30S ALONG THE FOOTHILLS TO NEAR 50F IN OUR DRIER
NORTHEAST PARTS. WARMING TREND WILL BEGIN SUNDAY BUT MODESTLY PER
THE LINGERING COOL EAST WINDS AROUND DYNAMIC LOW IN THE PLAINS.
HIGHS SUNDAY WILL STAY WELL BELOW NORMAL...MID 40S TO MID 50S.
MUST ALSO POINT OUT THAT A FROST OR FREEZE IS POSSIBLE EITHER
SATURDAY NIGHT OR SUNDAY NIGHT. KEEP THIS IN MIND IF YOU ARE
STARTING A GARDEN.

GOOD MODEL AGREEMENT EXISTS IN BUILDING AN ANOMALOUS HIGH OVER
WESTERN CANADA EARLY NEXT WEEK...ALLOWING FOR LOWER HEIGHTS AND
SOME DEGREE OF TROFFING OVER OUR REGION. AIRMASS WILL GRADUALLY
MODERATE AND WE SHOULD SEE HIGH TEMPS BACK NEAR NORMAL BY TUESDAY
AND MAYBE A LITTLE ABOVE BY NEXT WEDNESDAY. WILL KEEP SLIGHT POPS
FOR MAINLY THE MOUNTAINS AND FOOTHILLS MONDAY AND TUESDAY...WITH
BETTER CHANCE OF SHOWERS EMERGING BY WEDNESDAY AS NEXT PACIFIC
TROF PUSHES TOWARD THE NORTHERN ROCKIES.

JKL

&&

.AVIATION...

RAIN SHOWERS EAST OF KBIL...HEAVIEST NEAR THE DAKOTAS BORDER...
WILL GRADUALLY TAPER OFF INTO THIS EVENING. LOCAL MVFR WILL OCCUR
IN AND NEAR THIS SHOWER ACTIVITY...AND SCATTERED RAIN/SNOW SHOWERS
WILL CAUSE OCCASIONAL MOUNTAIN OBSCURATIONS. SHOWER ACTIVITY WILL
INCREASE OVER THE WESTERN MTNS AND FOOTHILLS ON THURSDAY. EXPECT
LOCAL MVFR ALONG THE FOOTHILLS AND FREQUENT MOUNTAIN OBSCURATIONS
TOMORROW. EAST WINDS WILL INCREASE AT KLVM THIS EVENING WITH GUSTS
NEAR 30 KTS. JKL

&&

.PRELIMINARY POINT TEMP/POPS...

    THU     FRI     SAT     SUN     MON     TUE     WED
-----------------------------------------------------------
BIL 041/053 039/049 037/043 035/051 034/058 038/065 044/069
    21/E    14/W    77/R    63/W    21/B    11/B    13/W
LVM 038/050 033/044 033/043 032/050 029/057 035/063 038/066
    36/W    25/W    77/O    63/W    22/W    23/W    33/W
HDN 038/055 036/054 037/045 035/051 031/060 034/066 041/070
    21/E    13/W    77/R    64/W    21/B    11/B    12/W
MLS 038/056 036/056 038/050 034/054 034/060 038/064 042/069
    31/E    12/W    55/R    52/W    21/B    11/B    12/W
4BQ 040/055 034/058 038/046 033/048 030/056 034/062 041/068
    31/N    12/W    66/R    64/W    21/B    11/B    12/W
BHK 038/054 033/056 035/049 032/049 030/056 034/059 038/065
    72/W    11/E    34/R    32/W    21/B    11/B    12/W
SHR 036/052 034/053 036/042 032/045 027/054 033/062 039/066
    33/W    13/W    88/O    75/W    31/B    11/B    13/W

&&

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

&&

$$
WEATHER.GOV/BILLINGS



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