Area Forecast Discussion
Issued by NWS Billings, MT

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242
FXUS65 KBYZ 161904
AFDBYZ

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BILLINGS MT
104 PM MDT SAT MAY 16 2015

.UPDATE...
QUICK UPDATE TO AFTERNOON FORECAST FOR RADAR TRENDS...MAINLY
BUMPING UP POPS IN THE BULL MOUNTAINS AND SECTIONS OF THE WEST
AS WRAP AROUND WORKS INTO THE FORECAST AREA. BT

&&

.SHORT TERM...VALID FOR TDY AND SUN...

VERY COMPLEX WEATHER PICTURE OUT THERE THIS MORNING AS LARGE UPPER
LOW EVOLVES SLOWLY OVER THE WESTERN CONUS. MAIN SOUTHERLY JET IS
OVER THE HIGH PLAINS FROM EASTERN COLORADO TO THE WESTERN
DAKOTAS...AND DIFFLUENCE WITH THIS FEATURE IS ENHANCING PCPN OVER
OUR EAST. DETACHED 60KT STREAK IS LIFTING FROM WY INTO SOUTHEAST
MT. STRONG UPPER DIFFLUENCE AS A RESULT IS SHIFTING WEST AS DRY
SLOT PUSHES INTO OUR CWA...WITH NVA APPROACHING FROM CENTRAL WY AS
OF 09Z...ALL SEEN CLEARLY ON WATER VAPOR IMAGERY. WE DID SEE A
PERIOD OF GOOD RAINFALL DURING THE NIGHT BUT MOST OF OUR AREA WILL
SEE A DECREASE IN PRECIPITATION THIS MORNING AS ASCENT SHIFTS TO
OUR N-NW. SHERIDAN HAS ACTUALLY BEEN DRY FOR A FEW HOURS NOW.
LATEST MODEL RUNS ARE IN LINE WITH THESE SATELLITE AND RADAR
TRENDS. THUS...HAVE MADE SOME SIGNIFICANT FORECAST CHANGES
ESPECIALLY FOR TODAY.

HAVE TRENDED POPS DOWN ESPECIALLY FROM BILLINGS SOUTH AND EAST
ONCE THE EARLY MORNING PCPN LIFTS OUT OF OUR CWA. WILL KEEP
HIGHEST POPS IN OUR WEST NEAR REGION OF STRONG DIFFLUENCE ALOFT.
THE MID LEVEL DRY SLOTTING WILL HELP OUR CONVECTIVE POTENTIAL THIS
AFTERNOON DUE TO WARMER SFC TEMPS AND DESTABILIZING...SHOULD SEE
HIGHS INTO THE 60S IN SHERIDAN AND ACROSS OUR EAST...ALLOWING FOR
500-1000 J/KG OF CAPE EVEN JUST A LITTLE EAST OF BILLINGS. HAVE
EXPANDED OUR POTENTIAL TSTM AREA FOR TODAY. BETTER SEVERE CHANCES
SHOULD REMAIN TO OUR EAST AND SOUTHEAST HOWEVER.

FOR BILLINGS...THIS WILL NOT BE A DAY OF RAIN...RATHER SCATTERED
SHOWERS UNDER WEAK UPPER LOW AND WITH PLENTY OF GROUND MOISTURE
AROUND. SFC TEMPS INTO THE MID TO UPPER 50S WILL HELP THIS CAUSE.
GREATEST POTENTIAL THIS AFTERNOON WILL ACTUALLY BE OVER THE HIGHER
TERRAIN SOUTH OF THE METRO AREA...AS RAP/HRRR SUGGEST.

IMPRESSIVE 110KT JET OVER SOUTHERN AZ WILL DRIVE INTO THE CENTRAL
PLAINS TONIGHT. WEAK UPPER LOW OVER OUR AREA WILL BEGIN TO SHIFT
EAST AND PHASE WITH THE CENTRAL PLAINS LOW...ALLOWING FOR TROWAL
PCPN TO DROP BACK INTO OUR REGION IN A DEVELOPING NW FLOW ALOFT.
THIS WILL INCREASE THE COVERAGE OF SHOWERS...AND AS WE COLD ADVECT
SNOW LEVELS WILL FALL OVER THE MOUNTAINS. STILL LOOKS LIKE SHOWERS
ARE LIKELY ACROSS THE ENTIRE REGION TONIGHT AND SUNDAY. MORE
INTERESTING FACET OF THIS SYSTEM MAY BE THE COLDER CANADIAN AIR
THAT PHASES WITH IT...AN AIRMASS ASSOCIATED WITH CLIPPER CURRENTLY
PUSHING INTO NORTHERN SASKATCHEWAN. LATEST GFS/ECMWF ARE A BIT
COLDER AND SHOW 850MB TEMPS FALLING BELOW ZERO ON SUNDAY. SO ITS
POSSIBLE OUR EASTERN AREAS MAY MIX WITH WET SNOW SUNDAY AFTERNOON
AND EVENING...THOUGH SFC TEMPS WILL REMAIN TOO WARM FOR
ACCUMULATION. IT IS ALSO POSSIBLE THAT BILLINGS COULD SEE A BRIEF
MIX WITH SNOW BY THE EVENING AS SFC WINDS TURN BACK TO THE NE.

ADDITIONAL PCPN FROM TODAY THROUGH SUNDAY WILL RANGE FROM A HALF
INCH TO INCH...LESS THAN PREVIOUSLY THOUGHT BUT STILL MUCH NEEDED
MOISTURE. SOME FOOTHILLS SITES HAVE ALREADY EXCEEDED IN INCH IN
FACT. BIGGEST OVERALL IMPACT MAY BE THE CHILLY NIGHT AND
POTENTIAL FREEZE ACROSS THE LOWER ELEVATIONS EARLY MONDAY MORNING.
RECORDS AT BILLINGS AND MILES CITY WILL BE CHALLENGED ON THE 18TH.

AS FOR OUR MOUNTAIN HIGHLIGHTS...WILL KEEP THE WINTER STORM
WARNING RUNNING FOR THE BEARTOOTH ABSAROKAS AS SOME GOOD SNOWFALL
FELL DURING THE NIGHT AND MORE IS EXPECTED TONIGHT INTO SUNDAY PER
AFOREMENTIONED TROWAL. BIGHORNS DO NOT LOOK PROMISING PER THE DRY
SLOTTING AND WARMER TEMPS. DO NOT SEE A RISK OF SNOW OVER THE
BIGHORNS UNTIL LATE TONIGHT OR EARLY SUNDAY...WHEN FLOW TURNS TO
THE NW...SO HAVE OPTED TO CANCEL THE ADVISORY. SHOULD STILL SEE A
FEW INCHES IN THE MOIST NW FLOW TOMORROW.

JKL

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

MONDAY WEAK RIDGING OVER THE AREA WITH UNSEASONABLY COOL HIGH
PRESSURE CENTERED OVER THE DAKOTAS. WILL BE A DRIER DAY BUT
EASTERLY SURFACE FLOW WILL KEEP TEMPERATURES BELOW NORMAL. GIVEN
RECENT MOISTURE AND UPSLOPE FLOW SHOULD SEE SOME MOUNTAIN SHOWER
ACTIVITY FOR THE BEARTOOTH AND ABSAROKA MOUNTAINS. MONDAY NIGHT A
SYSTEM OVER CALIFORNIA WILL BEGINS MOVING INTO THE GREAT BASIN AND
THIS CONTINUES INTO TUESDAY WITH THE WEAK RIDGING TRANSITIONINGINTO
WEAK DIFFLUENCE ALOFT. THIS GIVES BETTER SUPPORT TO SCATTERED
SHOWER ACTIVITY ACROSS THE SOUTHERN HALF OF THE AREA WHERE
MOISTURE WILL BE A LITTLE DEEPER. ECMWF IS A BIT MORE AGGRESSIVE
THAN THE GFS IN HOW FAR NORTH TO PUSH THIS MOISTURE SO HAVE A
COMPROMISE BUT WILL HAVE TO WATCH THIS PERIOD AS THE ECMWF IS
ADVERTISING A MUCH WETTER SOLUTION ESPECIALLY INTO WEDNESDAY.

LIGHT UPSLOPE AND WEAK FLOW ALOFT THURSDAY AND FRIDAY WILL KEEP
MAINLY DIURNAL SHOWERS IN THE FORECAST WITH BELOW NORMAL
TEMPERATURES. MODELS ADVERTISING A LESS POTENT LOW PRESSURE
SYSTEM PASSING SOUTH OF THE AREA ON SATURDAY BUT STILL COULD BRING
AN INCREASE IN PRECIPITATION TO THE AREA. BORSUM
&&

.AVIATION...

LOW CLOUDS WILL BE PERSISTENT THROUGH MUCH OF THE DAY WITH IFR TO
MVFR CONDITIONS PREVALENT. A FEW LIGHT SHOWERS WILL LINGER WEST OF
A HYSHAM TO BILLINGS TO RED LODGE LINE. MORE SHOWERS WILL DEVELOP
OVER MOST OF THE AREA THIS AFTERNOON AND KEEP MVFR CONDITIONS IN
PLACE. THE MOUNTAINS WILL SEE SNOW SHOWERS...WITH OBSCURATIONS
THROUGH THE DAY. TWH
&&

.PRELIMINARY POINT TEMP/POPS...

    TDY SUN     MON     TUE     WED     THU     FRI
-------------------------------------------------------
BIL 058 043/048 035/055 039/058 040/053 041/059 043/063
    4/T 77/W    21/E    12/W    43/W    22/W    33/W
LVM 050 039/051 033/053 035/057 038/054 037/060 039/062
    9/W 86/W    32/T    12/W    33/W    33/W    34/W
HDN 060 042/048 033/058 038/060 040/056 039/063 043/066
    4/T 76/W    21/B    12/W    33/W    21/E    33/W
MLS 062 044/046 032/055 035/055 039/056 039/060 043/064
    2/T 66/W    20/B    02/W    33/W    21/B    22/W
4BQ 067 045/049 031/055 036/053 038/054 038/059 043/063
    2/T 57/W    31/B    03/W    54/W    22/W    22/W
BHK 066 045/046 028/052 031/051 036/053 037/056 040/061
    2/T 67/W    30/B    02/W    43/W    22/W    22/W
SHR 063 041/047 032/056 037/056 038/053 037/061 041/063
    3/T 67/W    31/E    13/W    54/W    22/W    34/W

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...WINTER STORM WARNING IN EFFECT UNTIL 6 PM MDT SUNDAY ABOVE
      7000 FEET FOR ZONE 67.
WY...NONE.

&&

$$
WEATHER.GOV/BILLINGS



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