Area Forecast Discussion
Issued by NWS Billings, MT

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000
FXUS65 KBYZ 020939
AFDBYZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
339 AM MDT TUE JUN 2 2015

.SHORT TERM...VALID FOR TDY AND WED...

COOLER AND UNSETTLED WEATHER IS EXPECTED THE NEXT FEW DAYS...BUT
THAT WILL COME WITH A CHANCE OF A STRONG STORM AGAIN LATER TODAY.

TODAY...HIGHS WILL ONLY BE FROM 70 TO 75 F IN MOST AREAS IN THE
WAKE OF LAST NIGHT/S COLD FRONTAL PASSAGE. STRATIFORM RAIN THAT/S
TRAILING A MESOSCALE CONVECTIVE VORTEX OVER EAST CENTRAL MT AS OF
09 UTC IS GRADUALLY LIFTING NORTHWARD OUT OF SOUTHEASTERN MT...SO
MOST AREAS WILL BE DRY THIS MORNING. OVERNIGHT INFRARED SATELLITE
IMAGES ACTUALLY SUGGEST THERE WILL BE A FAIR AMOUNT OF SUNSHINE IN
MANY AREAS THIS MORNING...AND THAT GIVES US A BIT MORE CONFIDENCE
THAT SUFFICIENT DESTABILIZATION WILL OCCUR TO SUPPORT A NEW ROUND
OF AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS. MOST OF THE 00
UTC GUIDANCE SUITE SUPPORTS 500 J/KG OF MLCAPE OVER SOUTH CENTRAL
MT AND NORTH CENTRAL WY THIS AFTERNOON...AND SOME MODELS SIMULATE
UP TO 1000 J/KG OF MLCAPE...ESPECIALLY OVER SOUTHERN BIG HORN AND
SHERIDAN COUNTIES. MID- AND HIGH-LEVEL FLOW WILL REALLY STRENGTHEN
TODAY...YIELDING MUCH GREATER DEEP-LAYER SHEAR THAN THAT OBSERVED
ON MONDAY. FORECAST SOUNDINGS AT BILLINGS AND SHERIDAN SHOW 0-6-KM
BULK WIND SHEAR OF 50 TO 60 KT...WHICH IS FAVORABLE FOR ORGANIZED
STORMS...BUT COULD ACTUALLY PRESENT TOO MUCH SHEAR FOR SUSTAINED
UPDRAFTS IF BUOYANCY IS TOO SMALL. THERE/S A STRONG SIGNAL IN THE
00 UTC CONVECTION-ALLOWING MODEL OUTPUT FOR ISOLATED TO SCATTERED
SHOWER AND THUNDERSTORM DEVELOPMENT IN SOUTH CENTRAL MT AND NORTH
CENTRAL WY DURING THE AFTERNOON...AND THE RELATED 00 UTC SPC SSEO
GUIDANCE SHOWS RESPECTABLE PROBABILITIES OF UPDRAFT HELICITY
GREATER THAN 25 M2/S2...ESPECIALLY ACROSS BIG HORN...SHERIDAN AND
SOUTHERN ROSEBUD COUNTIES. IF SUFFICIENT MLCAPE IS PRESENT BY
AFTERNOON AND EARLY EVENING...THEN A FEW STRONG AND EVEN ISOLATED
SEVERE STORMS ARE POSSIBLE. HAILCAST OUTPUT APPLIED TO THE 00 UTC
NSSL WRF-ARW ENSEMBLE /WHICH DID VERIFY RATHER WELL YESTERDAY/
SUGGESTS THE MAXIMUM HAIL SIZE WITH THE MOST INTENSE STORMS WOULD
BE HELD CLOSE TO QUARTER SIZE...LIKELY A REFLECTION OF MLCAPE
BEING A BIT ON THE LOW SIDE FOR LONG-LIVED INTENSE UPDRAFTS.

FINALLY...NOTE THAT OVER SOUTHEASTERN MT WE DO HAVE A LOW CHANCE
OF SHOWERS AND STORMS IN THE FORECAST AS WELL TODAY...BUT WE FEEL
THAT CORNER OF THE STATE COULD ACTUALLY END UP BEING MAINLY DRY.

TONIGHT...THE CHANCE OF A STRONG STORM WILL LINGER INTO THE EARLY
EVENING FROM ABOUT LODGE GRASS AND SHERIDAN TO BROADUS...AND SOME
CHANCE OF WEAKER SHOWERS AND STORMS WILL PERSIST ELSEWHERE DURING
THE EVENING. EVEN THE WEAKER ACTIVITY WILL DECREASE OVERNIGHT. WE
MAY SEE SOME LOW CLOUDS /STRATUS/ DEVELOP AS WELL PER 00 UTC MOS
GUIDANCE...AND GIVEN RECENT MOISTURE PATCHY FOG IS POSSIBLE TOO.

WEDNESDAY...SOUTHWEST FLOW ALOFT WILL CONTINUE AND THUS A CHANCE
OF SHOWERS AND THUNDERSTORMS WILL AS WELL. THE POSSIBILITY OF LOW
CLOUDS WEDNESDAY MORNING AND EASTERLY /UPSLOPE/ WINDS IN THE LOWER
ATMOSPHERE MEANS THAT HIGHS WILL PROBABLY STAY BELOW 70 F IN MANY
AREAS. THAT WILL GREATLY LIMIT SURFACE-BASED INSTABILITY AND THAT
WILL KEEP ANY SHOWERS AND STORMS ON THE WEAKER SIDE. SCHULTZ

.LONG TERM...VALID FOR THU...FRI...SAT...SUN...MON...

MODELS WERE IN FAIRLY GOOD AGREEMENT FOR THE EXTENDED PERIOD. A
PACIFIC COAST TROUGH WILL DEVELOP INTO A CUTOFF LOW OVER CA EARLY
IN THE PERIOD. THE CUTOFF LOW WILL GRADUALLY MIGRATE NE BEGINNING
ON SUN. THE LOW WILL SEND PIECES OF VORTICITY NE INTO THE FORECAST
AREA THROUGH SAT BRINGING SCATTERED SHOWERS AND THUNDERSTORMS. FRI
NIGHT AND SAT WILL HAVE GOOD CHANCES OF PRECIPITATION AS THE GFS
SHOWS A SUBTROPICAL FEED OF MOISTURE INTO THE AREA. PRECIPITABLE
WATERS THROUGH MUCH OF THE PERIOD WILL BE ON THE ORDER OF /0.75/
INCHES TO AN INCH...WHICH WILL SUPPORT HEAVY RAINFALL WITH ANY
THUNDERSTORMS. THE AIRMASS WILL DRY OUT SOMEWHAT FOR SUN THROUGH
TUE AS AN UPPER RIDGE BUILDS OVER THE AREA AHEAD OF THE ADVANCING
CUTOFF LOW. REGARDING THE POSSIBILITY OF STRONG STORMS...THE BEST
COMBINATION OF CAPE AND SHEAR WILL BE ON THU BASED ON THE
GFS...ALTHOUGH THE SHEAR WAS MARGINALLY STRONG...AND THE CAPES
MAY BE INHIBITED BY COOL LOW-LEVEL EASTERLY FLOW.

A WARMING TREND IS EXPECTED SUN THROUGH TUE WITH HIGHS NEAR 80
DEGREES. ARTHUR

&&

.AVIATION...

VFR CONDITIONS WILL PREVAIL OVER THE AREA THIS MORNING. SCATTERED
SHOWERS AND THUNDERSTORMS WILL DEVELOP OVER THE CRAZY...BEARTOOTH
AND ABSAROKA MOUNTAINS THIS AFTERNOON AND OVERSPREAD THE AREA FROM
W TO E THROUGH THE EVENING. MVFR/IFR CONDITIONS WILL ACCOMPANY THE
THUNDERSTORMS WITH LOCALLY LOWER CONDITIONS POSSIBLE. THE
PRECIPITATION WILL END FROM W TO E OVERNIGHT. MVFR CEILINGS AND
AREAS OF FOG ARE POSSIBLE LATE TONIGHT ACROSS THE AREA. ARTHUR

&&

.PRELIMINARY POINT TEMP/POPS...

    TDY WED     THU     FRI     SAT     SUN     MON
-------------------------------------------------------
BIL 073 048/069 051/070 052/074 055/075 053/079 057/080
    4/T 32/T    43/T    33/T    53/T    32/T    23/T
LVM 070 045/065 047/070 049/071 049/073 049/076 054/077
    5/T 44/T    43/T    44/T    44/T    33/T    33/T
HDN 075 049/072 052/073 052/078 055/076 053/081 057/083
    4/T 32/T    54/T    33/T    53/T    32/T    22/T
MLS 072 050/072 053/068 053/076 057/076 054/080 057/082
    2/T 21/B    46/T    33/T    55/T    31/B    22/T
4BQ 078 049/072 054/070 054/076 056/075 053/078 057/080
    2/T 41/B    56/T    33/T    55/T    42/T    33/T
BHK 076 048/068 048/068 050/074 053/074 051/077 053/080
    3/T 21/B    36/T    32/T    55/T    41/B    22/T
SHR 075 047/068 048/070 050/073 052/072 049/075 053/077
    4/T 42/T    63/T    44/T    44/T    42/T    33/T

&&

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

&&

$$
WEATHER.GOV/BILLINGS


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