Area Forecast Discussion
Issued by NWS Billings, MT

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000
FXUS65 KBYZ 031506
AFDBYZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
906 AM MDT WED JUN 3 2015

.UPDATE...
WATER VAPOR IMAGERY PLUS H5 ANALYSIS SHOWS SHORTWAVE ENERGY
DEPARTING WELL TO OUR NORTHEAST WITH UPSTREAM PV IN SW FLOW ALOFT
LOCATED OVER OR/NV/CA. THE ENERGY TO OUR SOUTHWEST WILL BE OF
INTEREST TONIGHT...BUT LARGE SCALE SUBSIDENCE EXISTS OVER OUR
REGION NOW AND THIS WILL LIMIT CONVECTIVE DEVELOPMENT FOR MUCH OF
OUR CWA DURING THE DAY. FULLY EXPECT AFTERNOON ACTIVITY TO GET
GOING OVER THE MTNS AND FOOTHILLS. RAP/HRRR SOUNDINGS SHOW CAPPED
EAST WINDS FOR THE LOWER ELEVATIONS FROM BILLINGS EAST...SO
DIURNAL DEVELOPMENT SHOULD STRUGGLE TO EVOLVE OFF THE FOOTHILLS
INITIALLY UNTIL ASCENT FROM SW SHORTWAVE ARRIVES. THE OVERALL
THEME OF LATER DEVELOPMENT THAN YESTERDAY WITH GREATEST CHANCES OF
TSTMS AFTER 00Z IS COVERED WELL BY THE CURRENT FORECAST.

ONLY MINOR UPDATES MADE THIS MORNING. WILL LET FOG WORDING END AT
15Z BUT LARGE AREAS OF STRATUS STILL EXIST FROM BILLINGS EAST.
HAVE TWEAKED SKY COVER AND ADJUSTED TEMPS UP SLIGHTLY BASED ON
EXPECTED MIX DOWNS THIS AFTERNOON. HAVE ALSO PUSHED BACK ISOLD TS
AT BILLINGS TIL AFTER 21Z.

JKL

&&

.SHORT TERM...VALID FOR TDY AND THU...

COOL AND UNSETTLED WEATHER WILL CONTINUE THE NEXT FEW DAYS...WITH
THE HIGHEST CHANCE OF PRECIPITATION COMING TONIGHT INTO THURSDAY
MORNING FROM SHERIDAN COUNTY NORTHEAST ACROSS SOUTHEASTERN MT.

TODAY...SUBTLE MID-LEVEL HEIGHT RISES ARE EXPECTED AND THAT SHOULD
KEEP CONVECTION AT A MINIMUM AWAY FROM THE HIGHER TERRAIN. MOST OF
THE 00 UTC CONVECTION-ALLOWING MODEL GUIDANCE CONFIRMS THAT IDEA.
WE DID LEAVE SOME SLIGHT CHANCE POPS IN PLAY THIS AFTERNOON AS FAR
NORTHEAST AS BILLINGS AND LODGE GRASS SINCE FORECAST SOUNDINGS DO
SHOW AN UNCAPPED AND MODESTLY UNSTABLE BOUNDARY LAYER. MORE THAN
LIKELY...CONVECTION DURING THE DAY WILL LARGELY STAY CLOSE TO THE
HIGHER TERRAIN WHERE DIFFERENTIAL HEATING...UPSLOPE LOW-LEVEL FLOW
AND THE PRESENCE OF A WEAK STATIONARY FRONTAL BOUNDARY WILL LIKELY
AIDE SOME DEVELOPMENT. IT WILL JUST HAVE A HARD TIME PROPAGATING
DOWNSTREAM INTO THE LOWER ELEVATIONS DURING THE DAY WITH THE WEAK
HEIGHT RISES ALOFT. OTHERWISE...HIGHS TODAY WILL BE COOL...MAINLY
IN THE UPPER 60S AND LOWER 70S F. EARLY-DAY LOW CLOUDS /STRATUS/
COULD KEEP HIGHS A BIT COOLER THAN ADVERTISED IN SPOTS IF THEY DO
LINGER TOO LONG DURING THE DAY.

TONIGHT...THE LARGE-SCALE...SYNOPTIC-SCALE PATTERN WILL ONCE MORE
BECOME FAVORABLE FOR SHOWERS AND THUNDERSTORMS. THE PRIMARY SHORT
WAVE OF INTEREST IS EXPECTED TO CROSS CENTRAL WY THIS EVENING AND
MOVE INTO SOUTHEASTERN MT OVERNIGHT. WE ARE CONFIDENT IN MOISTURE
ACCOMPANYING THIS BATCH OF SEASONABLY MODEST FORCING WITH AROUND
ONE INCH OF PRECIPITABLE WATER IN PLACE. IN FACT...WE ARE A BIT
CONCERNED ABOUT LOCALLY HEAVY RAIN WITH THAT SHORT WAVE OVER THE
NORTHEAST BIGHORN MOUNTAINS AND SHERIDAN COUNTY...AND WE ACTUALLY
GAVE SOME CONSIDERATION TO ISSUING A FLASH FLOOD WATCH FROM LATE
AFTERNOON THROUGH TONIGHT FOR THOSE AREAS. HOWEVER...CONVECTION-
ALLOWING MODEL GUIDANCE IS NOT PARTICULARLY AGGRESSIVE WITH ITS
PRECIPITATION TOTALS IN THAT AREA AND FLASH FLOOD GUIDANCE ISN/T
THAT LOW...SO WE HELD OFF ON ISSUING A HEADLINE FOR NOW. WE NEED
TO NOTE THAT THE CONVECTION-ALLOWING GUIDANCE DOES PICK UP ON A
SECOND AREA OF MORE ENHANCED STORM ACTIVITY CENTERED ON WHEATLAND
COUNTY THIS EVENING TOO...AND THERE WILL BE AT LEAST SOME CHANCE
OF SHOWERS AND STORMS ACROSS THE WHOLE AREA. HOWEVER....UPDRAFT
HELICITY SIGNATURES FROM THE 00 UTC CONVECTION-ALLOWING MODELS ARE
MINIMAL AND GIVEN MARGINAL INSTABILITY...WE FEEL THAT THE OVERALL
RISK OF A STRONG STORM IS MUCH LOWER THAN THE PAST FEW DAYS.

THURSDAY...SHOWERS AND STORMS WILL BE ONGOING OVER SOUTHEASTERN MT
DURING THE MORNING AS THE AFOREMENTIONED SHORTWAVE TROUGH MOVES TO
THE NORTHEAST...AND THERE WILL BE AT LEAST A LOW-END CHANCE FOR A
SHOWER OR STORM ELSEWHERE TOO WITH THE SOUTHWEST FLOW ALOFT. GIVEN
CONTINUED EASTERLY LOW-LEVEL FLOW AND THE DISTINCT POSSIBILITY THE
SOURCE REGION OF THAT AIR OVER EASTERN MT WILL BE RAIN-COOLED...WE
MAY BE A BIT OPTIMISTIC WITH FORECAST HIGHS EVEN THOUGH WE LEANED
A BIT TOWARD THE RAW...2 METER TEMPERATURE GUIDANCE...PARTICULARLY
IN SOUTHEASTERN MT WHERE PRECIPITATION WILL OCCUR DURING THE DAY.
THE RELATIVELY COOL BOUNDARY LAYER WILL LIKELY MINIMIZE THE CHANCE
OF ANY STRONG STORMS ONCE AGAIN AS WELL. SCHULTZ

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

BEGINNING OF THE EXTENDED PERIOD CONTINUES TO LOOK WET...THEN A
DRYING TREND WAS FORECAST TO TAKE PLACE BEGINNING ON SUN. THE
NAEFS SHOWED HIGH PRECIPITABLE WATERS FROM /0.75/ TO 1 INCH ON
FRI...WITH HIGHER VALUES FRI NIGHT. FRI STARTS OFF WITH WEAK
RIDGING ALOFT...THEN A DIFFLUENT FLOW OVERTAKES THE REGION BETWEEN
THE RIDGE MOVING OFF TO THE E AND THE PACIFIC LOW OVER S CA. THIS
DIFFLUENCE WILL COMBINE WITH WEAK WAVES IN THE FLOW TO BRING A
GOOD CHANCE OF PRECIPITATION TO THE AREA LATE FRI INTO SAT. NOTED
THAT THE SREF FORECASTED A HIGH PROBABILITY OF CAPES OF AT LEAST
1000 J/KG FOR FRI THROUGH FRI EVENING...BUT THE SHEAR WAS NOT
IMPRESSIVE. IF THE ABOVE SCENARIO PANS OUT...THIS PERIOD WOULD BE
CONDUCIVE FOR SLOW-MOVING STORMS WITH HEAVY RAINFALL...AND
POSSIBLE FLOODING. WILL MENTION THIS POSSIBILITY IN THE HWO.

THE DIFFLUENCE WEAKENS SAT NIGHT AS THE CA LOW MOVES NE TOWARD WY.
THIS LOW DISSIPATES ON SUN AND UPPER RIDGING BUILDS OVER THE AREA
FROM THE W. RIDGING THEN PREVAILS OVER THE AREA THROUGH TUE. HAVE
FOLLOWED SUIT...AND GONE WITH A DRIER FORECAST FOR THIS PERIOD.
NOTE HOWEVER THAT THE GFS ENSEMBLES DID SHOW INCREASING
UNCERTAINTY WITH HOW THE PATTERN PLAYS OUT BEGINNING SUN NIGHT.
THERE ARE TWO TROPICAL SYSTEMS IN THE EASTERN PACIFIC AND THESE
SYSTEMS OFTEN CAUSE UNCERTAINTY IN THE MODELS/ FORECASTS.

UPPER RIDGING OR A MORE ZONAL FLOW WILL BE OVER THE AREA ON WED
WITH AN INCREASE IN PRECIPITABLE WATERS. ENERGY MOVING INTO THE
AREA SUPPORTED THE NEXT CHANCE OF PRECIPITATION.

NEAR SEASONAL TEMPERATURES FRI AND SAT WILL BE FOLLOWED BY A
WARMING TREND FOR THE REMAINDER OF THE PERIOD. ARTHUR
&&

.AVIATION...

PATCHY FOG AND STRATUS BROUGHT ABOUT LOW CEILINGS IN THE IFR TO
VLIFR RANGE TO THE REGION THIS MORNING. CONDITIONS HAVE IMPROVED
AROUND 16Z. ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS WILL
DEVELOP OVER THE HIGH TERRAIN THIS AFTERNOON AND SPREAD ONTO THE
PLAINS BY THIS EVENING...AFFECTING THE KLVM...KBIL AND KSHR AREAS.
EXPECT MVFR/IFR OR LOWER CONDITIONS WITH ANY PRECIPITATION DUE TO
HEAVY RAINFALL. SCATTERED TO NUMEROUS SHOWERS AND STORMS WILL
AFFECT AREAS FROM ROUNDUP TO KBIL TO BROADUS AND W THIS EVENING.
SCATTERED TO NUMEROUS SHOWERS AND STORMS WILL OVERSPREAD THE
ENTIRE AREA AFTER 06Z WITH THE BEST CHANCES FOR PRECIPITATION OVER
SHERIDAN COUNTY AND FAR SE MT. EXPECT IFR/LIFR CONDITIONS WITH THE
PRECIPITATION TONIGHT. AREAS OF MOUNTAIN OBSCURATION THIS
AFTERNOON WILL BECOME WIDESPREAD THIS EVENING...THEN BEGIN
DECREASING AFTER 06Z TONIGHT OVER THE W. ARTHUR/SINGER

&&

.PRELIMINARY POINT TEMP/POPS...

    TDY THU     FRI     SAT     SUN     MON     TUE
-------------------------------------------------------
BIL 072 052/072 051/074 055/075 054/077 054/080 059/085
    2/T 43/T    23/T    54/T    32/W    21/B    11/B
LVM 068 046/069 049/072 050/073 049/074 049/078 055/082
    3/T 42/T    34/T    54/T    33/W    31/B    12/T
HDN 074 053/072 051/077 055/077 054/079 054/083 059/087
    2/T 45/T    24/T    54/T    42/W    21/B    11/B
MLS 072 053/065 052/076 057/077 054/079 056/081 060/085
    1/B 57/T    22/T    55/T    31/U    11/B    11/B
4BQ 072 053/067 052/076 056/075 054/077 055/080 059/084
    1/B 67/T    23/T    55/T    31/B    11/B    11/B
BHK 070 048/063 050/075 054/075 051/077 051/079 054/083
    0/B 36/T    32/T    55/T    31/U    11/B    11/B
SHR 071 049/070 049/073 052/071 051/072 049/077 053/081
    3/T 64/T    33/T    54/T    53/W    32/W    12/T

&&

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

&&

$$
WEATHER.GOV/BILLINGS



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