Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 271942
AFDBYZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
142 PM MDT MON APR 27 2015

.SHORT TERM...VALID FOR TUE AND WED...

WARM AND DRY WEATHER WILL PREVAIL THROUGH WEDNESDAY...WITH ONLY A
LOW-END CHANCE OF A SHOWER OR STORM COME WEDNESDAY NIGHT.

TONIGHT...SURFACE HIGH PRESSURE WILL SCOOT EAST INTO THE DAKOTAS
AND ALLOW LIGHT RETURN FLOW TO BEGIN ACROSS THE AREA. WE DO HAVE
SOME PATCHY FOG IN THE FORECAST FROM BILLINGS EAST ACROSS SOUTH-
EASTERN MT BETWEEN 06 AND 15 UTC OWING TO RESIDUAL MOISTURE FROM
RECENT RAINFALL COMBINED WITH WEAK SURFACE WIND FIELDS.

TUESDAY...UPPER-LEVEL RIDGING WILL TAKE FIRM HOLD OF THE AREA AND
HIGHS SHOULD MAINLY BE BETWEEN 65 AND 75 F DESPITE RELATIVELY WEAK
MIXING ASSOCIATED WITH A MODEST BOUNDARY LAYER DEPTH AND LIGHT
WINDS.

WEDNESDAY...HIGHS WILL TAKE ANOTHER STEP UPWARD AS THE 500-MB
RIDGE AXIS SHIFTS EAST AND FLOW ALOFT TURNS SOUTHWESTERLY AHEAD OF
A SHORTWAVE TROUGH. FORECAST SOUNDINGS SUPPORT MIXING TO 700 MB
WHERE TEMPERATURES WILL BE BETWEEN +3 AND +6 C. THAT YIELDS HIGHS
WELL UP INTO THE 70S AND EVEN AROUND 80 F IN MOST AREAS. WE HELD
OFF ADDING ANY LOW-END SHOWER OR STORM CHANCES TO THE AFTERNOON
FORECAST OVER THE WESTERN PARTS OF SOUTH CENTRAL MT BECAUSE THE
CONSENSUS OF 12 UTC GUIDANCE HOLDS THE SURFACE COLD FRONT
ATTENDANT TO THE APPROACHING SHORTWAVE TROUGH WEST OF LIVINGSTON
DURING THE DAY.

WEDNESDAY NIGHT...A MODEST COLD FRONT WILL CROSS THE AREA...AND WE
HAVE SOME SLIGHT CHANCE TO CHANCE POPS FOR SHOWERS IN PLACE ACROSS
SOUTH CENTRAL MT WHERE FORCING WILL BE GREATEST. WE DID DECIDE TO
INCLUDE A SLIGHT CHANCE OF THUNDERSTORMS WITH THE SHOWERS AS WELL
WEDNESDAY EVENING GIVEN WEAK INSTABILITY DRIVEN BY STEEP MID-LEVEL
LAPSE RATES. SREF-BASED CALIBRATED THUNDERSTORM PROBABILITIES ARE
ONLY BETWEEN 10 AND 20 PERCENT AROUND LIVINGSTON...BUT THERE WAS
JUST ENOUGH INSTABILITY /LIFTED INDEX VALUES OF 0 TO -2 C/ FOR US
TO INCLUDE A SMALL THUNDERSTORM CHANCE IN THE EVENING. SCHULTZ

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

MODELS CONTINUE IN PRETTY GOOD AGREEMENT THROUGH THE BULK OF THE
EXTENDED FORECAST PERIOD. THIS PROMPTED SEVERAL SMALL
CHANGES...BASED ON MODEL CONSENSUS.

FAST MOVING PACIFIC TROF IS STILL PROGGED TO CRASH THE RIDGE ON
THURSDAY. KEPT LOW POPS IN PLACE...AS A LITTLE MORE ENERGY APPEARS
TO GET INTO THE REGION THAN WAS PREVIOUSLY ADVERTISED. BEST ENERGY
STILL STAYS NORTH...SO BREEZY AND SOMEWHAT DRIER CONDITIONS ARE
EXPECTED. KEPT COOLER TEMPS IN PLACE FOR THURSDAY AS TIMING OF
FRONT AND POTENTIAL CLOUD COVER SHOULD KEEP FROM WARMING UP TOO
MUCH. THIS WAVE INTRODUCES ZONAL FLOW ACROSS THE REGION...WHICH
PERSISTS THROUGH THE WORK WEEK. THIS SETS UP DOWNSLOPE FLOW ACROSS
THE REGION FOR FRIDAY AND SATURDAY...RESULTING IN DRIER AND WARMER
CONDITIONS FOR FRIDAY AND SATURDAY. THIS IS A SIGNIFICANT
DEPARTURE FROM PREVIOUS MODEL RUNS...AS PREVIOUS RUNS HAVE
INDICATED A A COLD CANADIAN AIRMASS INVADING THE REGION...BUT
ZONAL PATTERN HAS BEEN CONSISTENT OVER MORE RECENT RUNS. THEREFORE
TRENDING TEMPERATURES UPWARD HAS BEGUN.

A SHORTWAVE AND PACIFIC MOISTURE ARE PROGGED TO PUSH ACROSS THE
REGION SATURDAY NIGHT...TRANSITIONING THE FLOW ALOFT TO A MORE
NORTHWESTERLY DIRECTION...AND BECOMING MORE UNSETTLED AGAIN
THROUGH SUNDAY AND INTO MONDAY. MODELS DISAGREE ON HOW MUCH QPF
AND EXACTLY HOW TO HANDLE THIS WAVE...AND DIVERGE SIGNIFICANTLY
AFTERWARD...BUT GENERALLY AGREE THAT THERE SHOULD BE AT LEAST SOME
SCATTERED PRECIP POTENTIAL. AS FOR TEMPS...THE TIMING OF THE
DISTURBANCE ACROSS THE REGION SATURDAY EVENING/NIGHT...SHOULD
SUPPORT SOME WARMER TEMPERATURES...INTO MID 70S...FOR SATURDAY.
COOLER TEMPS CAN BE EXPECTED BEHIND THIS WAVE...WITH 60S SUNDAY
AND MONDAY. AAG

&&

.AVIATION...

VFR CONDITIONS WILL PREVAIL THROUGH THE EVENING AND OVERNIGHT.
THAT SAID...THERE IS SOME POTENTIAL FOR AREAS OF FOG ACROSS MUCH
OF THE REGION...BEGINNING LATE THIS EVENING...AND INTO TUESDAY
MORNING. AAG

&&

.PRELIMINARY POINT TEMP/POPS...

    TUE     WED     THU     FRI     SAT     SUN     MON
-----------------------------------------------------------
BIL 038/073 046/080 049/067 041/071 044/074 044/068 041/064
    00/U    00/U    22/T    11/U    11/B    22/T    22/T
LVM 032/074 040/078 042/064 035/068 041/068 039/065 035/060
    00/U    01/U    32/T    11/U    11/B    22/T    32/T
HDN 033/074 040/082 049/068 041/071 045/075 045/069 041/067
    00/U    00/U    12/T    11/U    11/B    12/T    22/T
MLS 034/073 043/081 050/068 042/071 045/076 046/071 042/067
    00/U    00/U    12/T    11/U    11/B    12/T    21/B
4BQ 033/070 040/080 047/068 040/070 045/075 045/070 043/066
    00/U    00/U    12/T    11/U    11/B    12/T    22/T
BHK 031/067 039/074 045/066 039/069 044/073 044/068 041/064
    00/U    00/U    12/T    11/U    11/B    12/T    21/B
SHR 032/069 035/077 044/065 037/067 042/072 041/066 041/063
    00/U    00/U    12/T    21/U    11/B    12/T    22/T

&&

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

&&

$$
WEATHER.GOV/BILLINGS



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