Area Forecast Discussion
Issued by NWS Billings, MT

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000
FXUS65 KBYZ 200949
AFDBYZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
349 AM MDT WED AUG 20 2014

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

WEAK SHORTWAVE IN THE SOUTHWESTERLY FLOW IS PUSHING ACROSS
SOUTHEAST MONTANA AND NORTHERN WYOMING THIS MORNING...CREATING AN
AREA OF SCATTERED SHOWERS. THIS WAVE WILL CONTINUE TO NORTHEAST
INTO NORTH DAKOTA BY THIS AFTERNOON. GIVEN THIS TRACK AND CURRENT
ORIENTATION OF THE SHOWERS FROM CODY TO SHERIDAN BROADUS...EXPECT
THE BEST CHANCE OF PRECIPITATION THIS MORNING TO REMAIN EAST OF
BILLINGS. THUS CONTINUE TO ADVERTISE SCATTERED POPS IN THIS
AREA...WITH JUST ISOLATED POPS FROM BILLINGS WEST THROUGH THE
MORNING.

SECONDARY SHORTWAVE TROUGH WILL PUSH IN FROM THE WEST THIS
AFTERNOON...AND CAN CURRENTLY BE SEEN ON WV IMAGERY OVER EASTERN
OREGON AND WESTERN IDAHO. EXPECT TO SEE SCATTERED SHOWERS AND
THUNDERSTORMS DEVELOP OVER THE MOUNTAINS OF SOUTHWEST AND SOUTH-
CENTRAL MONTANA THIS AFTERNOON AND ADVANCE EASTWARD LATE THIS
AFTERNOON. THERE REMAINS SOME TIMING AND PLACEMENT DIFFERENCES
BETWEEN THE GLOBAL AND HIGH RESOLUTION MODELS WITH THE EASTWARD
PROGRESSION AND WHETHER THESE WILL MAKE IT INTO BILLINGS LATE THIS
AFTERNOON. THUS HAVE KEPT SCATTERED POPS IN FROM BILLINGS WEST FOR
THIS AFTERNOON AND EVENING...WITH JUST ISOLATED POPS EAST. THE
CONSENSUS BETWEEN HIGH RESOLUTION MODELS SUGGESTS THAT IF WE CAN
GET SOME STORMS INTO BILLINGS IT WILL LIKELY BE AFTER 3 TO 4 PM.

TEMPERATURES TODAY MARK THE BEGINNING OF THE DOWNWARD TREND INTO
THE WEEKEND. INCREASING CLOUD COVER TODAY ALONG WITH HEIGHT FALLS
AND SCATTERED SHOWER AND THUNDERSTORM ACTIVITY WILL LIMIT HIGH
TEMPERATURES TO THE MID 80S. TEMPERATURES WILL CONTINUE TO FALL ON
THURSDAY WITH COLD AIR ADVECTION BEHIND THE INITIAL SHORTWAVE AND
WITH CONTINUED CLOUD COVER AND SCATTERED SHOWERS. EXPECT HIGH
TEMPERATURES TO BE IN THE MID 70S FOR CENTRAL AND WESTERN
ZONES...WITH SLIGHTLY WARMER AIR LINGERING IN THE EAST ALLOWING
FOR LOW 80S.

CONFIDENCE IN HOW THE PRECIPITATION WILL PLAY OUT THURSDAY REMAINS
LOW...AS FORECAST MODELS ARE STILL IN DISAGREEMENT WITH THE TRACK
OF THE SHORTWAVE. THE GFS/NAM SOLUTIONS REMAINS ON THE DRY SIDE AS
THEY WANT TO LIFT THE WAVE QUICKLY TOWARD THE NORTHEAST. THIS
SOLUTION ALLOWS US TO KEEP 700 MB WINDS SOUTHWESTERLY...TAPPING
INTO DRIER AIR FROM THE SOUTH AND ALSO OFFERS FAR LESS QG FORCING.
THE EC/GEM SOLUTIONS KEEP THE TRACK OF THE WAVE FURTHER SOUTH AND
ALLOW FOR MORE ROBUST QG FORCING TO PUSH ACROSS THE FORECAST AREA
THURSDAY AND THURSDAY EVENING. THIS TRACK ALSO ALLOWS THE 700 MB
FLOW TO WEAKEN AND ACTUALLY REVERSE TO THE NORTHEAST AS 700 MB
TROUGH PASSES. THUS IF THE TRACK REMAINS FARTHER
SOUTH...PRECIPITATION WILL BE MORE WIDESPREAD WITH ALL AROUND
HIGHER QPF AMOUNTS...WHEREAS THE GFS/NAM SOLUTIONS WILL BE MUCH
MORE SHOWERY. EITHER WAY...WE WILL BE DEALING WITH PRECIPITATION
AROUND ON THURSDAY AND THURSDAY NIGHT...BUT THE AMOUNT AND HOW
WIDESPREAD REMAINS UNCERTAIN. KEPT CHANCE TO LOW-END LIKELY POPS
IN THE FORECAST...BUT MAY NEED TO TWEAK UP OR DOWN TOMORROW
DEPENDING ON HOW THE MODELS TREND WITH THE TRACK OF THE LOW.

CHURCH

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

CONFIDENCE INCREASING FOR A COOLER AND MUCH WETTER PATTERN TO END
THE WEEK INTO THE EARLY PART OF THE WEEKEND. THIS CONFIDENCE IS
GAINED FROM THE FACT THAT THE GFS MODEL HAS BEEN TRENDING FARTHER
AND FARTHER SOUTH WITH THE MAIN ENERGY WITHIN THE TROUGH
APPROACHING FOR THE END OF THE WEEK. THIS ITERATION DROPS THE
BASE OF THE TROUGH ACROSS NORTHERN WYOMING WITH THE 700MB LOW
CRUISING RIGHT OVER SOUTHERN MONTANA. THIS IS MUCH FARTHER SOUTH
THAN RUNS YESTERDAY WHICH KEPT THE 700MB LOW OVER NORTHERN MONTANA
AND INHIBITED STRONG UPSLOPE FLOW. NOT THE CASE NOW...SO HAVE
RAISED POPS FOR FRIDAY AFTERNOON THROUGH SATURDAY MORNING.

THE SYSTEM LOOKS TO BE SWINGING IN A LITTLE EARLIER WITH
CONVECTIVE ACTIVITY STARTING IN EARNEST FRIDAY AFTERNOON OVER
WESTERN AND CENTRAL ZONES. PRECIPITABLE WATER AMOUNTS RISE TO
AROUND AN INCH...SO HEAVY RAIN PRODUCING THUNDERSTORMS LOOK LIKE A
GOOD BET. TRAINING STORMS COULD CAUSE QUICK ACCUMULATION OF WATER
WITH STREAMS AND CREEKS POSSIBLY RISING QUICKLY. SPEED OF STORMS
SHOULD LIMIT THIS SOMEWHAT. BUFKIT SOUNDINGS SHOW SKINNY CAPE WITH
MOIST ADIABATIC SOUNDINGS...SO THUNDERSTORM ACTIVITY WILL TURN TO
MORE SHOWERY FRIDAY NIGHT. FRIDAY NIGHT LOOKS TO BE THE BEST SHOT
OF RAINFALL AS THE TROUGH AXIS ADVANCES INTO THE GREAT BASIN.

THE SURFACE LOW WRAPS UP OVER NORTHEAST WYOMING FRIDAY NIGHT AND
SHIFTS INTO EASTERN MONTANA SATURDAY MORNING. THIS WILL BE THE
BEST SHOT OF RAIN OVER THE EAST...WITH LOCALLY HEAVY RAIN EXPECTED
WITH PWATS APPROACHING 1.25 INCHES. NORTHWEST WINDS WILL KICK UP
SATURDAY AS THE LOW STRENGTHENS AND SLIDES INTO THE DAKOTAS.
PUSHED THE HIGHER POPS FARTHER EAST FRIDAY NIGHT AND SATURDAY. THE
HIGHER ELEVATIONS SHOULD SEE A LITTLE SNOW OUT OF THIS. THE
HIGHEST PEAKS COULD SEE A COUPLE OF INCHES FRIDAY NIGHT...WITH THE
SNOW LEVEL POSSIBLY DROPPING TO AROUND 9 THOUSAND FEET BY SUNDAY
MORNING. CERTAINLY THE BEARTOOTH PASS COULD GET SOME LIGHT
ACCUMULATIONS BY THE TIME THIS EVENT IS OVER...MAINLY OVER THE
HIGHEST ELEVATIONS OF THE PASS.

ONE THING TO NOTE...THE NAM WAS HINTING AT A PRONOUNCED DRY SLOT
LATE FRIDAY NIGHT. THIS IS DUE TO A FARTHER NORTH PLACEMENT OF
THE 700MB LOW. THIS WAS AN OUTLIER...SO WILL NOT FACTOR THAT INTO
THE FORECAST BUT WILL NEED TO BE WATCHED. THE 06Z VERSION HAS
ALREADY BACKED OFF ON THIS SOLUTION A BIT...SO EXPECT IT TO COME
IN LINE WITH THE OTHER MODELS OVER TIME.

CYCLONIC FLOW WILL PERSIST FOR SUNDAY...BUT THE STRONGEST FORCING
WILL HAVE LEFT THE AREA AND THUS EXPECT A DOWNTICK IN SHOWER
ACTIVITY. ANOTHER WAVE SWINGS INTO THE FORECAST AREA FOR MONDAY
FOR THE NEXT ROUND OF SHOWERS. A PRONOUNCED CHANGE TO A WET
PATTERN LOOKS TO BE SHAPING UP. TEMPERATURES WILL CRASH INTO THE
UPPER 60S ON FRIDAY WITH HIGHS STRUGGLING TO REACH THE MID 60S ON
SATURDAY. LOWERED TEMPERATURES QUITE A BIT FOR SATURDAY WITH
CLOUDS AND SHOWERS AROUND. HIGHS WILL BE HELD BELOW SEASONAL
VALUES INTO EARLY NEXT WEEK WITH CYCLONIC FLOW. TWH
&&

.AVIATION...

SCATTERED SHOWERS WILL MOVE ACROSS AREAS MAINLY EAST OF KBIL THIS
MORNING. MORNING SHOWERS WILL BE MORE ISOLATED FROM KBIL WEST.
AFTER A BRIEF LULL IN ACTIVITY...MORE SHOWERS AND THUNDERSTORMS
ARE EXPECTED TO DEVELOP THIS AFTERNOON OVER NORTHERN WYOMING AND
SOUTHERN MONTANA. THIS ACTIVITY WILL DRIFT NORTHEAST ACROSS ALL OF
SOUTHERN MONTANA THIS AFTERNOON AND EVENING. HEAVIER SHOWERS WILL
CAUSE LOCALIZED MVFR CONDITIONS. LOCALIZED WIND SHEAR CAN BE
EXPECTED THIS MORNING WITH WINDS JUST OFF THE SURFACE BEING OUT OF
THE NORTHWEST UP TO 30KTS. OTHERWISE...VFR FLYING WEATHER IS
EXPECTED. MOUNTAINS WILL BE OCCASIONALLY OBSCURED. TWH
&&

.PRELIMINARY POINT TEMP/POPS...

    TDY THU     FRI     SAT     SUN     MON     TUE
-------------------------------------------------------
BIL 084 059/074 055/069 052/063 048/068 049/075 054/075
    3/T 46/T    56/T    76/T    33/T    22/T    33/T
LVM 079 051/074 050/067 046/061 044/067 045/073 049/073
    4/T 57/T    77/T    77/T    43/T    34/T    43/T
HDN 086 058/080 055/073 053/066 051/070 051/077 054/077
    2/T 45/T    55/T    76/T    33/T    22/T    33/T
MLS 086 060/084 057/072 054/068 052/068 052/075 056/074
    3/T 35/T    64/T    76/T    43/T    22/T    33/T
4BQ 087 059/085 057/076 056/070 053/068 053/076 055/076
    3/T 24/T    64/T    66/T    43/T    22/T    33/T
BHK 083 055/082 055/072 055/068 052/065 049/072 052/071
    4/T 34/T    74/T    66/T    43/T    22/T    33/T
SHR 084 054/082 052/072 050/067 048/068 049/074 051/073
    3/T 34/T    44/T    66/T    43/T    32/T    33/T

&&

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

&&

$$
WEATHER.GOV/BILLINGS


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