Area Forecast Discussion
Issued by NWS Billings, MT

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000
FXUS65 KBYZ 050923
AFDBYZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
323 AM MDT WED AUG 5 2015

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

A DEEP UPPER LOW WAS POSITIONED OVER WESTERN BRITISH COLUMBIA
THIS MORNING. THIS SYSTEM WILL BE THE WEATHER MAKER THE NEXT
COUPLE OF DAYS. THE FIRST IMPACT FROM THIS UPPER LOW WILL BE TO
KICK SEVERAL SHORTWAVES ACROSS THE GREAT BASIN AND INTO THE
FORECAST AREA. THE FIRST WAVE WAS ENTERING IDAHO THIS HOUR AND
WILL SHIFT ACROSS WESTERN AND CENTRAL ZONES THIS MORNING. THE NEXT
WAVE...WHICH IS STRONGER...WAS BACK IN NORTHWEST NEVADA AND
PROGGED TO ENTER WESTERN ZONES LATE THIS AFTERNOON AND CENTRAL
ZONES THIS EVENING. BOTH WAVES WILL PROVIDE ADEQUATE LIFT FOR
CONVECTION. THE EARLIER WAVE WAS ALREADY PRODUCING SHOWERS AND
THUNDERSTORMS IN IDAHO.

SHEAR WILL BE INCREASING THROUGH THE DAY WITH EFFECTIVE BULK
SHEAR REACHING AROUND 35KTS. CAPES REACH AROUND 800J/KG THIS
AFTERNOON. PARAMETERS LOOK A LITTLE BETTER FOR A FEW SEVERE STORMS
OVER WESTERN AND CENTRAL ZONES THAN WAS THE CASE YESTERDAY. THERE
IS A CONCERN THAT THE INITIAL SHORTWAVE WILL SPREAD TOO MUCH
CLOUDS EARLY IN THE AFTERNOON AND MINIMIZE THE DESTABILIZING
AFFECTS. THE SECOND WAVE MAY BE FAR ENOUGH BEHIND TO ALLOW FOR
INSTABILITY TO RECOVER FOR LATE AFTERNOON AND EARLY EVENING FOR A
FEW SEVERE STORMS. PWATS WERE ABOVE .75 INCHES EVERYWHERE WITH
CENTRAL ZONES HAVING PWATS AROUND AN INCH...SO STORMS WILL BE WET
WITH LOCALLY HEAVY RAIN. STORMS WILL BE MOVING FASTER THAN
YESTERDAY...SO THE FLASH FLOOD THREAT IS LESS THAN YESTERDAY.

THE WESTERN UPPER LOW WILL SLIDE ACROSS NORTHWEST MONTANA
THURSDAY. THIS PROCESS WILL ALLOW A COLD FRONT TO MOVE THROUGH THE
THURSDAY AFTERNOON. THE STRONGEST INFLUENCE FROM THE FRONT LOOKS
TO BE OVER WESTERN AND CENTRAL ZONES AS THE GRADIENT TIGHTEST IN
THESE LOCATIONS. 850MB WINDS INCREASE TO 25KTS THURSDAY AFTERNOON
AHEAD AND BEHIND THE FRONT. THIS WILL CAUSE WINDS TO INCREASE.
MODELS ADVERTISE FALLING DEWPOINTS WITH MIXING AHEAD OF THE FRONT
WITH SOME HUMIDITIES LOWERING TO THE TEENS. WILL NOT ISSUE ANY
FIRE WEATHER HIGHLIGHTS AS WILL NEED TO SEE HOW MUCH RAIN FALLS
OUT OF THE CONVECTION TODAY AND HOW THAT IMPACTS FUELS AND FIRE
WEATHER CONDITIONS. TWH

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

LIMITED CHANGES TO THE EXTENDED FORECAST ONCE AGAIN THIS
MORNING...WITH MODELS REMAINING IN FAIRLY GOOD AGREEMENT AS TO
OVERALL PATTERN. CHANGES AGAIN CENTERED AROUND TWEAKING PRECIP
POTENTIAL THIS WEEKEND AND TEMPS FOR EARLY NEXT WEEK.

THE LONG TERM PERIOD BEGINS WITH ZONAL FLOW ACROSS THE
REGION...AND A PACIFIC TROF LIFTING OUT OF NORTHERN CALIFORNIA.
ZONAL FLOW DOES NOT LOOK OVERLY STRONG...BUT SHOULD PRODUCE SOME
NEGLIGIBLE DOWNSLOPE FOW OVER THE REGION TO KEEP CONDITIONS CLEAR
FOR FRIDAY. THE APPROACHING TROF WEAKENS CONSISTENTLY AS IT MOVES
EASTWARD...FINALLY IMPACTING SOUTHWESTERN ZONES LATE SATURDAY
MORNING. PRECIP SHOULD SLOWLY SPREAD ACROSS THE REGION THROUGH THE
DAY SATURDAY...AND EXIT THE REGION SUNDAY AFTERNOON EVENING.
ALTHOUGH VERY CONSISTENT...HAVE KEPT POPS LOW DUE TO WEAKNESS AND
DISORGANIZATION OF THE WAVE BY THE TIME IT GETS HERE.

UPPER LEVEL RIDGING AMPLIFIES QUICKLY OVER THE REGION MONDAY...AS
A TROF OFF THE WASHINGTON COAST DIGS SOUTHWARD...RESULTING IN THE
BEGINNING OF ANOTHER WARM UP. TEMPS IN 90S CAN BE EXPECTED TO
RETURN FOR THE FIRST HALF OF THE WORK WEEK. MODELS DO DIVERGE A
BIT BEGINNING WEDNESDAY...WITH EASTWARD PROGRESSION OF RIDGE...AND
ADVANCEMENT OF DEEP PACIFIC TROF...SO LITTLE CONFIDENCE IN MIDWEEK
FORECAST. AAG

&&

.AVIATION...

VFR CONDITIONS WILL PREVAIL ACROSS THE REGION...UNDER
INCREASINGLY CLOUDY SKIES. SHOWERS AND THUNDERSTORMS ARE POSSIBLE
FOR ALL ROUTES BEGINNING IN WESTERN MOUNTAINS THIS MORNING...AND
SPREADING EAST THROUGH THE DAY. BEST CHANCES FOR THUNDER IS EAST
OF KBIL THIS AFTERNOON AND EVENING...SOME STRONGER STORMS ARE
POSSIBLE. LOCALIZED MVFR CONDITIONS ARE POSSIBLE IN HEAVIER
PRECIP. MOUNTAIN OBSCURATIONS ARE EXPECTED TO PERSIST THROUGHOUT
THE DAY. AAG

&&

.PRELIMINARY POINT TEMP/POPS...

    TDY THU     FRI     SAT     SUN     MON     TUE
-------------------------------------------------------
BIL 085 059/087 056/083 058/083 058/083 059/090 060/093
    4/T 51/N    11/U    13/T    32/T    21/U    11/B
LVM 080 050/081 047/083 052/080 052/082 052/087 053/090
    4/T 51/N    11/U    14/T    44/T    22/T    11/B
HDN 089 059/089 055/085 056/086 056/084 057/091 059/095
    4/T 51/N    11/U    13/T    33/T    21/U    11/B
MLS 089 063/085 057/084 058/085 059/082 059/089 062/094
    2/T 52/T    11/U    13/T    44/T    31/U    11/B
4BQ 090 060/085 056/084 058/085 058/081 058/088 060/093
    2/T 51/B    11/U    13/T    44/T    31/B    11/B
BHK 087 061/082 055/082 055/082 057/079 056/085 058/090
    2/T 53/T    11/B    13/T    44/T    42/T    11/B
SHR 087 056/084 052/083 055/084 054/081 053/088 054/092
    3/T 41/B    11/U    13/T    32/T    21/U    11/B

&&

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

&&

$$
WEATHER.GOV/BILLINGS


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