Area Forecast Discussion
Issued by NWS Billings, MT

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000
FXUS65 KBYZ 210954
AFDBYZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
354 AM MDT SUN SEP 21 2014

.SHORT TERM...VALID FOR TDY AND MON...

ANOTHER DAY OF ABUNDANT SUNSHINE FOR SOUTHERN MONTANA AND
NORTHERN WYOMING BEFORE CLOUDS AND SHOWER CHANCES INCREASE TONIGHT
THROUGH MONDAY. A POSITIVELY TILTED UPPER RIDGE WILL SHIFT EAST
ACROSS THE FORECAST AREA TODAY. A THERMAL RIDGE WILL SLIDE OVER
SOUTH CENTRAL MONTANA AS THE RIDGE AXIS MOVES EAST. SURFACE
PRESSURE PATTERN...WITH HIGH PRESSURE OVER THE CENTRAL
PLAINS...WILL LIMIT MIXING TODAY...AND THIS WILL KEEP HIGHS IN THE
MID TO UPPER 70S.

AN UPPER LOW CURRENTLY OVER SOUTHERN NEVADA IS PROGGED TO PUSH
INTO IDAHO TONIGHT. THIS SYSTEM HAS PRODUCED QUITE A BIT OF
LIGHTNING OVER NEVADA SATURDAY AND SATURDAY NIGHT. AS THE LOW
PUSHES NORTH...IT WILL RUN INTO THE RIDGE AND DRIER AIR ALOFT AND
TAKE SOME EDGE OFF OF THE DEEP MOISTURE AVAILABLE AT THIS TIME.
PRECIPITABLE WATER VALUES WERE 1.20 INCHES AT LAST VEGAS WHICH IS
4 STANDARD DEVIATIONS ABOVE NORMAL FOR THIS TIME OF YEAR. AS THE
SYSTEM MOVES NORTHEAST...PWATS WILL INCREASE TO AN INCH PLUS OVER
CENTRAL AND EASTERN ZONES LATE TONIGHT AND MONDAY.

EXPECT SHOWER AND THUNDERSTORM CHANCES TO INCREASE OVER SOUTHERN
LOCATIONS TONIGHT...ESPECIALLY LATE TONIGHT. RAISED POPS A BIT
MORE FOR LATE TONIGHT. JET FORCING REMAINS VERY WEAK WITH THIS
SYSTEM AND THE MAJORITY OF THE DYNAMICS STAY OVER WYOMING LATE
SUNDAY NIGHT THROUGH MONDAY. STILL...WITH INCREASING MOISTURE
REFLECTED IN PWATS INCREASING TO AROUND AN INCH...SHOULD BE ABLE
TO GENERATE A FEW SHOWERS AND THUNDERSTORMS...ESPECIALLY SOUTH.
SLOW STORM STORMS COULD CAUSE LOCALLY HEAVY RAIN. MIXING WILL
INCREASE MONDAY AS INSTABILITY INCREASES...SO DESPITE ADDED CLOUD
COVER...EXPECT HIGHS TO BE SIMILAR IF NOT A BIT WARMER ON MONDAY.
THE SYSTEM KICKS EAST MONDAY NIGHT ALLOWING POPS DECREASE FROM
WEST TO EAST. A LEE SURFACE TROUGH FORMS MONDAY AND MONDAY NIGHT
AS THE LOW PULLS EAST AND THERFORE INCREASED WINDS FROM LIVINGSTON
TO BIG TIMBER. TWH

.LONG TERM...VALID FOR TUE...WED...THU...FRI...SAT...

MADE SEVERAL MINOR CHANGES TO EXTENDED FORECAST...BASED ON MODELS
REMAINING IN PRETTY GOOD AGREEMENT AS TO THE OVERALL PATTERN
THROUGHOUT THE PERIOD.

MODELS SUPPORT UPPER LEVEL RIDGING DEVELOPING OVER THE REGION
THROUGH THE BEGINNING OF THE PERIOD. THIS RIDGE WILL RESULT IN DRY
CONDITIONS AND UNSEASONABLY WARM TEMPERATURES THROUGH AT LEAST
FRIDAY...WITH HIGHS NEAR 90 ON THURSDAY. CONTINUED AMPLIFIED
RIDGING PROMPTED INCREASED FORECAST TEMPERATURES FOR WEDNESDAY
THROUGH FRIDAY.

MODELS SUPPORT A DEEP UPPER LEVEL TROF MOVING ONTO THE PACIFIC
NORTHWEST COAST FRIDAY...WITH SOUTHWEST FLOW ALOFT OVER THE CWA
INCREASING THROUGH THE DAY FRIDAY. UNCERTAINTY WITH THIS SYSTEM
REMAINS HIGH...AS TIMING BECOMES A PROBLEM. THE EC IS RUNNING MUCH
MORE SLOWLY THAN GFS. THE EC CUTS OFF AN UPPER LEVEL LOW AND
STALLING IT OVER THE GREAT BASIN INTO SUNDAY. MEANWHILE THE GFS
PRESERVES THE TROF...WHICH TRAVERSES THE REGION FROM FRIDAY
THROUGH THE WEEKEND. TEND TO LEAN SLIGHTLY TOWARD THE EC...AS
SLOWER MOVEMENT OF AMPLIFIED PATTERN SEEMS MORE LIKELY. THEREFORE
HAVE WARMED TEMPERATURES SLIGHTLY FOR WEEKEND AS WELL...ESPECIALLY
EAST...SETTING UP MORE A TEMPERATURE GRADIENT ACROSS THE REGION AS
A RESULT OF THE SLOWER MOTION. THIS SYSTEM WILL BRING COOLER
TEMPERATURES TO THE REGION. IT IS REALLY JUST A MATTER OF EXACTLY
WHEN. AAG

&&

.AVIATION...

VFR CONDITIONS WILL PREVAIL THROUGH TODAY AND TONIGHT...UNDER
CLEAR TO PARTLY CLOUDY SKIES. NO AVIATION HAZARDS ARE EXPECTED.
AAG

&&

.PRELIMINARY POINT TEMP/POPS...

    TDY MON     TUE     WED     THU     FRI     SAT
-------------------------------------------------------
BIL 077 051/079 055/083 055/086 057/090 057/084 052/069
    0/U 03/T    21/B    11/U    11/U    11/U    22/T
LVM 077 048/077 050/079 048/085 049/087 049/081 045/066
    0/U 14/T    21/B    10/U    01/U    22/T    33/T
HDN 078 048/079 052/084 052/088 056/090 056/086 050/072
    0/U 03/T    21/B    11/U    11/U    11/U    12/T
MLS 076 048/082 054/084 054/089 058/091 058/087 053/073
    0/U 01/U    21/B    11/U    11/U    11/U    11/B
4BQ 076 049/082 054/083 052/088 057/091 057/087 055/073
    0/U 02/T    32/T    11/U    11/U    11/U    11/U
BHK 072 044/079 050/080 050/085 054/087 054/086 055/073
    0/U 01/U    21/B    11/U    11/U    11/U    11/U
SHR 076 049/075 050/079 049/085 052/088 052/085 050/070
    0/U 04/T    42/T    10/U    01/U    11/U    22/T

&&

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

&&

$$
WEATHER.GOV/BILLINGS


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