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000
FXUS65 KBYZ 212031
AFDBYZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
231 PM MDT TUE MAY 21 2013

.SHORT TERM...VALID FOR WED AND THU...

LARGE UPPER LOW OVER THE EASTERN DAKOTAS CONTINUES TO IMPACT OUR
FAR EASTERN ZONES THIS AFTERNOON AND WILL CONTINUE THROUGHOUT THE
NIGHT. EXPECT MOSTLY CLOUDY SKIES ALONG WITH A SLIGHT SHOWER
CHANCE FROM CUSTER AND POWDER RIVER COUNTIES EASTWARD.
ELSEWHERE...SOME CLOUDS AND AN ISOLATED SHOWER WILL BE POSSIBLE
OVER THE BEARTOOTH/ABSAROKA MOUNTAINS THIS EVENING WITH CLEAR TO
PARTLY CLOUDY SKIES EXPECTED ACROSS OUR CENTRAL AREAS.

LARGE UPPER LOW AND TROUGH CURRENTLY MOVING ONTO THE PACIFIC
NORTHWEST COAST WILL MOVE ONSHORE DURING THE DAY WEDNESDAY. THIS
WILL PROVIDE A SOUTHERLY AND DIVERGENT FLOW ALOFT TO OUR FORECAST
AREA WEDNESDAY THROUGH THURSDAY. NUMEROUS PIECES OF ENERGY WILL
EJECT FROM THIS LOW BEGINNING WEDNESDAY AFTERNOON INTO THURSDAY
NIGHT. AT THE SAME TIME...A STRONG LOW-LEVEL JET WILL DEVELOP
ACROSS OUR EASTERN THIRD OF THE FORECAST AREA WEDNESDAY NIGHT INTO
THURSDAY PROVIDING EASTERLY SURFACE WINDS TO THE ENTIRE AREA. BEST
CHANCES FOR SHOWERS AND THUNDERSTORMS WILL BE FROM ABOUT
YELLOWSTONE COUNTY WESTWARD WEDNESDAY AFTERNOON INTO THURSDAY
NIGHT. HAVE RAISED POPS TO LIKELY FOR THE BEARTOOTH/ABSAROKA
MOUNTAINS AND FOOTHILLS...AS WELL AS FROM ABOUT REED POINT WEST
AND NORTH WEDNESDAY EVENING AND NIGHT AND WILL MAINTAIN HIGH
CHANCE POPS FOR THURSDAY FROM BILLINGS WESTWARD.

CAN`T RULE OUT SEVERE THUNDERSTORMS WEDNESDAY EVENING AND AGAIN
THURSDAY. THERE WILL BE GOOD SPEED AND DIRECTIONAL SHEAR...CAPE
AND LAPSE RATES ACROSS THE CENTRAL AND WESTERN AREAS.
HOWEVER...SOUNDINGS SHOW THE AREA CAPPED SO THUNDERSTORMS WOULD BE
MORE ELEVATED IN NATURE RESULTING IN MORE OF A LARGE HAIL THREAT.
HOOLEY

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

NOT MANY CHANGES MADE TO THE EXTENDED PERIOD FORECAST...AS
INHERITED FORECAST WAS IN DECENT SHAPE.

THE PERIOD BEGINS FRIDAY MORNING WITH THE REGION UNDER THE
INFLUENCE OF SOUTHWESTERLY FLOW ALOFT...PRIMARILY DUE TO THE
SPINNING LOW PRESSURE SYSTEM OVER THE PACIFIC NORTHWEST.

BY SATURDAY EVENING AN EASTERLY LOW LEVEL JET FORMS OVER THE
EASTERN PORTION OF MONTANA. THIS WILL HELP BRING SOME MOISTURE
AND ADDED INSTABILITY TO THE REGION. EXPECT WINDS TO BE BLOWING
PRETTY GOOD IN PARTS OF FALLON AND CARTER COUNTIES AS THIS JET
STRENGTHENS BY SUNDAY AFTERNOON.

DUE TO THE NATURE OF THE PATTERN ALOFT...COUPLED WITH THE
PRESENCE OF SOME MOISTURE AT THE SURFACE...CANNOT RULE OUT THE
POTENTIAL FOR THUNDERSTORM ACTIVITY ALMOST EVERY DAY IN THE
PERIOD. SEVERITY WILL DEPEND ON AMOUNT OF DRY AIR ENTRAINMENT AT
MID LEVELS...ESPECIALLY DURING THIS UPCOMING WEEKEND. CAPE VALUES
IN THE EASTERN ZONES WILL EXCEED 1000 J/KG AT TIMES...SO THIS
NEEDS TO BE MONITORED.

FOR THE REST OF THE PERIOD...THE REGION WILL CONTINUE TO BE UNDER
THE INFLUENCE OF SW FLOW ALOFT...BEFORE THE MAIN FLOW BECOMES MORE
ZONAL. SINGER

&&

.AVIATION...

VFR CONDITIONS SHOULD PREVAIL AT ALL TERMINALS THROUGH THIS
EVENING AND TONIGHT. HOWEVER...CANNOT RULE OUT AN ISOLATED SHOWER
OR THUNDERSTORM NEAR THE BEARTOOTH AND SHERIDAN FOOTHILLS...WHICH
WOULD REDUCE VISIBILITIES AND INCREASE WIND GUST POTENTIAL. SINGER

&&

.PRELIMINARY POINT TEMP/POPS...

    WED     THU     FRI     SAT     SUN     MON     TUE
-----------------------------------------------------------
BIL 043/066 046/074 050/072 048/077 053/079 053/077 051/077
    12/T    33/T    43/T    22/T    22/T    23/T    33/T
LVM 039/066 043/065 041/068 040/078 041/080 042/078 041/075
    14/T    64/T    44/T    32/T    22/T    23/T    33/T
HDN 043/070 048/077 050/075 048/079 053/080 052/080 051/079
    11/N    32/T    33/T    22/T    22/T    23/T    33/T
MLS 042/065 046/072 051/077 051/079 057/082 058/079 054/079
    11/N    12/W    23/T    22/T    23/T    33/T    33/T
4BQ 040/065 046/074 052/079 050/081 055/085 052/081 052/081
    11/N    11/N    13/T    22/T    23/T    33/T    33/T
BHK 039/061 042/066 048/074 050/073 056/077 056/077 052/076
    31/N    11/N    13/T    22/T    33/T    33/T    33/T
SHR 037/066 045/075 047/075 046/079 048/083 048/079 046/076
    12/T    32/T    23/T    22/T    22/T    23/T    33/T

&&

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

&&

$$
WEATHER.GOV/BILLINGS