Severe Thunderstorm Warning 117, NWS Billings, MT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
300 PM MDT FRI JUL 22 2011

.SHORT TERM...VALID FOR SAT AND SUN...

CONVECTION HAS DEVELOPED OVER THE WESTERN HALF OF THE FORECAST
AREA EARLY THIS AFTERNOON...BASICALLY ALONG AND BEHIND THE COLD
FRONT LOCATED FROM NORTHWEST ROSEBUD COUNTY TO BILLINGS TO BIG
TIMBER. AHEAD OF THIS BOUNDARY VERY MOIST AND UNSTABLE CONDITIONS
EXIST WITH CAPE VALUES FROM ROSEBUD COUNTY TO FALLON COUNTY
RUNNING AROUND 3000 J/KG. GUSTY SOUTHEAST WINDS IN THIS
ENVIRONMENT COMBINED WITH INCREASING SOUTHERLY JET WINDS AHEAD OF
THE UPPER TROF TO BRING A GOOD POTENTIAL FOR ROTATING UPDRAFTS
LEADING TO SEVERE STORMS. THERE IS A TORNADO THREAT DUE TO THIS
ROTATION WHICH IS MAINLY EAST OF A MILES CITY TO EKALAKA LINE IN
THE VICINITY OF THE STRONGEST LOW LEVEL SOUTHEASTERLY FLOW. A
TORNADO WATCH IS IN EFFECT UNTIL 9 PM FOR AREAS EAST OF THE HYSHAM
TO BROADUS LINE...AGAIN WITH THE HIGHEST CHANCES OF TORNADOES
BEING EAST OF A MILES CITY TO EKALAKA LINE.

DRIER AIR IS PUSHING NORTHWARD OUT OF WYOMING WITH 30S TO LOWER
40S DEW POINTS FROM SHERIDAN INTO SOUTHERN POWDER RIVER COUNTY. AS
THIS AIR PUSHES FURTHER NORTH THIS AFTERNOON THE SEVERE THREAT
WILL GET SQUEEZED TO THE NORTH AND POSSIBLY OUT OF SOUTHERN
ROSEBUD AND POWDER RIVER COUNTIES BY 6 PM. BEHIND THE FRONT WILL
CONTINUE TO SEE SCATTERED SHOWERS AND THUNDERSTORMS UNTIL THE
EARLY MORNING HOURS AS A GOOD CHUNK OF QG FORCING MOVES OVER MID
LEVEL FRONTOGENESIS BANDING ACROSS THE FORECAST AREA. WITH
MULTICELL NATURE OF THE CONVECTION BEHIND THE FRONT COULD SEE A
VERY ISOLATED LARGE HAIL/STRONG WIND REPORT...BUT DO NOT EXPECT
WIDESPREAD SEVERE STORMS ONCE COLD FRONT HAS MOVED THROUGH.

THE REST OF THE WEEKEND LOOKS NICE WITH HIGH PRESSURE BUILDING
INTO THE AREA FOR DRY CONDITIONS WITH TEMPERATURES IN THE 80S ON
SATURDAY PUSHING TOWARD 90 DEGREES IN MANY AREAS SUNDAY. CHAMBERS

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

VERY MINOR CHANGES TO THE EXTENDED FORECAST...MAINLY FOR BORDER
ISSUES.  FORECAST IN GOOD SHAPE AS MODELS REMAIN IN GOOD
AGREEMENT.

HIGH PRESSURE RIDGE BEGINS TO BREAK DOWN MONDAY...AS UPPER TROF
APPROACHES THE REGION...SETTING UP WHAT APPEARS TO BE A PRETTY
UNSETTLED PERIOD. THE TROF SHOULD BRING GOOD POTENTIAL FOR
SHOWERS AND THUNDER...AS MONSOONAL MOISTURE...AND MOISTURE FROM
HURRICANE DORA...ARE PULLED IN BY SOUTHWEST FLOW. A WEAK COLD
FRONT SWINGS THROUGH THE REGION TUESDAY COOLING TEMPS A BIT. A
STRONGER FRONT PUSHES THROUGH LATE TUESDAY/WEDNESDAY AS TROF
PROCEEDS EASTWARD...DROPPING TEMPS SLIGHTLY BELOW SEASONAL
AVERAGES WEDNESDAY.

SOMEWHAT ZONAL FLOW DOMINATES MUCH OF THE LATER PORTION OF THE
EXTENDED...WITH WAVES SLIDING THROUGH THE FLOW. EACH WILL BRING AT
LEAST A SLIGHT CHANCE FOR SHOWERS AND THUNDER. ACTIVE WEATHER
SHOULD ALSO KEEP TEMPS AT OR SLIGHTLY BELOW SEASONAL LEVELS
THROUGH THURSDAY INTO FRIDAY. SOME SHORTWAVE RIDGING IS INDICATED AT
FOR FRIDAY...WITH TEMPS RISING A BIT. GILSTAD

&&

.AVIATION...

A COLD FRONT IS MOVING THROUGH THE REGION...BRINGING THUNDERSTORMS
TO THE AREA. SHOWERS AND THUNDERSTORMS HAVE BEEN BENIGN THUS
FAR...BUT SOME STORMS MAY YET BECOME SEVERE...ESPECIALLY NORTH OF
A HYSHAM TO BROADUS LINE. LOCALIZED MVFR/IFR CONDITIONS WILL BE
POSSIBLE IN HEAVIER PRECIP. OTHERWISE...VFR CONDITIONS WILL
PREVAIL UNDER INCREASING CLOUDINESS FROM WEST TO EAST. FROPA HAS
CAUSED A WIND SHIFT TO A MORE NORTHERLY DIRECTION IN WESTERN
TERMINALS. A SIMILAR WINDS SHIFT WILL FOLLOW THE FRONT EASTWARD. SHOWERS
AND THUNDERSTORMS ARE EXPECTED TO LINGER THROUGH THE OVERNIGHT
HOURS ACROSS THE EAST. GILSTAD

&&

.PRELIMINARY POINT TEMP/POPS...

    SAT     SUN     MON     TUE     WED     THU     FRI
-----------------------------------------------------------
BIL 055/082 059/090 063/094 063/088 059/084 060/084 060/087
    52/T    10/U    11/U    22/T    22/T    22/T    21/B
LVM 045/080 047/088 055/092 054/083 047/079 048/083 048/086
    41/U    00/U    12/T    23/T    22/T    22/T    21/B
HDN 055/084 056/093 061/098 063/088 057/085 059/084 059/087
    62/T    10/U    11/U    22/T    22/T    22/T    21/B
MLS 057/081 059/090 065/095 065/086 060/086 060/084 062/087
    62/T    10/U    11/U    22/T    33/T    22/T    22/T
4BQ 056/084 057/090 063/096 065/086 059/084 060/085 061/089
    52/T    11/U    11/U    22/T    33/T    22/T    22/T
BHK 058/077 056/086 061/094 064/088 060/083 060/082 060/085
    63/T    10/U    11/U    23/T    33/T    22/T    22/T
SHR 052/082 054/090 058/094 060/087 055/085 056/086 056/092
    31/U    10/U    01/U    22/T    22/T    22/T    21/B

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...TORNADO WATCH 671 IN EFFECT UNTIL 9 PM MDT THIS EVENING FOR
      ZONES 30>33-36-37-58.
WY...NONE.

&&

WEATHER.GOV/BILLINGS

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE BILLINGS MT
229 PM MDT FRI JUL 22 2011

MTZ030>033-036>038-057-058-WYZ098-099-232030-
TREASURE-NORTHERN ROSEBUD-CUSTER-FALLON-POWDER RIVER-CARTER-
SOUTHERN BIG HORN-NORTHERN BIG HORN-SOUTHERN ROSEBUD-
NORTHEAST BIG HORN MOUNTAINS-SHERIDAN FOOTHILLS-
229 PM MDT FRI JUL 22 2011

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTH CENTRAL
MONTANA...SOUTHEAST MONTANA AND NORTH CENTRAL WYOMING.

.DAY ONE...THIS AFTERNOON AND TONIGHT

A COLD FRONT WILL MOVE THROUGH THE AREA THIS AFTERNOON THROUGH MID
EVENING. ALONG AND AHEAD OF THE FRONT STRONG TO SEVERE
THUNDERSTORMS ARE POSSIBLE...BASICALLY EAST OF A HYSHAM TO BROADUS
LINE. ALONG AND EAST OF A MILES CITY TO EKALAKA LINE IS THE BEST
LOCATION FOR AN ISOLATED TORNADO. VERY HEAVY RAINFALL WITH THESE
STORMS MAY PRODUCE LOCALIZED FLASH FLOODING OVER EASTERN ZONES
THROUGH LATE TONIGHT. ADDITIONAL SHOWERS AND THUNDERSTORMS WILL
CONTINUE BEHIND THE FRONT THROUGH MUCH OF TONIGHT...BUT ARE NOT
EXPECTED TO BE SEVERE.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER
CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES.

MTZ028-029-034-035-039>042-056-063>068-232030-
SOUTHERN WHEATLAND-MUSSELSHELL-NORTHERN STILLWATER-YELLOWSTONE-
EASTERN CARBON-NORTHERN PARK-NORTHERN SWEET GRASS-GOLDEN VALLEY-
RED LODGE FOOTHILLS-JUDITH GAP-PARADISE VALLEY-LIVINGSTON AREA-
BEARTOOTH FOOTHILLS-ABSAROKA/BEARTOOTH MOUNTAINS-CRAZY MOUNTAINS-
229 PM MDT FRI JUL 22 2011

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL MONTANA
AND SOUTH CENTRAL MONTANA.

.DAY ONE...THIS AFTERNOON AND TONIGHT

AN APPROACHING UPPER LEVEL DISTURBANCE WILL BRING SCATTERED
SHOWERS AND THUNDERSTORMS TO THE REGION THIS AFTERNOON AND
TONIGHT. SOME OF THESE STORMS COULD PRODUCE GUSTY WINDS...SMALL
HAIL AND BRIEF HEAVY RAINFALL. DRIER WEATHER WILL RETURN SATURDAY
AND SUNDAY.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER
CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES.

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