Special Weather Statement, NWS Great Falls, MT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
455 PM MDT TUE JUN 28 2011

.DISCUSSION...
THIS AFTERNOON THROUGH THURSDAY EVENING...CENTRAL...NORTHCENTRAL AND
SOUTHWEST MT ENTERING AN ACTIVE WEATHER PERIOD FOR THE NEXT 36 HOURS
OR SO AS UNSTABLE CONDITIONS AND PLENTIFUL MOISTURE WILL PRODUCE
PERIODS OF THUNDERSTORMS THIS AFTN/EVE AND AGAIN TOMORROW.  HIGH
PRESSURE RIDGE OVER THE NORTHERN ROCKIES HAS BEEN WEAKENING AND
DRIFTING EAST WHILE DEEP UPPER LEVEL TROF OFF THE CALIF COAST BEGINS
TO TURN INLAND.  LEADING EDGE OF MOISTURE AND A EMBEDDED SHORTWAVE
FROM THE PACIFIC SYSTEM IS CURRENTLY ALONG THE MT/ID BORDER AND
BEGINNING TO FIRE THUNDERSTORMS ALONG THE BITTERROOT MTNS.  EXPECT
THESE STORMS WILL SPREAD EASTWARD INTO CENTRAL AND SOUTHWEST
COUNTIES OVER THE NEXT SEVERAL HOURS...WITH A FEW BRIEFLY REACHING
SEVERE STATUS...WITH HAIL AROUND 1 INCH IN DIAMETER AND WINDS
GUSTING TO AROUND 60 MPH.  MAIN CONVECTIVE ACTIVITY WILL BE AROUND
FERGUS/BLAINE COUNTIES TONIGHT BEFORE EXITING INTO ERN MT AFTER
MIDNIGHT.  REGION WILL SEE A BRIEF BREAK FROM PRECIPITATION DURING
THE MORNING HOURS ON WED...BUT AS THE PACIFIC SYSTEM MOVES INTO
NEVADA...MOISTURE AND INSTABILITY WILL REBUILD OVER OUR AREA SETTING
OFF ANOTHER ROUND OF STRONG TO SEVERE STORMS TOMORROW AFTN/EVE.
FORECAST MODELS IN GOOD AGREEMENT THAT THE UPPER TROF WILL BE SLOW
TO CLEAR THE AREA SO HAVE INCREASED CHANCES OF PRECIP OVER SOUTHWEST
MT WHERE RAIN SHOWERS WILL LINGER THRU THURS AFTN.  WARM TEMPS
EXPECTED AGAIN TOMORROW BEFORE THE STORMS ARRIVE...WITH 80S AND 90S
ACROSS THE VALLEYS/PLAINS.  SHARPLY COOLER TEMPS ARRIVE ON THURS AS
CANADIAN AIRMASS ARRIVES BEHIND THE UPPER TROF...WITH MOST LOCATIONS
ONLY REACHING THE MID 60S TO LOW 70S.
WARANAUSKAS

THURSDAY NIGHT THROUGH TUESDAY...LINGERING THUNDERSTORMS ARE
EXPECTED TO END THURSDAY NIGHT AND MAINLY THURSDAY EVENING AS AN
UPPER TROUGH MOVES EAST. THEN FRIDAY THROUGH SUNDAY MODELS POINT TO
A GENERALLY DRY WESTERLY FLOW ALOFT. ON THE FOURTH OF JULY THE GFS
MODEL DEVELOPS AN UPPER RIDGE OVER IDAHO AND WESTERN MONTANA WHILE
THE ECMWF MODEL CONTINUES THE WESTERLY FLOW ALOFT. THEN ON TUESDAY
THE GFS MODEL MOVES THE UPPER RIDGE OVER THE FORECAST AREA. THE
ECMWF MODEL ON THE OTHER HAND DEVELOPS AN UPPER RIDGE OVER THE
PACIFIC NORTHWEST AND WESTERN CANADA WITH NORTHWEST FLOW ALOFT
FARTHER EAST. THIS NORTHWEST FLOW USHERS IN A COOLER AIRMASS
ACCORDING TO THE ECMWF WHILE THE GFS CONTINUES WITH THE WARMER
AIRMASS. OTHER GUIDANCE SEEMS MORE IN LINE WITH THE GFS THOUGH THEY
ARE WEAKER WITH THE UPPER RIDGE. SO FOR THIS FORECAST HAVE LEANED
TOWARDS THE GFS SOLUTION. ALL IN ALL EXPECT A RELATIVELY DRY AND
WARM PERIOD. WILL GO WITH A SLIGHT CHANCE OF THUNDERSTORMS OVER FAR
SOUTHWEST MONTANA ON SUNDAY AND OVER ALL OF SOUTHWEST MONTANA ON THE
FOURTH OF JULY. DUE TO MODEL UNCERTAINTIES WILL GO WITH A MORE
WIDESPREAD SLIGHT CHANCE OF THUNDERSTORMS ON TUESDAY. INHERITED
WARMING TREND FROM FRIDAY INTO SUNDAY STILL LOOKS GOOD AND DID NOT
MAKE ANY BIG CHANGES WITH RESPECT TO FORECAST TEMPERATURES.
BLANK

&&

.AVIATION...
UPDATED 2255Z.
A BAND OF MOISTURE FUELING SCATTERED TO NUMEROUS THUNDERSTORMS WILL
MOVE FROM NEAR KHLN TO KHVR THIS EVENING. SMALL HAIL AND GUSTY WINDS
ARE EXPECTED TO AFFECT THE KHLN...KGTF AND KHVR TERMINALS AT TIMES.
NORTH AND SOUTH OF THIS BAND ONLY PARTLY TO MOSTLY CLOUDY SKIES ARE
EXPECTED. THUNDERSTORM ACTIVITY SHOULD MOVE OUT OF THE FORECAST AREA
AFTER 06Z WEDNESDAY WITH MOSTLY CLEAR TO PARTLY CLOUDY SKIES
PREVAILING THROUGH 18Z WEDNESDAY. ANOTHER BATCH OF MOISTURE WILL
AFFECT THE ENTIRE FORECAST AREA WITH SCATTERED TO NUMEROUS
THUNDERSTORMS AFTER 21Z WEDNESDAY. MPJ

&&

.HYDROLOGY...
HIGH TEMPERATURES WILL WARM TO NEAR TYPICAL SEASONAL VALUES THIS
WEEK...REMAINING WARM THROUGH WED. THIS WILL LEAD TO AN INCREASE IN
SNOW MELT DURING THE EARLY/MIDDLE PART OF THE WEEK. RESERVOIRS
ACROSS THE AREA REMAIN NEAR CAPACITY AND AS A RESULT MAY INCREASE
THE AMOUNT OF WATER RELEASED AND SUBSEQUENT WATER LEVELS. IN
ADDITION...STRONG TO SEVERE THUNDERSTORMS...SOME WITH HEAVY
RAINFALL...ARE POSSIBLE WEDNESDAY. ANY RAIN FALLING ON TOP OF SNOW
WILL LEAD TO FASTER SNOW MELT AND RISING WATER LEVELS.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  54  85  51  67 /  30  60  20  20
CTB  57  80  52  64 /  20  40  20  20
HLN  53  84  51  68 /  30  60  30  20
BZN  49  85  49  70 /  10  40  40  40
WEY  38  74  38  62 /  10  30  40  50
DLN  50  81  46  69 /  10  50  30  30
HVR  56  86  52  73 /  20  40  30  20
LWT  53  86  48  68 /  30  40  40  30

&&

.TFX WATCHES/WARNINGS/ADVISORIES...

FLOOD HIGHLIGHTS REMAIN IN EFFECT UNTIL FURTHER NOTICE.

&&

SHORT TERM...WARANAUSKAS
LONG TERM...BLANK
AVIATION...MPJ

WEATHER.GOV/GREATFALLS

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE GREAT FALLS MT
347 AM MDT TUE JUN 28 2011

MTZ008-012-015-053-055-291000-
BEAVERHEAD-CASCADE-MADISON-BROADWATER-GALLATIN-
347 AM MDT TUE JUN 28 2011

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

.DAY ONE...TODAY AND TONIGHT

FLOOD HIGHLIGHTS REMAIN IN EFFECT ACROSS PORTIONS OF THE REGION.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

FLOOD HIGHLIGHTS WILL REMAIN IN EFFECT ACROSS PORTIONS OF THE
REGION UNTIL FURTHER NOTICE.

STRONG TO SEVERE THUNDERSTORMS ARE EXPECTED TO IMPACT THE AREA ON
WEDNESDAY AFTERNOON AND EVENING. LARGE HAIL AND GUSTY OUTFLOW
WINDS IN EXCESS OF 50 MPH WILL BE POSSIBLE WITH SOME OF THESE
STORMS.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS ARE ENCOURAGED TO SEND FLOODING REPORTS TO THE NATIONAL
WEATHER SERVICE IN GREAT FALLS. SPOTTER ACTIVATION WILL LIKELY BE
NEEDED WEDNESDAY FOR POTENTIAL SEVERE WEATHER.

MTZ009>011-013-014-044>052-054-291000-
NORTHERN ROCKY MOUNTAIN FRONT-EASTERN GLACIER-HILL-CHOUTEAU-
CENTRAL AND SOUTHERN LEWIS AND CLARK-TOOLE-LIBERTY-
EASTERN PONDERA-BLAINE-SOUTHERN ROCKY MOUNTAIN FRONT-
EASTERN TETON-JUDITH BASIN-FERGUS-JEFFERSON-MEAGHER-
347 AM MDT TUE JUN 28 2011

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

.DAY ONE...TODAY AND TONIGHT

THE PROBABILITY OF WIDESPREAD HAZARDOUS WEATHER IS LOW.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

STRONG TO SEVERE THUNDERSTORMS ARE EXPECTED TO IMPACT THE AREA ON
WEDNESDAY AFTERNOON AND EVENING. LARGE HAIL AND GUSTY OUTFLOW
WINDS IN EXCESS OF 50 MPH WILL BE POSSIBLE WITH SOME OF THESE
STORMS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL LIKELY BE NEEDED WEDNESDAY FOR POTENTIAL
SEVERE WEATHER.

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