Severe Thunderstorm Warning 76, NWS Great Falls, MT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
255 PM MDT THU AUG 6 2009

.DISCUSSION...

TONIGHT THROUGH SATURDAY...MODELS STILL ON THE SAME PAGE IN HAVING
AN UPPER LOW MOVE INTO IDAHO FRIDAY THEN EVENTUALLY INTO EASTERN
MONTANA ON SATURDAY. ALSO MODELS CONTINUE TO DIFFER ON SHORTWAVE
DETAILS ASSOCIATED WITH THE UPPER LOW WHICH MAKES THE FORECAST
DIFFICULT. THEY DO SEEM TO BE POINTING TOWARDS DRIER AIR MOVING
INTO THE SOUTHERN AND CENTRAL ZONES LATER FRIDAY INTO FRIDAY
NIGHT SO HAVE LOWERED SOME CHANCES OF PRECIPITATION THERE. ECMWF
MODEL HAD BEEN CONSISTENT IN FORECASTING HEAVY RAIN FOR GLACIER
PARK FOR SEVERAL DAYS BUT THE LATEST RUN HAS MOVED THE AREA OF
FORECAST HEAVY RAIN FARTHER SOUTH. SEVERE THUNDERSTORMS WERE
OCCURRING OVER SOUTHWEST MONTANA THURSDAY AFTERNOON AND EXPECT
THEM TO SPREAD NORTH TO NORTHEAST THE REST OF THIS AFTERNOON AND
EARLY EVENING. NORTH CENTRAL MONTANA APPEARS TO BE TOO STABLE TO
SUPPORT NOT ONLY STRONG THUNDERSTORMS BUT POSSIBLY ANY
THUNDERSTORMS AT ALL. FRIDAY THREAT OF SEVERE THUNDERSTORMS IN THE
FAR EAST LOOKS OK. LOOKING AHEAD TO SATURDAY EXPECT PRECIPITATION
CHANCES TO DIMINISH AS THE UPPER LOW MOVES OFF TO THE EAST.

SATURDAY NIGHT THROUGH TUESDAY NIGHT...AS STRONG UPPER-LEVEL LOW
CONTINUES TO MOVE EASTWARD PRECIPITATION WILL GRADUALLY EXIT THE
FORECAST AREA SO TAPERED POPS FROM WEST TO EAST THROUGH SATURDAY
NIGHT AND SUNDAY. SOME DIFFERENCES BETWEEN THE GFS AND ECMWF IN
TERMS OF AMOUNT OF LINGERING MOISTURE BUT AS A WEAK UPPER-LEVEL
RIDGE BUILDS ON SUNDAY OVER THE AREA...AM ANTICIPATING DRIER
CONDITIONS SO LEANED MORE TOWARDS THE GFS SOLUTION DURING THE TIME
FRAME. IN ADDITION...CLOUDS MAY BE SLOW TO CLEAR OUT WHICH WILL KEEP
COOLER THAN AVERAGE TEMPERATURES AGAIN ON SUNDAY. DRIER CONDITIONS
EXPECTED TO CONTINUE THROUGH MONDAY AND TEMPERATURES WILL RETURN TO
SEASONAL LEVELS. OUR NEXT WEATHER SYSTEM WILL ARRIVE ON MONDAY NIGHT
AND TUESDAY AS YET ANOTHER TROUGH OF LOW PRESSURE MOVES INTO THE
PACIFIC NORTHWEST...HOWEVER THIS ONE APPEARS TO HAVE LESS MOISTURE
ASSOCIATED WITH IT AND WILL STAY FARTHER NORTH AS WELL. BOTH GFS AND
EC WANT TO BRING A WEAK COLD FRONT THROUGH THE FORECAST AREA ON
MONDAY NIGHT AND WHILE LITTLE MOISTURE WILL BE AVAILABLE...DID
INCREASE POPS TO SLIGHT CHANCE BOTH MONDAY AND TUESDAY PM DUE TO THE
POSSIBILITY FOR DIURNAL HEATING AND INSTABILITY. MLS

WEDNESDAY THROUGH THURSDAY...MODELS ARE IN BASIC AGREEMENT DURING
THIS PERIOD...WITH SOME DIFFERENCES IN TIMING OF FEATURES. BOTH GFS
AND ECMWF INDICATE WEAK SHORTWAVE TROUGHS AND RIDGES MOVING OVER THE
FORECAST AREA IN A SOUTHWEST TO WESTERLY FLOW ALOFT BUT AT DIFFERENT
TIMES. AN UNSETTLED PERIOD IS EXPECTED...AND DUE TO THE UNCERTAINTY
OF TIMING...PRECIPITATION PROBABILITIES WERE KEPT NEAR
CLIMATOLOGICAL AVERAGES. ISOLATED SHOWERS AND MAINLY AFTERNOON AND
EVENING THUNDERSTORMS ARE POSSIBLE ACROSS MUCH OF THE REGION.
SHOWERS AND THUNDERSTORMS SHOULD BE A LITTLE MORE NUMEROUS OVER THE
WESTERN AND SOUTHWESTERN MOUNTAINS. TEMPERATURES ARE EXPECTED TO BE
NEAR...OR A LITTLE ABOVE SEASONAL AVERAGES.   EK
&&

.AVIATION...
UPDATED 1745Z
VFR CONDITIONS SHOULD PREVAIL FOR THE FORECAST PERIOD WITH MVFR AND
IFR POSSIBLE NEAR SHOWERS AND THUNDERSTORMS AS WELL AS AT THE VERY
END OF THE FORECAST WHEN MORE STRATIFORM PRECIPITATION BEGINS.
EXPECTING SIGNIFICANT RAINFALL AND LOW CEILINGS THROUGHOUT TONIGHT
AND TOMORROW CAUSING MOUNTAIN OBSCURATION. WINDS SHOULD GENERALLY BE
LIGHT BUT GUSTY ERRATIC WINDS ARE POSSIBLE NEAR THUNDERSTORMS AND
STRONGER SHOWERS.

&&

.HYDROLOGY...
HAVE ISSUED A FLASH FLOOD WATCH FROM FRIDAY INTO SATURDAY ALONG
THE ROCKY MOUNTAIN FRONT. THIS IS MAINLY FOR THE BURN AREAS.
MODELS CONTINUE TO DIFFER ON WHERE HEAVIEST PRECIPITATION WILL BE
SO WILL JUST GO WITH A WATCH FOR NOW.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  53  67  51  69 /  70  80  50  60
CTB  50  61  48  67 /  60  90  90  60
HLN  56  71  52  71 /  70  70  40  50
BZN  53  77  48  74 /  60  50  40  50
WEY  41  60  37  58 /  50  50  50  50
DLN  50  65  44  65 /  60  60  40  40
HVR  52  71  51  71 /  60  80  80  50
LWT  52  70  49  69 /  70  80  40  50

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH FROM FRIDAY MORNING THROUGH SATURDAY AFTERNOON
FOR MTZ009-014-048.

SEVERE THUNDERSTORM WATCH UNTIL 9 PM MDT THIS EVENING FOR MTZ008-
012-014-015-048-050-052>055.

&&

SHORT TERM...BLANK
LONG TERM...GUSTAFSON
AVIATION...GUSTAFSON

WEATHER.GOV/GREATFALLS

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE GREAT FALLS MT
528 AM MDT THU AUG 6 2009

MTZ008-012-014-015-050>055-071200-
BEAVERHEAD-CASCADE-CENTRAL AND SOUTHERN LEWIS AND CLARK-MADISON-
JUDITH BASIN-FERGUS-JEFFERSON-BROADWATER-MEAGHER-GALLATIN-
528 AM MDT THU AUG 6 2009

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

.DAY ONE...TODAY AND TONIGHT

SCATTERED SHOWERS AND THUNDERSTORMS WILL AFFECT SOUTHWEST MONTANA
AND SOUTHERN PORTIONS OF CENTRAL MONTANA TODAY AND TONIGHT. A FEW
STORMS MAY BECOME SEVERE WITH DAMAGING WINDS AND HEAVY RAIN THIS
AFTERNOON AND EVENING.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

SHOWERS WILL BECOME WIDESPREAD ACROSS THE REGION FRIDAY THROUGH
SATURDAY...ALONG WITH A CHANCE OF THUNDERSTORMS. A FEW STORMS COULD
BECOME SEVERE WITH STRONG WINDS AND HEAVY RAIN THURSDAY AND FRIDAY.

.SPOTTER INFORMATION STATEMENT...

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

MTZ009>011-013-044>049-071200-
NORTHERN ROCKY MOUNTAIN FRONT-EASTERN GLACIER-HILL-CHOUTEAU-TOOLE-
LIBERTY-EASTERN PONDERA-BLAINE-SOUTHERN ROCKY MOUNTAIN FRONT-
EASTERN TETON-
528 AM MDT THU AUG 6 2009

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

.DAY ONE...TODAY AND TONIGHT

SCATTERED SHOWERS AND THUNDERSTORMS WILL AFFECT NORTH CENTRAL
MONTANA TODAY AND TONIGHT.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

SHOWERS WILL BECOME WIDESPREAD ACROSS THE REGION FRIDAY THROUGH
SATURDAY...ALONG WITH A CHANCE OF THUNDERSTORMS. PERIODS OF HEAVY
RAIN ARE EXPECTED...ESPECIALLY ALONG THE ROCKY MOUNTAIN FRONT.

.SPOTTER INFORMATION STATEMENT...

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

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
425 PM MDT THU AUG 06 2009

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0342 PM     HAIL             14 N CARDWELL           46.07N 111.90W
08/06/2009  E1.00 INCH       JEFFERSON          MT   TRAINED SPOTTER

            QUARTER SIZE HAIL. ALSO RELAYED REPORT OF WINDSHIELD
            BROKEN DUE TO HAIL NEAR HOMESTAKEPASS.

&&

HOENISCH

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE GREAT FALLS MT
425 PM MDT THU AUG 6 2009

MTZ008-015-052-062315-
BEAVERHEAD MT-JEFFERSON MT-MADISON MT-
425 PM MDT THU AUG 6 2009

...SIGNIFICANT WEATHER ADVISORY FOR NORTHWESTERN MADISON...NORTHERN
BEAVERHEAD AND SOUTHERN JEFFERSON COUNTIES UNTIL 515 PM MDT...

AT 425 PM MDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING A
STRONG THUNDERSTORM 13 MILES WEST OF TWIN BRIDGES...OR 20 MILES WEST
OF SHERIDAN...MOVING NORTHEAST AT 30 MPH.

HAIL UP TO ONE-HALF INCH IN DIAMETER AND WIND GUSTS UP TO 50 MPH ARE
EXPECTED WITH THIS STORM...ALONG WITH HEAVY RAIN.

* LOCATIONS IMPACTED INCLUDE...
   TWIN BRIDGES...
   SILVER STAR...
   WATERLOO...

IF THREATENING WEATHER APPROACHES YOUR AREA...TAKE SHELTER IN A
STURDY BUILDING.

LAT...LON 4564 11266 4569 11253 4573 11253 4576 11250
      4574 11246 4575 11220 4582 11242 4590 11231
      4559 11188 4541 11263 4556 11277
TIME...MOT...LOC 2226Z 236DEG 26KT 4554 11259

BRW