Severe Thunderstorm Warning 5, NWS Great Falls, MT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
545 PM MDT THU JUN 4 2015

UPDATED AVIATION SECTION

.DISCUSSION...

TONIGHT THROUGH SATURDAY...AN UPPER LEVEL TROUGH SEEN IN WV
IMAGERY OVER CENTRAL ALBERTA IS LIFTING AWAY TO THE NORTH-
NORTHEAST. A SOUTHWESTERLY JET STREAK ATTACHED TO THIS FEATURE IS
CAUSING 0-6 KM SHEAR VALUES TO EXCEED 40 KTS IN FORECAST SOUNDINGS
OVER PORTIONS OF NORTH CENTRAL MONTANA. AFTERNOON TEMPERATURES
HAVE REACHED OR EXCEEDED CONVECTIVE TEMPERATURES...PRODUCING
NUMEROUS SCATTERED SHOWERS AND THUNDERSTORMS. SHORT TERM GUIDANCE
SUGGESTS THIS ACTIVITY WILL BECOME MORE WIDESPREAD THROUGH THE
EVENING, TAPERING AFTER SUNSET WITH COOLER SURFACE TEMPERATURES.
LOCALLY HEAVY RAIN...SMALL HAIL AND GUSTY WINDS ARE POSSIBLE IN A
FEW OF THESE THUNDERSTORMS. THUNDERSTORM ACTIVITY RESUMES AGAIN
FRIDAY AFTERNOON, BUT MAINLY FOR SOUTHWEST MONTANA UNDER THE
DIFFLUENT FLOW OF THE CUTOFF LOW OVER THE GREAT BASIN. THE DRYING
TREND CONTINUES SATURDAY AS RIDGING DEVELOPS OVER THE PACIFIC
NORTHWEST INTO WESTERN AND NORTH CENTRAL MONTANA. ONLY ISOLATED
SHOWERS ARE EXPECTED OVER THE HIGHER TERRAIN OF SOUTHWEST MONTANA
ON SATURDAY. NUTTER

SATURDAY NIGHT THROUGH WEDNESDAY...FORECAST MODELS CONTINUE TO BUILD
HIGH PRESSURE ALOFT INTO THE FORECAST AREA FROM THE PACIFIC
NORTHWEST SATURDAY NIGHT THROUGH MONDAY, WHILE THE UPPER TROUGH OF
LOW PRESSURE STRETCHES AND WEAKENS OVER THE CENTRAL ROCKIES AND
GREAT BASIN. THIS WILL KEEP MOST OF THE AREA DRY, WITH ONLY A CHANCE
OF SHOWERS AND THUNDERSTORMS OVER FAR SOUTHWEST MONTANA.
TEMPERATURES WILL WARM SIGNIFICANTLY THROUGH THIS PERIOD, AS HIGHS
WILL REACH WELL INTO THE 80S FOR MOST AREAS BY MONDAY. OVERNIGHT
LOWS WILL ALSO BE MILD FOR THIS TIME OF YEAR, RANGING FROM THE MID
40S TO MID 50S. A SHORTWAVE TROUGH WILL THEN SWING SOUTHEAST FROM
THE GULF OF ALASKA ALONG THE MONTANA/CANADA BORDER MONDAY NIGHT
THROUGH TUESDAY, DRAGGING A WEAK CANADIAN COLD FRONT THROUGH THE
STATE. SURFACE WINDS WILL SHIFT MORE NORTHERLY BEHIND THE FRONT, BUT
TEMPERATURES WILL ONLY COOL 5 TO 10 DEGREES THROUGH WEDNESDAY.
HOWEVER, THE PASSAGE OF THE SHORTWAVE/COLD FRONT SYSTEM WILL BRING A
CHANCE OF SHOWERS AND THUNDERSTORMS ONCE AGAIN MONDAY NIGHT INTO
TUESDAY, BUT MAINLY TO THE MOUNTAINS. THE APPROACH OF ANOTHER UPPER
LEVEL TROUGH FROM THE PACIFIC OCEAN WILL PUT THE STATE UNDER THE
INFLUENCE OF A MORE MOIST AND UNSTABLE SOUTHWESTERLY FLOW ALOFT FOR
TUESDAY NIGHT INTO WEDNESDAY. THIS WILL BRING A MORE WIDESPREAD
CHANCE FOR SHOWERS AND THUNDERSTORMS TO THE AREA.
COULSTON

&&

.AVIATION...
UPDATED 2345Z.
AN UNSTABLE AIRMASS AND AFTERNOON HEATING ARE
CONTRIBUTING TO THE DEVELOPMENT OF SCATTERED SHOWERS AND
THUNDERSTORMS. CONVECTIVE ACTIVITY SHOULD END BY 06Z WITH CLEARING
SKIES. VFR CONDITIONS PREVAIL WITH MVFR CONDITIONS POSSIBLE IN THE
VICINITY OF THUNDERSTORMS ALONG WITH GUSTY ERRATIC WINDS.

&&

.HYDROLOGY...
LOCALLY HEAVY RAINS OF 1 TO 2 INCHES WERE OBSERVED IN
PORTIONS OF FERGUS COUNTY WEDNESDAY NIGHT. MCDONALD CREEK ALONG
HIGHWAY 200 AND SPRING CREEK UPSTREAM TO THE SOUTHEAST OF LEWISTOWN
HAVE RISEN TO NEAR BANKFULL STAGE. SCATTERED SHOWERS AND
THUNDERSTORMS REMAIN IN THE FORECAST...PEAKING DURING LATE AFTERNOON
HOURS. WIDESPREAD HEAVY RAINFALL HAS ENDED IN THIS AREA...SO WATER
LEVELS ARE EXPECTED TO STABILIZE OVERNIGHT AND DROP THROUGH FRIDAY
MORNING. PN

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  50  72  50  75 /  20  40  20  10
CTB  43  73  45  76 /  20  20  10  10
HLN  53  74  53  77 /  30  50  40  10
BZN  48  72  48  72 /  40  50  50  30
WEY  38  67  39  66 /  30  70  40  40
DLN  47  69  49  70 /  40  50  40  30
HVR  48  75  50  79 /  30  30  20  10
LWT  50  69  51  72 /  30  50  40  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...

SMALL STREAM FLOOD ADVISORY FOR SOUTHERN FERGUS COUNTY UNTIL 300 PM
MDT FRIDAY

&&

WEATHER.GOV/GREATFALLS

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE GREAT FALLS MT
527 PM MDT THU JUN 4 2015

MTZ011-013-050015-
HILL MT-CHOUTEAU MT-
527 PM MDT THU JUN 4 2015

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHEASTERN LIBERTY...
SOUTHWESTERN HILL AND NORTH CENTRAL CHOUTEAU COUNTIES UNTIL 615 PM
MDT...

AT 526 PM MDT...DOPPLER RADAR WAS TRACKING A STRONG THUNDERSTORM 23
MILES SOUTH OF INVERNESS...OR 24 MILES SOUTHEAST OF CHESTER...MOVING
EAST AT 15 MPH.

HALF INCH HAIL AND WINDS IN EXCESS OF 40 MPH WILL BE POSSIBLE WITH
THIS STORM.

THIS STORM WILL REMAIN OVER MAINLY RURAL AREAS OF SOUTHEASTERN
LIBERTY...SOUTHWESTERN HILL AND NORTH CENTRAL CHOUTEAU COUNTIES.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

TORRENTIAL RAINFALL IS ALSO OCCURRING WITH THIS STORM...AND MAY LEAD
TO FLASH FLOODING. DO NOT DRIVE YOUR VEHICLE THROUGH FLOODED
ROADWAYS.

&&

LAT...LON 4812 11026 4807 11081 4813 11083 4821 11083
      4822 11075 4829 11074 4841 11040
TIME...MOT...LOC 2326Z 252DEG 11KT 4821 11067

PN