Severe Thunderstorm Warning 28, NWS Great Falls, MT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
549 PM MDT TUE JUN 17 2008

UPDATED AVIATION DISCUSSION

.DISCUSSION...

ISOLATED STRONG AND SEVERE THUNDERSTORMS ARE EXPECTED OVER THE
FORECAST AREA THIS AFTERNOON AND EVENING AS INSTABILITY INTERACTS
WITH AN UPPER LEVEL DISTURBANCE. STORMS WILL CONTINUE DEVELOPING
OVER SOUTHWEST MONTANA THIS AFTERNOON...AND WILL MOVE ACROSS
CENTRAL MONTANA THIS EVENING. THEY WILL LIKELY INTENSIFY...AS THEY
INTERACT WITH DEEPER MOISTURE. DEEP MIXED LAYERS...COMBINED WITH
INCREASING MEAN FLOW ALOFT WILL SUPPORT A DAMAGING WIND THREAT
THIS AFTERNOON AND EVENING...ALONG WITH A LARGE HAIL THREAT AS
THEY APPROACH CENTRAL MONTANA. STORMS WILL MOVE INTO NORTH CENTRAL
MONTANA TOWARD MIDNIGHT...AS INSTABILITY LINGERS THERE. WIND
PROFILES WILL BE FAVORABLE FOR A SUPERCELL OR TWO THROUGH
TONIGHT...WITH VERY LARGE HAIL POSSIBLE IN CENTRAL MONTANA. FOR
TUESDAY AND WEDNESDAY AFTERNOONS...ADDITIONAL DISTURBANCES AND
INSTABILITY WILL SUPPORT AFTERNOON THUNDERSTORM
DEVELOPMENT...THOUGH LIMITED MOISTURE WILL LIMIT THE SEVERE
THREAT. OTHERWISE...TEMPERATURES WILL REMAIN NEAR TO ABOVE
SEASONAL AVERAGES. COHEN

THURSDAY NIGHT THROUGH SUNDAY NIGHT...MODELS MAINTAINING
SOUTHWESTERLY FLOW REGIME THRU THIS PERIOD.  CONTINUED WARM TEMPS
WITH AREAS OF MOISTURE WILL KEEP CHANCE OF AFTN/EVE THUNDERSTORMS
THURS EVE PRIMARILY ACROSS SOUTHERN HALF OF CWA.  UPPER RIDGE AXIS
BEGINS TO AMPLIFY OVER CENTRAL MT ON FRI BRINGING WARMER AND DRIER
AIRMASS THRU SAT...BUMPED TEMPS AND SLIGHTLY DECREASED POPS
ACCORDINGLY.  SHORTWAVE TROF ROTATING THRU BASE OF LARGE GULF OF AK
LOW SLIDES THROUGH ID PANHANDLE AND INTO NW MT ON SUN MORNING
BRINGING INCREASED CLOUD COVER AND COOLER TEMPS.  WARANAUSKAS

MONDAY THROUGH TUESDAY NIGHT...CURRENT SUITE OF GUIDANCE DEPICTS AN
UPPER LEVEL TROUGH OF LOW PRESSURE AFFECTING THE FORECAST AREA
DURING DAYS 7 AND 8. THE MOVEMENT OF THIS TROUGH INTO REGION WILL BE
THE RESULT OF A PREVIOUSLY STATIONARY CLOSED LOW OFF THE COAST OF
BRITISH COLUMBIA DRIFTING WEST. SOUTHWESTERLY FLOW ALOFT WILL BE
PRESENT OVER THE REGION DURING BOTH DAYS...HOWEVER A SURFACE COLD
FRONT MAY PASS THROUGH THE AREA DURING TUESDAY EVENING. AFTERNOON
AND EVENING SHOWER AND THUNDERSTORM ACTIVITY IS EXPECTED BOTH MONDAY
AND TUESDAY...WITH A GREATER LIKELIHOOD OF PRECIPITATION ON TUESDAY
IN THE PRESENCE OF THE SURFACE COLD FRONT. TEMPERATURES ARE
ANTICIPATED TO BE NEAR THE SEASONAL AVERAGE DURING THIS TIME. ZUMPFE

&&

.AVIATION...

DISTURBANCE IN SOUTHWEST FLOW ALOFT MOVES THROUGH THE REGION THIS
EVENING WITH AN ASSOCIATED COLD FRONT MOVING ACROSS THE AREA AS
WELL. WIDESPREAD SHOWERS AND THUNDERSTORMS HAVE DEVELOPED MAY IMPACT
ALL TERMINALS BUT KCTB THROUGH THIS EVENING. FRONT WILL MOVE THROUGH
THE AREA BY MIDNIGHT WITH WINDS SHIFTING TO THE WEST. SKIES WILL
CLEAR AFTER MIDNIGHT. VFR CONDITIONS WILL GENERALLY PREVAIL WITH THE
EXCEPTION OF MVFR CONDITIONS IN THE VICINITY OF SHOWERS AND
THUNDERSTORMS THIS EVENING. SOME THUNDERSTORMS THIS EVENING MAY
PRODUCE LARGE HAIL AND DAMAGING WINDS. HOENISCH

&&

.HYDROLOGY...
CONTINUED SNOW MELT WILL CAUSE ELEVATED WATER LEVELS ON AREA
RIVERS...CREEKS...AND STREAMS. RIVER LEVELS HAVE RISEN ABOVE
BANKFULL ON THE SMITH RIVER 13 MILES SOUTH OF ULM AND NEAR
INTERSTATE 90 IN SOUTHERN JEFFERSON COUNTY...AND RISES HAVE ALSO
BEEN NOTED ON BADGER CREEK NEAR BROWNING AND THE SUN RIVER WEST OF
GREAT FALLS. A FLOOD ADVISORY HAS BEEN ISSUED FOR THE SMITH RIVER
AND OTHER SMALL STREAMS IN CASCADE...BROADWATER...GALLATIN...
JEFFERSON...AND MADISON COUNTIES. OTHER AREAS WILL CONTINUE TO BE
MONITORED THROUGH THE WEEK.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  47  75  47  75 /  20  10  20  20
CTB  45  72  45  72 /  20  10  10  10
HLN  48  78  49  79 /  20  10  20  20
BZN  47  78  46  79 /  20  20  20  20
WEY  41  72  39  69 /  20  20  20  20
DLN  45  76  42  75 /  20  20  20  20
HVR  50  77  49  76 /  20   0  10  10
LWT  46  72  45  70 /  30  10  20  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...

...SMALL STREAM FLOOD ADVISORY CONTINUES FOR PORTIONS OF SOUTHWEST
AND CENTRAL MONTANA...

&&

SHORT TERM...COHEN
LONG TERM...WARANAUSKAS/ZUMPFE
AVIATION...HOENISCH

WEATHER.GOV/GREATFALLS

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE GREAT FALLS MT
1036 AM MDT TUE JUN 17 2008

MTZ008>015-044>055-181230-
BEAVERHEAD-NORTHERN ROCKY MOUNTAIN FRONT-EASTERN GLACIER-HILL-
CASCADE-CHOUTEAU-CENTRAL AND SOUTHERN LEWIS AND CLARK-MADISON-
TOOLE-LIBERTY-EASTERN PONDERA-BLAINE-
SOUTHERN ROCKY MOUNTAIN FRONT-EASTERN TETON-JUDITH BASIN-FERGUS-
JEFFERSON-BROADWATER-MEAGHER-GALLATIN-
1036 AM MDT TUE JUN 17 2008

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

.DAY ONE...TODAY AND TONIGHT

THUNDERSTORM OUTLOOK...
THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS MUCH OF
SOUTHWEST...CENTRAL...AND NORTH CENTRAL MONTANA THROUGH TONIGHT.

LOCATION...
THE SLIGHT RISK AREA IS GENERALLY SOUTH OF A LINE FROM CHINOOK...TO
LOMA...TO LINCOLN...AND INCLUDES GREAT FALLS...LEWISTOWN...
HELENA...AND BOZEMAN.

TIMING...
STRONG THUNDERSTORMS WILL DEVELOP BETWEEN 1 AND 3 PM THIS AFTERNOON
OVER SOUTHWEST MONTANA...AND WILL INTENSIFY AS THEY MOVE
NORTHEASTWARD OVER SOUTHWEST AND CENTRAL MONTANA LATE THIS
AFTERNOON AND THIS EVENING. THE SEVERE THUNDERSTORM THREAT WILL
SPREAD ACROSS CENTRAL MONTANA AFTER 4 PM THIS AFTERNOON...AND
WILL LIKELY END ACROSS THE ENTIRE AREA BY 11 PM THIS EVENING.

IMPACTS...
DAMAGING WIND GUSTS OVER 70 MPH AND HAIL TO THE SIZE OF GOLF BALLS
WILL BE THE PRIMARY CONCERNS WITH THE STRONGEST STORMS. INTENSE
LIGHTNING AND LOCALLY HEAVY RAIN WILL ALSO BE CONCERNS. AN
ISOLATED TORNADO CANNOT BE COMPLETELY RULED OUT IN CENTRAL MONTANA
EARLY THIS EVENING.

RECOMMENDED ACTIONS...
STORM SPOTTERS AND EMERGENCY MANAGEMENT PERSONNEL ACROSS THE
NATIONAL WEATHER SERVICE GREAT FALLS WARNING AREA SHOULD MONITOR
CHANGING WEATHER CONDITIONS THROUGH TONIGHT.

OTHER HAZARDOUS WEATHER...
A SMALL STREAM FLOOD ADVISORY REMAINS IN EFFECT FOR PORTIONS OF
CENTRAL AND SOUTHWEST MONTANA. VERY HEAVY RAIN WITH STORMS MAY
CAUSE FLOODING OF LOW-LYING AND POORLY DRAINED AREAS TODAY AND
TONIGHT.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

STRONG TO SEVERE THUNDERSTORMS WILL BE POSSIBLE WEDNESDAY AND
THURSDAY AFTERNOONS ACROSS CENTRAL AND SOUTHWEST MONTANA.

THE SMALL STREAM FLOOD ADVISORY REMAINS IN EFFECT THROUGH
WEDNESDAY AFTERNOON.

WITH ABOVE NORMAL TEMPERATURES EXPECTED FOR THE REMAINDER OF THE
WEEK...INCREASED SNOWMELT IS EXPECTED OUT OF THE MOUNTAINS. AS A
RESULT...RIVER...CREEK...AND STREAM LEVELS WILL REMAIN HIGH
THROUGHOUT THE WEEK. THE MAIN AREAS OF CONCERN WILL BE NEAR THE
MOUNTAINS. THIS SITUATION WILL CONTINUE TO BE MONITORED FOR
ADDITIONAL FLOOD HIGHLIGHTS.

.SPOTTER INFORMATION STATEMENT...

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

COHEN