Severe Thunderstorm Warning 37, NWS Great Falls, MT

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE GREAT FALLS MT
1145 AM MDT WED JUN 25 2008

UPDATED AVIATION SECTION

.UPDATE...MOSTLY CLEAR SKIES OVER CWA THIS MORNING AS RIBBON OF DRY
AIR ALOFT PASSES OVERHEAD.  PATCHES OF MOISTURE UPSTREAM SEEN IN WV
IMAGERY WILL ARRIVE THIS AFTN/EVE AND SHOULD PRODUCE ISOLD -TSRA
FROM DILLON TO LEWISTOWN...SMALL HAIL AND GUSTY WINDS ARE POSSIBLE
WITH SOME OF THESE STORMS.  NO CHANGES MADE TO GOING GRIDS.
WARANAUSKAS

.DISCUSSION...

CURRENT UPPER AIR ANALYSIS INDICATES STRENGTHENING WESTERLY FLOW
ALOFT...WITH A 50 KT 500 MB SPEED MAXIMUM OVERHEAD AND A SECONDARY
SPEED MAXIMUM OVER SOUTHEAST OREGON. THESE SPEED MAXIMA WILL PLAY
KEY ROLES IN THE SEVERE THUNDERSTORM THREAT ACROSS EASTERN
PORTIONS OF THE FORECAST AREA THIS AFTERNOON. LATEST SURFACE
ANALYSIS PLACES A WEAK SURFACE LOW OVER EASTERN IDAHO...WHICH IS
FORECAST TO MOVE INTO CENTRAL MONTANA AS A NORTH-SOUTH ELONGATED
SURFACE TROUGH THIS AFTERNOON. CORRESPONDINGLY...LOW LEVEL FLOW
WILL BACK...DEVELOPING AN EASTERLY COMPONENT AFTER NOON TODAY OVER
THE EASTERN THIRD OF THE FORECAST AREA. LOW-LEVEL MOISTURE WILL
INCREASE IN AREAS THAT EXPERIENCE THESE BACKED WINDS...AS
DEWPOINTS OVER SOUTHEAST MONTANA ARE CURRENTLY IN THE LOW TO MID
50S. WHILE MIXING PROCESSES THIS AFTERNOON WILL PREVENT THESE HIGH
OF DEWPOINTS TO BE EXPERIENCED...SUFFICIENTLY MOIST LOW LEVELS WILL
RESULT IN MODERATE INSTABILITY THIS AFTERNOON ALONG AND SOUTHEAST
OF A LINE FROM LEWISTOWN TO BOZEMAN. AN 850 MB CONVERGENCE AXIS IS
FORECAST TO MOVE ACROSS THE FORECAST AREA LATE THIS
AFTERNOON...PROVIDING ASCENT TO FURTHER BE ENHANCED BY THE
INTERACTION BETWEEN THE AFOREMENTIONED 500 MB SPEED MAXIMA.
ISOLATED THUNDERSTORMS ARE EXPECTED TO FORM OVER HIGHER TERRAIN OF
CENTRAL AND SOUTHWEST MONTANA AFTER 200 PM TODAY...PARTICULARLY
AROUND THE LITTLE BELTS AND SNOWY MOUNTAINS. STRONG FLOW OF 40 TO
50 KTS IN THE INSTABILITY-BEARING LAYER WILL RESULT IN ORGANIZED
STORM STRUCTURES...WITH A LARGE HAIL AND DAMAGING WIND THREAT
WITH ANY STORM THAT FORMS...PARTICULARLY OVER JUDITH BASIN AND
FERGUS COUNTIES...WHERE WIND DIRECTIONS ARE FORECAST TO CHANGE
WITH HEIGHT. MEAN STORM MOTION IS EXPECTED TO BE TO THE EAST-
NORTHEAST AT 25 TO 30 KTS...THOUGH ANY STORMS THAT MOVE TO THE
SOUTHEAST WILL NEED TO BE CLOSELY MONITORED FOR AN ENHANCED LARGE
HAIL AND DAMAGING WIND POTENTIAL. THE MOST LIKELY TIME FOR SEVERE
WEATHER WILL BE FROM 3 PM TO 8 PM TODAY. THIS THREAT IS MENTIONED
IN THE HAZARDOUS WEATHER OUTLOOK...THOUGH THE ABSENCE OF ANY
SUBSTANTIAL SHORTWAVE TROUGHS THIS AFTERNOON PRECLUDES A
WIDESPREAD ENOUGH THREAT FOR MENTION IN THE GRIDS AND FORECAST.
ELSEWHERE...PARTLY CLOUDY SKIES ARE EXPECTED THIS AFTERNOON WITH
TEMPERATURES NEAR TO SLIGHTLY ABOVE SEASONAL AVERAGES. THE THREAT
FOR STORMS WILL LINGER TONIGHT OVER FAR SOUTHWEST MONTANA AND
EASTERN PORTIONS OF CENTRAL MONTANA...AS THE UPPER LEVEL TROUGH
THAT WAS ORIGINALLY A PERSISTENT LOW OVER THE GULF OF ALASKA IS
EJECTED ACROSS THE REGION. HEIGHT FALLS AT 500 MB WILL COMMENCE
TONIGHT WITH THE APPROACH OF THIS TROUGH...RESULTING IN COOLER
TEMPERATURES ACROSS THE REGION ON THURSDAY. SUFFICIENT ASCENT WITH
THIS SYSTEM MAY ALLOW FOR SCATTERED SHOWERS AND THUNDERSTORMS OVER
CENTRAL AND NORTH CENTRAL MONTANA THURSDAY AFTERNOON...WITH
STRONGER STORMS OVER SOUTHWEST MONTANA IN THE BETTER INSTABILITY.
HOWEVER ABSENCE OF MOISTER LOW LEVELS WILL PRECLUDE A SEVERE
WEATHER THREAT THURSDAY AFTERNOON. AN UPPER LEVEL RIDGE WILL BEGIN
TO BUILD INTO THE REGION ON FRIDAY...AS A SURFACE HIGH DEVELOPS
OVER SOUTHERN MONTANA...AND TEMPERATURES BEGIN WARMING. COHEN

FRIDAY NIGHT THROUGH MONDAY NIGHT...AREA WILL BE UNDER THE INFLUENCE
OF A STRONG RIDGE OF HIGH PRESSURE ALOFT OVER THE WESTERN U.S. DRY
NORTHWEST FLOW ALOFT AT THE BEGINNING OF THE PERIOD WILL TRANSITION
TO MORE OF A WESTERLY OR SOUTHWESTERLY FLOW ALOFT LATE IN THE
WEEKEND/EARLY NEXT WEEK. MODELS ARE INDICATING THE POSSIBILITY OF
SOME WEAK SHORTWAVES SUNDAY THROUGH MONDAY NIGHT ALONG WITH AT LEAST
A LITTLE INCREASE IN MOISTURE. CONSISTENCY AMONGST MODELS AND ALSO
RUN-TO-RUN CONSISTENCY FOR A PARTICULAR MODEL IS NOT GOOD ON THE
SHORTWAVE DETAILS. EXPECT SOME WEAK INSTABILITY OVER SW MONTANA ON
SUNDAY AND OVER MOST OF THE AREA ON MONDAY. IN LINE WITH THIS ADDED
A SLIGHT CHANCE OF THUNDERSTORMS OVER ALL OF SW MONTANA AND A
PORTION OF CENTRAL MONTANA ON SUNDAY WITH A SLIGHT CHANCE OF
THUNDERSTORMS OVER THE ENTIRE AREA ON MONDAY. TEMPERATURES WILL BE
WELL ABOVE NORMAL FOR LATE JUNE. BLANK

TUESDAY AND WEDNESDAY..MODELS SHOW FAIRLY STRONG UPPER LEVEL
RIDGE OVER THE INTER-MOUNTAIN WEST FOR VERY WARM AND MOSTLY
DRY WEATHER. SOME MODELS DO PUT THE RIDGE AXIS EAST OF CENTRAL
MONTANA FOR A MOIST AND UNSTABLE SOUTHWEST FLOW ALOFT. SO
WILL GO WITH ISOLATED THUNDERSTORMS...MAINLY OVER THE MOUNTAINS.
WILLIAMSON DC

&&

.AVIATION...
UPDATED 1745Z.
WEAK HIGH PRESSURE WILL BE THE DOMINANT WEATHER FEATURE PRESENT IN
THE REGION DURING THE NEXT 24 HOURS. VFR FLIGHT CONDITIONS ARE
ANTICIPATED TO PREVAIL DURING THIS TIME. ISOLATED SHOWER AND
THUNDERSTORM ACTIVITY IS EXPECTED TO OCCUR OVER HIGH TERRAIN NEAR
KBZN AND KLWT FROM 21Z THRU 03Z...HOWEVER THERE IS A LOW LIKELIHOOD
THAT ANY ACTIVITY WILL BE WITHIN 5NM OF EITHER TERMINAL. NO OTHER
AVIATION RELATED IMPACTS ARE ANTICIPATED DURING THE FORECAST PERIOD.
ZUMPFE

&&

.HYDROLOGY...
SNOW MELT IS DECREASING ACROSS THE AREA...LEADING TO SLIGHT DROPS
IN LOCAL RIVER AND STREAM LEVELS. LATEST FORECAST MODELS SHOW
CONTINUED GRADUAL DECREASES IN LEVELS THROUGH THE NEXT FEW DAYS.
DESPITE LOWER LEVELS...SOME AREAS IN SOUTHWEST MONTANA REMAIN AT
OR NEAR FLOOD STAGE WITH SOME MINOR LOWLAND FLOODING REPORTED. A
SMALL STREAM ADVISORY REMAINS IN EFFECT FOR MADISON...GALLATIN...
AND JEFFERSON COUNTIES. THE FLOOD WARNING FOR THE GALLATIN RIVER
NEAR LOGAN CONTINUES AS THE RIVER IS JUST ABOVE FLOOD STAGE. MUCH
WARMER TEMPERATURES THIS WEEKEND AND EARLY NEXT WEEK COULD RESULT
IN INCREASED SNOW MELT ONCE AGAIN...ALONG WITH ELEVATED LEVELS ON
LOCAL RIVERS AND STREAMS...PARTICULARLY IN GALLATIN COUNTY.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  82  53  77  47 /  10  10  20  10
CTB  77  51  73  45 /   0  10  20  10
HLN  85  55  82  49 /  10  10  20  10
BZN  85  48  81  45 /  20  20  20  20
WEY  76  43  70  40 /  20  20  20  20
DLN  79  45  76  41 /  20  10  20  10
HVR  81  52  78  48 /  10  10  30  20
LWT  79  51  75  45 /  20  20  30  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
SMALL STREAM FLOOD ADVISORY CONTINUES INTO WEDNESDAY AFTERNOON
FOR PORTIONS OF SOUTHWEST MONTANA.

FLOOD WARNING CONTINUES FOR THE GALLATIN RIVER NEAR LOGAN UNTIL
FURTHER NOTICE.

&&

UPDATE...WARANAUSKAS
SHORT TERM...COHEN
LONG TERM...BLANK/WILLIAMSON DC
AVIATION...ZUMPFE

WEATHER.GOV/GREATFALLS

HAZARDOUS WEATHER OUTLOOK...CORRECTED
NATIONAL WEATHER SERVICE GREAT FALLS MT
520 AM MDT WED JUN 25 2008

MTZ008-015-050>055-261130-
BEAVERHEAD-MADISON-JUDITH BASIN-FERGUS-JEFFERSON-BROADWATER-
MEAGHER-GALLATIN-
520 AM MDT WED JUN 25 2008

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

.DAY ONE...TODAY AND TONIGHT

ISOLATED STRONG TO SEVERE THUNDERSTORMS WILL BE POSSIBLE THIS
AFTERNOON AND EVENING OVER PORTIONS OF SOUTHWEST AND CENTRAL
MONTANA. THE GREATEST CHANCE FOR SEVERE THUNDERSTORMS WILL BE
SOUTHEAST OF A LINE FROM LEWISTOWN TO BOZEMAN...WHERE THE
STRONGEST STORMS WILL BE CAPABLE OF PRODUCING HAIL LARGER THAN
PENNIES AND WIND GUSTS OVER 60 MPH. THE MOST LIKELY TIME FOR
SEVERE THUNDERSTORMS WILL BE FROM 300 PM TO 800 PM MDT.

ALSO...THE GALLATIN RIVER NEAR LOGAN REMAINS ABOVE FLOOD
STAGE...WHERE A FLOOD WARNING CONTINUES. ADDITIONALLY....A FLOOD
ADVISORY REMAINS IN EFFECT FOR SMALL STREAMS IN GALLATIN...
JEFFERSON...AND MADISON COUNTIES.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

STRONG THUNDERSTORMS WILL BE POSSIBLE OVER FAR SOUTHWEST MONTANA
THURSDAY AFTERNOON.

ALSO...THE FLOOD WARNING REMAINS IN EFFECT FOR THE GALLATIN RIVER
NEAR LOGAN UNTIL FURTHER NOTICE.

MUCH WARMER TEMPERATURES THIS WEEKEND AND EARLY NEXT WEEK COULD RESULT
IN INCREASED SNOW MELT ONCE AGAIN...ALONG WITH ELEVATED LEVELS ON
AREA RIVERS...CREEKS...AND STREAMS IN SOUTHWEST MONTANA...PARTICULARLY
IN GALLATIN COUNTY.

.SPOTTER INFORMATION STATEMENT...

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

MTZ009>014-044>049-261130-
NORTHERN ROCKY MOUNTAIN FRONT-EASTERN GLACIER-HILL-CASCADE-
CHOUTEAU-CENTRAL AND SOUTHERN LEWIS AND CLARK-TOOLE-LIBERTY-
EASTERN PONDERA-BLAINE-SOUTHERN ROCKY MOUNTAIN FRONT-
EASTERN TETON-
520 AM MDT WED JUN 25 2008

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

.DAY ONE...TODAY AND TONIGHT

THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW.

.SPOTTER INFORMATION STATEMENT...

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

COHEN