Severe Thunderstorm Warning 32, NWS Great Falls, MT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
555 PM MDT SAT JUN 21 2008

UPDATED AVIATION DISCUSSION

.DISCUSSION...

TONIGHT THROUGH MONDAY...THE UPPER LEVEL RIDGE THAT BROUGHT VERY
WARM AND DRY WEATHER TO SOUTHWEST...CENTRAL AND NORTH CENTRAL
MONTANA TODAY WILL SHIFT EAST THIS EVENING. THE SOMEWHAT MOIST
SOUTHWEST FLOW BETWEEN THE RIDGE AND AN APPROACHING PACIFIC TROUGH
WILL BRING ISOLATED SHOWERS AND THUNDERSTORMS TO THE AREA THIS
EVENING...WITH THE MAIN THREAT FROM THEM BEING GUSTY WINDS AND
POSSIBLE SMALL HAIL. STORMS WILL DIMINISH ACROSS THE EASTERN TFX
ZONES LATER THIS EVENING...WHILE THE APPROACHING TROUGH WILL
CONTINUE ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS ACROSS
THE WESTERN ZONES OVERNIGHT. STRONG MID LEVEL LIFT ACCOMPANYING A
COLD FRONT AHEAD OF THE TROUGH WILL SPREAD SCATTERED SHOWERS AND
THUNDERSTORMS ACROSS THE AREA FROM THE WEST DURING THE DAY ON
SUNDAY. THE FORECAST MODELS CONTINUE TO MOVE THE FRONT THROUGH THE
AREA QUICKLY THROUGHOUT THE DAY. HOWEVER...THE FRONT WILL BE
POSITIONED OVER THE EASTERN ZONES INTO SOUTHWEST MONTANA DURING
THE AFTERNOON. STRONG WIND SHEAR OF 40 TO 50 KNOTS ALONG THE
FRONT WILL HELP FOCUS POTENTIALLY SEVERE THUNDERSTORMS THERE.
DAMAGING WINDS ARE THE MOST LIKELY THREAT...WHILE LARGE HAIL WILL
ALSO BE POSSIBLE. BREEZY WESTERLY WINDS WILL ALSO DEVELOP BEHIND
THE FRONT. STORMS WILL DECREASE DURING THE EVENING AS THE
SHORTWAVE AND COLD FRONT EXIT THE AREA. A MORE STABLE WESTERLY
FLOW ALOFT WILL LINGER OVER THE AREA LATE SUNDAY NIGHT THROUGH
MONDAY. HOWEVER...THE AIRMASS WILL BECOME SLIGHTLY UNSTABLE MONDAY
AFTERNOON FOR A SLIGHT CHANCE OF THUNDERSTORMS. TEMPERATURES
TONIGHT WILL BE ABOVE NORMAL AHEAD OF THE FRONT...BUT THEY WILL
COOL BACK TO NEAR NORMAL FOR SUNDAY THROUGH MONDAY.  COULSTON

MONDAY NIGHT THROUGH SATURDAY...PERIOD IS DOMINATED BY WEST TO
WEST-SOUTHWEST FLOW ALOFT THROUGH MUCH OF NEXT WEEK WITH WEAK
ENERGY SKIRTING THE REGION FROM TIME TO TIME AS SHORTWAVES EJECT
FROM A BROAD/LOW AMPLITUDE TROUGH IN THE EASTERN PACIFIC INTO
WESTERN CANADA. THIS WILL MAINTAIN WARM AND GENERALLY DRY
CONDITIONS ACROSS THE REGION WITH TEMPERATURES NEAR TO SOMEWHAT
ABOVE AVERAGE. AFTERNOON INSTABILITY BUT LIMITED MOISTURE WILL
ALLOW FOR THE DEVELOPMENT OF ONLY ISOLATED AFTERNOON AND EVENING
CONVECTION EACH DAY WITH SLIGHTLY BETTER COVERAGE ON THURSDAY AS
A SHORTWAVE TROUGH MOVES BY TO THE NORTH. HOENISCH

&&

.AVIATION...
UPDATED 2355Z.
GENERALLY VFR CONDITIONS ARE EXPECTED ACROSS CENTRAL...NORTH
CENTRAL...AND SOUTHWEST MONTANA THROUGH 00Z MONDAY. SCATTERED
THUNDERSTORMS THIS AFTERNOON...CAPABLE OF PRODUCING WIND GUSTS OVER
35 KTS...WILL DIMINISH BY 05Z SUNDAY. A WEAK COLD FRONT WILL CHANGE
EASTERLY AND SOUTHEASTERLY SURFACE WINDS TO WESTERLY SUNDAY
MORNING...AS SOME SCATTERED SHOWERS MOVE ACROSS THE REGION. AS
INSTABILITY DEVELOPS BEHIND THE COLD FRONT SUNDAY AFTERNOON AND A
WEATHER DISTURBANCE MOVES ACROSS THE REGION...SCATTERED
THUNDERSTORMS WILL DEVELOP ACROSS THE REGION...GENERALLY ALONG AND
SOUTH OF A LINE FROM KHVR TO KGTF TO KHLN...WITH THE STRONGEST
STORMS OVER SOUTHWEST MONTANA. THE STRONGEST STORMS SUNDAY AFTERNOON
WILL BE CAPABLE OF PRODUCING WIND GUSTS OVER 45 KTS ALONG WITH HAIL.
CEILINGS WILL LOWER TO NEAR 5000 FEET NEAR STORMS. OUTSIDE OF
THUNDERSTORMS...WIND SPEEDS WILL GENERALLY BE UNDER 15 KTS...THOUGH
WIND GUSTS TO NEAR 25 KTS WILL BE POSSIBLE OVER NORTH CENTRAL
MONTANA SUNDAY AFTERNOON. COHEN

&&

.HYDROLOGY...
UPDATED 1036 AM MDT.
SNOW MELT FROM WARMING TEMPERATURES WILL CONTINUE ELEVATED WATER
LEVELS ON AREA RIVERS...CREEKS...AND STREAMS. RIVER LEVELS REMAIN
NEAR OR SLIGHTLY ABOVE BANKFULL NEAR INTERSTATE 90 IN SOUTHERN
JEFFERSON COUNTY. MAIN STEM RIVER LEVELS IN BROADWATER...
MADISON...AND GALLATIN COUNTIES HAVE GENERALLY REMAINED STEADY OR
HAVE BEEN SLOWLY RISING. THE GALLATIN RIVER NEAR LOGAN IS FORECAST
TO REMAIN AT OR ABOVE FLOOD STAGE UNTIL FURTHER NOTICE AND THE
GALLATIN RIVER NEAR GALLATIN GATEWAY CONTINUES TO SLOWLY RISE.
THEREFORE...WILL CONTINUE THE FLOOD WARNING FOR THE GALLATIN RIVER
NEAR LOGAN UNTIL FURTHER NOTICE. WILL ALSO EXTEND THE SMALL STREAM
FLOOD ADVISORY FOR JEFFERSON...BROADWATER...MADISON...AND GALLATIN
COUNTIES INTO SUNDAY AFTERNOON. HOWEVER...MAIN STEM RIVER LEVELS
IN THESE COUNTIES ARE GENERALLY FORECAST TO BEGIN FALLING AFTER
SUNDAY AS TEMPERATURES BEGIN TO COOL. WILL REEVALUATE STATUS OF
ADVISORY ON SUNDAY. EMANUEL/COULSTON

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  56  79  49  78 /  10  30  20  10
CTB  53  76  46  75 /  20  30  20  10
HLN  55  81  51  82 /  10  30  20  10
BZN  52  81  49  80 /  10  30  30  10
WEY  44  74  41  72 /  10  30  30  10
DLN  48  76  42  77 /  10  30  30  10
HVR  53  81  49  80 /  10  40  20  10
LWT  50  75  48  74 /  10  40  30  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

SHORT TERM...COULSTON
LONG TERM...HOENISCH
AVIATION...COHEN

WEATHER.GOV/GREATFALLS

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE GREAT FALLS MT
1135 AM MDT SAT JUN 21 2008

MTZ015-052-053-055-221200-
MADISON-JEFFERSON-BROADWATER-GALLATIN-
1135 AM MDT SAT JUN 21 2008

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTHWEST
MONTANA.

.DAY ONE...TODAY AND TONIGHT

VERY WARM TEMPERATURES WILL ALLOW THE SNOWMELT TO CONTINUE IN THE
MOUNTAINS THROUGH THE WEEKEND. RIVER LEVELS IN SOUTHWEST MONTANA WILL
REMAIN HIGH. THE FLOOD WARNING FOR THE GALLATIN RIVER NEAR LOGAN
WILL CONTINUE TODAY...AS WILL SMALL STREAM FLOOD ADVISORIES
ACROSS THE AREA.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

THE FLOOD WARNING FOR THE GALLATIN RIVER NEAR LOGAN WILL CONTINUE
UNTIL FURTHER NOTICE...AND THE SMALL STREAM FLOOD ADVISORIES WILL
CONTINUE THROUGH SUNDAY AFTERNOON. COOLER TEMPERATURES SHOULD
GENERALLY ALLOW RIVER LEVELS TO GRADUALLY FALL THROUGH EARLY NEXT
WEEK.

A DISTURBANCE MAY ALSO BRING SCATTERED THUNDERSTORMS TO THE AREA
ON SUNDAY. SOME THUNDERSTORMS MAY BECOME SEVERE WITH GUSTY WINDS
AND LARGE HAIL.

.SPOTTER INFORMATION STATEMENT...

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

MTZ008>014-044>051-054-221200-
BEAVERHEAD-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-JUDITH BASIN-FERGUS-MEAGHER-
549 AM MDT SAT JUN 21 2008

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

.DAY ONE...TODAY AND TONIGHT

VERY WARM TEMPERATURES WILL ALLOW THE SNOWMELT TO CONTINUE IN THE
MOUNTAINS THROUGH THE WEEKEND. RIVER LEVELS IN SOUTHWEST...CENTRAL
AND NORTH CENTRAL MONTANA WILL REMAIN HIGH.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

A DISTURBANCE MAY ALSO BRING SCATTERED THUNDERSTORMS TO THE AREA
ON SUNDAY. SOME THUNDERSTORMS MAY BECOME SEVERE WITH GUSTY WINDS
AND LARGE HAIL.

.SPOTTER INFORMATION STATEMENT...

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