Special Weather Statement, NWS Great Falls, MT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
253 PM MDT FRI JUL 20 2012

.DISCUSSION...

TONIGHT THROUGH SUNDAY...FORECAST CONTINUES TO LOOK ON TRACK FOR
THE UPPER LEVEL WAVE TO MOVE THROUGH NORTHWEST MONTANA THIS
AFTERNOON AND EVENING. NUMEROUS THUNDERSTORMS ARE IN PROGRESS OVER
THE IDAHO PANHANDLE WITH SCATTERED THUNDERSTORMS BEGINNING TO
DEVELOP OVER MY SOUTHWEST AND WEST CENTRAL ZONES. ACTIVITY ACROSS
THE WESTERN HALF OF MY CWA WILL INCREASE THROUGH THE AFTERNOON
AND EVENING HOURS. STILL APPEARS TO BE A RISK FOR A FEW STORMS TO
BECOME STRONG TO SEVERE...MAINLY OVER MY NORTHWEST ZONES.
HOWEVER...AT LEAST ONE MODEL DEVELOPS A SECOND BAND OF POTENTIALLY
SEVERE THUNDERSTORMS FROM THE LITTLE BELT MOUNTAINS TO NORTHERN
FERGUS AND SOUTHERN BLAINE COUNTIES DURING THE EVENING HOURS. EVEN
FOR STORMS THAT ARE EXPECTED TO REMAIN SUB-SEVERE THERE IS A
DISTINCT RISK FOR VERY HEAVY AND INTENSE RAIN IN A SHORT PERIOD OF
TIME CAUSING LOCALIZED FLOODING. ACTIVITY SHOULD MOVE INTO
NORTHEAST MONTANA AFTER MIDNIGHT WITH SKIES CLEARING FROM THE
SOUTHWEST. SATURDAY SHOULD BE ANOTHER WARM AND GENERALLY DRY DAY
WITH PERHAPS A RISK OF AN ISOLATED STORM OR TWO OVER THE SOUTHWEST
MONTANA MOUNTAINS DURING THE AFTERNOON AND EVENING. TEMPERATURES
WARM UP A FEW MORE DEGREES ON SUNDAY WITH MONSOON MOISTURE
INCREASING FROM SOUTH TO NORTH THROUGH THE DAY. MODELS ARE
BEGINNING TO COME INTO BETTER AGREEMENT THAT SCATTERED
THUNDERSTORMS WILL DEVELOP OVER SOUTHWEST AND SOUTH CENTRAL
MONTANA...POSSIBLY AS FAR NORTH AS A LINE FROM HELENA TO GREAT
FALLS TO LEWISTOWN. THE ALSO APPEARS TO BE AT LEAST A SLIGHT RISK
FOR SOME STORMS TO BECOME STRONG TO SEVERE. MPJ

SUNDAY NIGHT THROUGH FRIDAY...LONG-RANGE FORECAST MODELS MAINTAINING
GOOD CONSISTENCY AND AGREEMENT ON EXPECTED CONDITIONS FOR THE WEEK
AHEAD.  PERIOD BEGINS WITH BROAD UPPER LEVEL RIDGE DRIFTING INTO ERN
MT ON SUN EVE...ALLOWING MONSOONAL MOISTURE TO GENERATE SCATTERED
SHOWERS AND THUNDERSTORMS SUN NIGHT MAINLY OVER SOUTHWEST MT.
SOUTHWEST FLOW ALOFT OVER OUR REGION STRENGTHENS ON MONDAY IN
RESPONSE TO A VIGOROUS PACIFIC LOW PRESSURE SYSTEM MAKING ITS WAY
ALONG THE US/CAN BORDER.  A SURFACE COLD FRONT FROM THIS SYSTEM
SHOULD CROSS THE CONTINENTAL DIVIDE MONDAY EVE WHERE IT WILL TAP
INTO THE MONSOONAL MOISTURE TO BRING ANOTHER ROUND OF
THUNDERSTORMS...WITH MODELS SHOWING WIDER COVERAGE OF STORMS
PARTICULARLY OVER THE CENTRAL MT COUNTIES.  MODELS HAVE ALSO
SLIGHTLY INCREASED PRECIPITABLE WATER VALUES...THOUGH SURFACE DEW
POINTS ARE SOMEWHAT DRY...SO A MIX OF DRY/WET STORMS SEEMS LIKELY.
THE COLD FRONT WILL BE WELL DOWNSTREAM BY TUES MORNING AS THE LOW
PRESSURE CENTER LIFTS INTO SRN ALBERTA.  WESTERLY FLOW AND A RETURN
TO DRY CONDITIONS DEVELOP BEHIND THE FRONT ALONG WITH SOME BREEZY TO
LOCALLY GUSTY WINDS ON TUES...LIKELY INCREASING WILDLAND FIRE DANGER
OVER PORTIONS OF CENTRAL/SOUTHWEST MT.  THE UPPER LEVEL RIDGE
GRADUALLY REBUILDS OVER THE NRN ROCKIES THRU MIDWEEK AND THE NEXT
PUSH OF MONSOONAL MOISTURE BEGINS TO ARRIVE THURS WITH SCATTERED
THUNDERSTORMS POSSIBLE THURS AND FRI EVENING.  HIGH TEMPERATURES
REMAIN ABOUT 5-8 DEGREES ABOVE NORMAL ON MON BUT THE COLD FRONT
PASSAGE WILL DROP BACK HIGHS INTO THE LOW-MID 80S FOR TUES/WED.
TEMPS THEN REBOUND UPWARD A FEW DEGREES EACH DAY FOR THE LATTER HALF
OF THE WEEK...REACHING THE UPPER 80S TO LOW 90S BY FRIDAY.
WARANAUSKAS

&&

.AVIATION...
UPDATED 1740Z.
VFR CONDITIONS EXPECTED TODAY WITH WIDESPREAD MID-LEVEL CEILINGS
OVER CENTRAL/SOUTHWEST MT. UPPER LEVEL TROF CURRENTLY IN NORTHERN
OREGON WILL MOVE TO NORTHWEST MT BY THIS EVE. INCREASING INSTABILITY
AND VEERING WINDS FROM THE APPROACHING TROF WILL LEAD TO DEVELOPMENT
OF SCATTERED STRONG-TO-SEVERE THUNDERSTORMS THIS AFTN/EVE...
ESPECIALLY ALONG LINE FROM KCTB TO KHVR. STORM ACTIVITY WILL ALSO
EXTEND SOUTH TO KGTF/KHLN/KLWT BUT HAVE LESSER CHANCE OF SEVERE
CONDITIONS THERE. BRIEF MVFR CONDITIONS FROM HEAVY RAINFALL AND
STRONG SHIFTING OUTFLOW WINDS POSSIBLE NEAR ANY STORM CELLS. SKY
COVER WILL DIMINISH OVER AERODROMES AFTER 06Z. BRITTON

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  59  89  57  92 /  30   0  10  10
CTB  54  82  50  89 /  40   0  10  10
HLN  58  90  58  93 /  30  10  10  20
BZN  51  92  50  93 /  10  10  10  20
WEY  42  81  41  83 /  20  10  10  20
DLN  52  88  52  89 /  10  10  10  20
HVR  60  90  55  93 /  30  10  10  10
LWT  56  87  54  89 /  30  10  10  10

&&

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

WEATHER.GOV/GREATFALLS

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE GREAT FALLS MT
1040 AM MDT FRI JUL 20 2012

MTZ009>013-044>051-211200-
NORTHERN ROCKY MOUNTAIN FRONT-EASTERN GLACIER-HILL-CASCADE-
CHOUTEAU-TOOLE-LIBERTY-EASTERN PONDERA-BLAINE-
SOUTHERN ROCKY MOUNTAIN FRONT-EASTERN TETON-JUDITH BASIN-FERGUS-
1040 AM MDT FRI JUL 20 2012

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

.DAY ONE...TODAY AND TONIGHT

SCATTERED SHOWERS AND THUNDERSTORMS ARE EXPECTED ACROSS NORTH
CENTRAL MONTANA TODAY. SOME STORMS COULD BE SEVERE...WITH DAMAGING
WINDS...LARGE HAIL...FREQUENT LIGHTNING...AND HEAVY RAINFALL. VERY
HEAVY RAIN IN SHORT AND INTENSE BURSTS COULD LEAD TO LOCALIZED
FLOODING. THE BEST TIME FRAME FOR SEVERE WEATHER TO OCCUR WILL BE
FROM NOON UNTIL 9 PM TODAY. BE PREPARED FOR POSSIBLE SEVERE
THUNDERSTORMS THIS AFTERNOON AND EVENING.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED THIS AFTERNOON AND EVENING. ANY
SPOTTER REPORTS OF SEVERE WEATHER WOULD GREATLY BE APPRECIATED.

MTZ008-014-015-052>055-211200-
BEAVERHEAD-CENTRAL AND SOUTHERN LEWIS AND CLARK-MADISON-JEFFERSON-
BROADWATER-MEAGHER-GALLATIN-
1040 AM MDT FRI JUL 20 2012

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTHWEST
MONTANA.

.DAY ONE...TODAY AND TONIGHT

THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME.

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