721
FXUS65 KTFX 040255
AFDTFX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
855 PM MDT FRI JUL 3 2009
UPDATE
NO MAJOR GRID CHANGES TONIGHT WITH SHORT TERM FORECAST
LOOKING PRETTY GOOD. SOME ISOLATED THUNDERSTORMS ARE STILL MOVING
AROUND OVER PORTIONS OF THE SOUTHWEST AND NORTHEAST CORNERS OF THE
CWA. THE POTENTIAL FOR SEVERE WEATHER DOES EXIST WITH THESE STORMS
AND WILL CONTINUE TO BE MONITORED CLOSELY. THE STORMS WILL
CONTINUE TO BE ACTIVE FOR A COUPLE HOURS BUT EXPECT THEM TO TAPER
OFF IN THE EARLY MORNING HOURS.
AVIATION
UPDATED 2350Z.
VFR CONDITIONS WILL PREVAIL ACROSS THE FORECAST AREA THROUGH
SATURDAY AFTERNOON. HOWEVER...ISOLATED TO SCATTERED SHOWERS AND
THUNDERSTORMS WILL CONTINUE TO AFFECT PORTIONS OF SOUTHWEST
MONTANA AND NORTHEASTERN PORTIONS OF CENTRAL MONTANA WITH LOCAL
MVFR CONDITIONS IN BRIEF HEAVY RAINFALL THROUGH 03Z SATURDAY.
CONDITIONS WILL STABILIZE OVERNIGHT BUT THE AIRMASS IS EXPECTED TO
BECOME MARGINALLY UNSTABLE AGAIN SATURDAY AFTERNOON WITH ISOLATED
TO SCATTERED THUNDERSTORMS DEVELOPING AFTER 18Z. MPJ
PREV DISCUSSION
/ISSUED 548 PM MDT FRI JUL 3 2009/
TODAY THROUGH SUNDAY EVENING...UPPER RIDGE THAT WAS
CENTERED OVER THE FOUR CORNERS AREA A FEW DAYS AGO HAS NOW DRIFTED
EAST WITH ITS AXIS NOW OVER THE GREAT PLAINS. SOUTHWEST FLOW ON THE
RIDGE'S WEST SIDE CONTINUES TO PUSH PACIFIC MOISTURE INTO
MONTANA...LEADING TO ANOTHER ROUND OF SHOWERS AND THUNDERSTORMS THIS
AFTN/EVE OVER CENTRAL AND SOUTHWEST PORTIONS OF THE CWA. LATEST
MODEL DATA HAS SLIGHTLY REDUCED THE POTENTIAL FOR STRONG-TO-SEVERE
STORMS DUE IN PART TO COOLER-THAN-FORECAST SURFACE TEMPERATURES.
HOWEVER...POTENTIAL IS STILL HIGH ENOUGH FOR POSSIBLE STRONG STORMS
BEARING HAIL AND GUSTY OUTFLOW WINDS LATER THIS AFTN. WHATEVER
CONVECTION DEVELOPS SHOULD DISSIPATE TOWARD SUNSET AS AIRMASS
BECOMES MORE STABLE. GOOD AGREEMENT IN MODELS ON LITTLE CHANGE IN
CONDITIONS FOR TOMORROW...WITH SOUTHWEST FLOW ALOFT BRINGING IN
ADDITIONAL MOISTURE FOR ONE MORE ROUND OF SHOWERS AND
THUNDERSTORMS. SOME STORMS COULD BE STRONG WITH HAIL AND GUSTY
WINDS. LOOKS LIKE REGION WILL GET A BREAK FROM THE STORMS ON SUNDAY
AS THE UPPER RIDGE REBUILDS OVER THE NORTHERN ROCKIES AND MOIST
PACIFIC FLOW LESSENS. SOME CONVECTION IS POSSIBLE BUT WILL BE MORE
ISOLATED IN COVERAGE. TEMPERATURES WILL REMAIN 4 TO 7 DEG ABOVE
NORMAL THROUGH THE WEEKEND. WARANAUSKAS
SUNDAY NIGHT THROUGH WEDNESDAY NIGHT...ECMWF AND GFS MODELS AGREE IN
STARTING THE PERIOD WITH AN UPPER RIDGE OVER THE FORECAST AREA.
THEREAFTER EXPECT SOUTHWEST FLOW ALOFT. THOSE TWO MODELS ALSO AGREE
ON ROTATING A WEATHER DISTURBANCE ALOFT THROUGH THE FORECAST AREA
MONDAY NIGHT. AHEAD OF THE DISTURBANCE MODELS DEVELOP GOOD LIFT AND
MOISTURE..MAINLY IN THE NORTH. SO INCREASED POPS FOR THAT AREA.
ECMWF AND GFS ALSO AGREE IN DEVELOPING AN UPPER LOW OVER THE PACIFIC
NORTHWEST ON WEDNESDAY WITH INCREASED MOISTURE FOR NORTHWEST
MONTANA. IN LINE WITH THIS INCREASED THE CHANCES OF PRECIPITATION
FOR THE ROCKY MOUNTAIN FRONT. INHERITED TREND OF COOLING HIGH
TEMPERATURES FROM MONDAY TO WEDNESDAY LOOKS FINE BUT STARTED OFF
WARMER ON MONDAY WITH HIGHS WELL ABOVE NORMAL. BY WEDNESDAY LOWERED
INHERITED HIGH TEMPERATURES ON THE ORDER OF 5 TO 10 DEGREES OVER THE
PLAINS. BLANK
THURSDAY THROUGH FRIDAY....MODELS REMAIN IN FAIR AGREEMENT DURING
THIS PERIOD...WITH SOME DIFFERENCES IN TIMING OF FEATURES. A
LONGWAVE UPPER LEVEL TROUGH PERSISTS ALONG THE WEST COAST RESULTING
IN A SOUTHWESTERLY FLOW ALOFT ACROSS THE FORECAST AREA. WEAK
DISTURBANCES IN THIS SOMEWHAT MOIST AND UNSTABLE FLOW WILL BE
RESPONSIBLE FOR PARTLY TO MOSTLY CLOUDY SKIES WITH ISOLATED SHOWERS
AND MAINLY AFTERNOON AND EVENING THUNDERSTORMS. SHOWERS AND
THUNDERSTORMS WILL BE MORE NUMEROUS OVER THE MOUNTAINS. THE WARMEST
AIR STAYS MOSTLY SOUTH AND EAST OF THE FORECAST AREA...HOWEVER
TEMPERATURES ARE EXPECTED TO CLIMB TO NEAR SEASONAL AVERAGES. EK
PRELIMINARY POINT TEMPS/POPS
GTF 53 83 55 86 / 30 20 20 20
CTB 48 80 50 84 / 20 10 20 10
HLN 55 87 56 89 / 30 20 20 20
BZN 53 86 53 89 / 40 30 30 30
WEY 43 72 43 75 / 50 40 40 30
DLN 51 79 52 82 / 40 30 30 30
HVR 52 84 52 89 / 30 20 30 20
LWT 51 77 52 82 / 40 30 30 30
TFX WATCHES/WARNINGS/ADVISORIES
NONE.
SHORT TERM...GUSTAFSON
LONG TERM...COULSTON
AVIATION...MPJ
WEATHER.GOV/GREATFALLS
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