Damaging Wind in Montana, May 25, 2006

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
823 PM MDT THU MAY 25 2006

.SHORT TERM...FOR NORTHEAST MONTANA...TONIGHT...
AN UPPER TROUGH IS VISIBLE ON THE WATER VAPOR SATELLITE CHANNEL
BEGINNING TO DIG INTO THE PACIFIC NORTHWEST. THE PARENT UPPER LOW
IS STILL CUT OFF AND OFF THE SOUTHERN BRITISH COLUMBIA COAST AND
ONLY VERY SLOWLY DRIFTING TO THE SOUTHEAST TOWARD THE PACIFIC
NORTHWEST COAST. WEST TO SOUTHWEST FLOW ALOFT HAS BEEN RE-
ESTABLISHED ACROSS EASTERN MONTANA AND IS EVIDENT ON THE 00Z KGGW
SOUNDING. THE UPPER FLOW WILL CONTINUE TO SLOWLY BACK INTO THE
SOUTHWEST DURING THE NEXT 24 HOURS. THUNDERSTORMS DEVELOPED OFF TO
THE SOUTHWEST OF THE CWA THIS AFTERNOON AND GENERALLY WEAKENED AS
THEY MOVED INTO OUR SOUTHWEST ZONES AND FURTHER AWAY FROM THE
HIGHER TERRAIN. ANOTHER AREA OF THUNDERSTORMS DEVELOPED ACROSS OUR
NORTHEAST ZONES THIS AFTERNOON ALONG A WEAK FRONTAL BOUNDARY/WIND
SHIFT LINE...BUT ALL OF THE SEVERE WEATHER REMAINED WELL NORTH OF
THE CWA.  AS OF 8 PM ADDITIONAL STORMS ARE FIRING ALONG THE
BOUNDARY ACROSS OUR EASTERN ZONES...WITH THE STRONGEST CELL IN
NORTHERN ROSEBUD COUNTY. THESE STORMS WILL BEAR CLOSE WATCHING
DURING THE NEXT COUPLE OF HOURS ACROSS OUR SOUTHEAST ZONES. A
SURFACE LOW IS IN THE PROCESS OF DEVELOPING ACROSS NORTHERN
WYOMING/SOUTHERN MONTANA IN RESPONSE TO THE HEIGHT FALLS AND JET
ENERGY ASSOCIATED WITH THE UPPER TROUGH TO OUR WEST. THE LOW WILL
CONTINUE TO DEEPEN OVERNIGHT AND MOVE INTO EASTERN MONTANA. AS THE
LOW MOVES NORTHEAST IT SHOULD PUT OUR SOUTHERN ZONES INTO A DRY
SLOT OVERNIGHT. OVERALL THE ONGOING FORECAST LOOKS TO BE IN GOOD
SHAPE...AND AM NOT PLANNING ON ANY CHANGES RIGHT NOW. CONTINUING
TO MONITOR ONGOING CONVECTION....WHICH HAS THE POTENTIAL OF
TURNING QUITE STRONG/SEVERE ACROSS OUR SOUTHEAST ZONES FOR THE
NEXT COUPLE OF HOURS. CB

...PREVIOUS SHORT TERM...
ONE WEAK FRONTAL SYSTEM IS MOVING SLOWLY INTO EASTERN MONTANA THIS
AFTERNOON. THIS FRONT WHICH IS ONLY A WIND SHIFT LINE BETWEEN EAST
WINDS TO THE EAST AND WEST WINDS TO THE WEST WILL BECOME QUASI-
STATIONARY NEAR THE NORTH DAKOTA BORDER TONIGHT. INSTABILITY
FOCUSED ALONG THIS FRONT MAY BE ENOUGH FOR A FEW THUNDERSTORMS TO
DEVELOP THIS AFTERNOON AND EVENING. WILL MAINTAIN ISOLATED
THUNDERSTORMS IN THE FORECAST.

MONTANA WILL SPEND THE NEXT FEW DAYS IN SOUTHWEST FLOW ALOFT
BETWEEN UPPER LOW OVER THE PACIFIC NORTHWEST AND AN UPPER RIDGE
TO THE EAST. MODELS AGREE ON THE BIG PICTURE BUT DIFFER ON SOME
DETAILS THAT COULD MAKE A DIFFERENCE IN WHEN AND WHERE IT RAINS
THE NEXT FEW DAYS. UPPER TROUGH ASSOCIATED WITH THE LOW WILL DIG
OVER THE WEST COAST FRIDAY AND SATURDAY BRINGING FREQUENT
SHORTWAVES INTO MONTANA.

SURFACE LOW WILL DEVELOP OVER NORTHERN WYOMING ON FRIDAY AND MOVE
INTO NORTH DAKOTA FRIDAY NIGHT. A STRONG COLD FRONT WILL MOVE EAST
ACROSS THE FORECAST AREA FRIDAY NIGHT BRINGING MUCH COOLER WEATHER
FOR THE WEEKEND. FRIDAY SHOULD DRY MOST OF THE DAY. AIRMASS WILL
BECOME INCREASINGLY UNSTABLE FRIDAY AFTERNOON WHICH MAY ALLOW
THUNDERSTORMS TO DEVELOP. THERE WILL BE A BETTER CHANCE FOR
THUNDERSTORMS WITH THE COLD FRONT PASSAGE FRIDAY. WITH UPPER LEVEL
DYNAMICS FOCUSED OVER CENTRAL AND WESTERN MONTANA FRIDAY NIGHT
AND SATURDAY...THE BEST CHANCE FOR PRECIP WILL BE OVER THE WESTERN
ZONES.

UPPER TROUGH REMAINS TO THE WEST ON SATURDAY WITH SHORTWAVES
MOVING NORTHEAST ACROSS WEST AND CENTRAL MONTANA. THIS WILL KEEP
THE BEST CHANCE FOR PRECIP TO THE WEST OF GLASGOW AND JORDAN ON
SATURDAY. WITH INSTABILITY SHIFTED EAST WILL SEE MAINLY SHOWERS.
FORRESTER

.LONG TERM...SATURDAY NIGHT THROUGH THURSDAY...
MODELS ARE SIMILAR TO PREVIOUS RUNS WITH A STRONG UPPER TROUGH
MOVING ACROSS THE AREA SATURDAY NIGHT AND SUNDAY. THE ASSOCIATED
STRONG SURFACE LOW MOVES NE FROM WYOMING INTO NORTH DAKOTA AND
MANITOBA DURING THIS PERIOD. A PATTERN LIKE THIS TYPICALLY HAPPENS
AT LAST A COUPLE OF TIMES IN LATE SPRING...CAPABLE OF PRODUCING
RAINFALL FOR MOST OF A 24 HOUR PERIOD. CLIMATE-WISE WE ARE NEARING
THE WETTEST TIME OF THE YEAR TOO...SO HAVE RAISED POPS FOR
SATURDAY NIGHT AND SUNDAY TO LIKELY. THIS TYPE OF PATTERN WITH
RELATIVELY COOL AIRMASS ARRIVING FROM THE NORTH IN THE LOWER
LEVELS DOESNT PRODUCE MUCH CONVECTION...MORE OF A STEADY RAIN.
MODEL FORECAST SOUNDINGS CONFIRM THIS...SO CHANGED PRECIP TYPE.

LITTLE TO ADD TO THE REST OF THE FORECAST. A WEAK BROAD TROUGH
LINGERS OVER THE AREA MONDAY AND TUESDAY...WITH A SW FLOW ALOFT
CONTINUING. THICKNESSES START BELOW NORMAL...THEN CLIMB A LITTLE.
EXPECT IN THIS PATTERN THERE WILL BE OTHER SHORTWAVES FREQUENTLY ARRIVE
FOR SLIGHT CHANCES OF THUNDERSTORMS MOST EVERY FORECAST PERIOD.
SIGNS OF GRADUAL UPPER RIDGING FROM THE SOUTH LATE IN THE
PERIOD...BUT MAY NOT BE ENOUGH TO BRING ANY BIG CHANGES. LATEST
ECMWF WAS STRONGER WITH THE RIDGE THOUGH. SIMONSEN

&&

.AVIATION...
WIDELY SCATTERED THUNDERSTORMS TONIGHT WITH ONLY BRIEF IMPACT ON
REDUCING VISIBILITY. SCATTERED CLOUD LAYERS WILL BE AT 6K AGL AND
12K FT AGL. MOSTLY CLEAR SKIES FRIDAY MORNING WILL GIVE WAY IN THE
AFTERNOON TO SIMILAR CONDITIONS AS THURSDAY...WIDELY SCATTERED
THUNDERSTORMS. SIMONSEN

&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...NONE.

&&

WEATHER.GOV/GLASGOW