Severe Thunderstorm Warning 17, NWS Glasgow, MT

NORTHEAST MONTANA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
230 PM MDT FRI JUN 20 2003

.SHORT TERM...TONIGHT THROUGH MONDAY...
THE THREAT OF SEVERE WEATHER WILL BE DURING THE NEXT 12 HOURS OR
SO...THEN MUCH COOLER AND MORE STABLE WEATHER INTO EARLY NEXT WEEK.
AN OPEN TROUGH IN THE PACIFIC NORTHWEST WILL EXPAND EAST TONIGHT AND
SATURDAY. AS THE TROUGH MOVES EAST IT WILL CONTINUE TO DEEPEN...AND
WILL COVER THE NORTHWEST QUARTER OF THE CONUS BY SUNDAY MORNING. AS
THE TROUGH SLIDES EAST A STRONG COLD FRONT CURRENTLY IN WEST CENTRAL
MT WILL WORK THROUGH THE CWA TONIGHT...AND MODELS ARE IN GOOD
AGREEMENT THAT THE FRONT WILL EXIT INTO THE DAKOTAS BETWEEN 09-12Z
SATURDAY.

SPC SWODY1 HAS THE ENTIRE CWA IN A SLIGHT CHANCE THROUGH 12Z
SATURDAY. GREATEST INSTABILITY AND THUS THREAT OF SEVERE WEATHER
THIS EVENING/TONIGHT PROGGED TO BE EAST OF A LINE FROM SCOBEY-WOLF
POINT-TERRY WITH LIS -4 TO -6C AND SFC CAPE OF 1000-1500J/KG.  THIS
COUPLED WITH SUFFICIENT LOW LEVEL MOISTURE WITH SFC DEW POINTS NEAR
60F SHOULD PROVIDE ENOUGH JUICE FOR SCATTERED SEVERE THUNDERSTORMS
AND A FEW SUPERCELLS.  MAIN THREATS LOOK TO BE DAMAGING WINDS AND
LARGE HAIL. LIS LITTLE CHANGED FROM 12Z TO 18Z SOUNDINGS...AND
THERE IS A FAIRLY STRONG CAP IN PLACE AROUND 800H. CLOUDS THAT HAVE
WORKED INTO THE AREA ARE GOING TO MAKE IT MORE DIFFICULT TO BREAK
THE CAP DUE TO LESS HEATING.

AFTER THE FRONT PUSHES OFF TO OUR EAST TOMORROW MORNING THE
ATMOSPHERE BECOMES MUCH MORE STABLE AND NO SEVERE WEATHER IS
ANTICIPATED. DAY 2 OUTLOOK FROM SPC HAS A SLIGHT RISK FROM ABOUT
DICKINSON ND EAST. GOOD DOWNSLOPING IS EXPECTED WITH W-NW FLOW AT
THE SFC...HOWEVER...WITH SW FLOW ALOFT AND FALLING HEIGHTS AND
THICKNESSES DURING THE DAY DONT WANT TO RULE OUT SHOWERS...ALTHOUGH
WILL DROP POPS A CATEGORY TO SLIGHT CHANCE.

MODELS IN REASONABLE AGREEMENT THAT A CLOSED UPPER LOW WILL BE NEAR
THE CENTRAL SASKATCHEWAN/ALBERTA BORDER WITH CYCLONIC FLOW INTO
NORTHEAST MT.  BELOW NORMAL TEMPERATURES EXPECTED SUNDAY ALONG WITH
THE CHANCE OF SHOWERS. BEST CHANCE OF SHOWERS LOOKS TO CORRESPOND TO
BEST HEATING OF THE DAY AND WILL INCREASE POPS DURING THE
AFTERNOON/EVENING.

THE PATTERN REMAINS UNSETTLED MONDAY. CLOSED LOW MOVES MOVES
NORTHEAST TOWARDS WESTERN HUDSON BAY...BUT ANOTHER TROUGH MOVES IN
FROM THE WEST WITH SW FLOW. CURRENT FCST LOOKS TO HANDLE THIS WELL
WITH A CHANCE OF SHOWERS AND THUNDERSTORMS. CB

.LONG TERM...MONDAY NIGHT THROUGH FRIDAY
PERIOD DOMINATED BY MEAN LONG WAVE TROUGH OVER WESTERN CONUS AND
SOUTHWEST CANADA. MAINLY SEASONABLY COOL AND UNSETTLED WEATHER
LIKELY RESULT. MODELS IN PRETTY GOOD INITIAL AGREEMENT HOLDING
CURRENT WESTERN TROUGH QUASI-STATIONARY THROUGH END OF SHORT TERM
FORECAST WINDOW...THEN ROTATING ANOTHER TROUGH INTO MEAN TROUGH FROM
GULF OF ALASKA WITH POSSIBLY A BRIEF BREAK BETWEEN. TIMING AND
EVOLUTION OF THIS PATTERN 4 DAYS IN THE FUTURE VERY DIFFICULT TO
CALL WITH CONFIDENCE...HENCE WILL BROADBRUSH WITH CHANCE POPS EVEN
THOUGH THERE MAY BE A DEFINITE BREAK SOMETIME BETWEEN THESE SYSTEMS.
GFS AND CANADIAN TENDING TO DAMP LONG WAVE BY MIDDLE OF NEXT WEEK AS
SYSTEM FILLS/FLATTENS...WHILE ECMWF MAINTAINS MORE AMPLIFIED TROUGH.
WILL GO WITH GFS/CANADIAN TREND...FINALLY ENDING CHANCE POPS
THURSDAY NIGHT AND FRIDAY AND ALLOWING FOR SLIGHT WARMING UNDER MORE
ZONAL FLOW. HAVE MADE RELATIVELY FEW AND MINOR CHANGES TO GOING
FORECAST DUE TO PERSISTENCE OF THIS SYSTEM. DNS

KGGW BTT 055/073 049/069 047/068 92622323
     TTTB 049/069 049/070 049/074 049/076 8633333300
KGDV BTT 058/074 049/069 045/070 92632323
     TTTB 050/071 050/072 050/076 050/077 8633333300

.GGW...NONE.

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