Area Forecast Discussion
Issued by NWS Glasgow, MT

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FXUS65 KGGW 200123 AAA
AFDGGW

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE GLASGOW MT
723 PM MDT FRI SEP 19 2014

.SHORT TERM...FOR NORTHEAST MONTANA...TONIGHT THROUGH SUNDAY...

EARLY UPDATE TO CANCEL NPW...MAIN UPDATE WAS TO SPREAD POPS A BIT
MORE SOUTH TO LINE UP WITH RADAR RETURNS. THE STORMS ARE WEAK
WITH NO HEIGHT NOR MUCH LIGHTNING...SO KEPT AT ISOLATED. OTHERWISE
WITH WIND DIMINISHED MUCH BELOW 20 MPH...WENT AHEAD AND CANCELLED
THE LAKE WIND ADVISORY. SCT

PREVIOUS DISCUSSION...
SYNOPTIC SET UP...HOT HIGH PRESSURE IS CENTERED OVER COLORADO
WITH ITS INFLUENCE EXTENDING OUT TO SOUTHERN MONTANA...NEW MEXICO
AND NEVADA AND MISSOURI. A CLOSED LOW EXISTS OVER THE COAST OF
CALIFORNIA WITH ZONAL FLOW EXTENDING FROM THE PACIFIC NORTHWEST
AND BRITISH COLUMBIA TO WESTERN ONTARIO AND THE UPPER MISSISSIPPI
VALLEY.

THIS AFTERNOON THROUGH THIS EVENING...A WEAK SHORTWAVE IS
EMBEDDED IN THE ZONAL FLOW OVER THE INTERNATIONAL BORDER OF
NORTHEAST MONTANA. THIS IS PRODUCING A WEAK COLD FRONT AT THE
SURFACE AND SOME RAIN SHOWERS OVER ITS UP-SLOPE IN THE FAR
NORTHEAST CORNER OF THE CWA. SHOWERS ARE EXPECTED TO MOVE DOWN
MT/ND BORDER AND THEN TAPER OFF OR EXIT TO THE EAST DURING THE
EARLY EVENING HOURS.

SATURDAY MORNING...A SHORTWAVE ORIGINATING OVER THE BRITISH
COLUMBIA/ALBERTA BORDER AT THE TOP OF THE ZONAL FLOW WILL DROP
DOWN THROUGH NORTHEAST MONTANA DURING THE MORNING HOURS FOR A
REPEAT PERFORMANCE OF SCATTERED SHOWERS THAT SHOULD BE GONE BY
NOON. COOL HIGH PRESSURE WILL FILTER IN BEHIND THE SERIES OF FRONT
NEAR THE SURFACE AS WELL.

SATURDAY AFTERNOON THROUGH SUNDAY...LARGE SYNOPTIC RIDGE WILL
AMPLIFY OUT OF THE ZONAL FLOW PULLING THE CALIFORNIA CLOSED LOW IN
UNDERNEATH IT. THE CLOSED LOW WILL MIGRATE UP TO WYOMING UNDER THE
RIDGE KEEPING THE LOW/S INFLUENCE OUT OF MONTANA. WITH WARM RIDGE
IN PLACE ALOFT AND COOL HIGH PRESSURE IN PLACE AT THE SURFACE
CONDITIONS WILL BE STABLE...DRY...AND CLEAR THROUGHOUT THESE
PERIODS. GAH

.LONG TERM...SUNDAY NIGHT THROUGH FRIDAY...
ONLY MINOR ADJUSTMENTS TO THE GOING FORECAST. MODELS IN GOOD
AGREEMENT WITH CLOSED LOW LIFTING OUT OF GREAT BASIN UNDERNEATH A
RIDGE OVER WESTERN CANADA. AS THE LOW DRIFTS ACROSS WYOMING COULD
SEE SOME STORMS DEVELOP ACROSS SOUTHERN MONTANA WHICH MAY WORK
INTO THE SOUTHERN ZONES. DRY AND WARM WEATHER THEN EXPECTED UNTIL
THE END OF THE WEEK WHEN A DEEP TROF PUSHES ACROSS THE PACIFIC
COAST. MODEL UNCERTAINTY LEADS TO LOW CONFIDENCE IN THE LATE
PERIODS OF THE FORECAST. EBERT

PREVIOUS LONG TERM DISCUSSION...THE EXTENDED PERIOD BEGINS MONDAY
NIGHT WITH AN AMPLIFIED LONG- WAVE RIDGE IN PLACE OVER WESTERN
CONUS AND CANADA. A CLOSED OFF LOW CENTERED OVER THE NORTHERN
REACHES OF THE GREAT BASIN WILL CUT ACROSS THE RIDGE AS THE RIDGE
AXIS SHIFTS EAST. THE LOW WILL GENERALLY CUT UNDER NORTHEAST
MONTANA...MAINLY AFFECTING SOUTHERN MONTANA. THE RIDGE IN PLACE
WILL BRING MORE WARMING TO THE REGION WITH TEMPERATURES RAMPING UP
ABOVE NORMAL AGAIN.

MONDAY NIGHT THE LOW OPENS AND MOVES ACROSS A SURFACE TROUGH. THIS
COULD LEAD TO SOME INSTABILITY THAT COULD PRODUCE A FEW SHOWERS
AND ISOLATED THUNDERSTORMS INTO TUESDAY. ON WEDNESDAY THE RIDGE
REESTABLISHES ITSELF AS A DEEP TROUGH/EASTERN PACIFIC STORM PUSHES
UP AGAINST THE CASCADE RANGE. THERE IS A VERY DISTINCT COLD FRONT
ASSOCIATED WITH THIS STORM SYSTEM. THE MAIN QUESTION IS IF IT HAS
ENOUGH STRENGTH TO BREAK DOWN THE RIDGE OVER EASTERN MONTANA. HERE
IS WHERE THE MODELS DIFFER. THE EC HAS THE FRONT STALLING OUT TO
OUR WEST...WHILE THE GFS PUSHES THE FRONT ACROSS EASTERN MONTANA
FRIDAY NIGHT AND SATURDAY. THE SIGNIFICANCE OF THE STRONG FRONT IS
THE WARM TEMPERATURES IN PLACE. SO WHERE THE FRONT HITS THERE WILL
BE RAIN AND THUNDER FROM THE CANADIAN BORDER TO THE MEXICAN
BORDER. MODEL DIFFERENCES ADD TO THE UNCERTAINTY AFTER MID WEEK. SCT

&&

.AVIATION...
VFR.

MAINLY CLEAR SKIES AND LIGHT WINDS ARE EXPECTED INTO THE OVERNIGHT
BUT A WEAK COLD FRONT WILL PUSH THROUGH AT ABOUT DAYBREAK. SHOWERS
ASSOCIATED WITH IT ARE EXPECTED TO REMAIN NORTHEAST OF THE 4 MAIN
AIRPORTS. LIGHT WINDS TONIGHT ARE EXPECTED TO INCREASE FROM THE
NORTHEAST SATURDAY. TFJ

&&

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

&&

$$

WEATHER.GOV/GLASGOW






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