Area Forecast Discussion
Issued by NWS Glasgow, MT

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FXUS65 KGGW 041504
AFDGGW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
904 AM MDT MON MAY 4 2015

.SHORT TERM...FOR NORTHEAST MONTANA...TODAY THROUGH WEDNESDAY...
GOING FORECAST OVERALL IN GOOD SHAPE. THE BIGGEST DILEMMA IS
REGARDING EXTENDING THE LAKE WIND ADVISORY. WINDS OFF THE SURFACE
TONIGHT WILL BE A TAD STRONGER. WILL MAKE THIS DETERMINATION WITH
THE AFTERNOON PACKAGE. TFJ

PREVIOUS DISCUSSION...
TODAY BEGINS WITH AN UPPER LEVEL RIDGE OVER THE WEST AND THE
RIDGE AXIS LINED UP WITH THE SPINE OF THE NORTHERN AND CANADIAN
ROCKIES. THE AXIS WAS PASS ACROSS NORTHEAST MONTANA TODAY. THEN
TONIGHT FLOW ALOFT WILL BEGIN TO BACK AROUND TO THE SOUTHWEST AS A
CLOSED UPPER LOW PUSHES UP AGAINST VANCOUVER ISLAND. THE BOUNDARY
BETWEEN THE COOLER AIR OF THE TROUGH AND THE WARMER AIR OF THE
RIDGE WILL REMAIN WELL TO OUR WEST THROUGH TUESDAY. DURING THE
PERIOD THICKNESS HEIGHTS CONTINUE TO INCREASE. WITH HEIGHTS
REACHING ABOVE 565DM TUESDAY SHOULD BE THE WARMEST DAY OF THE
SHORT TERM.

TODAY AND TUESDAY...A DEVELOPING SURFACE LOW IN THE LEE OF THE
CANADIAN ROCKIES WILL SET UP A BRISK SOUTHEAST WIND OVER THE
REGION. THE TIGHT GRADIENT WILL RESULT IN ADVISORY STRENGTH WINDS
OVER FORT PECK LAKE. EAST WINDS HAVE ALREADY BECOME BRISK THIS
MORNING...SO MOVED UP NPW START TIME TO 15Z. THEN TUESDAY THE
SURFACE TROUGH SETTLES OVER CENTRAL MONTANA WHICH WILL ALSO
DEVELOP GUSTY SOUTHEAST WINDS. ANOTHER ADVISORY MIGHT BE NEEDED.

TUESDAY NIGHT AND WEDNESDAY...THE SOUTHEAST SURFACE WINDS WILL
TEND TO RAISE RH LEVELS...AND THE SURFACE LOW WILL TEND TO
INCREASE INSTABILITY. THE SOUTHWEST FLOW ALOFT WILL CONTINUE TO
BRING IN ADDITIONAL MOISTURE. THEN THE COLD FRONT CROSSES THE
DIVIDE AND SPREADS ACROSS THE PRAIRIE. MODELS PRODUCE WEAK TO
MODERATE CAPE AND NEGATIVE LIFTED INDEX NUMBERS. INITIALLY
THUNDERSTORMS AND SHOWERS ARE EXPECTED. THEN WEDNESDAY AFTERNOON
THE UNSTABLE AREAS SHIFT INTO THE EASTERN COUNTIES OF THE CWA.
MODELS ARE PRODUCING QPF ENOUGH FOR WETTING RAINS. SPC HAS
NORTHEAST MONTANA IN THE GENERAL THUNDERSTORMS ZONE FOR TUESDAY.
SCT

.LONG TERM...WEDNESDAY NIGHT THROUGH MONDAY...
THE UPPER TROUGH/LOW WILL DIG TOWARDS CALIFORNIA WEDNESDAY NIGHT
AND THURSDAY WHILE RIDGE REMAINS TO THE EAST. MEANWHILE...THIS
TROUGH IS EXPECTED TO SPLIT ON THURSDAY. THIS WILL KEEP SOUTHWEST
FLOW ALOFT OVER THE FORECAST AREA INTO THE WEEKEND.

MODEL DIFFERENCES ARE APPARENT IN THE TIMING AND TRACK OF THE
SHORTWAVES WITHIN THE SW FLOW ALOFT. FOR EXAMPLE...THE ECMWF IS
QUICKER THAN THE GFS IN MOVING WEDNESDAY`S SYSTEM TO THE EAST. THE
EC CURRENTLY MOVES THE SYSTEM TO THE EAST BY WEDNESDAY EVENING
WHILE THE GFS LINGERS WRAP AROUND RAIN OVER EASTERN MONTANA
THROUGH THURSDAY AFTERNOON. MEANWHILE...BOTH MODELS BRING A WAVE
INTO CENTRAL MONTANA ON THURSDAY WITH ENOUGH MOISTURE FOR A CHANCE
OF SHOWERS. WILL MAINTAIN CHANCES FOR SHOWERS WEDNESDAY NIGHT AND
THURSDAY AS SEE IF THE MODELS CAN SORT OUT THEIR DIFFERENCES IN
FUTURE RUNS.

SURFACE HIGH BUILDS INTO EASTERN MONTANA THURSDAY NIGHT WHILE A
SHORTWAVE RIDGE MOVES THROUGH THE AREA. EXPECT MAINLY DRY WEATHER
WITH A COOL NIGHT.

ON FRIDAY...NORTHERN BRANCH UPPER TROUGH DIGS INTO MONTANA AND AT
THIS POINT...THE MODELS KEEP IT OVER MONTANA FOR MOST OF THE
WEEKEND. THIS WILL CAUSE THE SOUTHERN BRANCH TROUGH/LOW TO STAY
SOUTH OF THE FORECAST AREA AS IT MOVES EAST OVER THE WEEKEND. IT
IS A CHANGE FROM LAST NIGHT`S MODEL RUNS THAT LIFTED THIS SOUTHERN
LOW OVER MONTANA DURING THE WEEKEND. FRIDAY STILL LOOKS DRY FOR
THE MOST PART AS IT LOOKS LIKE IT WILL BE FRIDAY NIGHT BEFORE THE
MOISTURE FROM THESE SYSTEMS REACHES NORTHEAST MONTANA. ECMWF IS
FASTER THAN THE GFS WITH MOVING THE SYSTEM THROUGH THE AREA.
EITHER WAY... IT LOOKS LIKE A COOL WEEKEND WITH CHANCES OF
SHOWERS. MAYBE COLD ENOUGH FOR SNOW SHOWERS AT TIMES.

FLOW ALOFT TURNS MORE ZONAL SUNDAY AND MONDAY BUT SHORTWAVES IN
THE FLOW ALOFT COULD CONTINUE TO BRING A FEW SHOWERS AT TIMES. FORRESTER


&&

.AVIATION...
VFR CONDITIONS WILL PREVAIL TODAY AND TONIGHT WITH EITHER CLEAR
SKIES OR A FEW MID AND HIGH CLOUDS.

A SURFACE LOW PUSHES INTO WESTERN MONTANA TODAY WILL INCREASE
SOUTHEAST WINDS TO 10 TO 20 KNOTS BY LATE MORNING. THE SOUTHEAST
WINDS WILL CONTINUE TONIGHT.


&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...
LAKE WIND ADVISORY UNTIL 9 PM MDT THIS EVENING FOR FORT PECK
LAKE FOR CENTRAL AND SOUTHEAST PHILLIPS...CENTRAL AND SOUTHERN
VALLEY...GARFIELD...MCCONE...PETROLEUM.

&&

$$

WEATHER.GOV/GLASGOW





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