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000
FXUS65 KGGW 131623
AFDGGW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
923 AM MST FRI DEC 13 2013

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

MORNING UPDATE...
CHANGES FOR THIS MORNING WAS TO INCREASE POPS ACROSS THE CENTRAL
PORTIONS OF THE CWA WHERE RADAR ECHOS AND SURFACE OBS ARE SHOWING
OFF LIGHT SNOWFALL. ON AND OFF ISOLATED TO SCATTERED SNOW SHOWERS
ARE ANTICIPATED TO LAST THROUGH THE DAY AS THE SURFACE LAYER UP TO
ABOUT 875 MB IS IN THE SNOW GROWTH ZONE ON THE MORNING UPPER AIR
SOUNDING. WINDS WERE ALSO TWEAKED SLIGHTLY. GAH


PREVIOUS SHORT TERM DISCUSSION...
NORTHWEST FLOW ALOFT WILL CONTINUE THROUGH THE WEEKEND. A
SHORTWAVE TROUGH WILL MOVE THROUGH MONTANA TODAY FOLLOWED BY
ANOTHER WAVE MOVING THROUGH THE NORTHEAST CORNER OF THE STATE TONIGHT.
THESE WAVES COULD BRING SOME LIGHT SNOW MAINLY TO THE NORTHEAST
HALF OF THE FORECAST AREA. MEANWHILE...A FRONTAL BOUNDARY THAT IS
NEAR HAVRE... JORDAN AND MILES CITY AT 10Z (3 AM MST) WILL MOVE
SOUTHWEST TODAY AND BECOME STATIONARY OVER CENTRAL MONTANA
TONIGHT. WITH COLD AIR ADVECTION TODAY... TEMPERATURES WILL NOT
RISE MUCH TODAY AND IS AREAS LIKE ZORTMAN AND WINNETT WHERE IT WAS
IN THE LOWER 30S AT 2 AM... TEMPERATURES WILL LIKELY FALL.

A WEAK UPPER RIDGE IN THE NW FLOW ALOFT BUILDS INTO MONTANA ON
SATURDAY AND THE FRONT MOVES BACK EAST. THIS FRONT WILL SLOWLY
MOVE INTO WESTERN NORTH DAKOTA BY SUNDAY MORNING AS SHORTWAVE
TROUGHS STAY TO THE NORTH AND EAST OF MONTANA OVER THE WEEKEND.
TEMPERATURES WILL WARM FROM WEST TO EAST ACROSS NORTHEAST MONTANA
MOST NOTICEABLY ON SUNDAY AS WEST WINDS DEVELOP TO PROVIDE BETTER
MIXING. FORRESTER


.LONG TERM...SUNDAY NIGHT THROUGH FRIDAY...
THE EXTENDED PERIOD BEGINS ON SUNDAY NIGHT WITH THE FLOW PATTERN
ALOFT FROM THE NORTHWEST ACROSS NORTHEAST MONTANA. THE 00Z RUN OF
THE MODELS PRODUCES RISING 1000-500MB THICKNESSES ACROSS THE
NORTHERN PLAINS THROUGH WEDNESDAY...RESULTING IN A FAIRLY MILD
TEMPERATURE REGIME ACROSS NORTHEAST MONTANA THROUGH THIS PORTION
OF THE WEEK. IN FACT...EXPECT THAT MANY LOCATIONS THROUGHOUT THE
CWA WILL SEE HIGHS AT OR ABOVE FREEZING WITH EXCEPTIONS IN THE
DEEPER VALLEYS AND IN THE FAR NORTHEAST. DO EXPECT MAINLY DRY
CONDITIONS TO PREVAIL THROUGH THIS PERIOD AS WELL.

AN UPPER LEVEL TROUGH WILL DEEPEN ACROSS THE WESTERN U.S.
BEGINNING WEDNESDAY NIGHT AS AN ARCTIC FRONT PROGRESSES SOUTHWARD
FROM THE INTERNATIONAL BORDER. THE UPPER TROUGH WILL PROVIDE
ENOUGH LIFT AND ALLOW SOME MOISTURE TO SPILL OVER THE ARCTIC AIR
MASS BEHIND THE FRONT...PRODUCING A CHANCE FOR SNOWFALL. WHILE
THERE ARE PLACEMENT/TIMING DIFFERENCES BETWEEN THE LATEST GFS AND
ECMWF...THERE IS DECENT CONSENSUS AMONG THE OPERATIONAL MODELS ON
PLACING THE MOST CONCENTRATED QPF IN THE NORTHERN ZONES WEDNESDAY
NIGHT AND EARLY THURSDAY. THE ECMWF IS THEN MORE PROGRESSIVE
KICKING THE SNOWFALL SOUTH AND EAST OF THE CWA THURSDAY EVENING
WHILE THE GFS IS SLOWER AND HAS IT HANGING ON INTO PART OF FRIDAY.
LEANED WITH THE ECMWF SOLUTION FOR NOW...THE STRENGTH OF THE
ARCTIC SURFACE HIGH LENDS CREDENCE TO THE IDEA THAT THE EVOLUTION
OF PRECIPITATION MAY SIDE ON THE MORE PROGRESSIVE END OF THE
SPECTRUM. THEREFORE...GRADUALLY SHIFT HIGHER CHANCE POPS
SOUTHEASTWARD...BUT MAINTAINED SLIGHT CHANCE POPS IN THE NORTH FOR
THURSDAY AFTERNOON. FOR THURSDAY NIGHT DID KEEP SLIGHT CHANCE POPS
BUT IF THE ECMWF SOLUTION HOLDS THE NORTHERN ZONES ESPECIALLY
COULD BE COMPLETELY DRY BY THURSDAY NIGHT.

WITH RESPECT TO TEMPERATURES...FORECAST CHALLENGES CONTINUE. THE
GFS IS MUCH COLDER AND SHOWS A STRONGER INITIAL SURFACE HIGH
THURSDAY NIGHT. THIS SOLUTION CARRIES 850MB TEMPERATURES ACROSS
THE REGION IN THE -30S FOR A TIME. AS AN ASIDE...THIS STRONG HIGH
ALSO SUGGESTS QPF IS TOO FAR NORTH ON THURSDAY NIGHT/FRIDAY AND SO
AGAIN ADDS CONFIDENCE ON A MORE PROGRESSIVE SOLUTION. THE ECMWF
AND THE GFS THEN MAINTAIN A SURFACE HIGH OF ABOUT 1040MB ACROSS
THE DAKOTAS FOR FRIDAY NIGHT. WHILE THE HEART OF THE COLD AIR MAY
AS A RESULT BE FURTHER EAST...SHOULD SEE CLEARING SKIES AND LIGHT
WINDS IN PROXIMITY TO THE HIGH...AND WITH POTENTIAL FOR NEW SNOW
COVER...FRIDAY NIGHT COULD WIND UP BEING A FRIGID NIGHT ACROSS
NORTHEAST MONTANA. THE ECMWF SOLUTION CARRIES 850MB TEMPERATURES
IN THE -18C TO -25C RANGE BY THURSDAY NIGHT AND CONTINUES SIMILAR
READINGS INTO FRIDAY NIGHT. AGAIN...THE GFS IS EVEN COLDER. FOR
NOW TRENDED TEMPERATURES DOWNWARD FOR THE END OF THE EXTENDED...BUT
DEPENDING UPON HOW QUICKLY THE SNOW EXITS THURSDAY NIGHT...AS WELL
AS FACTORS SUCH AS SKY COVER...STRENGTH AND POSITION OF THE SURFACE
HIGH...ETC...WILL HELP DETERMINE THE OVERALL EXTENT OF THE ARCTIC
AIR. FOR NOW EXPECT THAT THE POTENTIAL EXISTS FOR A LARGE PORTION
OF THE CWA TO EXPERIENCE LOWS IN THE -10S AND -20S BY NEXT FRIDAY
NIGHT. MEANWHILE...HIGHS FRIDAY AND SATURDAY MAY NOT CLIMB ABOVE
ZERO FOR A LARGE PORTION OF THE AREA. MALIAWCO


&&

.AVIATION...
LOW STRATUS WILL MEAN A CONTINUATION OF MVFR TO IFR CEILINGS TODAY
ACROSS THE TERMINALS. LIGHT SNOW SHOWERS OR FLURRIES WILL OCCASIONALLY
DROP VISIBILITIES THROUGH THE DAY. WINDS WILL BE FROM THE EAST TODAY
AT AROUND 10 KTS. MALIAWCO


&&

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


&&

$$

WEATHER.GOV/GLASGOW