Area Forecast Discussion
Issued by NWS Glasgow, MT

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000
FXUS65 KGGW 202219
AFDGGW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
319 PM MST SAT DEC 20 2014

.SHORT TERM...FOR NORTHEAST MONTANA...TONIGHT THROUGH MONDAY...
ANOTHER SHORTWAVE SYSTEM CURRENTLY OVER THE PACIFIC NORTHWEST IS
POISED TO BRING MIXED PRECIPITATION TO NORTHEAST MONTANA ON
SUNDAY.

TONIGHT CONDITIONS WILL BE RELATIVELY QUIET AS WEAK RIDGING
DOMINATES. A POTENT WARM FRONT WILL PUSH THROUGH NORTHEAST MONTANA
AHEAD OF DEVELOPING SURFACE LOW OVER SOUTHERN ALBERTA. AT THE SAME
TIME...AN INVERSION KEEPS TEMPS AT THE SURFACE COLD.

THIS SETUP OF WARM AIR ALOFT/COLD AIR AT THE SURFACE WILL SET THE
STAGE FOR WHAT COULD BE A SIGNIFICANT FREEZING RAIN EVENT ON
SUNDAY. BEFORE SUNRISE ON SUNDAY MOISTURE FROM THE AFOREMENTIONED
SHORTWAVE FEATURE WILL BEGIN TO OVERRUN THE SUB FREEZING COLD AIR
AT THE SURFACE...RESULTING IN WIDESPREAD FREEZING RAIN SPREADING
FROM WEST TO EAST THROUGH THE MORNING HOURS. THUS WITH HOLIDAY
TRAVEL IN MIND...ISSUED A FREEZING RAIN ADVISORY FOR SUNDAY
AFTERNOON FOR PETROLEUM...PHILLIPS...GARFIELD...AND VALLEY COUNTIES.
BY THE AFTERNOON TEMPS ARE EXPECTED TO HAVE WARMED ENOUGH FOR ALL
RAIN OR SNOW...WITH THE EXCEPTION OF ALONG THE CANADIAN BORDER
WHERE ENOUGH COLD AIR COULD REMAIN AT THE SURFACE FOR A CONTINUED
FREEZING RAIN THREAT. A THREAT THAT WILL NEED TO BE CLOSELY MONITORED.

SUNDAY EVENING A COLD FRONT WILL QUICKLY PUSH THROUGH CHANGING THE
PRECIP TYPE TO JUST RAIN AND SNOW...AND EVENTUALLY ALL SNOW AFTER
MIDNIGHT. GUSTY NORTHWEST WINDS WILL ALSO DEVELOP BEHIND THE
FRONT...LASTING INTO MONDAY. ALSO MONDAY WRAPAROUND PRECIPITATION
NOW LOOKS TO CONTINUE...ESPECIALLY ALONG THE NORTH DAKOTA BORDER
WHERE SOME MORE SUBSTANTIAL ACCUMULATIONS MAY OCCUR. THIS WILL
NEED TO BE MONITORED FOR A POSSIBLE ADVISORY. GILCHRIST

.LONG TERM...MONDAY NIGHT THROUGH SATURDAY...

AFTERNOON UPDATE...
CHANGES WERE FOCUSED ON THE PERIOD WHEN A SHORTWAVE MOVING
THROUGH HAS THE ABILITY TO CREATE A SNOW STORM WEDNESDAY THROUGH
THURSDAY. MULTIPLE MODELS ARE POINTING TOWARD AND OVERRUNNING SNOW
EVENT JUST AHEAD OF THE COLD FRONT ENTERING MID DAY THURSDAY.
HOWEVER.... MODEL ARE UNCERTAIN AS TO WHERE A MID LEVEL JET AND
ITS SUBSEQUENT SURFACE LOW WILL PASS AND FORM. BECAUSE OF THIS
SNOW TOTALS COULD RANGE FROM 6 INCHES TO A TRACE. WITH A MODEL
BLEND CURRENT GUESS IS FOR ABOUT 1 TO 2 INCHES TOTAL BUT CHANCES
AND TOTALS COULD EASILY CREEP UP IN LATER FORECAST AND MODELS
SHARPEN INTO VIEW. NORTHWEST FLOW LATER IN THE WEEK REINFORCES THE
COLD AIR ACROSS THE REGION. GAH

PREVIOUS LONG TERM DISCUSSION...
THE PERIOD BEGINS MONDAY NIGHT WITH A LONG-WAVE TROUGH CENTERED
OVER THE MIDDLE OF THE COUNTRY AND A LARGE RIDGE OFF THE WEST
COAST. THIS PATTERN WILL GENERATE A NORTHWEST FLOW ALOFT FOR
NORTHEAST MONTANA. THE COLD AIR BOUNDARY WILL BE LOCATED WELL TO
THE SOUTH. THEREFORE TEMPERATURES WILL BEGIN CLOSE TO NORMAL.

ON TUESDAY THE WEST COAST RIDGE SHIFTS EAST AND BEGINS TO NUDGE TO
BOUNDARY TOWARDS MONTANA AS A WARM FRONT. THE RIDGE AXIS THEN
LEANS OVER TO THE EAST ON WEDNESDAY. THE FLOW ALOFT WILL BE
DIRECTLY FROM THE OCEAN OFF THE COAST OF WASHINGTON AND BC WHICH
WILL PICK UP MOISTURE. THE COLD AIR BOUNDARY WILL ONCE AGAIN BE
PUSHED SOUTH AROUND WEDNESDAY AND THURSDAY. THE MOISTURE AND THE
FRONT COULD BRING RAIN AND/OR SNOW INTO NORTHEAST MONTANA POSSIBLY
WEDNESDAY AFTERNOON AND EVENING. FROM THIS POINT ON THE EC AND GFS
DIFFER IN STORM LOCATION. SO THERE IS UNCERTAINTY CONCERNING SNOW
LOCATION. THE EC SENDS IT MORE TO THE SOUTH...WHEREAS THE GFS
SPREADS SNOW MAINLY SOUTH OF THE MISSOURI RIVER.

BY 00Z THURSDAY AN ENERGETIC TROUGH MOVES INTO THE PAC-NW AND
PUSHES ACROSS THE DIVIDE WEDNESDAY NIGHT AND THURSDAY. WITH THE
COLD FRONT PUSHED WELL TO THE SOUTH THE DISTURBANCE WILL LIKELY BE
ALL SNOW. WHILE NORTHEAST MONTANA WILL END UP WITH AN INCH OR
TWO...MOST QPF TRENDS SOUTH...GENERATING AREAS OF HEAVY SNOW FOR
OUR NEIGHBORS LATE IN THE WEEK. SCT

&&

.AVIATION...
FLIGHT CATEGORY: MAINLY VFR... IFR LATE IN CYCLE.

FOG: LIGHT RADIATION FOG IS ANTICIPATED ALONG THE MISSOURI AND
MILK RIVER VALLEY AFTER MIDNIGHT. MVFR VISIBILITY IS POSSIBLE BUT
TOO LOW TO INCLUDE IN THE TAFS.

STORM AND FREEZING RAIN: AFTER 12Z LATE IN THE CYCLE KGGW SHOULD
EXPERIENCE DETERIORATING CONDITIONS TO IFR AS A WINTER STORM SYSTEM
MOVES THROUGH THE AREA. OTHER TERMINALS WILL DROP AROUND 18Z PRECIPITATION
SHOULD BEGIN AS SLEET OR FREEZING RAIN IN THE MORNING BUT
TRANSITION TO ALL RAIN AS CONDITIONS WARM THROUGH THE AFTERNOON.

AREA WIND: OUT OF THE WEST AROUND 10 KTS DURING THE AFTERNOON... VEERING TO
THE SOUTH OVERNIGHT.

GAH

&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...
FREEZING RAIN ADVISORY FROM 5 AM TO NOON MST SUNDAY FOR CENTRAL
AND SOUTHEAST PHILLIPS...CENTRAL AND SOUTHERN VALLEY...
GARFIELD...NORTHERN PHILLIPS...NORTHERN VALLEY...PETROLEUM...
SOUTHWEST PHILLIPS.

&&

$$

WEATHER.GOV/GLASGOW





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