Area Forecast Discussion
Issued by NWS Glasgow, MT

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FXUS65 KGGW 270340
AFDGGW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
840 PM MST WED NOV 26 2014

.SHORT TERM...FOR NORTHEAST MONTANA...TONIGHT THROUGH FRIDAY...
UPDATE...SNOW CONTINUES TO SPREAD NORTHEAST ACROSS THE REGION
TONIGHT AND LAST INTO THURSDAY. EXPECT THE PRECIPITATION TYPE TO
REMAIN AS SNOW THROUGH THE EARLY OVERNIGHT HOURS AND BECOME A
WINTRY MIX BY 6AM WITH SOME FREEZING RAIN MIXED IN...BECOMING ALL
RAIN SOUTH OF THE MISSOURI RIVER LATER IN THE MORNING HOURS.
UPDATED THE NEAR TERM WITH CURRENT CONDITIONS AND LEFT THE
REMAINDER OF THE FORECAST ALONE FOR NOW.    PROTON

PREVIOUS DISCUSSION...
OVERRUNNING PRECIPITATION IS EVIDENT ON RADAR ACROSS PETROLEUM
COUNTY AS WELL AS THE LITTLE ROCKIES IN PHILLIPS COUNTY TOWARD
SAND SPRINGS IN GARFIELD COUNTY. WEB CAMS...ROAD REPORTS...AND
SPOTTERS CONFIRM SNOW IS BEGINNING TO ACCUMULATE WITH ADDITIONAL
ENHANCEMENT EXPECTED AS THE AFTERNOON PROGRESSES.

THIS EVENING THE BOUNDARY DRIVING THIS SNOWFALL WILL BEGIN TO
LIFT NORTHWARD AS A WARM FRONT...LIFTING BETTER POTENTIAL FOR
SNOWFALL WITH IT. AFTER MIDNIGHT TEMPS ALOFT OVER PETROLEUM COUNTY
AND SURROUNDING AREAS LOOK TO WARM ENOUGH TO ALLOW FOR A SWITCH OF
PRECIP TYPE OVER TO FREEZING RAIN.

THURSDAY MORNING THE AREA OF FREEZING RAIN WILL LIFT NORTHWARD
WITH THE WARM FRONT...FINALLY REACHING THE CANADIAN BORDER DURING
THE AFTERNOON HOURS. SOUTHERLY WINDS WILL HELP WARM TEMPS BEHIND
THE FRONT STARTING EARLY IN THE MORNING...BUT THE IMPACTS OF
FREEZING RAIN WILL BE SIGNIFICANT ESPECIALLY WITH EXPECTED HOLIDAY
TRAVELERS. THUS CONTINUED THE CURRENT HIGHLIGHT PACKAGE WITH ONE
CHANGE...WE UPGRADED THE WATCH FOR THE EASTERN AND NORTHERN ZONES
TO A WINTER WEATHER ADVISORY FOR LIGHT SNOW TRANSITIONING TO
FREEZING RAIN AS ICE AMOUNTS LOOK TO BE LESS THAN ONE TENTH OF ONE
INCH. THIS WILL NEED TO BE CLOSELY MONITORED AS FREEZING RAIN IS
DEFINITELY HIGH IMPACT.

BY THURSDAY EVENING THE WARM FRONT WILL WRAP UP INTO SOUTHERN
SASKATCHEWAN. THERE REMAINS SOME QUESTION AS TO HOW FAR NORTH THE
BOUNDARY WILL LIFT. BUT CONFIDENCE IS HIGH THAT MOISTURE WILL BEGIN
TO DECREASE...THUS COVERAGE OF MIXED PRECIPITATION WILL DECREASE.
WITH THAT SAID THURSDAY EVENING INTO FRIDAY WILL NEED TO BE
MONITORED FOR POSSIBLE IMPACTS DUE TO PATCHY FREEZING
RAIN...MAINLY NORTH OF THE MISSOURI RIVER. GILCHRIST

.LONG TERM...FRIDAY NIGHT THROUGH WEDNESDAY...

THE EXTENDED PERIOD BEGINS FRIDAY EVENING WITH THE STATIONARY
FRONTAL BOUNDARY POISED SOMEWHERE NEAR THE INTERNATIONAL BORDER OR
JUST NORTH OF IT...AND READY TO RETREAT ONCE AGAIN AS A WESTERN
TROUGH EXTENSION OF THE HUDSON BAY ARCTIC LOW RAPIDLY PUSHES
SOUTH THROUGH MONTANA. THIS BRINGS VERY COLD AIR INTO THE
REGION...850MB TEMPERATURES OF -22C TO -24C. ALSO AS THE FRONT
PASSES OVER NORTHEAST MONTANA...PRECIPITATION FOLLOWS IT. SO AT
FIRST EXPECT LIQUID PRECIPITATION...BECOMING ALL SNOW BY SATURDAY
MORNING. THERE CONTINUES TO BE UNCERTAINTY ABOUT THE TIMING OF
WHEN THE FRONTAL BOUNDARY MOVES SOUTH THROUGH NEMONT. THIS WILL
DETERMINE TO A GREAT EXTENT WHEN RAIN SHIFTS OVER TO SNOW. 00Z
SATURDAY THROUGH 12 SUNDAY...SNOW AMOUNTS RANGE FROM AROUND AN
INCH AND A HALF IN THE EAST TO 4 AND A HALF INCHES IN THE LITTLE
ROCKIES. THE COLDEST DAY WILL BE SATURDAY AND THE COLDEST NIGHT
WILL BE SATURDAY NIGHT. SUNDAY AND SUNDAY NIGHT WILL SEE A SLIGHT
IMPROVEMENT ON TEMPERATURES...BUT FOR TRAVEL PURPOSES...ALL
SNOWFALL WILL END LIKELY PRIOR TO SUNDAY MORNING.

THE UNCERTAINTY OF THE COLD FRONT TIMING DOES BRING A CONTINUING
CHALLENGE TO THE TEMPERATURE FORECAST THROUGH SATURDAY NIGHT.
BUT THE EC AND THE GFS DRIFTED TOGETHER A BIT MORE...WITH THE GFS
DOING THE MOST DRIFTING. THE MAIN EDITS THEREFORE WERE TO UPDATE
TEMPERATURES AS A BLEND...AND WEATHER PARAMETERS BASED ON THE
LATEST GUIDANCE.

MONDAY AND BEYOND...IN GENERAL A WARM FRONT WILL AGAIN MOVE EAST
ACROSS MONTANA WHICH WILL BEGIN A SLOW WARMING TOWARDS NORMAL
THROUGH THE REST OF THE WEEK. SCT

PREVIOUS DISCUSSION...
SYNOPTIC SET UP...A STRONG BROAD ARCTIC AIR-MASS EXISTS OVER THE
MAJORITY OF CANADA. AN ESPECIALLY DEEP AND VIGOROUS TROUGH
EXTENSION SETS OVER BRITISH COLUMBIA AND ALBERTA. A RELATIVELY
WARMER BROAD RIDGE SETS OVER THE WESTERN HALF OF THE US. NORTHEAST
MONTANA SETS AT THE EDGE OF THESE TWO LARGE AIR-MASSES IN ZONAL
FLOW ALOFT WITH THE SHARPENED FRONTAL GRADIENT JUST NORTH OF THE
INTERNATIONAL BORDER. OVER THE NORTHEAST PACIFIC SPLIT FLOW HAS
SET UP CENTERED OFF THE COAST OF THE PACIFIC NORTHWEST WITH THE
TROUGH OFF SHORE OF CALIFORNIA AND A WEAK RIDGE OVER THE GULF OF
ALASKA.

FRIDAY NIGHT THROUGH SATURDAY...COLD FRONT NORTH OF THE
INTERNATIONAL BORDER WILL DROP THROUGH THE REGION BRING IN WITH
IT SNOW SHOWERS FOLLOWED BY VERY COLD AIR. 850 MB TEMPERATURES
NEGATIVE 20S CELSIUS. TOTAL SNOWFALL WITH THIS PASSAGE CURRENTLY
LOOKS TO BE AROUND 1 TO 4 INCHES.

SUNDAY THROUGH MONDAY NIGHT...CENTER OF THE COLD AIR-MASS SHOULD
SLUMP OFF TO THE EAST MONDAY NIGHT AS THE RIDGE OVER THE GULF OF
ALASKA IS FLATTENED SLIGHTLY AND MOVES ACROSS THE REGION IN THE
FLOW. TEMPERATURES WILL RISE HERE SLIGHTLY AND DECREASE THE
CHANCES FOR POPS TO BELOW CLIMATOLOGY AND THEREFORE MENTION.
MONDAY ITSELF WILL SEE A SMALL CHANCE FOR CHINOOK WARMING WITH
HIGHS IN THE 20S.

TUESDAY ONWARD...CONFIDENCE AT THIS POINT BREAKS DOWN. MODELS
HINT AT A TROUGH MOVING THROUGH DURING THIS TIME BUT HAVE A 24
HOURS DISCREPANCY IN TIMING. BY WEDNESDAY...A LARGER AND
THEREFORE HIGHER CONFIDENCE RIDGE MOVES THROUGH THE REGION
BEGINNING YET ANOTHER WARM-UP. GAH

&&

.AVIATION...
FLIGHT CATEGORY: LOW MVFR TO IFR.

SYNOPSIS: THE NW TO SE ORIENTATED FRONTAL BOUNDARY...NOW SITUATED
TO OUR SOUTHWEST...IS SLOWLY MOVING NORTHEAST AS A WARM FRONT.
OVERRUNNING MOISTURE FROM THE NW WILL FLOW ALONG THIS BOUNDARY TO
BRING ABOUT CONTINUOUS PRECIPITATION. LIGHT SNOW WILL MOVE FAR
ENOUGH NORTHEAST TO BEGIN AFFECTING KGGW AND KGDV BY THIS EVENING.
ALL TERMINALS SHOULD BE AFFECTED BY MID MORNING WITH PERSISTENT
IFR POSSIBLE.

FREEZING RAIN: THERE IS A SIGNIFICANT THREAT FOR FREEZING RAIN
WHICH CAN ACCUMULATE ICE ON RUNWAYS AND AIRCRAFT WINGS. FREEZING
RAIN CHANCES WILL BEGIN AROUND 11Z AND PERSIST THROUGH AT LEAST
00Z. AFTERWARD... FREEZING RAIN IS STILL A POSSIBILITY THROUGH FRIDAY
BUT CHANCES FOR PRECIP WILL BE TOO LOW TO DECLARE IN THE TAFS
DIRECTLY.

CEILINGS: BETWEEN 1 TO 2 KFT WITH FUEL LOADING FOR MOST SITES.
BRIEF IFR WITH DROPS BELOW 1KFT WILL BE POSSIBLE THIS EVENING. MORE
PERSISTENT CEILINGS BELOW 1K FEET ARE LIKELY NEAR THE END OF THE
CYCLE WITH CONTIGUOUS SNOW FALL.

VSBY: OBSTRUCTIONS TO VISIBILITY DOWN TO 3 TO 2SM ARE POSSIBLE
WITH SNOW. SNOW AND VSBY REDUCTION WILL LIKELY BECOME SUSTAINED
FOR KGGW AND KGDV AFTER MIDNIGHT AND SPREAD TO KOLF AND KSDY
AFTER 12Z.

AREA WINDS: EAST AROUND 5 TO 15KTS...VEERING FURTHER TO THE SOUTHEAST
OVERNIGHT.

BEYOND THE TAF CYCLE: THERE IS A SMALL CHANCE FOR WIDESPREAD FOG
AND LOW STRATUS THURSDAY NIGHT.

GAH

&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING UNTIL 5 PM MST THURSDAY FOR GARFIELD...
PETROLEUM...SOUTHWEST PHILLIPS.

WINTER WEATHER ADVISORY UNTIL 5 PM MST THURSDAY FOR CENTRAL AND
SOUTHEAST PHILLIPS...CENTRAL AND SOUTHERN VALLEY...MCCONE...
NORTHERN PHILLIPS...PRAIRIE.

WINTER WEATHER ADVISORY FROM 5 AM TO 5 PM MST THURSDAY FOR
DANIELS...DAWSON...EASTERN ROOSEVELT...NORTHERN VALLEY...
RICHLAND...SHERIDAN...WESTERN ROOSEVELT...WIBAUX.

&&

$$

WEATHER.GOV/GLASGOW




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