Area Forecast Discussion
Issued by NWS Glasgow, MT

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000
FXUS65 KGGW 221621
AFDGGW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
921 AM MST MON DEC 22 2014

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

MORNING UPDATE... CHANGES FOR THIS MORNING WERE FOCUSED ON
SHARPENING UP POP FIELDS WITH HIGHER PERCENTAGES IN RADAR ECHOS AND
LOWER PERCENTAGES OUTSIDE. WIND FIELDS WERE ALSO TWEAKED TO
REFLECT LATEST MESOSCALE MODEL GUIDANCE. CURRENT STORMS SYSTEM
SHOULD MAINTAIN A SHARP LINE OF PRECIPITATION EAST FROM OPHEIM TO
CIRCLE TO TERRY THROUGH ABOUT MIDNIGHT AND THEN DROP OFF. GAH


PREVIOUS SHORT TERM DISCUSSION...
THE SHORT TERM PERIOD BEGINS WITH A BROAD TROUGH OVER CENTRAL
CONUS AND A HIGH PRESSURE RIDGE NUDGED UP AGAINST THE WEST
COAST. THE STATIONARY BOUNDARY BETWEEN THE COLD CANADIAN AIR AND
THE WARMER PACIFIC AIR RUNS FROM WEST OF THE NORTHERN ROCKIES
SOUTHEAST THROUGH SOUTHERN WYOMING...PLACING NORTHEAST MONTANA
WELL NORTH OF THE BOUNDARY. SOUTHERN PORTIONS OF THE UPPER TROUGH
BEGIN TO CLOSE OFF TODAY OVER SOUTH DAKOTA AND NEBRASKA...STACKING
UP WITH A CLOSED SURFACE TROUGH...WHICH NUDGES UP AGAINST
NORTHEAST MONTANA TODAY. MODELS ARE SHOWING 0.15 TO 0.20 INCH OF
QPF AND SNOW RATIONS OF 10-15 TO 1 FOR THE EASTERN ZONES
TODAY...COVERED BY AN EXISTING WSW FOR SNOW AND BLOWING SNOW. THE
LATEST SNOW TOTALS RANGE FROM 2 TO 4 INCHES THROUGH TONIGHT. THE
NORTHWEST GUSTY WIND WILL BE SUSTAINED BY CAA ALOFT AND THE
SURFACE LOW OVER THE DAKOTAS. SNOW WILL SLOWLY TAPER OFF LATE
TONIGHT...ESSENTIALLY ENDING BY TUESDAY.

TUESDAY...THE WESTERN RIDGE MOVES EAST BRINGING WARMING AIR ALOFT.
HOWEVER THE LACK OF MIXING WILL PREVENT MUCH WARMING...ENDING UP
SLIGHTLY ABOVE NORMAL. HOWEVER CONDITIONS WILL REMAIN DRY.

WEDNESDAY...AS THE RIDGE LEANS EAST A CANADIAN COLD FRONT BEGINS TO
COLLAPSE IT. SO THERE WILL BE SOME LIGHT MIXED PRECIPITATION AND
INCREASED OVERCAST AS THE FRONT MOVES OVER NEMONT. TEMPERATURES
WILL CONTINUE CLOSE TO THOSE ON TUESDAY. SCT


.LONG TERM...WEDNESDAY NIGHT THROUGH MONDAY...
UPPER TROUGH MOVES INLAND WEDNESDAY NIGHT AND SPLITS BY THE TIME
IT REACHES MONTANA ON THURSDAY. THE SOUTHERN BRANCH DIGS INTO FOUR
CORNERS REGION OF THE DESERT SW WHILE THE NORTHERN BRANCH WILL BE
ACROSS SOUTHERN CANADA AND MAYBE AS FAR SOUTH AS NORTHERN
MONTANA. THE NORTHERN BRANCH IS DRY WHILE THE SOUTHERN BRANCH IS
VERY MOIST. IT IS WHERE THE MODELS FORECAST THE NORTHERN EDGE OF
THE MOISTURE THAT HAS THE MOST IMPACT ON HOW MUCH SNOW NORTHEAST
MONTANA RECEIVES FROM THIS SYSTEM. THE SURFACE LOW DEVELOPMENT IS
FORECASTED TO BE IN COLORADO WHICH IS FREQUENTLY FAR ENOUGH SOUTH
TO LIMIT THE SNOW AMOUNTS IN THE FORECAST AREA. AT THIS POINT...
IT LOOKS LIKE THE BEST CHANCE OF PRECIP FROM THIS SYSTEM FOR
NORTHEAST MONTANA WILL BE ALONG AND JUST NORTH OF THE COLD FRONT
THAT WILL DROP SOUTH THROUGH THE FORECAST AREA WEDNESDAY EVENING.
THE GFS  IS SLOWER THAN THE ECMWF AND CMC WITH THIS FRONT AND
WANTS TO KEEP SNOW OVER THE FORECAST AREA THROUGH THURSDAY WHILE
THE ECMFW AND CMC GENERALLY LIMIT THE SNOW TO WEDNESDAY NIGHT AND
KEEP IT MAINLY SOUTH OF THE MISSOURI RIVER. WILL FOCUS THE
FORECAST CLOSER TO THE MOST CONSISTENT ECMWF FOR NOW BUT ALLOW FOR
CHANCES OF SNOW TO THE NORTH GIVEN THE MODEL DIFFERENCES. WILL
CONTINUE TO MENTION THIS SYSTEM IN THE HWO.

BY THURSDAY NIGHT... HIGH PRESSURE BUILDS INTO THE AREA ENDING THE
CHANCES FOR SNOW. THE SURFACE HIGH REMAINS OVER THE AREA ON FRIDAY
WITH DRY AND SEASONABLY COLD TEMPERATURES.

DRY WEATHER CONTINUES ON SATURDAY WITH A SHORTWAVE RIDGE.

THE NEXT UPPER TROUGH MOVES INTO THE AREA ON SUNDAY WITH A COLD
FRONT. THE SYSTEM HAS LIMITED MOISTURE. WILL MENTION A SLIGHT
CHANCE OF SNOW FOR NOW. SYSTEM COULD LINGER INTO MONDAY WILL
MAINTAIN A SLIGHT CHANCE OF SNOW MAINLY SOUTH. FORRESTER


&&

.AVIATION...
FLIGHT CATEGORY: VFR TO IFR

SYNOPSIS: A COLD FRONT WILL MOVE TO THE SOUTH EARLY THIS MORNING.
AN UPPER LEVEL DISTURBANCE WILL BRING SNOW STORM ACROSS FAR
EASTERN MONTANA TODAY IMPACTING MOST OF THE TERMINALS. HIGH PRESSURE SYSTEM
WILL BUILD INTO THE AREA TONIGHT DIMINISHING THE SNOW BY MIDNIGHT. KGGW
WILL REMAIN RELATIVELY UNTOUCHED BY THE STORM IN COMPARISON TO THE
OTHER TERMINALS.

CIGS: MAINLY 1 TO 2 KFT IN FUEL LOADING TODAY IMPROVING THROUGH THE
LATE EVENING HOURS.

VSBY: VISIBILITY WILL VARY DUE TO CHANGING INTENSITY OF SNOW AND
POSSIBLY BLOWING SNOW. HEAVIER SNOW BANDS HAVE BEEN MAINTAINING 1
TO 2 SM IN IFR.

WIND: NORTHWEST 15 TO 25 KNOTS AND GUSTY THROUGH MIDNIGHT... THEN
CALMING TO 10 TO 15 KTS.

GAH


&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL 11 PM MST THIS EVENING FOR CENTRAL
AND SOUTHERN VALLEY...DANIELS...DAWSON...EASTERN ROOSEVELT...
MCCONE...NORTHERN VALLEY...PRAIRIE...RICHLAND...SHERIDAN...
WESTERN ROOSEVELT...WIBAUX.


&&

$$

WEATHER.GOV/GLASGOW




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