Area Forecast Discussion
Issued by NWS Glasgow, MT

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000
FXUS65 KGGW 012328 AAA
AFDGGW

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE GLASGOW MT
428 PM MST SUN FEB 1 2015

UPDATED AVIATION DISCUSSION BELOW...

.SHORT TERM...FOR NORTHEAST MONTANA...TONIGHT THROUGH TUESDAY...

WATER VAPOR IMAGERY AND 500 MB HEIGHT FIELD SHOWS THE WESTERN
STATES SHORT-WAVE RIDGE ALREADY BEING WEAKENED BY THE NEXT
APPROACHING SHORT-WAVE INTO THE PACIFIC NORTHWEST. THIS
DISTURBANCE IS THE IMMEDIATE FOCUS FOR THE SHORT TERM FORECAST
PERIOD. CLOUDS WILL INCREASE AND LOWER BEGINNING THIS EVENING.
MOISTURE AND FORCING WILL COMBINE TO ALLOW SCATTERED SNOW SHOWERS
TO BEGIN OVER OUR FAR WESTERN ZONES AROUND 06Z TONIGHT.

AFTER 12Z EARLY MONDAY MORNING...SNOW IS EXPECTED TO BECOME MORE
WIDESPREAD AND STRATIFORM AS THE LOWER-LEVEL CLOUDS FILL IN FROM
THE WEST. AGAIN...ACCUMULATIONS ARE EXPECTED TO BE ON THE LIGHTER
SIDE.

A VERY BRIEF RESPITE FROM PRECIPITATION IS EXPECTED MONDAY
AFTERNOON AND EVENING BEFORE A STRONGER SHORT-WAVE TROUGH ROTATES
AROUND THE PERIPHERY OF THE HUDSON BAY LOW. THIS SECOND
DISTURBANCE HAS STRONGER SUPPORT AND MORE MOISTURE WHICH WILL
LIKELY RESULT IN A WIDESPREAD 2 TO 3 ADDITIONAL INCHES OF
SNOW...THE MAJORITY OF WHICH WILL FALL DURING THE PRE-DAWN HOURS
ON TUESDAY. SNOW WILL THEN TAPER OFF TOWARD THE SOUTH THROUGH LATE
TUESDAY.

OVERALL...EXPECT TEMPERATURES TO STRUGGLE TO WARM NORTH OF THE
MISSOURI RIVER WHILE LOCATIONS SW OF FORT PECK LAKE HAVE THE
POTENTIAL TO THAW A BIT OVER THE NEXT FEW DAYS. BMICKELSON

.LONG TERM...TUESDAY NIGHT THROUGH SUNDAY...

SNOW EVENT FROM MONDAY-TUESDAY ENDS LATE TUESDAY WITH THE EXIT OF
MID-LEVEL WAVE EASTWARD. A BROAD BUT SOMEWHAT FLAT RIDGE FORMS IN
THE WAKE OF THIS WAVE OVER THE WESTERN CONUS. TOP OF THE RIDGE
WILL BE OVER THE MONTANA AREA AND SOME SHORTWAVE IMPULSES RUNNING
AROUND THE TOP OF THE RIDGE COULD GIVE SOME SHOWERS THURSDAY WITH
A BETTER CHANCE FOR A SHOWER FRIDAY AS A COLD FROPA MIGRATES DOWN
FROM CANADA. CONDITIONS MAY BE WARM ENOUGH FOR SOME RAIN AHEAD OF
THE FRONT WITH A RELATIVELY QUICK CHANGE OVER FROM RAIN TO SNOW AS
THE FRONT PROGRESSES SOUTHWARD. RIDGE FLATTENS FURTHER SATURDAY
FOLLOWING THE FRONT AND REBOUNDS ON SUNDAY.

MODELS HAVE SOME DIVERSITY WITH THE SCENARIO FOR THE POSSIBLE
FROPA ON FRIDAY WITH THE EC BEING LESS AGGRESSIVE WITH THE
SOUTHWARD MOVEMENT OF THE FRONT AND THE PRODUCTION OF SNOW BEHIND
IT. MARTIN

PREVIOUS LONG TERM DISCUSSION...
A PACIFIC RIDGE AND BROAD EASTERN CONUS TROUGH
WILL MAINTAIN NORTHWEST FLOW ALOFT ACROSS THE NORTHERN HIGH PLAINS
AS THE EXTENDED PERIOD BEGINS TUESDAY NIGHT. AN UPPER LEVEL
SHORTWAVE WILL BE EXITING NORTHEAST MONTANA AND PUSHING INTO THE
DAKOTAS. THE TIMING AND TRACK OF THIS FEATURE WILL BE CRITICAL FOR
TEMPERATURE FORECASTS OVERNIGHT. IF THE SYSTEM PUSHES OUT MORE
PROGRESSIVELY...SKY CONDITIONS COULD ABRUPTLY CLEAR. GIVEN 850MB
TEMPERATURES IN THE -15C TO -20C RANGE AND ABUNDANT NEW SNOW
COVER...EFFICIENT RADIATIONAL COOLING COULD RESULT. THE RESULT
WOULD BE LOWS WELL BELOW ZERO ACROSS THE REGION. HOWEVER...SHOULD
THE SYSTEM EXIT MORE SLOWLY THE RESULT WOULD BE LINGERING CLOUD
COVER AND TEMPERATURES SOMEWHAT LESS COLD. WILL HAVE A MIDDLE OF
THE ROAD APPROACH FOR NOW...SLIGHTLY COLDER THAN THE 00Z MODEL
GUIDANCE...ESPECIALLY CONSIDERING THAT GUIDANCE LIKELY DOES NOT
FACTOR IN ALL THE NEW SNOW COVER OUT THERE.

MODELS EXHIBIT FAIRLY GOOD AGREEMENT HAVING THE PACIFIC RIDGE
TRANSLATE EASTWARD DURING THE MIDDLE AND LATTER HALF OF THE
WEEK...LEADING TO GRADUALLY WARMING TEMPERATURES AND DRY
CONDITIONS. AT SOME POINT A SHORTWAVE TROUGH UPSTREAM MAY FLATTEN
THE RIDGE AND BRING ABOUT RENEWED PRECIPITATION CHANCES TO THE
CWA. WILL CARRY A SLIGHT CHANCE POP FOR FRIDAY AND SATURDAY AS
CURRENT MODEL GUIDANCE SHOWS A FAIR AMOUNT OF VARIANCE ON SPECIFIC
HANDLING OF SHORTWAVES. PRECIPITATION TYPE MAY ALSO PROVE TO BE A
CHALLENGE. ENSEMBLE 500MB HEIGHTS SHOW INCREASING SPREAD THIS FAR
OUT INTO THE EXTENDED PERIOD...LENDING TO FURTHER UNCERTAINTY.
FUTURE SHIFTS WILL BE ABLE TO MAKE REFINEMENTS AS GUIDANCE ARRIVES
AT CONSENSUS. MALIAWCO


&&

.AVIATION...

A SHORT-WAVE DISTURBANCE WILL RIDE UP AND OVER THE NORTHERN
ROCKIES LATER TONIGHT AND INCREASE CLOUDINESS FROM THE WEST
OVERNIGHT...EVENTUALLY BRINGING SOME MVFR/IFR CONDITIONS IN LOW
CEILINGS AND LIGHT SNOW SHOWERS TO THE TAF SITES DURING THE
OVERNIGHT AND EARLY MORNING HOURS AFTER WINDS TURN MORE OUT OF THE
NORTH. AS SNOW SHOWERS END MONDAY AFTERNOON...LOW-LEVEL IFR
CEILINGS ARE EXPECTED TO REMAIN THROUGH THE END OF THE TAF CYCLE.
BMICKELSON

&&

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

&&

$$

WEATHER.GOV/GLASGOW




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