Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 261541
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
930 AM MDT SUN APR 26 2015

.UPDATE... WIDESPREAD MOSTLY CLOUDY TO OVERCAST SKIES OVER THE
FORECAST AREA THIS MORNING AS EXTENSIVE MOISTURE PLUME COVERS MOST
OF MONTANA.  AREAS OF VERY LIGHT RAIN, RAIN/SNOW MIX, AND LIGHT SNOW
CONTINUE THROUGH THE SOUTHWEST COUNTIES, EXTENDING NORTH TO THE
LITTLE/BIG BELT MTNS AND ALONG THE ROCKY MTN FRONT NORTH OF LINCOLN.
SHOULD SEE THE PRECIPITATION AND SOME OF THE CLOUD COVER SLOWLY
DECREASE FROM WEST TO EAST THIS AFTN AS WATER VAPOR SATELLITE
IMAGERY SHOWS MAIN MOISTURE PLUME HEADING STEADILY NORTH- AND
EASTWARD. ANY ADDITIONAL RAINFALL OR SNOW SHOULD BE VERY LIGHT,
AROUND A TRACE TO MAYBE 0.01-0.03 OF AN INCH.  CURRENT FORECAST IN
GOOD SHAPE...JUST A FEW MINOR ADJUSTMENTS TO BUMP UP PRECIP CHANCES
AROUND HELENA AND NORTHERN LEWIS & CLARK COUNTY THROUGH MIDDAY.
WARANAUSKAS

&&

.DISCUSSION...

TODAY THROUGH TUESDAY...A DISTURBANCE IN THE MOIST SOUTHERLY FLOW
ALOFT WILL BRING WIDESPREAD SNOW AND RAIN TO SOUTHWEST MONTANA
TODAY. SO FAR, THE MAIN AREA OF SNOW HAS BEEN LIMITED TO THE
MOUNTAINS WEST OF THE DIVIDE AND INTO WESTERN BEAVERHEAD COUNTY,
BUT PRECIPITATION SHOULD SPREAD EAST ACROSS SOUTHWEST MONTANA
THROUGH THE MORNING. SNOW AMOUNTS WILL GENERALLY BE LIGHT IN THE
VALLEYS (LESS THAN 2 INCHES), AS IT WILL MOSTLY MIX WITH RAIN AND
WILL MAINLY ACCUMULATE ON GRASSY AREAS. HOWEVER, TOTAL WET SNOW
ACCUMULATIONS OF 2 TO 4 INCHES (WITH UP TO 7 INCHES ON HIGHER
PEAKS) ARE EXPECTED ABOVE 6000 FEET. THIS WILL LIKELY CAUSE
DIFFICULT DRIVING OVER MOUNTAIN PASSES. HAVE THEREFORE ISSUED A
WINTER WEATHER ADVISORY THROUGH TODAY FOR ELEVATIONS ABOVE 6000
FEET IN BEAVERHEAD, JEFFERSON, MADISON, AND GALLATIN COUNTIES.
PRECIPITATION WILL DECREASE FROM THE WEST BEGINNING THIS AFTERNOON
AS THE DISTURBANCE MOVES EAST OF THE AREA. ACROSS NORTH CENTRAL
MONTANA, NORTHERLY UPSLOPE WINDS HAVE PUSHED LOW CLOUDS INTO THE
AREA FROM CANADA. HOWEVER, MOISTURE FROM THE SOUTHWEST MONTANA
DISTURBANCE WILL LIKELY BRING AREAS OF LIGHT PRECIPITATION TO THE
FAVORED UPSLOPE AREAS AROUND GREAT FALLS AND LEWISTOWN. THE NARROW
UPPER LEVEL TROUGH OF LOW PRESSURE CAUSING THE SOUTHERLY FLOW
ALOFT WILL MOVE EAST THROUGH THE AREA OVERNIGHT, WHICH WILL FORCE
THE SHOWERS AND CLOUDINESS EAST OF THE AREA. TEMPERATURES WILL
REMAIN SLIGHTLY BELOW NORMAL. HIGHS TODAY WILL MOSTLY BE IN THE
40S TO LOWER 50S, AS LOWS TONIGHT FALL INTO THE 20S TO LOWER 30S.
HIGH PRESSURE ALOFT WILL THEN MOVE INTO THE AREA FOR MONDAY
THROUGH TUESDAY, WHICH WILL KEEP THE AREA DRY AND MOSTLY CLEAR.
TEMPERATURES WILL ALSO WARM TO WELL ABOVE NORMAL, WITH HIGHS
REACHING THE MID 60S TO MID 70S ON TUESDAY.  COULSTON

TUESDAY NIGHT THROUGH SUNDAY...THE PERIOD BEGINS WITH THE UPPER
RIDGE MOVING TO EASTERN MONTANA BY EARLY WEDNESDAY AS AN UPPER
TROF APPROACHES THE PACIFIC NORTHWEST. SOUTHWEST FLOW ALOFT WILL
BEGIN TO BRING AN INCREASE IN MOISTURE TO THE AREA. SHOWERS
WEDNESDAY AFTERNOON WILL BE CONFINED TO THE ROCKY MOUNTAIN FRONT.
BY LATE WEDNESDAY NIGHT, THE UPPER TROF WILL CROSS THE CONTINENTAL
DIVIDE AND RESULT IN WIDESPREAD SCATTERED SHOWERS THROUGH THE DAY
THURSDAY. THURSDAY NIGHT WILL FIND THE TROF ALREADY OVER EASTERN
MONTANA AND PRECIPITATION WILL BE ENDING OVER THE PLAINS. THE
MODELS BEGIN TO OFFER VARYING SOLUTIONS FOR FRIDAY. THOUGH THEY
ALL HAVE GENERALLY WESTERLY FLOW ALOFT, THE GFS BRINGS A WEAK
UPPER TROF ACROSS THE AREA. SCATTERED SHOWERS WILL BE POSSIBLE
OVER SOUTHWEST MONTANA AND OVER THE WESTERN PLAINS. BOTH THE
CANADIAN AND GFS MODELS HAVE DOWN SLOPE WESTERLY FLOW ALOFT FOR
SATURDAY WHILE THE ECMWF BRINGS A WEAK UPPER TROF THROUGH AND
SUBSEQUENT PRECIPITATION. HAVE GONE WITH A COMPROMISE SOLUTION
SATURDAY BY KEEPING THE PLAINS DRY AND DEVELOPING SOME MOUNTAIN
SHOWERS. SAME SOLUTION FOR SUNDAY AS THE CANADIAN AND GFS MODELS
TRY TO DEVELOP UPPER RIDGING OVER THE AREA WHILE THE ECMWF IS
FASTER WITH AN UPPER TROF MOVING INTO THE PACIFIC NORTHWEST.
SOUTHWEST MOUNTAINS SHOULD SEE SOME SHOWERS WHILE THE PLAINS
CONTINUE TO BE DRY. TEMPERATURES WILL CONTINUE ABOVE SEASONAL
AVERAGES.

&&

.AVIATION...
UPDATED 1155Z.
SOUTHWEST FLOW ALOFT CONTINUES TO BRING MOISTURE AND
INSTABILITY TO THE AREA. SCATTERED RAIN AND SNOW SHOWERS WILL
CONTINUE OVER PORTIONS OF SOUTHWEST AND CENTRAL MONTANA.
PRECIPITATION WILL DECREASE AND BECOME MORE ISOLATED AFTER 18Z.
MVFR/IFR CONDITIONS PREVAIL DUE TO LOW CEILINGS AND PRECIPITATION.
CONDITIONS IMPROVING TO GENERALLY VFR CONDITIONS AFTER 20Z.
MOUNTAINS OBSCURED THROUGH 20Z.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  50  32  65  38 /  60  10   0   0
CTB  50  28  64  33 /  30  10   0   0
HLN  52  32  65  38 /  90  10   0   0
BZN  49  26  61  33 / 100  30   0   0
WEY  50  24  60  27 /  90  30   0   0
DLN  49  28  61  35 / 100  20   0   0
HVR  55  29  66  36 /  10  10   0   0
LWT  49  29  64  38 /  60  20   0   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL 6 PM MDT THIS EVENING FOR MTZ008-
015-052-055.

&&

$$

WEATHER.GOV/GREATFALLS


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