Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 250543
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1140 PM MDT FRI APR 24 2015

UPDATED AVIATION SECTION

.UPDATE...

RAIN IS GRADUALLY CHANGING TO SNOW OVER PORTIONS OF SOUTHWEST
MT...INCLUDING THE VALLEY LOCATIONS. SNOW ACCUMULATIONS OF AN INCH
OR TWO ARE POSSIBLE ON GRASSY AREAS IN THE VALLEYS OF THE
SOUTHWEST...WITH 3 TO 5 INCHES IN THE MOUNTAINS. MOUNTAIN PASS
ROADWAYS HAVE BEEN MELTING MOST OF THE SNOW THIS EVENING...BUT ARE
LIKELY TO BECOME SNOW COVERED AFTER MIDNIGHT. FOR NOW I WILL HOLD
OFF ON AN ADVISORY...BUT CONTINUE TO MONITOR PASS CONDITIONS
OVERNIGHT. OTHERWISE...LIGHT RAIN IS MAINLY AFFECTING AREAS EAST OF
HIGHWAY 87 FROM GREAT FALLS TO HAVRE...WITH JUST A FEW ISOLATED
SHOWERS WEST OF I-15. OVERNIGHT LOWS LOOK ON TRACK. THE REST OF THE
FORECAST IS ON TRACK. BRUSDA

&&

.AVIATION...
UPDATED 0540Z.

THE DISTURBANCE ALOFT RESPONSIBLE FOR THE WIDESPREAD LIGHT TO
MODERATE RAIN AND SNOW ALONG AND EAST OF A KDLN-KGTF-KHVR LINE WILL
CONTINUE TO MOVE NORTHEAST OUT OF THE AREA THROUGH 15Z. THE
PRECIPITATION WILL GRADUALLY DECREASE FROM THE WEST OVERNIGHT, BUT
MOUNTAINS WILL GENERALLY REMAIN OBSCURED BY THE WIDESPREAD MVFR/IFR
CONDITIONS. VFR CONDITIONS ARE GENERALLY EXPECTED WEST OF THIS AREA
OF PRECIPITATION. AFTER 15Z, SCATTERED SHOWERS WILL LINGER OVER
MOUNTAIN AREAS, WITH SOME SHOWERS POSSIBLY MOVING OUT ONTO THE EAST
SLOPES OF THE ROCKIES (INCLUDING KCTB AND KGTF) AFTER 18Z DUE TO THE
WEAKLY DESTABILIZING AIRMASS. HOWEVER, CONDITIONS SHOULD REMAIN VFR
DURING THIS TIME. THESE PLAINS SHOWERS WILL LIKELY DIMINISH AFTER
00Z WITH THE LOSS OF DAYTIME HEATING. A WEAK COLD FRONT WILL MOVE
SOUTH OF THE CANADIAN BORDER DURING THE DAY, AND THE MORE NORTHERLY
WINDS BEHIND IT MAY BRING LOWER CLOUDS (POSSIBLY MVFR) TO THE HI-
LINE AREA (INCLUDING KCTB AND KHVR) AFTER 02Z.  COULSTON

&&

.PREV DISCUSSION...
/ISSUED 550 PM MDT FRI APR 24 2015/

TONIGHT THROUGH SUNDAY...UPPER LEVEL TROUGH/LOW CURRENTLY CENTERED
OVER SW BC WILL SLOWLY DRIFT INLAND THROUGH THE WEEKEND WHILE
SEVERAL SHORTWAVES MOVE THROUGH WESTERLY FLOW TO THE S OF THE LOW
AND LIFT NE ACROSS MT. FIRST SHORTWAVE CURRENTLY MOVING INTO EASTERN
WA/OR WILL MOVE INTO WESTERN MT THIS EVENING THEN TRACK NE ACROSS
CENTRAL MT INTO SK LATE TONIGHT THROUGH EARLY SATURDAY MORNING.
LIGHT SHOWERS ALREADY OCCURRING ACROSS MUCH OF SW AND CENTRAL MT
THIS AFTERNOON WILL INCREASE AND TRACK NE TONIGHT AS THE SHORTWAVE
APPROACHES AND THE FRONTOGENIC ZONE FROM SW TO NE ACROSS THE AREA
INTENSIFIES. MODELS REMAIN IN GOOD AGREEMENT FOCUSING A SWATH OF
0.25" TO 0.50" OF PRECIPITATION FROM THE SW AND CENTRAL MT MTNS
NORTH THROUGH THE BEARS PAW AND VICINITY WITH LOCAL AMOUNTS IN
EXCESS OF 0.50" LIKELY ACROSS PARTS OF JUDITH BASIN, EASTERN
CHOUTEAU, SOUTHERN HILL, BLAINE AND FERGUS COUNTIES. A BRIEF PERIOD
OF DRYING MOVES ACROSS THE REGION BEHIND THE EXITING SHORTWAVE ON
SATURDAY WITH ADDITIONAL BUT LESS ORGANIZED ENERGY SHIFTING INTO ID
AND SW MT LATE SATURDAY AFTERNOON THROUGH SUNDAY. HOENISCH

SUNDAY NIGHT THROUGH FRIDAY...THE PERIOD BEGINS WITH AN UPPER
TROF...AND ASSOCIATED SHOWERS... EXITING THE AREA TO THE EAST
WHILE A POSITIVE TILT UPPER RIDGE BUILDS INTO WESTERN MONTANA.
DRY AND STABLE CONDITIONS WILL RULE MONDAY AND TUESDAY AS THE
UPPER RIDGE AXIS SHIFTS EAST OF THE CONTINENTAL DIVIDE. MODELS
BEGIN TO DISAGREE WITH THEIR SOLUTIONS WEDNESDAY. BOTH THE GFS
AND CANADIAN MODELS MAINTAIN THE UPPER RIDGE OVER THE AREA WHILE
THE ECMWF MOVES A WEAK SHORTWAVE ACROSS CENTRAL MONTANA. HAVE
GONE WITH THE DRIER SOLUTION. BY THURSDAY...ALL THREE MODELS
BRING SOME MOISTURE THROUGH THE RIDGE AND DEVELOP SCATTERED
SHOWERS OVER PORTIONS OF SOUTHWEST MONTANA. FRIDAY WILL FIND THE
RIDGE AXIS PUSHED TO EASTERN MONTANA WHILE UNSTABLE AND MOIST
SOUTHWEST FLOW ALOFT STRENGTHENS IN ADVANCE OF AN UPPER TROF THAT
MOVES ONSHORE OF THE WEST COAST. THIS WILL RESULT IN SCATTERED
SHOWERS DEVELOPING FRIDAY AFTERNOON. TEMPERATURES WILL REMAIN
ABOVE SEASONAL AVERAGES WITH AFTERNOON READINGS GENERALLY IN THE
70S FROM TUESDAY THROUGH THE REMAINDER OF THE WEEK.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  36  56  34  52 / 100  10  30  40
CTB  33  54  29  53 /  10  10  20  30
HLN  35  57  36  54 /  60  20  50  70
BZN  34  54  35  52 / 100  30  50  60
WEY  30  51  27  50 /  70  40  40  60
DLN  34  52  35  51 / 100  30  60  60
HVR  40  61  32  57 / 100  30  10  20
LWT  36  54  35  51 / 100  30  20  50

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

WEATHER.GOV/GREATFALLS


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