Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 291730
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1130 AM MDT FRI MAY 29 2015

.DISCUSSION...
THE ONLY CHANGES TO THE FORECAST WERE TO LOWER SKY COVER FOR SOME
OF THE MOUNTAINS OF THE ROCKY MOUNTAIN FRONT AND CENTRAL MONTANA
AS THEY WERE ABOVE THE LOW LEVEL MOISTURE AND ALSO TO LOWER THE
CHANCES OF PRECIPITATION SLIGHTLY FOR THE REST OF THIS MORNING.
STILL EXPECT WEAK INSTABILITY OVER THE MOUNTAINS THIS AFTERNOON
FOR ISOLATED SHOWERS AND THUNDERSTORMS WHICH IS IN LINE WITH THE
CURRENT FORECAST. BLANK

&&

.AVIATION...

UPDATED 1730Z.

FAIRLY WIDESPREAD MVFR CEILINGS OVER THE PLAINS OF MONTANA AND
SCATTERED MVFR CEILINGS IN THE SOUTHWEST VALLEYS WILL BECOME VFR
THIS AFTERNOON WITH SCATTERED SHOWERS AND THUNDERSTORMS DEVELOPING
OVER THE WESTERN AND SOUTHWEST MOUNTAINS. THESE WILL DISSIPATE THIS
EVENING WITH CEILINGS THEN NEAR AND ABOVE 15000 FT. BY LATE SATURDAY
MORNING SCATTERED SHOWERS WILL AGAIN DEVELOP OVER THE WESTERN
MOUNTAINS.

&&

.PREV DISCUSSION...
/ISSUED 526 AM MDT FRI MAY 29 2015/

TODAY THROUGH SUNDAY...ANY LINGERING SHOWERS ACROSS THE AREA THIS
MORNING ARE LIMITED TO THE MOUNTAINS OF NORTH CENTRAL AND
SOUTHWEST MONTANA, WHERE MID LEVEL CLOUDINESS IS STILL WIDESPREAD.
HOWEVER, WITH MOST OF THE AREA RECEIVING SHOWERS YESTERDAY AND
OVERNIGHT, AREAS OF LOW CLOUDS AND FOG HAVE DEVELOPED AS OF THIS
MORNING ACROSS THE ENTIRE AREA. FOG IS NOT DENSE AT THIS TIME, BUT
WILL CONTINUE TO MONITOR THE SITUATION, ESPECIALLY ALONG THE HI-
LINE, WHERE SKIES HAVE BECOME MOSTLY CLEAR. OTHERWISE, AN UPPER
LEVEL HIGH PRESSURE RIDGE WILL BUILD INTO MONTANA TODAY, PARTIALLY
CLEARING OUT THE LOW AND MID LEVEL CLOUDINESS. HOWEVER, A
DISTURBANCE WILL MOVE THROUGH THE RIDGE WITH ITS WARM AND WEAKLY
UNSTABLE AIR THIS AFTERNOON AND EVENING, BRINGING AT LEAST
ISOLATED SHOWERS AND THUNDERSTORMS TO THE AREA. THE BEST CHANCE
FOR SHOWERS AND THUNDERSTORMS DURING THIS PERIOD WILL COME ON
SATURDAY AFTERNOON AND EVENING. ANOTHER WEAK DISTURBANCE WILL
MOVE THROUGH THE RIDGE DURING THIS TIME FRAME. A JET MAX
ASSOCIATED WITH THE DISTURBANCE WILL COMBINE WITH DEEPER PACIFIC
MOISTURE AND A MORE UNSTABLE AIRMASS THAN EXPECTED TODAY TO BRING
A MORE WIDESPREAD CHANCE OF SHOWERS AND THUNDERSTORMS TO THE AREA
ON SATURDAY. IN FACT, THE INSTABILITY AND WIND SHEAR COULD BE
STRONG ENOUGH TO CAUSE SOME STORMS ACROSS CENTRAL MONTANA TO
PRODUCE BRIEF HEAVY RAIN, SMALL HAIL, AND GUSTY WINDS, SO HAVE
MENTIONED THESE IN THE FORECAST. AS OF THIS TIME, THE STORM
PREDICTION CENTER HAS THIS AREA UNDER A MARGINAL RISK FOR SEVERE
THUNDERSTORMS. CURRENTLY, THE VARIOUS INGREDIENTS ONLY INDICATE
STRONG STORM POTENTIAL, BUT WILL CONTINUE TO MONITOR THE
SITUATION. YET ANOTHER WEAK DISTURBANCE/JET MAX/PACIFIC MOISTURE
SYSTEM WILL MOVE THROUGH THE AREA ON SUNDAY, BUT THE INSTABILITY
AND SHEAR ARE FAIRLY WEAK WITH THIS SYSTEM. THEREFORE, WHILE THERE
WILL BE ANOTHER CHANCE FOR SHOWERS AND THUNDERSTORMS, IT IS
UNLIKELY THAT STORMS WILL BECOME STRONG. PART OF WHAT WILL DRIVE
STORM DEVELOPMENT THROUGH THIS PERIOD IS A STEADILY WARMING
AIRMASS ASSOCIATED WITH THE UPPER RIDGE. HIGHS WILL WARM FROM
MOSTLY THE 60S TO LOWER 70S TODAY TO THE UPPER 60S AND 70S ON
SUNDAY, WITH MANY LOCATIONS APPROACHING 80 DEGREES FOR THE FIRST
TIME THIS YEAR. OVERNIGHT LOWS WILL ALSO REMAIN MILD, WITH MOST
PLACES ONLY FALLING INTO THE MID 40S TO LOWER 50S.  COULSTON

SUNDAY NIGHT THROUGH THURSDAY...THE REGION WILL BE UNDERNEATH A
FLAT UPPER LEVEL RIDGE SUNDAY NIGHT THAT WILL GRADUALLY SHARPEN
MONDAY. HOWEVER, MOISTURE AHEAD OF A LOW PRESSURE TROF OVER THE
WEST COAST WILL BE MOVING ACROSS THE ROCKIES AND THE AIRMASS WILL
BECOME UNSTABLE AGAIN BY MONDAY AFTERNOON. A PACIFIC COLD FRONT
ASSOCIATED WITH THE TROF TO THE WEST WILL CROSS THE AREA MONDAY
NIGHT AND BRING COOLER TEMPERATURES TO THE REGION TUESDAY. THE
UPPER LEVEL LOW WILL BROADEN AND BECOME NEARLY STATIONARY OVER THE
WESTERN US. MOISTURE WILL CONTINUE TO MOVE INTO THE REGION AND
HEIGHTS ALOFT WILL CONTINUE TO FALL. THIS WILL KEEP SHOWERS AND
THUNDERSTORMS IN THE FORECAST MOISTURE THROUGH THURSDAY. THE LOW
PRESSURE ALOFT WILL KEEP THE AIRMASS COOL AND TEMPERATURES, AFTER
BEGINNING THE PERIOD SUNDAY NIGHT AND MONDAY WELL ABOVE NORMALS,
WILL TREND LOWER TO NEAR NORMALS BY THURSDAY. ZELZER

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  68  48  73  52 /  10  20  50  30
CTB  66  43  70  47 /  20  30  50  30
HLN  74  51  75  54 /  20  30  50  40
BZN  68  46  72  50 /  20  20  40  40
WEY  63  35  65  43 /  30  20  30  30
DLN  71  48  73  51 /  20  30  50  40
HVR  67  43  77  48 /   0  10  30  40
LWT  65  46  74  50 /  10  20  60  40

&&

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

$$

WEATHER.GOV/GREATFALLS



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