Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 210335 AAA
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
925 PM MDT WED MAY 20 2015

.UPDATE... VERY PLEASANT WITH LOTS OF MOSTLY CLEAR SKIES ACROSS THE
FORECAST AREA THIS EVENING.  ONLY AREA OF WEATHER IS ACROSS FAR
SOUTHWEST MT WHERE SOME MID-LEVEL CLOUDS AND VERY SPOTTY LIGHT
SHOWERS HAVE MOVED NORTH FROM EASTERN IDAHO.  COVERAGE ON THE
SHOWERS HAS BEEN A BIT LOWER THAN FORECAST, SO HAVE TWEAKED PRECIP
CHANCES DOWN ABOUT 10-15 PERCENT ACROSS NORTHERN BEAVERHEAD/MADISON/
GALLATIN COUNTIES BETWEEN NOW AND THURS MORNING. REST OF FORECAST IN
GOOD SHAPE, SO NO OTHER ADJUSTMENTS NEEDED.
WARANAUSKAS

&&

.DISCUSSION...

TONIGHT THROUGH FRIDAY...GENERALLY LIGHT UPPER LEVEL FLOW FROM THE
SOUTHEAST WILL CONTINUE OVER MUCH OF MONTANA THROUGH THE END OF
THE WORK WEEK. SCATTERED AFTERNOON AND EVENING SHOWERS AND A FEW
THUNDERSTORMS WILL AFFECT SOUTHWEST MONTANA EACH DAY. THESE STORMS
WILL BE FUELED PRIMARILY BY WEAK INSTABILITY AND DEFORMATION ALOFT
BETWEEN AN UPPER LEVEL RIDGE TO THE NORTH AND A BROAD TROUGH ALONG
THE CALIFORNIA COAST. SHOWER AND THUNDERSTORM ACTIVITY WILL SPREAD
A BIT FURTHER NORTH EACH DAY AND SHOULD REACH SOUTHERN AND EASTERN
PORTIONS OF CENTRAL MONTANA BY FRIDAY. NOT SEVERE WEATHER IS
EXPECTED WITH THESE STORMS SINCE CAPE AND SHEAR ARE RELATIVELY
WEAK. HOWEVER, AFTERNOON HIGH TEMPERATURES WILL WARM SEVERAL
DEGREES EACH DAY WITH UPPER 60S TO MID 70S EXPECTED BY FRIDAY. MPJ

FRIDAY NIGHT THROUGH TUESDAY...DO NOT SEE ANY WEATHER SYSTEMS THAT
WOULD HAVE A WIDESPREAD NEGATIVE IMPACT ON TRAVEL OR OUTDOOR
ACTIVITIES OVER THE LONG HOLIDAY WEEKEND. THERE WILL BE SEVERAL
UPPER LOWS TO CONTEND WITH DURING THE PERIOD BUT ALMOST ALL OF THEM
WILL NOT BE OVER THE FORECAST AREA. MODELS ARE IN BETTER AGREEMENT
TONIGHT WITH THEIR HANDLING THESE UPPER LOWS. ON SATURDAY ONE UPPER
LOW WILL BE OVER FAR SOUTHEAST MONTANA WITH ANOTHER OVER THE GREAT
BASIN AND A THIRD IN THE VICINITY OF THE PACIFIC NORTHWEST. NONE
WILL HAVE MUCH BEARING ON OUR FORECAST AREA. SCATTERED SHOWERS AND
POSSIBLY A FEW THUNDERSTORMS WILL BE DUE PRIMARILY TO UPSLOPE FLOW.
ON SUNDAY AN UPPER LOW WILL BE OVER THE WESTERN DAKOTAS WITH ANOTHER
IN THE AREA FROM NORTHERN CALIFORNIA TO TO OREGON. THERE MIGHT BE A
LITTLE LESS SHOWER ACTIVITY THEN ON SATURDAY. ON MEMORIAL DAY AN
UPPER LOW IS FORECAST TO BE OVER THE GREAT BASIN WHICH COULD LEAD TO
SCATTERED SHOWERS OR THUNDERSTORMS OVER SOUTHWEST MONTANA. FARTHER
NORTH MODELS DIFFER WITH THE GFS HAVING AN UPPER TROUGH OVER CENTRAL
MONTANA AND SCATTERED SHOWERS IN THAT SAME AREA. THE ECMWF ON THE
OTHER HAND DOES NOT SHOW THIS FEATURE AND IS DRY. TUESDAY
DIFFERENCES CONTINUE WITH THE UPPER AIR PATTERN AS THE ECMWF HAS AN
UPPER LOW OVER SOUTHERN IDAHO WITH SHOWERS OR THUNDERSTORMS FOR
SOUTHWEST MONTANA. THE GFS ON THE OTHER HAND HAS AN UPPER RIDGE OVER
IDAHO AND WESTERN MONTANA BUT DUE TO PRIMARILY TERRAIN EFFECTS HAS
SCATTERED SHOWERS OR THUNDERSTORMS MAINLY OVER THE WESTERN
MOUNTAINS. SEASONABLE HIGH TEMPERATURES M0STLY IN THE 60S CAN BE
EXPECTED OVER THE HOLIDAY WEEKEND. BLANK

&&

.AVIATION...
UPDATED 2320.

MOSTLY CLEAR SKIES AND WIDESPREAD VFR CONDITIONS WILL CONTINUE OVER
CENTRAL AND NORTH CENTRAL MONTANA THROUGH THURSDAY. PARTLY TO MOSTLY
CLOUDY SKIES WITH VFR CONDITIONS WILL PREVAIL ACROSS SOUTHWEST
MONTANA. SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ARE EXPECTED
IN FAR SOUTHWEST MONTANA DURING THE AFTERNOON AND EVENING HOURS.
GUSTY SURFACE WINDS OF 10 TO 20 MPH FROM THE EAST/SOUTHEAST WILL
DIMINISH BY ABOUT 02Z THURSDAY...AND GUST AGAIN THURSDAY AFTERNOON
AT KHVR.
DB/MPJ

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  38  69  43  71 /   0  10  10  20
CTB  34  67  38  69 /   0   0  10  10
HLN  43  70  46  73 /  10  30  30  30
BZN  39  66  40  70 /  20  30  30  40
WEY  32  60  32  63 /  40  50  30  60
DLN  41  64  42  68 /  30  50  50  50
HVR  35  71  38  73 /   0   0   0  10
LWT  37  66  41  68 /   0   0  10  30

&&

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

$$

WEATHER.GOV/GREATFALLS


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