Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 211611
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1011 AM MDT THU MAY 21 2015

.DISCUSSION...HAVE OPTED TO NOT MAKE ANY UPDATES THIS MORNING AS
THE GOING FORECAST APPEARS TO BE IN EXCELLENT SHAPE. SCATTERED
SHOWERS AND THUNDERSTORMS WILL DEVELOP OVER SOUTHWEST AND SOUTH
CENTRAL MONTANA THIS AFTERNOON AND MOVE INTO SOUTHERN PORTIONS OF
CENTRAL MONTANA BY EVENING. CONVECTION WILL BE DRIVEN BY DIURNAL
INSTABILITY SO EXPECT THAT PRECIPITATION WILL TAPER OFF RAPIDLY
AFTER SUNSET. ALSO DO NOT EXPECT THAT ANY STORMS WILL BECOME
STRONG TO SEVERE AS INSTABILITY AND SHEAR ARE WEAK. HOWEVER, ANY
STORMS THAT DO FORM COULD PRODUCE SOME LOCALLY HEAVY RAIN. MPJ

&&

.AVIATION... UPDATED 1050Z. VFR CONDITIONS ARE ONCE AGAIN EXPECTED.
CLEAR SKIES TO A FEW CLOUDS AROUND 12000 FT CAN BE EXPECTED NEAR AND
NORTH OF A LINE FROM KLWT THROUGH KGTF. SOUTH OF THAT LINE EXPECT
ISOLATED SHOWERS THIS MORNING WITH SCATTERED SHOWERS BUT NUMEROUS
SHOWERS OVER THE MOUNTAINS THIS AFTERNOON. ALSO EXPECT SCATTERED
THUNDERSTORMS THIS AFTERNOON. GUSTY WINDS TO NEAR 40 KTS CAN BE
EXPECTED WITH A FEW OF THE THUNDERSTORMS. SHOWERS AND THUNDERSTORMS
WILL MOSTLY DISSIPATE NEAR AND AFTER MIDNIGHT. CONFIDENCE IN
FORECAST WINDS IS ABOVE AVERAGE. BLANK

&&

.PREV DISCUSSION...
/ISSUED 450 AM MDT THU MAY 21 2015/
THURSDAY THROUGH SATURDAY...
SHOWERS AND THUNDERSTORMS WILL BECOME MORE PREVALENT OVER THE NEXT
FEW DAYS AS MOISTURE FROM A LOW PRESSURE SYSTEM MOVING ACROSS THE
SOUTHERN US IS EJECTED UP INTO FROM THE SOUTH. THE SYSTEM LOOKS TO
STAY FAR ENOUGH TO THE SOUTH TO ELIMINATE THE CHANCE OF A
WIDESPREAD WETTING RAIN...INSTEAD AFTERNOON SHOWERS AND
THUNDERSTORMS LOOK TO DEVELOP EACH AFTERNOON AND SHOULD INCREASE
IN COVERAGE OF THE AREA THROUGH THE FIRST HALF OF THE WEEKEND.
RELATIVELY WEAK SHEAR WILL LIMIT THE CHANCES FOR ANY OF THE
SHOWERS OR THUNDERSTORMS TO DEVELOP INTO SEVERE STORMS...BUT
STRONG STORMS ARE POSSIBLE AND COULD PRODUCE SMALL HAIL AND GUSTY
WINDS ALONG WITH BRIEF HEAVY RAINFALL. MODELS SUGGEST THAT THERE
IS ENOUGH WIND ALOFT TO ALLOW FOR STORMS TO MOVE OFF OF ANY
INITIATION POINT AND THIS SHOULD LIMIT THE POTENTIAL FOR LONG
DURATION HEAVY RAINS FROM NEARLY STATIONARY STORMS. TEMPERATURES
ARE EXPECTED TO BE NEAR OR SLIGHTLY ABOVE SEASONAL AVERAGES
THROUGH FRIDAY WITH ONLY A SLIGHT COOLDOWN TO SEASONAL AVERAGES ON
SATURDAY. WINDS SHOULD BE LIGHT AND EASTERLY AGAIN TODAY...WITH
SOME LOCATIONS BECOMING GUSTY IN THE AFTERNOON...ESPECIALLY NEAR
ANY SHOWER OR THUNDERSTORM. SUK

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 MOSTLY IN THE 60S CAN BE
EXPECTED OVER THE HOLIDAY WEEKEND. BLANK

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  69  42  70  47 /  20  10  20  30
CTB  68  38  69  41 /   0   0  10  10
HLN  70  45  71  49 /  40  30  30  30
BZN  66  40  69  43 /  50  20  40  30
WEY  59  32  62  35 /  60  40  60  40
DLN  64  41  67  44 /  70  50  40  40
HVR  71  38  74  43 /   0   0  10  30
LWT  66  42  68  45 /   0  10  40  50

&&

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

$$

WEATHER.GOV/GREATFALLS


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