Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 051758
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1155 AM MDT SUN JUL 5 2015

AVIATION SECTION UPDATED

.UPDATE...WIDESPREAD OVERCAST SKIES COVER MOST OF THE FORECAST
AREA THIS MORNING EXCEPT FOR PARTLY CLOUDY CONDITIONS OVER FAR
SOUTHWEST MT. BANDS OF DRIZZLE AND LIGHT RAIN ARE ALSO OCCURRING
ACROSS THE HILINE AND PARTS OF CENTRAL MT. AS EXPECTED,
TEMPERATURES ARE SIGNIFICANTLY COOLER WITH CURRENT TEMPS RANGING
FROM THE UPPER 40S NEAR CUT BANK TO THE LOW 60S NEAR DILLON, WITH
MUCH OF THE REGION IN THE LOW-MID 50S. ALL THIS WEATHER IS
ASSOCIATED WITH AN UPPER-LEVEL TROF THAT IS MAKING EASTWARD
PROGRESS THROUGH THE NORTHERN ROCKIES TODAY. SKIES HAVE ALREADY
BEGUN TO CLEAR WEST OF THE DIVIDE AND THIS CLEARING WILL MOVE INTO
OUR AREA BY LATE AFTN/EVE. GOING FORECAST IS IN GOOD SHAPE; JUST MADE
SOME MINOR ADJUSTMENTS TO INCREASE RAIN CHANCES AND AMOUNTS FOR
LOCATIONS FROM GREAT FALLS NORTH TO THE US/CAN BORDER TO BETTER
MATCH CURRENT RADAR IMAGERY.
WARANAUSKAS

&&

.AVIATION... UPDATED 1755Z. MIX OF VFR TO IFR CONDITIONS ACROSS
CENTRAL AND SOUTHWEST MT THIS AFTN AS AN UPPER-LEVEL TROF CONTINUES
TO MOVE SLOWLY EASTWARD ACROSS THE STATE.  LOWEST CEILING CONDITIONS
ARE MOSTLY ASSOCIATED WITH BANDS OF DRIZZLE/LIGHT RAIN FROM KGTF
NORTH TO US/CAN BORDER.  AS TROF AXIS MOVES INTO SOUTHWEST MT LATER
THIS AFTN THERE WILL BE A CHANCE FOR ISOLATED -TSRA VCNTY KBZN.
SHOULD SEE GRADUAL IMPROVEMENT BACK TO VFR ACROSS THE REGION THIS
EVE AS THE TROF SWINGS INTO EASTERN MT.  WINDS REMAINING AT/BELOW 15
KTS TODAY.
WARANAUSKAS

&&

.PREV DISCUSSION...
/ISSUED 550 AM MDT SUN JUL 5 2015/
TODAY THROUGH TUESDAY...THE COLD FRONT HAS PUSHED NEARLY AS FAR
SOUTH AS BOZEMAN AT THIS TIME. GUSTY NORTH WINDS WILL ACCOMPANY
THE FRONT`S PASSAGE FOR A FEW HOURS. SHOWERS AND THUNDERSTORMS
CONTINUE TO DEVELOP ACROSS MUCH OF NORTH CENTRAL MONTANA AND ALONG
THE HI-LINE WHERE SEVERE THUNDERSTORMS WERE REPORTED EARLIER THIS
EVENING. SCATTERED SHOWERS AND THUNDERSTORMS THIS MORNING WILL
GRADUALLY DECREASE AND BECOME ISOLATED DURING THE AFTERNOON. MUCH
COOLER AIR WILL MOVE OVER THE AREA IN THE WAKE OF THE FRONTAL
PASSAGE AND SATELLITE IMAGERY INDICATES A LARGE AREA OF LOW CLOUDS
WILL PUSH ACROSS THE AREA THROUGH THE MORNING. SHOWERS GRADUALLY
END FROM THE NORTH OVERNIGHT TONIGHT WITH SKIES CLEARING. DRY
NORTHWEST FLOW ALOFT RETURNS MONDAY THOUGH ENOUGH INSTABILITY
WILL PERSIST FOR ISOLATED AFTERNOON SHOWERS OVER THE SOUTHWEST
MOUNTAINS. BY TUESDAY, SHORT WAVE ENERGY, ALONG WITH A CANADIAN
COLD FRONT, WILL COMBINE TO BRING SCATTERED SHOWERS AND
THUNDERSTORMS TO THE AREA DURING THE AFTERNOON. TEMPERATURES WILL
BE 15 TO 20 DEGREES COOLER THAN SEASONAL AVERAGES TODAY BUT WILL
REBOUND TO NEAR 80 DEGREES MONDAY AND TUESDAY.

TUESDAY NIGHT THROUGH SUNDAY...A PASSING SHORTWAVE TROUGH IN A MOIST
NORTHWESTERLY FLOW ALOFT WILL COMBINE WITH NORTHERLY UPSLOPE SURFACE
WINDS TO BRING A CHANCE OF SHOWERS AND THUNDERSTORMS TO THE AREA
TUESDAY NIGHT, ESPECIALLY ALONG THE NORTH AND EAST FACING SLOPES.
THE FLOW ALOFT WILL THEN TRANSITION TO WESTERLY ON WEDNESDAY THEN
SOUTHWESTERLY ON THURSDAY AS AN UPPER LEVEL LOW MOVES ONSHORE INTO
CALIFORNIA. THIS WILL KEEP A CHANCE OF MAINLY AFTERNOON AND EVENING
SHOWERS AND THUNDERSTORMS OVER THE MOUNTAIN AREAS. THIS UPPER LOW
THEN OPENS UP INTO A SHORTWAVE TROUGH, BUT THE FORECAST MODELS
DIFFER ON THE SPEED OF THIS SHORTWAVE MOVING INTO MONTANA. THE GFS
IS THE FASTER OF THE TWO MODELS (AND IS FASTER THAN LAST NIGHT`S
MODEL RUN), BRINGING THE SHORTWAVE INTO THE STATE FRIDAY
AFTERNOON/EVENING. THE ECMWF MOVES IT IN ON SATURDAY AND IS A BIT
MORE SHALLOW WITH THE SHORTWAVE THAN THE GFS. THERE IS ALSO A
DIFFERENCE IN THE PLACEMENT OF THE SHORTWAVE. THE GFS MOVES IT ALONG
THE SOUTHERN MONTANA BORDER, WHILE THE ECMWF KEEPS IT ALONG THE
NORTHERN BORDER. BECAUSE OF BOTH THE TIMING AND PLACEMENT
DISCREPANCY, HAVE DECIDED TO GO WITH CHANCES OF SHOWERS AND
THUNDERSTORMS FRIDAY THROUGH SATURDAY SIMILAR TO CLIMATOLOGICAL
NORMALS. THE MODELS AGREE ON BUILDING AN UPPER LEVEL RIDGE OF HIGH
PRESSURE INTO THE STATE ON SUNDAY, SO HAVE GONE WITH A DECREASING
CHANCE OF SHOWERS AND THUNDERSTORMS TO END THE PERIOD. TEMPERATURES
WILL GRADUALLY WARM FROM ABOUT 5 DEGREES ABOVE NORMAL ON WEDNESDAY
TO AROUND 10 TO 15 DEGREES ABOVE NORMAL ON FRIDAY, THEN THE PASSAGE
OF THE SHORTWAVE WILL COOL TEMPERATURES BACK DOWN TO AROUND 5
DEGREES ABOVE NORMAL FOR SATURDAY THROUGH SUNDAY. COULSTON

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  63  43  77  50 /  80   0   0  10
CTB  64  40  74  47 /  80   0   0  20
HLN  70  50  82  56 /  30  10   0  10
BZN  73  47  79  49 /  20  20  10  10
WEY  74  39  74  41 /  40  40  10  20
DLN  78  49  80  51 /  30  20  10  10
HVR  70  45  75  48 /  80   0   0   0
LWT  61  45  74  51 /  50  20  10  10

&&

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

$$

WEATHER.GOV/GREATFALLS



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