Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 060257
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
857 PM MDT SUN JUL 5 2015

.UPDATE...FORECAST HAS BEEN UPDATED TO ADD AREAS OF FOG AND
DRIZZLE TO MUCH OF NORTH CENTRAL MONTANA OVERNIGHT. HAVE ALSO
INCREASED POPS A BIT AS RADAR CONTINUES TO SHOW WEAK ECHOES ACROSS
NORTH CENTRAL MONTANA ALONG WITH SCATTERED SHOWERS AND
THUNDERSTORMS IN THE SOUTHWEST. MODELS CONTINUE TO SHOW
PRECIPITATION EXITING THE FORECAST AREA OVERNIGHT BUT FOG AND
DRIZZLE WILL LIKELY KEEP MANY AREAS WET AND CLOUDS WILL BE SLOWER
TO EXIT THAN EARLIER EXPECTED. HAVE ALSO MADE SOME TWEAKS TO
OVERNIGHT LOWS BASED ON CURRENT TEMPERATURES. THIS MAINLY AFFECTED
LOW POPULATION RURAL AREAS AND DID NOT APPEAR TO CHANGE ANY CITIES
OR SPOTS NORMALLY COVERED BY THE MEDIA. MPJ

&&

.AVIATION... UPDATED 2350Z.

UPPER LEVEL TROUGH CURRENTLY OVER WESTERN MONTANA SWEEPS SOUTHEAST
OVERNIGHT LEAVING THE FORECAST AREA BENEATH A GENERALLY DRY
NORTHWEST FLOW ALOFT BY 18Z MONDAY. LOW CLOUDS AND FOG WILL PERSIST
ACROSS NORTH CENTRAL MONTANA OVERNIGHT WITH WIDESPREAD IFR/MVFR
CONDITIONS EXPECTED TO IMPROVE AFTER 14Z. SCATTERED SHOWERS AND
THUNDERSTORMS SOUTH OF A LINE FROM KHLN TO KLWT THROUGH 06Z. MPJ

 &&

&&

.PREV DISCUSSION...
/ISSUED 550 PM MDT SUN JUL 5 2015/
TONIGHT THROUGH TUESDAY...AN UPPER LEVEL DISTURBANCE WILL CONTINUE
TO MOVE SLOWLY SOUTHEASTWARD THRU THE REGION TONIGHT. EXPECT
LIGHT RAIN TO CONTINUE INTO THE EVENING HOURS OVER NORTH CENTRAL
MT. AN ISOLATED RUMBLE OF THUNDER IS ALSO POSSIBLE...ESPECIALLY
NEAR THE DIVIDE. THE CLOUDS CONTINUE TO RESIDE OVER THE NORTH ON
MONDAY MORNING...BEFORE DECREASING DURING THE AFTERNOON HOURS.
OVER THE SOUTHWEST...A FEW THUNDERSTORMS WILL ROTATE AROUND AN
UPPER LEVEL LOW. A FEW OF THESE STORMS WILL AFFECT AREAS MAINLY
NEAR THE MT/ID BORDER ON MONDAY. FOR TUESDAY...THE FLOW ALOFT WILL
BE NORTHERLY AS AN UPPER LEVEL DISTURBANCE WORKS ITS WAY SOUTHWARD
INTO THE REGION. THE CHANCES FOR SCATTERED SHOWERS/THUNDERSTORMS
WILL BE ON THE INCREASE AS WELL DURING THE AFTERNOON HOURS.
TEMPERATURES WILL REBOUND A BIT ON MONDAY AS SKIES CLEAR OUT A BIT
BY THE AFTERNOON HOURS. ON TUESDAY...THE WARMING TREND
CONTINUES...WITH AFTERNOON HIGHS NEAR NORMAL IN MANY AREAS. BRUSDA

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  42  77  50  79 /  20   0  10  40
CTB  41  74  48  75 /  10   0  10  30
HLN  51  82  56  84 /  30   0  10  30
BZN  48  79  49  81 /  30  10  10  30
WEY  41  73  41  72 /  70  10  20  30
DLN  50  78  52  80 /  40  10  10  20
HVR  44  76  48  81 /  30   0   0  20
LWT  45  74  50  78 /  70  10   0  30

&&

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

$$

WEATHER.GOV/GREATFALLS


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