Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 020553
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1155 PM MDT TUE SEP 1 2015

.UPDATE...
ANOTHER QUIET WEATHER NIGHT ACROSS CENTRAL AND SOUTHWEST MT...NO
FORECAST ADJUSTMENTS NEEDED THIS EVENING. SKIES ARE MOSTLY CLEAR
EXCEPT FOR SOME PATCHY MID- AND HIGH- LEVEL CLOUDS FROM DILLON TO
LEWISTOWN AND SECOND AREA FROM CUT BANK TO SWEETGRASS. WE WILL SEE
HIGH CLOUD COVER GRADUALLY INCREASE FROM THE WEST OVERNIGHT AS
LATEST SATELLITE IMAGERY SHOWS LEADING EDGE OF MOISTURE FROM A
WEATHER SYSTEM MOVING THROUGH WA/BC IS ALREADY IN FAR WESTERN MT,
BUT NO PRECIPITATION IS EXPECTED THROUGH TONIGHT AND WED MORNING.
WARANAUSKAS

&&

.AVIATION...
UPDATED 0555Z.

VFR CONDITIONS WILL PREVAIL AT ALL TAF SITES. LIGHT WINDS OVERNIGHT
WILL MIX WITH GUSTY WINDS BY 18Z AT MOST SITES BEFORE DECREASING
AROUND SUNSET.  SOME LEE SIDE MOUNTAIN WAVE TURBULENCE WILL AGAIN BE
POSSIBLE AT HIGHER ALTITUDES.

&&

.FIRE WEATHER...
RED FLAG WARNINGS CONTINUE ALONG THE ROCKY MTN
FRONT AND ADJACENT PLAINS UNTIL 9 PM THIS EVENING. A NEW RED FLAG
HAS ALSO BEEN ISSUED FOR PARTS OF SOUTHWEST MT (FIRE ZONE 118) FOR
NOON TO 9 PM WEDNESDAY.

LITTLE CHANGE IN CONDITIONS EXPECTED NEXT 24 HRS AS BROAD
SOUTHWEST FLOW ALOFT KEEPS THE REGION WARM AND DRY WITH BREEZY
DAYTIME WINDS. A PACIFIC WEATHER SYSTEM COMING ASHORE THIS
EVENING IN WASH/BR. COLUMBIA WILL MAKE SLOW EASTWARD PROGRESS
TOMORROW. LEADING EDGE OF SHOWERS FROM THIS SYSTEM MAY REACH THE
ROCKY MTN FRONT BY WED EVE, BUT MAIN MOISTURE PLUME WILL NOT
ARRIVE UNTIL THURS. BEST CHANCE FOR RAIN WILL BE ALONG THE ROCKY
MTN FRONT EAST TO THE LITTLE BELT MTNS WITH WETTING RAINS LOOKING
MORE LIKELY IN THAT AREA. PRECIPITATION WILL BE MORE SPOTTY WITH
ONLY LIGHT AMOUNTS (LESS THAN 0.1 INCH) FOR LOCATIONS EAST AND
NORTH OF THE LITTLE BELTS ON THURS.
WARANAUSKAS

&&

.PREV DISCUSSION...
/ISSUED 530 PM MDT TUE SEP 1 2015/
TONIGHT THROUGH THURSDAY...THE PERIOD WILL START OFF DRY WITH A WEST
TO SOUTHWEST FLOW ALOFT ONLY BRINGING SOME HIGH LEVEL CLOUDS. THE
FLOW ALOFT WILL THEN BACK TO THE SOUTHWEST AS AN UPPER TROUGH
DEVELOPS NEAR THE PACIFIC NORTHWEST COAST THURSDAY AFTERNOON.
WESTERLY WINDS WEDNESDAY WILL SHIFT TO THE NORTHWEST WEDNESDAY NIGHT
AS COOLER AIR MOVES OVER MOST OF THE AREA AND SETS UP A BOUNDARY
OVER SOUTHWEST MONTANA WITH SOMEWHAT WARMER AIR OVER FAR SOUTHWEST
MONTANA. DO NOT EXPECT ANY PRECIPITATION THROUGH WEDNESDAY BUT THEN
A BAND OF RAIN SETS UP OVER THE NORTHWEST PORTION OF THE FORECAST
AREA WEDNESDAY NIGHT AND CONTINUES INTO AT LEAST THURSDAY MORNING.
THEN FOR THURSDAY AFTERNOON INCREASED MOISTURE AND LIFT OVER THE
RELATIVELY COOLER AIR AND ALSO TERRAIN EFFECTS COULD LEAD TO SOME
SHOWERS OVER CENTRAL MONTANA. BLANK

THURSDAY NIGHT THROUGH TUESDAY...AN UPPER LEVEL LOW PRESSURE TROF
WILL BE OVER THE PACIFIC NORTHWEST THURSDAY NIGHT WITH THE LOW
BEGINNING TO CLOSE AND SLOWING DOWN. THE ASSOCIATED COLD FRONT WILL
BE CROSSING THE ZONES DURING THE NIGHT AND SHOULD BE WELL INTO
SOUTHWEST MONTANA BY MORNING...AND COOLER TEMPS WILL FOLLOW ON
FRIDAY. THE AIR MASS WILL MOISTEN WELL AHEAD OF THE TROF AND
THURSDAY NIGHT AND FRIDAY PRECIPITATION SHOULD BE RATHER
WIDESPREAD...AND MODELS HAVE INCREASED PRECIP VALUES AHEAD OF THE
TROF DURING THE PAST 24 HOURS. THE ECMWF AND GFS ARE QUITE SIMILAR
THROUGH 12Z SAT. BEYOND THIS POINT, THE ECMWF REMAINS A CLOSED LOW
WHILE THE GFS MOVES EAST AS AN OPEN WAVE. WITH THE SLOWER MOVEMENT
OF THE ECMWF, PRECIP WOULD START LATER AND TEMPERATURES WOULD BE
SLOWER TO COOL. WITH THE FASTER MOVEMENT, THE GFS BRINGS THE TROF
OVER THE IDAHO PANHANDLE SATURDAY NIGHT AND THE TROF IS BROADENED AS
A SHORTWAVE MOVES INTO THE TROF FROM THE WEST. THE MODELS DIFFER
HERE AS WELL. THE GFS SHORTWAVE IS MUCH WEAKER AND THE AIR MASS
BEGINS TO DRY SUNDAY NIGHT. THE DEEPER LOW OF THE ECMWF WOULD DELAY
MOVEMENT OF THE TROF EAST AND DELAY ANY DRYING OF THE AIR MASS UNTIL
MONDAY. THIS WOULD KEEP PRECIPITATION IN THE FORECAST LONGER AS WELL
AND KEEP TEMPERATURES COOLER INTO MONDAY. WITH THE MODEL
UNCERTAINTY, WILL REMAIN CAUTIOUS AND BLEND THROUGH THIS PERIOD. THE
AIR MASS WILL BE QUITE DRY AGAIN MONDAY NIGHT AND TUESDAY, HIGH
PRESSURE ALOFT WILL BE BUILDING, AND TEMPERATURES RISING BACK ABOVE
SEASONAL NORMALS. ZELZER

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  54  81  49  65 /   0   0  30  50
CTB  50  72  44  62 /   0   0  60  80
HLN  50  82  48  68 /   0  10  20  30
BZN  48  85  45  73 /   0   0  10  20
WEY  39  76  39  71 /   0   0  10  10
DLN  48  83  46  70 /   0   0  10  30
HVR  50  83  50  70 /   0   0  30  20
LWT  55  86  48  67 /   0   0  10  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...

RED FLAG WARNING FROM NOON TO 9 PM MDT WEDNESDAY FOR MTZ118.

&&

$$

WEATHER.GOV/GREATFALLS


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