Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 310916
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
316 AM MDT FRI JUL 31 2015

.DISCUSSION...

TODAY THROUGH SUNDAY...CLEAR SKIES PREVAIL OVER MT THIS MORNING
WITH A BROAD RIDGE OF HIGH PRESSURE SITUATED OVER THE INTERIOR
WESTERN U.S.. TEMPERATURES TREND WARMER AS THIS PATTERN PERSISTS
THROUGH SATURDAY. DEEP LAYER MIXING WILL OCCUR BOTH DAYS WITHIN A
THERMAL TROUGH. THIS MIXING WILL RAISE FIRE WEATHER CONCERNS WITH
BREEZY DAYTIME WINDS AND LOW AFTERNOON RELATIVE HUMIDITY. CONCERNS
ARE HEIGHTENED SATURDAY AFTERNOON AS MODELS DEVELOP A SUBTLE WAVE
IN THE LOWER TROPOSPHERIC FLOW THAT WILL INCREASE WINDS WITH A
WEAK SURFACE PRESSURE GRADIENT ACROSS CENTRAL MT. TEMPERATURES
TREND A FEW DEGREES COOLER ON SUNDAY AS MONSOONAL MOISTURE BEGINS
TO ENCROACH SOUTHWEST MT PRODUCING ISOLATED MOUNTAIN
THUNDERSTORMS. NUTTER

SUNDAY NIGHT THROUGH FRIDAY...SUNDAY NIGHT AND MONDAY A STRONG UPPER
RIDGE WILL BE OVER THE FORECAST AREA. A WEATHER DISTURBANCE ALOFT
WILL BE APPROACHING FROM THE SOUTHWEST ON MONDAY AND MONSOONAL
MOISTURE WILL INCREASE AHEAD OF THE DISTURBANCE. SCATTERED
THUNDERSTORMS WILL DEVELOP FROM THE ROCKY MOUNTAIN FRONT INTO
SOUTHWEST MONTANA MONDAY AFTERNOON THEN SPREAD NORTHEAST MONDAY
NIGHT INTO TUESDAY. THE GFS MODEL CONTINUES TO BE WEAKER AND FASTER
WITH THE WEATHER DISTURBANCE ALOFT THAN THE ECMWF MODEL. OTHER
DISTURBANCES EMBEDDED IN A SOUTHWEST FLOW ALOFT THROUGH THE END OF
THE WEEK WILL AIDE IN BRINGING ADDITIONAL THUNDERSTORMS TO THE
FORECAST AREA THROUGH THE WEEK. THE GFS AND ECMWF MODELS ARE IN A
LITTLE BETTER AGREEMENT WITH THEIR PRECIPITATION FORECASTS THAN
EARLIER RUNS SO HAVE RAISED THE CHANCES OF PRECIPITATION A BIT FROM
THOSE OF THE INHERITED FORECAST. THE STRONG UPPER RIDGE WILL RESULT
IN HIGHS IN THE UPPER 80S TO LOWER 90S MONDAY BUT THE UPPER RIDGE
WILL THEN WEAKEN SO TUESDAY WILL USHER IN A SPELL OF COOLER
TEMPERATURES. BLANK

&&

.AVIATION...
UPDATED 0525Z.

THERE WILL BE VFR CONDITIONS WITH MAINLY CLEAR SKIES. CONFIDENCE IN
WIND FORECASTS IS ABOVE AVERAGE. BLANK

&&

.FIRE WEATHER...
TEMPERATURES WILL CONTINUE TO INCREASE THIS AFTERNOON AND ON
SATURDAY AS HIGH PRESSURE STRENGTHENS OVER THE REGION. AFTERNOON
HUMIDITY WILL BE IN THE TEENS FRIDAY LOW TEENS SATURDAY WITH
OVERNIGHT HUMIDITY RECOVERY AT MID SLOPES AND RIDGETOPS BECOMING
INCREASINGLY POOR THROUGH THE WEEKEND. AFTERNOON INSTABILITY
COMBINED WITH THE DRY CONDITIONS WILL RESULT IN HAINES INDEX
VALUES OF 5 OR 6 SATURDAY AFTERNOON AND A PERIOD OF BREEZY WINDS
WITH GUSTS AROUND 20 MPH IS POSSIBLE, PARTICULARLY OVER WESTERN
PORTIONS OF NORTH CENTRAL MT. THE UPPER LEVEL RIDGE OF HIGH
PRESSURE WEAKENS SOME SUNDAY AND MONDAY WITH HUMIDITY AND
TEMPERATURES LIKELY TO MODERATE SOME EARLY NEXT WEEK. HOWEVER A
WEAK WEATHER SYSTEM MOVING INTO THE REGION FROM THE SW WILL BRING
A CHANCE FOR THUNDERSTORMS LATE MONDAY AND THE INCREASE IN
LIGHTNING AND POTENTIAL FOR GUSTY THUNDERSTORM WINDS FOLLOWING
THIS PERIOD OF VERY WARM AND DRY CONDITIONS MAY LEAD TO ADDITIONAL
FIRE WEATHER CONCERNS ON MONDAY. HOENISCH

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  92  58  95  57 /   0   0   0   0
CTB  93  55  94  53 /   0   0   0   0
HLN  94  57  97  57 /   0   0   0   0
BZN  91  53  92  54 /   0   0   0   0
WEY  82  40  83  42 /   0   0   0   0
DLN  88  51  89  54 /   0   0   0   0
HVR  92  56  96  56 /   0   0   0   0
LWT  90  56  93  57 /   0   0   0   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
FIRE WEATHER WATCH FROM SATURDAY AFTERNOON THROUGH SATURDAY
EVENING FOR MTZ112 AND MTZ114.

&&

$$

WEATHER.GOV/GREATFALLS



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