Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 301135
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
530 AM MDT TUE JUN 30 2015

AVIATION SECTION UPDATED

.DISCUSSION...

TODAY THROUGH THURSDAY...A WEAK UPPER LEVEL DISTURBANCE IS
SUPPORTING SCATTERED SHOWERS WITH ISOLATED LIGHTNING OVER SOUTHWEST
MONTANA EARLY THIS MORNING. THIS ACTIVITY WILL CONTINUE TO DISSIPATE
OR MOVE EAST OF THE CWA BEFORE NOON. A MORE POTENT SHORTWAVE TROUGH
IS CROSSING THE NORTHERN ROCKIES AND FLATTENING THE BROAD WESTERN
RIDGE INTO A TIGHTER, MORE ZONAL FLOW ACROSS NORTHERN MONTANA. WATER
VAPOR IMAGERY REVEALS A SHARP TRANSITION TO DRIER AIR ALOFT AND
SUGGESTS STRONG SUBSIDENCE BEHIND THE TROUGH AXIS. THIS - ALONG WITH
A DEVELOPING LEE SURFACE TROUGH - WILL CAUSE WINDS OF 20 TO 30 MPH
TO MIX DOWN TO THE SURFACE WITH DAYTIME HEATING AND A DEEPENING DRY
BOUNDARY LAYER. MINIMUM RELATIVE HUMIDITY WILL DROP TO NEAR 20
PERCENT...ALTHOUGH ISOLATED AREAS COULD DIP INTO THE TEENS CAUSING
NEAR CRITICAL FIRE WEATHER CONDITIONS FOR A SHORT PERIOD THIS
AFTERNOON. WINDS WILL TAPER QUICKLY AFTER SUNSET THIS EVENING.
THE NEXT SHORTWAVE CUTS ACROSS NORTH CENTRAL MONTANA WITH
ADDITIONAL SHOWERS AND THUNDERSTORMS WEDNESDAY AFTERNOON. FAIR AND
DRY WEATHER PREVAILS ON THURSDAY. TEMPERATURES REMAIN WELL ABOVE
NORMAL...BUT THE STRETCH OF RECORD BREAKING HEAT HAS ENDED. NUTTER

THURSDAY NIGHT THROUGH TUESDAY. WESTERLY FLOW ALOFT
WILL KEEP CONDITIONS WARM AND DRY ACROSS MOST OF CENTRAL/SOUTHWEST
MT ON FRI/SAT.  BOTH GFS AND ECMWF MODELS STILL DEPICTING A
SHORTWAVE TROF AND ASSOCIATED SURFACE COLD FRONT TO MOVE THROUGH THE
HILINE AND CENTRAL COUNTIES ON SAT, BUT FRONT`S ARRIVAL IS A BIT
LATER (NOW EXPECTED SAT AFTN/EVE) THAN YESTERDAY`S MODELS RUNS
SUGGESTED. COVERAGE OF SHOWERS AND THUNDERSTORMS WITH THE FRONT
REMAINS SCATTERED AT BEST AND CONCENTRATED OVER LIBERTY/HILL/BLAINE
COUNTIES. MODEL SOLUTIONS BEGIN TO DIVERGE ON SUN WITH THE
DIFFERENCES CONTINUING INTO EARLY NEXT WEEK.  ALTHOUGH RAW MODEL AND
ENSEMBLES SHOW A HIGH PRESSURE CENTER PARKED OVER THE FOUR CORNERS
REGION, AGREEMENT IS CURRENTLY POOR ON HOW THE RIDGE WILL EVOLVE IN
OUR REGION.  THE GFS GENERALLY KEEPS TO ITS EARLIER SOLUTION IN
EXPANDING THE RIDGE AXIS THROUGH MT AND INTO SW CANADA WHILE
BRINGING MONSOONAL MOISTURE NORTHWARD FOR SCATTERED AFTN/EVE
THUNDERSTORMS PRIMARILY OVER SOUTHWEST MT FOR SUN-TUE.  THE ECMWF IS
CONSIDERABLY DRIER, LIMITING THE INFLUENCE OF THE RIDGE BY KEEPING
THE REGION IN THE SOUTHWEST FLANK OF A DEEP UPPER-LEVEL TROF IN
SOUTH-CENTRAL CANADA.  GIVEN THE REASONABLE CONTINUITY OF THE GFS
RUNS, CURRENT GRIDS INCLUDE A MENTION OF THUNDER ACROSS SOUTHWEST MT
AND TREND TEMPERATURES WARMER (BACK INTO THE UPPER 80S AND LOW 90S)
FOR THE START OF NEXT WEEK. WARANAUSKAS

&&

.AVIATION... UPDATED 1130Z.

LATEST RADAR/SATELLITE IMAGERY SHOWING LAST REMNANTS OF -SHRA
PUSHING PAST KBZN AND KLWT WITH SKIES STEADILY CLEARING FROM THE
WEST.  EXPECT VFR CONDITIONS ACROSS THE REGION TODAY. EXCEPTION IS
IFR/MVFR VISIBILITIES AT KHVR DUE TO SMOKE FROM CANADIAN WILDLAND
FIRES. SHOULD SEE IMPROVEMENT IN SITUATION THERE LATER THIS MORNING
WHEN WINDS SHIFT TO WEST-SOUTHWEST. WESTERLY SURFACE WINDS WILL BE
BREEZY THIS AFTN WITH GUSTS 25-30 KTS ALONG A KHLN-TO-KLWT LINE AND
NORTH TO US/CAN BORDER. WARANAUSKAS

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  91  59  88  57 /  10  10  10  10
CTB  86  54  82  51 /  10  10  30  20
HLN  94  62  93  61 /  10  10  10  10
BZN  91  52  90  50 /  10  10  10  10
WEY  82  44  81  41 /  20  10  10  10
DLN  89  56  88  53 /  10  10  10   0
HVR  92  58  87  56 /  10  10  40  20
LWT  89  57  86  55 /  10  10  10  10

&&

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

$$

WEATHER.GOV/GREATFALLS


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