Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 280555
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1155 PM MDT MON JUL 27 2015

UPDATED AVIATION SECTION

.DISCUSSION...
RADAR IMAGERY HAS SHOWN THAT PRECIPITATION HAS TAPERED
OFF ACROSS PORTI0NS OF THE FORECAST AREA THIS EVENING. HOWEVER,
LATEST MODEL RUNS CONTINUE TO SHOW WIDESPREAD RAIN (AND SOME
MOUNTAIN SNOW) OVERNIGHT. HAVE OPTED TO UPDATE THE FORECAST UNDER
THE ASSUMPTION THAT THE MODELS ARE MOVING OUT THE UPPER LEVEL
TROUGH ABOUT 4 TO 8 HOURS SLOWER THAN WHAT ACTUALLY APPEARS TO BE
HAPPENING. HAVE THEREFORE USED FUTURE MODEL POP/QPF TIMES AND
BLENDED THEM WITH THE GOING FORECAST TO MOVE PRECIPITATION OUT
FASTER. TEMPERATURES AND WIND GRIDS CONTINUE TO LOOK REASONABLE SO
DID NOT MAKE ANY CHANGES TO THESE PARAMETERS. IF THIS SOLUTION
WORKS OUT FAVORABLY AM EXPECTING THAT WIDESPREAD PRECIPITATION
SHOULD BE OVER WITH BY EARLY TOMORROW AFTERNOON. MPJ

&&

.AVIATION...
UPDATED 0555Z.
WRAP AROUND CIRCULATION FROM A DISTURBANCE ALOFT OVER NORTHEAST
MONTANA CONTINUES TO BRING RAIN AND LOW CLOUDS TO MOST OF NORTHERN
AND CENTRAL MONTANA. CONDITIONS WILL SLOWLY IMPROVE FROM SOUTHWEST
TO NORTHEAST OVERNIGHT AS PRECIPITATION ENDS. PRECIPITATION SHOULD
END OVER THE EASTERN PORTION OF THE AREA BY EARLY AFTERNOON.
MVFR/IFR CONDITIONS PREVAIL DUE TO LOW CEILINGS AND PRECIPITATION.
VFR CONDITIONS WILL PREVAIL AFTER 18Z. SURFACE WINDS WILL
BE GUSTY THROUGH 00Z. MOUNTAINS OBSCURED THROUGH 18Z.

&&

.HYDROLOGY...
AREAS OF RAIN WILL CONTINUE TO MOVE ACROSS THE AREA THROUGH EARLY
TUESDAY. THIS SETUP IS SIMILAR TO A LATE WINTER EARLY SPRING
SYSTEM WHERE SOME FLOOD PRONE LOCATIONS...LIKE THE NORTH SLOPES OF
THE BEARS PAW MOUNTAINS... HIGHWOODS... AND LITTLE BELTS MAY
EXPERIENCED PROLONGED PERIODS OF ENHANCED PRECIPITATION. BECAUSE
CONDITIONS AHEAD OF THE SYSTEM HAVE BEEN DRY THERE IS A HIGH
CONFIDENCE THAT THE SOILS WILL BE ABLE TO ABSORB A SIGNIFICANT
AMOUNT OF MOISTURE...HOWEVER IF RAINFALL RATES OVERWHELM SOIL
ABSORPTION RATES SOME MINOR FLOODING COULD OCCUR ESPECIALLY IN
LOCATIONS LIKE SMALL STREAMS AND FIRE BURN SCARS.

&&

.PREV DISCUSSION...
/ISSUED 531 PM MDT MON JUL 27 2015/

TONIGHT THROUGH WEDNESDAY...WATER VAPOR IMAGERY REVEALS A CLOSED
UPPER LEVEL CIRCULATION OVER THE NORTHERN IDAHO PANHANDLE. STEADY
RAIN HAS SPREAD ACROSS MUCH OF CENTRAL AND SOUTHWEST MONTANA AMID
A FAVORABLE SYNOPTIC ENVIRONMENT FOR ASCENT. ISOLATED
THUNDERSTORMS ARE FORMING ALONG THE MORE UNSTABLE AIRMASS AT THE
LEADING EDGE OF THE STRATIFORM PRECIPITATION. ALTHOUGH MOST
THUNDERSTORMS ARE NOW MOVING INTO EASTERN MT...ISOLATED
THUNDERSTORMS REMAIN POSSIBLE WITH STEEPENING MID LEVEL LAPSE
RATES AS THE UPPER TROUGH AXIS MOVES ACROSS THE ZONES. RAINFALL
ASSOCIATED WITH THE DEEPENING WEATHER SYSTEM IS FORECAST TO WRAP
AROUND ON A STRENGTHENING NORTHERLY FLOW TONIGHT. RAINFALL AMOUNTS
EXCEEDING 1.3 INCHES ARE POSSIBLE OVER HILL AND BLAINE COUNTIES. A
FLASH FLOOD WATCH HAS BEEN ISSUED TO COVER THE POSSIBILITY OF
LOCALLY HEAVY RAINFALL OVERWHELMING THE ABILITY OF SOIL TO ABSORB
THE MOISTURE. ANY FLOOD IMPACTS IN THESE AREAS ARE EXPECTED TO BE
BRIEF AND LOCALIZED. PRECIPITATION ENDS FROM WEST TO EAST EARLY
TUESDAY AS SYNOPTIC SUBSIDENCE INITIATES CLEARING TUESDAY NIGHT
AND WEDNESDAY. NUTTER

WEDNESDAY NIGHT THROUGH MONDAY...MEDIUM RANGE PERIOD LOOKS GENERALLY
QUIET AND DRY WITH ZONAL FLOW ALOFT OVER THE AREA. MONSOONAL
MOISTURE MAKES ITS WAY OVER SOUTHWEST MONTANA BEGINNING SATURDAY
ALLOWING FOR THE POSSIBILITY OF ISOLATED MOUNTAIN THUNDERSTORMS.
MONSOONAL MOISTURE CONTINUES TO INVADE SOUTHWEST MONTANA SUNDAY WITH
SCATTERED THUNDERSTORMS DEVELOPING DURING THE AFTERNOON AND EVENING
HOURS. AT THE SAME TIME, WEAK SHORT WAVE ENERGY MOVES ALONG THE
INTERNATIONAL BOUNDARY PRODUCING ISOLATED CONVECTIVE ACTIVITY ALONG
THE HI-LINE. MODEL SOLUTIONS DIVERGE SIGNIFICANTLY MONDAY WITH THE
GFS MAINTAINING WESTERLY FLOW ALOFT AND WEAK IMPULSES ACROSS
SOUTHERN CANADA. THE EUROPEAN DEVELOPS AN UPPER RIDGE OVER WESTERN
MONTANA. HAVE GONE WITH A GENERALLY DRY SOLUTION MONDAY, THE
EXCEPTION BEING SOUTHWEST MONTANA WHERE ISOLATED THUNDERSTORMS ARE
STILL POSSIBLE. TEMPERATURES WILL BE NEAR TO SLIGHTLY ABOVE SEASONAL
AVERAGES THROUGH THE PERIOD.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  50  71  52  80 /  60  20   0   0
CTB  50  72  50  79 /  40  10   0   0
HLN  46  72  50  82 /  50  20   0   0
BZN  46  71  48  80 /  60  20   0   0
WEY  32  63  32  72 /  60  20   0   0
DLN  39  69  44  78 /  30  10   0   0
HVR  53  73  51  82 /  90  50  10   0
LWT  49  69  49  78 /  90  60  10   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH THROUGH TUESDAY MORNING FOR MTZ011-013-047.

&&

$$

WEATHER.GOV/GREATFALLS


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