Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 071129
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
525 AM MDT TUE JUL 7 2015

UPDATED AVIATION DISCUSSION

.DISCUSSION...

TODAY THROUGH THURSDAY...ISOLATED SHOWERS AND THUNDERSTORMS HAVE
ALREADY DEVELOPED ALONG THE CANADIAN BORDER ALONG THE LEADING
EDGE OF A SHORTWAVE TROUGH WITH ITS ASSOCIATED WEAK CANADIAN COLD
FRONT. AS THIS FRONT MOVES SOUTH THROUGH THE AREA TODAY, THE
COVERAGE OF SHOWERS AND THUNDERSTORMS WILL INCREASE OVER NORTH
CENTRAL AND SOUTHWEST MONTANA FROM THE NORTH AS THE AIRMASS
BECOMES MORE UNSTABLE. WITH PRECIPITABLE WATER VALUES AROUND 1
INCH, BRIEF HEAVY RAIN WILL BE POSSIBLE FROM THESE STORMS.
ALTHOUGH GUSTY WINDS AND SMALL HAIL ARE ALSO POSSIBLE FROM SOME OF
THE STRONGER STORMS, THE INSTABILITY AND WIND SHEAR ARE FORECAST
TO BE RELATIVELY WEAK, SO SEVERE THUNDERSTORMS ARE UNLIKELY.
WINDS WILL ALSO SHIFT MORE NORTHERLY BEHIND THE FRONT, WHICH WILL
LIKELY CONTINUE THE SPREAD OF SMOKE FROM FIRES IN THE PACIFIC
NORTHWEST AND CANADA, SO HAVE KEPT MENTION OF SMOKE IN THE
FORECAST INTO THIS EVENING. HOWEVER, THE SHOWERS SHOULD HELP SCOUR
OUT SOME OF THE SMOKE. WILL NEED TO MONITOR THE SITUATION TO
DETERMINE IF MENTION OF SMOKE SHOULD BE CONTINUED BEYOND THIS
EVENING. SHOWERS AND THUNDERSTORMS WILL DIMINISH FROM THE NORTH
OVERNIGHT TONIGHT, BUT THE SHORTWAVE TROUGH WILL LINGER OVER
SOUTHWEST MONTANA THROUGH THE DAY ON WEDNESDAY, KEEPING A
PERSISTENT CHANCE OF SHOWERS AND THUNDERSTORMS THERE. WEAK
SHORTWAVE RIDGING WILL THEN MOVE INTO THE AREA ON WEDNESDAY NIGHT,
ALLOWING MOST OF THE LINGERING STORMS TO DIMINISH. HOWEVER, AN
UPPER LEVEL LOW PRESSURE AREA WILL MOVE ONSHORE INTO CALIFORNIA
AND NEVADA ON THURSDAY, TAPPING INTO SOME MONSOONAL MOISTURE. THE
RESULTING MOIST, UNSTABLE, AND DIFFLUENT SOUTHWESTERLY FLOW ALOFT
INTO SOUTHWEST MONTANA WILL MOVE A DISTURBANCE INTO SOUTHWEST AND
POSSIBLY CENTRAL MONTANA, FOR A CHANCE OF SHOWERS AND
THUNDERSTORMS THERE ONCE AGAIN. AS THE NORTHWESTERLY FLOW ALOFT
TODAY TRANSITIONS TO A MORE SOUTHERLY ONE BY THURSDAY,
TEMPERATURES WILL WARM FROM A FEW DEGREES BELOW NORMAL TODAY TO
ALMOST 10 DEGREES ABOVE NORMAL FOR THURSDAY.
COULSTON

THURSDAY NIGHT THROUGH TUESDAY...MONSOONAL MOISTURE AHEAD OF AN
UPPER LOW OVER CALIFORNIA WILL HAVE WORKED ITS WAY INTO SOUTHWEST
MONTANA BY THURSDAY EVENING AND SCATTERED SHOWERS AND
THUNDERSTORMS FROM THURSDAY AFTERNOON WILL LINGER INTO THURSDAY
NIGHT. FRIDAY THE UPPER LOW WILL WEAKEN AS IT MOVES INTO SOUTHERN
IDAHO AND WYOMING DURING THE AFTERNOON AND INTO MONTANA FRIDAY
NIGHT. MODEL RUNS DIFFER ON THE DETAILS OF THE REMNANTS OF THE
UPPER LOW AND THEIR ASSOCIATED PRECIPITATION PATTERNS. DUE TO
THESE DIFFERENCES HAVE DECIDED TO CONTINUE WITH THE INHERITED
FORECAST OF SCATTERED SHOWERS AND THUNDERSTORMS OVER SOUTHWEST
MONTANA AS WELL THE ROCKY MOUNTAIN FRONT WITH SHOWER AND
THUNDERSTORM ACTIVITY EXPECTED TO BE ISOLATED OVER THE NORTHERN
PLAINS. SATURDAY THE ECMWF MODEL RUN DEVELOPS AN UPPER RIDGE OVER
WESTERN MONTANA WHILE THE GFS MODEL RUN HAS THE AREA STILL BEING
AFFECTED BY THE REMNANTS OF THE UPPER LOW. EVEN WITH THESE
DIFFERENCES BOTH MODEL RUNS HAVE PRECIPITATION FORECASTS IN LINE
WITH THE INHERITED FORECAST OF SCATTERED SHOWERS AND THUNDERSTORMS
MAINLY OVER THE ROCKY MOUNTAIN FRONT AND SOUTHWEST MONTANA. SUNDAY
THROUGH TUESDAY THE GFS AND ECMWF MODEL RUNS HAVE SOUTHWEST FLOW
ALOFT WITH SOME EMBEDDED MOISTURE. THE INHERITED FORECAST WAS
PRETTY DRY DURING THIS PERIOD SO HAVE INCREASED THE CHANCES OF
PRECIPITATION TO AT LEAST HAVE A MENTION OF PRECIPITATION. BLANK

&&

.AVIATION...
UPDATED 1125Z.

EXPECT GENERALLY VFR CONDITIONS. A WEATHER DISTURBANCE ALOFT WILL
MOVE INTO NORTHWEST MONTANA THIS MORNING AND THEN INTO CENTRAL
MONTANA THIS AFTERNOON. PRECEDING THIS DISTURBANCE WILL BE A COLD
FRONT WHICH WHICH MOVED THROUGH KCTB NEAR 10Z AND WILL SPREAD
SOUTHEAST OVER THE PLAINS THIS MORNING. HAVE FAIR CONFIDENCE WITH
THE TIMING OF THE FRONT IN THE TAFS. SCATTERED SHOWERS AND
THUNDERSTORMS MOVED INTO THE NORTHWEST PLAINS AND ADJOINING
MOUNTAINS VERY EARLY THIS MORNING AND WILL SPREAD SOUTH AHEAD OF THE
DISTURBANCE MENTIONED ABOVE. EXPECT LOCAL MVFR CEILINGS AND
VISIBILITIES IN HEAVIER RAIN WITH THUNDERSTORMS. SHOWERS AND
THUNDERSTORMS WILL DIMINISH THIS EVENING BUT A FEW WILL LINGER OVER
SOUTHWEST MONTANA THROUGH THE NIGHT. ALSO THERE IS A SMOKE LAYER
BEING REPORTED AROUND 24000 FT. THIS IS DUE TO SMOKE FROM WILDFIRES
IN WA AND BC. BLANK

&&

.FIRE WEATHER...
SCATTERED THUNDERSTORMS WILL SPREAD SOUTH OVER NORTH CENTRAL AND
SOUTHWEST MONTANA TODAY. HOWEVER, WITH THE PRECIPITATION ON SUNDAY
AND CONTINUED COOLER THAN NORMAL TEMPERATURES, MUCH OF THE AREA
GOT SOME, ALBEIT BRIEF, RELIEF FROM THE EXTREME DRY CONDITIONS.
ALSO, WITH PRECIPITABLE WATER VALUES GENERALLY AROUND 1 INCH, THE
STORMS TODAY WILL LIKELY BE AT LEAST A MIX OF WET AND DRY
THUNDERSTORMS, WITH THE POTENTIAL OF WETTING RAIN FROM SOME
STORMS. THIS WILL LIKELY HINDER SPREADING OF ANY POTENTIAL NEW
FIRE STARTS FROM LIGHTNING, EVEN THOUGH GUSTY WINDS ARE A THREAT
FROM THUNDERSTORMS. WILL THEREFORE NOT ISSUE ANY FIRE WEATHER
WATCHES/WARNINGS AT THIS TIME. HOWEVER, AS TEMPERATURES WARM
THROUGH THE LATTER PART OF THE WEEK, CONDITIONS MAY DRY OUT ONCE
AGAIN. THIS SITUATION WILL CONTINUE TO BE MONITORED.
COULSTON

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  75  50  80  52 /  40  40  10  10
CTB  72  46  79  48 /  50  30  10   0
HLN  81  56  83  57 /  30  50  20  10
BZN  81  51  78  51 /  30  40  30  20
WEY  74  41  69  42 /  30  30  50  40
DLN  80  51  77  52 /  20  30  40  30
HVR  80  48  84  51 /  30  20  10   0
LWT  77  50  78  53 /  30  30  20  10

&&

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

$$

WEATHER.GOV/GREATFALLS


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