Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 031511
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
911 AM MDT FRI JUL 3 2015

.DISCUSSION...

TODAY...UPDATES TO ZONES NOT PLANNED...HIGH PRESSURE WILL REMAIN
IN PLACE OVER THE REGION. SMOKE IS STILL A PROBLEM ACROSS THE
AREA. RESTRICTED VISIBILITIES ARE MAINLY TO THE NORTH AND EAST BUT
CONDITIONS SHOULD SHOW SOME IMPROVEMENT DURING THE DAY. CURRENT
FORECAST ON TRACK. ZELZER

&&

.AVIATION
UPDATED 1102Z.

UPPER LEVEL HIGH PRESSURE WILL MAINTAIN A WNW FLOW ALOFT OVER THE
REGION WITH GENERALLY CLEAR TO PARTLY CLOUDY SKIES. THUNDERSTORM
DEVELOPMENT OVER THE HIGHER TERRAIN THIS AFTERNOON WILL BE VERY
LIMITED AND NOT LIKELY TO IMPACT ANY TERMINALS. SMOKE WILL CONTINUE
TO IMPACT THE HAVRE TERMINAL AND TO A LESSER EXTENT THE KLWT
TERMINAL THIS MORNING BEFORE IMPROVEMENT IS EXPECTED THIS AFTERNOON.
HOENISCH

&&

.FIRE WEATHER...
LOW AFTERNOON HUMIDITIES AND VERY WARM/HOT TEMPERATURES WILL
CONTINUE THOUGH SATURDAY. A CANADIAN COLD FRONT WILL MOVE SOUTH
INTO THE REGION SATURDAY EVENING. THUNDERSTORMS WILL ACCOMPANY THE
FRONTAL PASSAGE OVER NORTH CENTRAL MT WITH SHOWERS AND A FEW
THUNDERSTORMS POSSIBLE FURTHER SOUTH THROUGH CENTRAL AND SW MT
SATURDAY NIGHT. IN ADDITION TO GUSTY AND ERRATIC WINDS NEAR
THUNDERSTORMS...EXPECT A WIND SHIFT TO THE NORTH...WITH A PERIOD
OF NORTHERLY WIND GUSTS TO NEAR 40 MPH POSSIBLE BEHIND THE FRONT.
COOLER TEMPERATURES AND HIGHER HUMIDITIES ARE EXPECTED ON SUNDAY.
HOENISCH

&&

.PREV DISCUSSION...
/ISSUED 502 AM MDT FRI JUL 3 2015/

TODAY THROUGH SUNDAY...WEST-NORTHWEST FLOW ALOFT CONTINUES OVER
THE REGION TODAY AS AN UPPER LEVEL RIDGE EXTENDS FROM THE
4-CORNERS REGION INTO THE PACIFIC NW. THIS WILL BRING WARMER
TEMPERATURES TO THE FORECAST AREA WITH AFTERNOON HIGH TEMPS ABOUT
10-15 DEGREES ABOVE SEASONAL AVERAGES. AFTERNOON THUNDERSTORM
DEVELOPMENT WILL BE VERY ISOLATED AND MAINLY LIMITED TO THE
CENTRAL MT MTNS. UPPER LEVEL LOW NOW CENTERED IN FAR NW CANADA
WILL DROP INTO NORTHERN AB/SK SATURDAY WITH TROUGHING EXTENDING
SOUTHWESTWARD INTO THE NORTHERN ROCKIES AND MT SATURDAY NIGHT AND
SUNDAY. SATURDAY WILL BE VERY WARM AGAIN FOR MOST OF THE FORECAST
AREA WITH A CANADIAN COLD FRONT PUSHING SOUTH OF THE BORDER
SATURDAY AFTERNOON THEN CONTINUING SOUTH INTO CENTRAL MT SATURDAY
EVENING. THUNDERSTORM DEVELOPMENT IS EXPECTED SATURDAY AFTERNOON,
INITIALLY JUST ALONG AND BEHIND THE FRONT ACROSS THE HI-LINE AREA,
WITH THUNDERSTORM ACTIVITY PUSHING SOUTH ACROSS NORTH CENTRAL AND
CENTRAL MT SATURDAY EVENING AND OVERNIGHT. SOME STORMS COULD BE
STRONG TO MARGINALLY SEVERE LATE SATURDAY AFTERNOON AND EVENING,
PARTICULARLY ALONG THE HI-LINE. A PERIOD OF GUSTY NORTH WINDS WILL
FOLLOW THE FRONTAL BOUNDARY AS IT PUSHES SOUTH THROUGH THE REGION
SATURDAY EVENING AND OVERNIGHT. TIMING OF THE FRONTAL PASSAGE IS
STILL SOMEWHAT DIFFICULT TO PIN DOWN AS THE FRONTAL PUSH WILL
LIKELY BE COMPLICATED/ENHANCED BY OUTFLOW FROM AFTERNOON/EVENING
CONVECTIVE ACTIVITY. TROUGHING IN THE UPPER LEVELS MOVES INTO THE
REGION SATURDAY NIGHT AND SUNDAY WITH SCATTERED SHOWERS AND
POSSIBLY SOME THUNDERSTORMS FOCUSED MORE OVER CENTRAL AND SW MT
THROUGH SUNDAY AFTERNOON. SIGNIFICANT COOLING IS EXPECTED SUNDAY
WITH TEMPERATURES NEARLY 20 DEGREES COOLER THAN SATURDAY AFTERNOON
OVER MUCH OF THE FORECAST AREA. HOENISCH

SUNDAY NIGHT THROUGH FRIDAY...MEDIUM RANGE FORECAST MODELS ARE IN
GOOD AGREEMENT WITH THE GENERAL PATTERN THROUGH WEDNESDAY NIGHT, BUT
THEN THEY DIFFER ON THE TIMING OF MOVING FEATURES. THE REX BLOCK
PATTERN OVER THE NORTHEASTERN PACIFIC OCEAN WILL KEEP THE AREA UNDER
THE INFLUENCE OF DISTURBANCES SWINGING SOUTH AROUND THE HUDSON BAY
LOW. THE FIRST DISTURBANCE WILL EXIT THE AREA SUNDAY NIGHT, ALLOWING
THE SCATTERED SHOWERS AND THUNDERSTORMS TO DECREASE. WEAK HIGH
PRESSURE ALOFT WILL MOVE OVER THE AREA ON MONDAY, BUT IT WILL TAP
INTO SOME PACIFIC MOISTURE, WHICH WILL BRING A CHANCE OF SHOWERS AND
THUNDERSTORMS MAINLY TO SOUTHWEST MONTANA. AS THE HIGH PRESSURE
CENTER IN THE NORTHERN PORTION OF THE REX BLOCK WEAKENS MONDAY NIGHT
THROUGH WEDNESDAY, ANOTHER DISTURBANCE WITH AN ASSOCIATED COLD FRONT
WILL MOVE SOUTH THROUGH WESTERN CANADA AND MONTANA. THE RESULTING
MOIST NORTHWESTERLY FLOW ALOFT WILL COMBINE WITH MORE NORTHERLY
UPSLOPE SURFACE WINDS BEHIND THE FRONT TO BRING A GOOD CHANCE OF
SHOWERS AND THUNDERSTORMS TO THE AREA. AT THIS POINT, THE MODELS
BEGIN TO DIFFER. THE GFS WANTS TO LIFT THE UPPER LOW REMAINING FROM
THE REX BLOCK OFF THE CALIFORNIA COAST NORTHEAST AS A SHORTWAVE
TROUGH OVER THE GREAT BASIN AND INTO SOUTHWEST MONTANA BY FRIDAY.
HOWEVER, THE ECMWF IS ABOUT 24 HOURS LATER WITH THIS PROGRESSION AND
KEEPS THE AREA UNDER THE INFLUENCE OF AN UPPER LEVEL HIGH PRESSURE
RIDGE AFTER WEDNESDAY NIGHT. THE GFS SOLUTION WOULD LIKELY KEEP A
CHANCE OF MAINLY AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS
OVER SOUTHWEST MONTANA. THE ECMWF SOLUTION WOULD MOST LIKELY BE
DRIER, BUT IT DEPICTS MORE PRECIPITATION THAN WOULD BE EXPECTED.
HAVE THEREFORE GONE WITH A COMPROMISE SOLUTION WITH A CHANCE OF
STORMS OVER SOUTHWEST MONTANA. TEMPERATURES WILL BE CLOSE TO NORMAL
BEFORE THE PASSAGE OF THE COLD FRONT TUESDAY INTO TUESDAY NIGHT,
THEN THEY WILL FALL TO AROUND 5 TO 10 DEGREES BELOW NORMAL FOR
WEDNESDAY, BEFORE REBOUNDING BACK TO AROUND 10 DEGREES ABOVE NORMAL
BY FRIDAY. COULSTON

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  92  60  89  54 /  10   0  10  40
CTB  90  55  81  49 /  10  10  30  50
HLN  96  63  96  63 /  10   0  10  20
BZN  91  53  93  54 /  10  10   0  20
WEY  82  43  83  47 /  10  10  10  10
DLN  90  55  91  58 /  10   0  10  10
HVR  93  60  89  53 /  10  10  20  50
LWT  89  59  89  54 /  20  10  10  50

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
&&

$$

WEATHER.GOV/GREATFALLS



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