Area Forecast Discussion
Issued by NWS Great Falls, MT

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000
FXUS65 KTFX 040011
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
610 PM MDT FRI JUL 3 2015

UPDATED AVIATION DISCUSSION

.DISCUSSION...
TONIGHT THROUGH SUNDAY...ANOTHER HOT DAY EXPECTED OVER THE REGION
ON SATURDAY...THEN A CHANGE IN THE WEATHER PATTERN IS EXPECTED ON
SATURDAY NIGHT. IT WILL BE MILD TONIGHT...WITH ANY PRECIPITATION
LIMITED TO MAINLY MOUNTAIN AREAS. ON SATURDAY...IT WILL BE A HOT
4TH FOR MANY AREAS...WITH HIGHS IN THE UPPER 80S NORTH AND IN THE
MID TO UPPER 90S SOUTH. A CANADIAN COLD FRONT WILL MOVE SOUTHWARD
INTO THE REGION DURING THE LATE AFTERNOON AND EVENING HOURS. THE
COLD FRONT SHOULD MOVE THROUGH THE GREAT FALLS AREA AROUND MID
EVENING AND THEN MOVE INTO THE HELENA AREA BY LATE EVENING. GUSTY
NORTH WINDS ALONG WITH SCATTERED SHOWERS/THUNDERSTORMS ARE
EXPECTED ALONG THE FRONT. SOME STORMS COULD PRODUCE STRONG WIND
GUSTS...WITH AN ISOLATED SEVERE THUNDERSTORM POSSIBLE. THE
NORTHERLY WINDS BEHIND THE COLD FRONT COULD CAUSE IMPACTS DURING
THE EVENING HOURS ON SATURDAY...ESPECIALLY OVER THE PLAINS. ON
SUNDAY...THE GFS/EC MODELS ARE MUCH COLDER THAN THEY HAVE BEEN
WITH HIGHS IN THE UPPER 50S TO LOWER 60S...ALONG WITH AN AREA OF
RAIN OVER NORTH CENTRAL MT. THUS TEMPERATURES HAVE BEEN LOWERED A
BIT FOR MOST AREAS ON SUNDAY...AND SHOWERS REMAIN IN THE FORECAST
FOR MUCH OF THE REGION. BRUSDA

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

&&

.AVIATION

UPDATED 0010Z. EXPECT VFR CONDITIONS WITH GENERALLY CLEAR SKIES INTO
SATURDAY MORNING. DURING THE LATER AFTERNOON SCATTERED THUNDERSTORMS
WILL DEVELOP NORTH OF A KGTF-KLWT LINE. SOME OF THESE THUNDERSTORMS
COULD BE ACCOMPANIED BY WIND GUSTS TO 40 KTS. A COLD FRONT WILL
SWEEP SOUTHEAST THROUGH THE AREA LATE TONIGHT THROUGH SATURDAY
MORNING WITH WINDS SHIFTING TO THE NORTHWEST BEHIND IT. HAVE
MODERATE CONFIDENCE IN THE TIMING OF THE WIND SHIFT MENTIONED IN THE
TAFS. BLANK

&&

.FIRE WEATHER...
LOW AFTERNOON HUMIDITIES AND VERY WARM/HOT TEMPERATURES WILL
CONTINUE SATURDAY. ONE COLD FRONT WILL SWEEP SOUTHEAST THROUGH THE
AREA SATURDAY AND BRING GUSTY NORTHWEST WINDS. A SECOND COLD FRONT
WILL PUSH SOUTH SATURDAY AFTERNOON AND EVENING AND BRING GUSTY
NORTHERLY WINDS ALONG WITH SCATTERED SHOWERS AND THUNDERSTORMS.
STORMS WILL BE A MIX OF WET AND DRY THUNDERSTORMS. IN ADDITION TO
GUSTY AND ERRATIC WINDS NEAR THE THUNDERSTORMS...A PERIOD OF
NORTHERLY WINDS TO NEAR 40 MPH IS POSSIBLE BEHIND THE SECOND FRONT.
FIRE WEATHER HIGHLIGHTS ARE NOT BEING ISSUED AT THIS TIME AS WHERE
THERE ARE LOW RELATIVE HUMIDITIES WINDS WILL BE RELATIVELY LIGHT
WHILE WHERE WINDS ARE GUSTY RELATIVE HUMIDITIES ARE EXPECTED TO BE
HIGHER. THIS SITUATION IS BEING CLOSELY MONITORED AND FIRE WEATHER
HIGHLIGHTS COULD STILL BE ISSUED SHOULD EXPECTED CONDITIONS CHANGE.
BLANK

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  61  91  56  67 /   0  10  50  40
CTB  57  86  50  65 /  10  30  50  40
HLN  63  97  63  73 /   0  10  30  30
BZN  53  92  54  76 /  10  10  20  20
WEY  43  84  47  74 /  10  10  20  40
DLN  55  91  57  80 /   0  10  10  30
HVR  60  89  54  72 /  10  20  50  40
LWT  60  89  55  66 /  10  10  50  40

&&

.TFX WATCHES/WARNINGS/ADVISORIES...

&&

$$

WEATHER.GOV/GREATFALLS


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