Area Forecast Discussion
Issued by NWS Great Falls, MT

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000
FXUS65 KTFX 040544
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1140 PM MDT FRI JUL 3 2015

UPDATED AVIATION SECTION

.DISCUSSION...
ONLY MINOR CHANGES WERE MADE TO THE INHERITED FORECAST FOR
TONIGHT. REMOVED THE FORECAST OF A COUPLE OF THUNDERSTORMS OVER
CENTRAL MONTANA FOR THIS EVENING AS RADAR SHOWS NO PRECIPITATION
AND DO NOT EXPECT ANY PRECIPITATION FOR THE REST OF TONIGHT.
LOWERED SKY COVER TO HAVE MORE CLEAR SKIES AND IN LINE WITH THIS
LOWERED THE CHANCES OF PRECIPITATION TO MAINLY ZERO. ALSO TRENDED
WINDS DOWN SLIGHTLY. IT STILL LOOKS LIKE A COLD FRONT WILL MOVE
THROUGH THE NORTHWEST ZONES AFTER MIDNIGHT AND SHOULD BE NEAR A
HAVRE TO GREAT FALLS LINE BY 6 AM. AGAIN DO NOT EXPECT ANY
PRECIPITATION WITH THE FRONT MUCH LESS ANY CLOUDS. BLANK

&&

.AVIATION...
UPDATED 0540Z.

VFR CONDITIONS WILL GENERALLY CONTINUE THROUGH SATURDAY EVENING,
UNLESS OTHERWISE STATED. A WEAK THUNDERSTORM DEVELOPED AROUND 04Z
JUST SOUTH OF KGTF, BUT IT IS DIMINISHING AS IT MOVES SOUTHEAST AND
SHOULD NOT IMPACT ANY OTHER TERMINALS. OTHERWISE, SKIES WILL REMAIN
MOSTLY CLEAR ACROSS THE FORECAST AREA THROUGH SATURDAY MORNING.
HOWEVER, A COLD FRONT WILL MOVE SOUTH OF THE CANADIAN BORDER AFTER
10Z, THEN SOUTHEAST THROUGH CENTRAL MONTANA BY 18Z AND OUT OF THE
AREA BY 00Z. WINDS WILL SHIFT MORE NORTHERLY BEHIND THE FRONT WITH
POTENTIAL GUSTS UP TO 25 KT AT TIMES, ESPECIALLY OVER THE PLAINS OF
NORTH CENTRAL AND CENTRAL MONTANA. ISOLATED TO SCATTERED SHOWERS AND
THUNDERSTORMS WILL LIKELY DEVELOP BEHIND THE FRONT AS WELL AFTER 20Z
ACROSS NORTH CENTRAL AND CENTRAL MONTANA, WHERE WIND GUSTS IN EXCESS
OF 40 KT, BRIEF HEAVY RAIN (POSSIBLY REDUCING CONDITIONS TO MVFR AT
TIMES), AND SMALL HAIL ARE POSSIBLE. AS WINDS SHIFT MORE
NORTHEASTERLY ACROSS THIS AREA FROM THE NORTH BETWEEN 02Z AND 06Z,
THUNDERSTORMS WILL DECREASE, BUT SHOWERS WITH LOWER (POSSIBLY MVFR
AT TIMES) CEILINGS AND MOUNTAIN OBSCURATION WILL BECOME MORE
WIDESPREAD. ONLY ISOLATED THUNDERSTORMS ARE EXPECTED TO MOVE INTO
SOUTHWEST MONTANA AFTER 00Z.
COULSTON

&&

.FIRE WEATHER...
LOW AFTERNOON HUMIDITIES AND VERY WARM/HOT TEMPERATURES WILL
CONTINUE SATURDAY. ONE COLD FRONT WILL SWEEP SOUTHEAST THROUGH THE
AREA LATE TONIGHT AND SATURDAY MORNING AND BRING 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. 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
CONDITIONS CHANGE. BLANK

&&

.PREV DISCUSSION...
/ISSUED 610 PM MDT FRI JUL 3 2015/
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

&&

.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 /   0  10  20  20
WEY  43  84  47  74 /   0  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 /   0  10  50  40

&&

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

$$

WEATHER.GOV/GREATFALLS


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