Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 041756
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1155 AM MDT SAT JUL 4 2015

AVIATION SECTION UPDATED

.UPDATE...
LATEST ANALYSIS SHOWS WIND SHIFT PORTION OF THE EXPECTED COLD
FRONT HAS MADE IT THROUGH THE HILINE AND PARTS OF CENTRAL MT AND
IS CURRENTLY LOCATED SOUTH OF GREAT FALLS AND LEWISTOWN. WINDS
HAVE SHIFTED TO NORTHERLY AND ARE GUSTING TO AROUND 25-30 MPH
BEHIND THE FRONT, BUT THERE IS NO MOISTURE AS YET SO SKIES REMAIN
CLEAR AND HAZY. MAIN PORTION OF THE FRONT WITH THE MUCH COOLER
TEMPERATURES IS STILL NORTH OF CALGARY SO WILL BE SEVERAL HOURS
BEFORE THAT CROSSES THE US/CAN BORDER AND MAKES ITS WAY SOUTH
THROUGH OUR REGION. GOING FORECAST IS ESSENTIALLY ON TRACK WITH
THE COOL SURGE ARRIVING THIS EVENING WITH ACCOMPANYING ISOLATED
TO SCATTERED SHOWERS AND THUNDERSTORMS. ONLY FORECAST ADJUSTMENTS
THIS MORNING WERE TO SLIGHTLY LOWER FORECAST HIGH TEMPS FOR THIS
AFTN ALONG THE ROCKY MTN FRONT AND REDUCE PRECIPITATION CHANCES
ALONG THE HILINE THROUGH NOON.
WARANAUSKAS

&&

.AVIATION... UPDATED 1755Z. VFR CONDITIONS EXPECTED. THE WIND SHIFT
LINE ASSOCIATED WITH A CANADIAN COLD FRONT ARRIVING LATER THIS
EVENING HAS MADE IT THRU KGTF/KLWT AND WILL MAKE SLOW PROGRESS
SOUTHWARD THIS AFTN. WINDS WILL GUST TO 20-25 KTS FOR AN HOUR OR TWO
BEHIND THIS LINE, BUT NO PRECIPITATION EXPECTED UNTIL MAIN PORTION
OF THE FRONT MOVES INTO MONTANA AFTER 00Z.  ISOLATED TO SCATTERED
-SHRA/-TSRA WILL DEVELOP ALONG/BEHIND THE COLD AIR BOUNDARY TONIGHT
SO HAVE CONTINUED MENTION OF VCSH/VCTS AT ALL LOCAL TAF SITES BUT
ADJUSTED START TIMES TO LATER IN THE EVENING.  GUSTY WINDS WILL BE
THE MAIN STORM THREAT WITH 30-40 KT WINDS POSSIBLE. WARANAUSKAS

&&

.FIRE WEATHER...
LOW AFTERNOON HUMIDITIES AND VERY WARM/HOT TEMPERATURES WILL
CONTINUE TODAY. A COLD FRONT WILL PUSH SOUTH THIS 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 THUNDERSTORMS, A PERIOD
OF NORTHERLY WINDS TO NEAR 40 MPH IS POSSIBLE BEHIND THE FRONT.
FIRE WEATHER HIGHLIGHTS ARE NOT BEING ISSUED AT THIS TIME AS WHERE
THERE ARE LOW RELATIVE HUMIDITIES, WINDS WILL BE RELATIVELY LIGHT
AND 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.

&&

.PREV DISCUSSION...
/ISSUED 540 AM MDT SAT JUL 4 2015/
TODAY THROUGH MONDAY...A QUIET AND SUNNY START TO INDEPENDENCE DAY
IS IN STORE FOR THE AREA THIS MORNING BEFORE CONDITIONS BEGIN TO
CHANGE DURING THE AFTERNOON. A COLD FRONT WILL CONTINUE TO MOVE
OUT OF CANADA THIS MORNING AND PUSH SOUTH ACROSS THE PLAINS DURING
THE LATE AFTERNOON AND EARLY EVENING. WINDS WILL SHIFT TO THE
NORTH BEHIND THE FRONT AND MAY BECOME GUSTY FOR A FEW HOURS. IN
ADDITION TO THE NORTHERLY WINDS, SCATTERED THUNDERSTORMS WILL
DEVELOP BEHIND THE FRONT. GUSTY WINDS, BRIEF HEAVY RAIN, AND SMALL
HAIL WILL BE POSSIBLE WITH THESE STORMS. THUNDERSTORMS WILL BE
MOST WIDESPREAD DURING THE EVENING ACROSS NORTH CENTRAL MONTANA
AND ALONG THE HI-LINE. WINDS WILL SHIFT TO THE NORTHEAST LATE THIS
EVENING AND THUNDERSTORMS WILL DECREASE ALTHOUGH RAIN SHOWERS WILL
LIKELY PERSIST OVERNIGHT. MUCH COOLER AIR WILL MOVE IN BEHIND THE
FRONTAL PASSAGE SUNDAY. LINGERING SHOWERS AND ISOLATED
THUNDERSTORMS WILL ALSO CONTINUE THROUGH THE AFTERNOON AND EVENING
HOURS. BY MONDAY AFTERNOON, SHORT WAVE ENERGY EMBEDDED WITHIN THE
NORTHWEST FLOW ALOFT WILL GENERATE SCATTERED AFTERNOON
THUNDERSTORMS OVER SOUTHWEST MONTANA. ONE MORE DAY OF 90+
TEMPERATURES TODAY BEFORE THE COOLER AIR ARRIVES IN THE WAKE OF
THE COLD FRONTAL PASSAGE. AFTERNOON READINGS ON SUNDAY WILL BE
MOSTLY IN THE 60S ACROSS CENTRAL AND NORTHERN MONTANA AND IN THE
70S ACROSS THE SOUTHWEST. TEMPERATURES WILL REBOUND ON MONDAY,
THOUGH READINGS WILL LIKELY REMAIN BELOW SEASONAL AVERAGES.

MONDAY NIGHT THROUGH SATURDAY...MODELS ARE IN FAIRLY GOOD AGREEMENT
ON THE LARGE SCALE FEATURES DURING THIS PERIOD. A SHORTWAVE IN THE
NORTHWESTERLY FLOW ALOFT WILL COMBINE WITH A CANADIAN COLD FRONT TO
BRING SCATTERED SCATTERED SHOWERS AND THUNDERSTORMS TO THE FORECAST
AREA TUESDAY INTO WEDNESDAY. TEMPERATURES WILL ALSO REMAIN NEAR
SEASONAL AVERAGES DURING THIS TIME. AN UPPER LEVEL LOW PRESSURE AREA
OFF THE CALIFORNIA COAST IS THEN FORECAST TO MOVE ONSHORE THURSDAY
INTO THURSDAY NIGHT AND MOVE NORTHEAST OVER THE GREAT BASIN ON
FRIDAY INTO MONTANA BY SATURDAY. WHILE THE FORECAST MODELS ARE IN
BETTER AGREEMENT WITH THE TIMING OF THIS ON THE 04/00Z RUNS THAN
THEY WERE ON THE 03/00Z MODEL RUNS, THIS CURRENT SOLUTION IS ABOUT
24 HOURS LATER THAN THE FORECAST MODELS INDICATED ON THE 03/00Z
RUNS. THIS COULD BE EXPLAINED BY THE FACT THAT THE 03/00Z MODELS MAY
HAVE UNDERESTIMATED THE STRENGTH OF THE BLOCKING RIDGE OF HIGH
PRESSURE OVER THE CENTRAL CONUS. REGARDLESS, AS THE FLOW ALOFT
SHIFTS FROM NORTHWESTERLY TO WESTERLY ON THURSDAY, THE MAIN CHANCE
FOR THUNDERSTORM ACTIVITY WILL BE FOCUSED ACROSS SOUTHWEST MONTANA.
THEN, AS THE FLOW ALOFT BECOMES MORE SOUTHWESTERLY WITH THE UPPER
RIDGE OVER THE CENTRAL CONUS SHIFTING TO THE EAST, THE CHANCE FOR
STORMS WILL SPREAD OVER THE ENTIRE FORECAST AREA FOR FRIDAY INTO
SATURDAY. WITH UNCERTAINTY REGARDING COVERAGE OF THESE STORMS, HAVE
KEPT CHANCES NEAR SEASONAL NORMALS. WITH THIS SHIFT IN THE FLOW
ALOFT, TEMPERATURES WILL ALSO WARM TO AROUND 10 DEGREES ABOVE NORMAL
THURSDAY THROUGH SATURDAY. COULSTON

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  90  55  63  43 /  10  50  40   0
CTB  82  50  63  42 /  30  50  40   0
HLN  97  62  70  51 /  10  30  30  10
BZN  93  55  73  49 /  10  20  20  20
WEY  84  48  72  41 /  10  20  40  40
DLN  92  57  77  51 /  10  10  30  20
HVR  89  55  66  46 /  20  50  40   0
LWT  91  55  63  46 /  10  50  40  10

&&

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

$$

WEATHER.GOV/GREATFALLS



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