275
FXUS65 KTFX 211106
AFDTFX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
505 AM MDT SAT SEP 21 2019
SYNOPSIS
RAIN SHOWERS WITH MOUNTAIN SNOW WILL DECREASE THIS MORNING, AS
THE LOW PRESSURE TROUGH EXITS THE REGION TO THE EAST. A FEW LIGHT
SHOWERS MAY THEN REDEVELOP OVER THE MOUNTAINS IN THE AFTERNOON AS
SKIES BEGIN TO CLEAR, BUT TEMPERATURES WILL REMAIN BELOW NORMAL.
HIGH PRESSURE WILL THEN BRING DRY CONDITIONS WITH NEAR NORMAL
TEMPERATURES FOR SUNDAY. A SERIES OF DISTURBANCES WILL BRING
STRONG WINDS AT TIMES MONDAY THROUGH WEDNESDAY WITH A CHANCE OF
MAINLY MOUNTAIN PRECIPITATION, BEFORE A MUCH COOLER AND WETTER
PATTERN MOVES IN TO END NEXT WEEK.
DISCUSSION
TODAY THROUGH SUNDAY...
THE LOW PRESSURE TROUGH AND ITS ASSOCIATED BAND OF RAIN AND
MOUNTAIN SNOW EXTENDING FROM RAYNOLDS PASS AND WEST YELLOWSTONE
NORTHEAST THROUGH BOZEMAN, THE LITTLE BELT MOUNTAINS AND LEWISTOWN
WILL GRADUALLY MOVE EAST OF THE AREA THROUGH THIS MORNING.
ADDITIONAL WET SNOWFALL IN THE MOUNTAINS ABOVE 8000 FEET WILL
LIKELY BE IN THE 1 TO 3 INCH RANGE AND WILL NOT CAUSE SIGNIFICANT
ADDITIONAL IMPACTS. WILL THEREFORE ALLOW THE WINTER WEATHER
ADVISORY FOR MADISON AND GALLATIN COUNTIES TO EXPIRE AT 6 AM. IN
THE COOLER AIR ALOFT ON THE BACK SIDE OF THE TROUGH AND NEAR THE
TROUGH AXIS, THE AIRMASS IS WEAKLY UNSTABLE. THIS, COMBINED WITH
THE NORTHERLY UPSLOPE LOW/MID LEVEL WIND, HAS CAUSED RAIN SHOWERS
TO FORM OVER THE PLAINS OF NORTH CENTRAL MONTANA AFTER MIDNIGHT.
THESE SHOWERS SHOULD ALSO DECREASE AND MOVE EAST OUT OF THE AREA
THIS MORNING WITH THE TROUGH. SKIES SHOULD BECOME PARTLY CLOUDY
THIS AFTERNOON WITH THE INFLUX OF DRIER AIR, BUT THE ADDED HEATING
FROM THE SUNSHINE WILL HELP CAUSE A FEW LIGHT SHOWERS TO
REDEVELOP OVER THE MOUNTAINS, MAINLY OVER CENTRAL AND SOUTHWEST
MONTANA. HOWEVER, COOL AIR WILL REMAIN IN PLACE, AS HIGHS WILL
RANGE FROM JUST BELOW NORMAL IN THE NORTH TO AROUND 15 DEGREES
BELOW NORMAL IN THE SOUTHWEST. HIGH PRESSURE ALOFT WILL THEN MOVE
INTO MONTANA TONIGHT INTO SUNDAY, WHICH WILL KEEP THE AREA DRY
WITH NEAR TO SLIGHTLY ABOVE NORMAL HIGHS AND AN INCREASE IN
WESTERLY WINDS. COULSTON
SUNDAY NIGHT THROUGH WEDNESDAY...
AN UPPER-LEVEL LOW PRESSURE TROUGH SPLITS AS IT APPROACHES MONTANA
FROM THE WEST ON MONDAY, WHICH WILL KEEP TEMPERATURES CLOSE TO
NORMAL WITH MAINLY MOUNTAIN SHOWERS AND GUSTY WESTERLY WINDS. OF
PARTICULARLY CONCERN IS MONDAY EVENING THROUGH EARLY TUESDAY MORNING
ALONG THE NORTHERN ROCKY MOUNTAIN FRONT, WHERE A FEW WIND GUSTS
REACHING WARNING CRITERIA ARE POSSIBLE, SO THIS WILL NEED TO BE
MONITORED. A BRISK WESTERLY FLOW ALOFT WILL THEN MOVE INTO THE AREA
IN THE WAKE OF THE TROUGH FOR TUESDAY INTO WEDNESDAY, WHICH WILL
CONTINUE BREEZY WESTERLY SURFACE WINDS OVER MUCH OF THE AREA WITH
SLIGHTLY COOLER THAN NORMAL TEMPERATURES AND A CHANCE FOR LIGHT
PRECIPITATION AT TIMES.
THURSDAY THROUGH NEXT SATURDAY...
LONG RANGE MODELS ARE NOW IN GREAT
AGREEMENT ON A SIGNIFICANT PATTERN CHANGE TO MUCH COLDER AND WETTER
BEGINNING SOMETIME THURSDAY. A STRONG COLD FRONT IS POISED TO MOVE
SOUTH ALONG THE ROCKY MOUNTAINS AND ADJACENT PLAINS AND THROUGH THE
ENTIRE STATE BY LATE THURSDAY INTO FRIDAY MORNING. A RAIN/SNOW MIX
AT THE BEGINNING LIKELY QUICKLY BECOMES A WET SNOW FOR MANY, IF NOT
ALL, LOCATIONS IN THE MOUNTAINS AND EVEN SOME PARTS OF THE ADJACENT
HIGH-ELEVATION VALLEYS AND HIGH PLAINS DURING THIS TIME. HIGH
TEMPERATURES ON FRIDAY AS OF NOW APPEAR TO STRUGGLE INTO THE 30S AND
40S FOR MANY LOCATIONS; LOWS COULD FALL INTO THE 20S (MOUNTAINS) AND
30S FOR MUCH OF THE AREA AT NIGHT. DETAILS ON PRECIPITATION AMOUNTS,
INCLUDING SNOW ACCUMULATIONS, WILL BE HONED IN ON WITH FUTURE
FORECAST SHIFTS LEADING UP TO THE MAJOR WEATHER PATTERN CHANGE.
AVIATION
UPDATED 505 AM MDT SAT SEP 21 2019 (21/12Z TAFS)
RAIN SHOWERS, MOUNTAIN SNOW, AND AREAS OF FOG/LOW CLOUDS WILL
CONTINUE LOW VFR/MVFR CONDITIONS WITH MOUNTAIN OBSCURATION ACROSS
MUCH OF THE AREA THROUGH AROUND 15Z. AFTER 15Z, CONDITIONS WILL
GENERALLY IMPROVE TO VFR THROUGH 18Z AS SKIES BECOME MOSTLY CLEAR
WITH SOME GUSTY WESTERLY WINDS AT TIMES, ESPECIALLY OVER THE PLAINS.
WEAK INSTABILITY MAY DEVELOP WITH THESE CLEARING SKIES, WHICH MAY
ALLOW ISOLATED SHOWERS TO FORM OVER THE MOUNTAIN AREAS AFTER 18Z.
HIGH PRESSURE ALOFT BUILDING INTO THE AREA AFTER 00Z WILL KEEP SKIES
MOSTLY CLEAR WITH LIGHT WINDS. COULSTON
PRELIMINARY POINT TEMPS/POPS
GTF 64 43 74 48 / 60 10 0 10
CTB 64 42 71 47 / 10 0 0 0
HLN 62 40 73 44 / 60 0 0 20
BZN 56 35 70 39 / 50 10 0 10
WEY 47 25 58 27 / 50 40 0 10
DLN 58 35 66 40 / 20 0 0 20
HVR 68 42 77 47 / 10 10 0 10
LWT 57 40 70 45 / 70 10 0 10
TFX WATCHES/WARNINGS/ADVISORIES
WINTER WEATHER ADVISORY UNTIL 6 AM MDT EARLY THIS MORNING ABOVE
8000 FEET FOR GALLATIN...MADISON.
HTTP://WWW.WEATHER.GOV/GREATFALLS
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