578
FXUS65 KTFX 170611
AFDTFX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1211 AM MDT SUN MAY 17 2026
KEY MESSAGES
- LIGHT MOUNTAIN SNOW AND LOWER ELEVATION RAIN WILL CONTINUE
THROUGH THE DAY.
- COOLER TEMPERATURES WILL PERSIST THROUGH TUESDAY MORNING BEFORE
MORE SEASONAL TEMPERATURES RETURN MID-WEEK.
- ANOTHER SYSTEM ARRIVES ON WEDNESDAY BRINGING ANOTHER ROUND OF
LIGHT MOUNTAIN SNOW AND LOWER ELEVATION RAIN AS WELL AS A
CHANCE FOR AFTERNOON THUNDERSTORMS.
DISCUSSION
- METEOROLOGICAL OVERVIEW:
AN UPPER LEVEL TROUGH WILL CONTINUE ITS WAY ACROSS THE REGION
BRINGING A CHANCE FOR LIGHT MOUNTAIN SNOW AND LOWER ELEVATION RAIN
THROUGHOUT THE DAY. AS THE TROUGH STARTS TO DEPART, NORTHERLY FLOW
BEHIND IT WILL KEEP TEMPERATURES WELL BELOW NORMAL THROUGH
MONDAY. MORE ZONAL FLOW RETURNS ON TUESDAY, ALLOWING FOR SEASONAL
TEMPERATURES TO RETURN. JUST AS TEMPERATURES START TO GRADUALLY
WARM UP, A SHORTWAVE TROUGH IS EXPECTED TO MOVE INTO THE REGION ON
WEDNESDAY BRINGING ANOTHER CHANCE FOR SHOWERS AND THUNDERSTORMS.
MOUNTAIN SNOW WILL GENERALLY STAY ABOVE PASS LEVEL FOR THIS STORM
WITH ONLY SLIGHT PROBABILITIES OF SNOW LEVELS DROPPING LOW ENOUGH
TO PROVIDE IMPACTS AT PASS LEVEL.
TOWARDS THE END OF THE WEEK CLUSTER GUIDANCE POINTS TOWARDS UPPER-
LEVEL RIDGING BUILDING ALONG THE WEST COAST BRINGING A RETURN TO
NORTHWESTERLY FLOW OVER MONTANA. THE RESULT WILL BE MORE SEASONAL TO
ABOVE-NORMAL TEMPERATURES WITH GENERALLY DRY CONDITIONS PERSISTING
ACROSS THE REGION.
- FORECAST CONFIDENCE & SCENARIOS:
SUNDAY SNOW:
OVERALL, SNOWFALL AMOUNTS HAVE DECREASED COMPARED TO PREVIOUS MODEL
RUNS WITH THE MOUNTAINS AND VALLEYS OF SOUTHWEST MONTANA EXPECTED TO
SEE AN ADDITIONAL 1 TO 3 INCHES WITH ISOLATED HIGHER AMOUNTS
POSSIBLE ALONG THE PEAKS. FOR THE NORTHERN ROCKY MOUNTAINS AND THE
LITTLE BELTS, 2 TO 4 INCHES ARE POSSIBLE AT PASS LEVEL WITH HIGHER
AMOUNTS EXPECTED ALONG THE PEAKS. BUT GENERALLY, THE MODELS HAVE
MOVED AWAY FROM THE PREVIOUSLY FORECASTED 6 TO 12 INCHES ALONG THE
PEAKS. THIS IS NOT TO SAY IT IS COMPLETELY OUT OF THE RANGE OF
POSSIBILITIES. BUT THE PROBABILITY OF OCCURRENCE NOW SITS AT AROUND
10-20%.
WHILE THERE IS STILL SOME POTENTIAL FOR ENHANCED SNOWFALL ALONG
NORTH-FACING SLOPES, THE MODELS HAVE BACKED OFF SIGNIFICANTLY
COMPARED TO PREVIOUS RUNS. IN PARTICULAR, THE PROBABILITIES FOR
SNOWFALL AMOUNTS GREATER THAN 6 INCHES HAVE DECREASED SIGNIFICANTLY
ACROSS THE REGION. THAT BEING SAID, THERE IS STILL ENOUGH SNOWFALL
EXPECTED TO PRODUCE IMPACTS THAT ARE WORTHY OF THE CURRENT SUITE OF
WINTER WEATHER ADVISORIES. SO NO CHANGES ADDITIONS OR SUBTRACTIONS
WERE MADE TO THE ADVISORIES WITH THIS FORECAST PACKAGE.
WEDNESDAY PRECIPITATION:
GIVEN THAT THIS SHORTWAVE TROUGH IS NOT EXPECTED TO BE AS COLD AS
THE CURRENT SYSTEM MOVING THROUGH, LIGHT SNOW WILL BE PRIMARILY
CONFINED TO THE HIGHER PEAKS OF THE MOUNTAINS. LOCATIONS AT AND
BELOW PASS LEVEL MAY PICK UP A FEW FLAKES BUT NOTHING LOOKS
PARTICULARLY IMPACTFUL AT THIS TIME. LOWER ELEVATIONS WILL SEE A
CHANCE FOR RAIN THROUGHOUT THE DAY WITH A CHANCE FOR THUNDERSTORMS
IN THE AFTERNOON/EVENING HOURS. CURRENTLY, THE EURO FOCUSES MORE OF
THE INSTABILITY IN CENTRAL MONTANA WHEREAS THE GFS PUSHES IT TOWARDS
SOUTHWEST MONTANA AND THE EASTERN HI-LINE. SO THE GENERALIZED 15-20%
CHANCE FOR A THUNDERSTORM ACROSS A LARGE PORTION OF THE REGION
MATCHES THE CURRENT CONFIDENCE OF SUGGESTING THERE COULD BE
SOMETHING BUT THERE IS STILL A BIT OF UNCERTAINTY AS TO WHERE IT
WILL HAPPEN. -THOR
AVIATION
17/06Z TAF PERIOD
A LARGE UPPER LEVEL DISTURBANCE MOVING OVER THE WESTERN US WILL
CONTINUE TO SPREAD LOW TO MID-LEVEL CLOUD COVER ACROSS THE
NORTHERN ROCKIES THROUGH THE 1706/1806 TAF PERIOD, WITH THE LOWEST
CIGS EXPECTED TO SHIFT FROM SOUTHWEST MONTANA TO OVER THE VALLEYS
AND PLAINS OF CENTRAL AND NORTH CENTRAL MONTANA THROUGH 09-15Z
SUNDAY. PRECIPITATION COVERAGE AND INTENSITY WILL BEGIN TO SHIFT
NORTHWARD OVER THIS SAME TIMEFRAME AS A COLD FRONT DROPS SOUTH
FROM CANADA AND ACROSS THE NORTHERN ROCKIES, WITH THE MOST
PERSISTENT PRECIPITATION OCCURRING IN EASTERLY AND NORTHERLY
UPSLOPE AREAS OF CENTRAL AND NORTH CENTRAL MONTANA. WHILE
MVFR/LOW-VFR WILL GENERALLY DOMINATE OVER THE NEXT 24 HOURS THERE
WILL BE TIMES OF LIFR/IFR CONDITIONS, MOST NOTABLY AT THE KCTB,
KGTF, AND KLWT TERMINALS. - MOLDAN
PRELIMINARY POINT TEMPS/POPS
GTF 40 27 52 29 / 80 40 10 0
CTB 38 25 55 29 / 70 10 0 0
HLN 43 30 54 32 / 70 30 10 0
BZN 45 28 49 26 / 30 30 20 10
WYS 37 21 43 19 / 20 20 10 0
DLN 45 23 50 26 / 40 20 0 0
HVR 44 29 53 28 / 80 50 10 0
LWT 39 27 45 25 / 70 60 40 10
TFX WATCHES/WARNINGS/ADVISORIES
WINTER WEATHER ADVISORY UNTIL MIDNIGHT MDT TONIGHT FOR BIG BELT,
BRIDGER AND CASTLE MOUNTAINS-EAST GLACIER PARK REGION-ELKHORN
AND BOULDER MOUNTAINS-LITTLE BELT AND HIGHWOOD MOUNTAINS-
SOUTHERN ROCKY MOUNTAIN FRONT-UPPER BLACKFOOT AND MACDONALD PASS.
WINTER WEATHER ADVISORY UNTIL 6 AM MDT EARLY THIS MORNING FOR
GALLATIN VALLEY-GALLATIN AND MADISON COUNTY MOUNTAINS AND
CENTENNIAL MOUNTAINS-MADISON RIVER VALLEY.
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