990
FXUS65 KTFX 311343
AFDTFX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
743 AM MDT MON MAR 31 2025
KEY MESSAGES
- A MIX OF RAIN AND SNOW SHOWERS TODAY, WITH A FEW THUNDERSTORMS
IN THE AFTERNOON AND EARLY EVENING.
- WIDESPREAD SNOW EXPECTED MONDAY NIGHT INTO TUESDAY, WITH HEAVY
SNOW POSSIBLE IN A FEW AREAS, PARTICULARLY THE HIGHER TERRAIN.
- UNSETTLED WEATHER CONTINUES THROUGH LATE THIS WEEK BEFORE A
QUIETER PATTERN ARRIVES FOR THE WEEKEND.
UPDATE
THE MAIN FOCUS OF THE UPDATE THIS MORNING WAS TO INCREASE THUNDER
MENTION ACROSS CENTRAL AND SOUTHWEST MONTANA THIS AFTERNOON AND
EARLY EVENING. HIGH RESOLUTION ENSEMBLE 50TH PERCENTILE
INSTABILITY ACROSS THESE AREAS THIS AFTERNOON IS ON THE ORDER OF
250-400 J/KG, WHICH WOULD BE SUFFICIENT TO RESULT IN THUNDER EVEN
WITH SURFACE TEMPERATURES LARGELY TOPPING OUT IN THE 40S AND LOW
50S TODAY.
SHOWERS THAT DEVELOP ARE LIKELY TO BE A MIX OF RAIN AND SNOW
TODAY, WITH SNOW FAVORED IN THE MOUNTAINS AND RAIN BEING MORE
FAVORED AT THE LOWER ELEVATIONS.
NO CHANGES WERE MADE TO SNOW AMOUNTS FOR TONIGHT INTO TUESDAY
WITH THE UPDATE THIS MORNING. CHANGES TO THIS TIMEFRAME WILL BE
POSSIBLE LATER THIS MORNING AS ADDITIONAL MODEL GUIDANCE ARRIVES
AND ADJUSTS CONFIDENCE LEVELS. -AM
DISCUSSION
/ISSUED 547 AM MDT MON MAR 31 2025/
- METEOROLOGICAL OVERVIEW:
AFTER A BRIEF REPRIEVE FROM THE UNSETTLED WEATHER YESTERDAY
AFTERNOON THROUGH THIS MORNING, OUR NEXT ROUND OF UNSETTLED
WEATHER WILL ARRIVE OVERNIGHT TONIGHT WITH AREAS OF HEAVY SNOW
LOOKING LIKELY THROUGH THE DAY ON TUESDAY. EVEN THOUGH THE
HEAVIEST PRECIPITATION WILL EXIT THE AREA BY WEDNESDAY, A FEW
LIGHT SNOW SHOWERS WILL LINGER ACROSS THE AREA WEDNESDAY AND
THURSDAY AS UPPER LEVEL TROUGHING LINGERS ACROSS THE NORTHERN
ROCKIES. WARMER AND DRIER CONDITIONS WILL LIKELY RETURN TO THE
AREA LATER FRIDAY THROUGH THE WEEKEND AS AN UPPER LEVEL RIDGE
BEGINS TO MOVE INTO THE AREA.
- FORECAST CONFIDENCE & SCENARIOS:
SNOW TUESDAY: AS AN UPPER LEVEL TROUGH PUSHES INTO THE AREA
OVERNIGHT TONIGHT AND THROUGH THE DAY ON TUESDAY, EXPECT
WIDESPREAD MOUNTAIN SNOWFALL TO DEVELOP WITH A MIX OF RAIN AND
SNOW IN THE LOWER ELEVATIONS. CURRENT MODEL RUNS HAVE BEEN FAIRLY
CONSISTENT WITH A WIDESPREAD AREA OF LIGHT TO MODERATE
PRECIPITATION THROUGH THE DAY ON TUESDAY, THOUGH ENSEMBLE DATA,
ALONG WITH SOME HIGH RESOLUTION MODELS, HAVE BEGUN TO SHOW THE
POTENTIAL FOR A FOCUSED AREA OF HEAVIER PRECIPITATION, WITH UP TO
AN INCH OF RAIN/RAIN EQUIVALENT FALLING DURING THE DAY ON TUESDAY.
WHILE THE EXACT LOCATION FOR THIS AREA OF HEAVIER PRECIPITATION
VARIES FROM MODEL TO MODEL (IN THOSE MODELS THAT HAVE THIS
FEATURE), THERE SEEMS TO BE A GENERAL CONSENSUS THAT THE MOST
LIKELY PLACEMENT WOULD BE AROUND THE LITTLE BELT AND SNOWY
MOUNTAINS, POSSIBLY AFFECTING GREAT FALLS AND LEWISTOWN TUESDAY
AFTERNOON AND EVENING. A SUBJECTIVE ANALYSIS OF MODEL RUNS WOULD
GIVE THIS HEAVIER AREA OF PRECIPITATION AROUND A 50% CHANCE OF
OCCURRENCE, NOT FACTORING IN THE PLACEMENT UNCERTAINTY, SO WHILE I
HAVEN’T EXPLICITLY FORECAST THIS BAND IN THE FORECAST GRIDS, I
DID GO AHEAD AND 1) UPGRADE THE EXISTING WINTER STORM WATCH TO A
WARNING, AND 2) I ISSUED A WINTER WEATHER ADVISORY, MAINLY FOR THE
NORTHERN SLOPES OF THE LITTLE BELT AND SNOWY MOUNTAINS TO
HIGHLIGHT THE POTENTIAL FOR THIS EVENT. WHILE THE POSSIBILITY FOR
ANY ONE LOCATION TO SEE THESE HIGHER END AMOUNTS IS LOW IN THIS
CORRIDOR (20-50% AS OF MONDAY MORNING), THIS BAND COULD BRING SOME
HEAVY IMPACTS, SO IT WILL BE WORTH KEEPING AN EYE ON WITH FUTURE
UPDATES.
REST OF THE WEEK: EXPECT AREAS OF LIGHT SNOW (OR RAIN SNOW MIX AT
LOWER ELEVATIONS) TO LINGER THROUGH THURSDAY OR FRIDAY AS THE
UPPER LEVEL TROUGH LINGERS AROUND THE NORTHERN ROCKIES. A PERIOD
OF MORE SETTLED WEATHER LOOKS LIKELY FOR THE WEEKEND AND EARLY
NEXT WEEK AS AN UPPER LEVEL RIDGE BUILDS INTO THE AREA, WITH THE
GENERAL CONSENSUS BEING THAT THE RIDGE WILL BUILD IN BY SATURDAY,
THOUGH AROUND 10% OF THE ENSEMBLE MEMBERS DO DELAY THE RIDGE UNTIL
SUNDAY. LUDWIG
AVIATION
31/12Z TAF PERIOD
MOISTURE IN THE SOUTHWESTERLY FLOW ALOFT WILL KEEP BROKEN TO
OVERCAST MOUNTAIN TOP OBSCURING LOW VFR CEILINGS OVER MUCH OF
SOUTHWEST, CENTRAL, AND NORTH CENTRAL MONTANA THROUGH AT LEAST
01/00Z. BREAKS IN CLOUDS MAY ALSO CAUSE AREAS OF MVFR/IFR FOG TO
DEVELOP IN SOME AREAS. IFR/LIFR CEILINGS ALREADY AT THE KCTB
TERMINAL WILL LIKELY LINGER THROUGH AT LEAST 15Z BEFORE STARTING
TO LIFT. WEAK INSTABILITY BETWEEN 18Z AND 03Z WILL ALSO CAUSE
SCATTERED SHOWERS WITH ISOLATED THUNDERSTORMS TO DEVELOP, BUT
HAVE KEPT MENTION OF THUNDERSTORMS OUT OF TAFS AT THIS TIME, AS
THE LIKELIHOOD OF STORMS DIRECTLY IMPACTING ANY CERTAIN TERMINAL
IS LOW. DEEPER MOISTURE WILL THEN START TO LOWER CEILINGS AND
SPREAD MOUNTAIN OBSCURING PRECIPITATION NORTHEAST OVER THE AREA
AFTER 00Z. -COULSTON
REFER TO WEATHER.GOV/ZLC FOR MORE DETAILED REGIONAL AVIATION
WEATHER AND HAZARD INFORMATION.
PRELIMINARY POINT TEMPS/POPS
GTF 52 33 42 31 / 50 70 70 60
CTB 45 29 45 27 / 30 30 40 40
HLN 53 31 43 31 / 70 60 70 60
BZN 49 26 39 25 / 50 60 70 60
WYS 42 18 36 15 / 80 60 70 70
DLN 48 26 40 25 / 50 40 40 30
HVR 50 28 44 26 / 10 30 50 30
LWT 49 28 39 29 / 30 60 80 70
TFX WATCHES/WARNINGS/ADVISORIES
WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO MIDNIGHT MDT
TUESDAY NIGHT FOR CASCADE COUNTY BELOW 5000FT-FERGUS COUNTY
BELOW 4500FT-GALLATIN VALLEY-GATES OF THE MOUNTAINS-JUDITH BASIN
COUNTY AND JUDITH GAP-MEAGHER COUNTY VALLEYS-SNOWY AND JUDITH
MOUNTAINS-SOUTHERN ROCKY MOUNTAIN FRONT-UPPER BLACKFOOT AND
MACDONALD PASS.
WINTER STORM WARNING FROM 6 PM THIS EVENING TO MIDNIGHT MDT
TUESDAY NIGHT FOR BIG BELT, BRIDGER AND CASTLE MOUNTAINS-ELKHORN
AND BOULDER MOUNTAINS-GALLATIN AND MADISON COUNTY MOUNTAINS AND
CENTENNIAL MOUNTAINS-LITTLE BELT AND HIGHWOOD MOUNTAINS.
HTTP://WWW.WEATHER.GOV/GREATFALLS
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