417
FXUS65 KTFX 110536
AFDTFX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1136 PM MDT THU SEP 10 2026
AVIATION SECTION UPDATED.
KEY MESSAGES
- WINDS WILL GRADUALLY SUBSIDE THROUGH THE EVENING HOURS TONIGHT.
- A COLD FRONT WILL BRING COLDER TEMPERATURES AND INCREASING
CHANCES FOR RAIN DURING THE DAY ON FRIDAY, MOST NOTABLY OVER
THE PLAINS OF CENTRAL AND NORTH CENTRAL MONTANA.
- A LARGE UPPER LEVEL DISTURBANCE WILL BRING EVEN COOLER
TEMPERATURES AND BETTER CHANCES FOR WIDESPREAD PRECIPITATION
DURING THE DAY ON SUNDAY, WITH MOUNTAIN SNOWFALL ALONG THE
CONTINENTAL DIVIDE.
DISCUSSION
/ISSUED 506 PM MDT THU SEP 10 2026/
- METEOROLOGICAL OVERVIEW:
A SIGNIFICANT PATTERN SHIFT IS EXPECTED TO END THE WORK WEEK AND
THROUGH THE WEEKEND AFTER A BREEZY AND WARM DAY TODAY. LONGWAVE
TROUGHING OVER THE PACIFIC NORTHWEST THIS AFTERNOON WILL CONTINUE
TO DIG SOUTH ALONG THE WESTERN SEABOARD THROUGH SATURDAY NIGHT
BEFORE LIFTING NORTHEAST AND OVER THE NORTHERN ROCKIES THROUGH
SUNDAY. AN EMBEDDED WAVE WITHIN THE LONGWAVE TROUGH WILL INITIALLY
SLIDE EAST AND OVER THE NORTHERN ROCKIES THROUGH THE OVERNIGHT HOURS
TONIGHT AND THE DAY ON FRIDAY, WITH A COLD FRONT DIVING SOUTH FROM
CANADA AND ACROSS MONTANA DURING THIS TIMEFRAME. PRECIPITATION WILL
ACCOMPANY THE PASSAGE OF THIS EMBEDDED WAVE AND ATTENDANT COLD
FRONT, MOST NOTABLY ALONG AND NORTH OF THE MONTANA HWY 200 CORRIDOR.
ADDITIONALLY, HIGH TEMPERATURES WILL FALL INTO THE 50S ACROSS THE
PLAINS OF CENTRAL AND NORTH CENTRAL MONTANA ON FRIDAY, WITH THE 60S
TO LOW 70S BEING OBSERVED FURTHER SOUTH ACROSS SOUTHWEST MONTANA
WHERE THE FRONT WILL ARRIVE LATER IN THE DAY.
BY SATURDAY TEMPERATURES WILL RANGE FROM THE 50S OVER THE PLAINS TO
60S IN THE VALLEYS OF CENTRAL AND SOUTHWEST MONTANA, WITH EXPANSIVE
CLOUD COVER ALONG AND NORTH OF THE I-90 CORRIDOR AS PACIFIC MOISTURE
STREAMS NORTHEAST AHEAD OF THE APPROACHING LONGWAVE TROUGH. LOW
LEVEL NORTH TO EAST UPSLOPE FLOW OVER CENTRAL AND NORTH CENTRAL
MONTANA MAY SUPPORT LIGHT PRECIPITATION ACROSS THE ISLAND RANGES AND
ALONG THE ROCKY MOUNTAIN FRONT, WITH OTHERWISE DRY CONDITIONS
EXPECTED ELSEWHERE DURING THE DAY ON SATURDAY. AS BETTER FORCING
ARRIVES SATURDAY NIGHT AND ON SUNDAY PRECIPITATION WILL BECOME MORE
WIDESPREAD ACROSS CENTRAL AND NORTH CENTRAL MONTANA, ESPECIALLY
ALONG WEST OF THE I-15 CORRIDOR WHERE LOW TO MID-LEVEL EASTERLY FLOW
WILL INCREASE. PRECIPITATION IS EXPECTED TO PERSIST THROUGH MUCH OF
THE DAY ON SUNDAY, WITH TEMPERATURES STRUGGLING TO RISE INTO THE 40S
TO MID-50S OVER THE PLAINS AND UPPER 50S TO LOW 60S IN THE VALLEYS. -
MOLDAN
- FORECAST CONFIDENCE & SCENARIOS:
LOWER ELEVATION RAINFALL THIS WEEKEND...
CONFIDENCE WITH RESPECT TO RAINFALL AMOUNTS, ESPECIALLY ALONG AND
NORTH OF THE US HWY 12 CORRIDOR, REMAINS LOW GIVEN A HIGH
VARIABILITY WITHIN THE PROBABILISTIC DATA SET. THIS IS ESPECIALLY
TRUE GIVEN THAT "LOW END", OR NBM10PCT VALUES, ARE ZERO ACROSS ALL
OF CENTRAL AND NORTH CENTRAL MONTANA; WITH EVEN THE NBM25PCT VALUES,
WHICH REPRESENT A "REASONABLE LOW END" SCENARIO, SUGGESTING A
SCENARIO IN WHICH THE ENTIRE REGION SEE'S LESS THAN 0.1" OF
RAINFALL. IDEALLY FOR A HIGHER CONFIDENCE FORECAST THE SPREAD
BETWEEN THE 25TH AND 75TH ("REASONABLE HIGH END" SCENARIO)
PERCENTILES WOULD BE CLOSER, BUT IN THIS CASE OVER THE PLAINS THEY
ARE GENERALLY 0.5" TO 1".
LISTED BELOW ARE NBM5.0 SCENARIOS FOR "LOW END" (NBM10PCT), " MOST
LIKELY" (NBM50PCT), AND "HIGH END" (NBM90PCT) RAINFALL AMOUNTS FOR
SELECT LOCATIONS ACROSS NORTH CENTRAL, CENTRAL, AND SOUTHWEST
MONTANA.
12Z SATURDAY - 12Z MONDAY RAINFALL SCENARIOS
LOCATION LOW END | MOST LIKELY | HIGH END
BROWNING 0.00" | 0.96" | 2.60"
CUT BANK 0.00" | 0.86" | 2.39"
HAVRE 0.00" | 0.40" | 2.02"
GREAT FALLS 0.00" | 0.53" | 1.82"
LEWISTOWN 0.00" | 0.42" | 1.46"
HELENA 0.00" | 0.42" | 1.42"
WHITE SULPHUR SPRINGS 0.00" | 0.30" | 1.20"
BOZEMAN 0.00" | 0.12" | 1.03"
DILLON 0.00" | 0.00" | 0.74"
ENNIS 0.00" | 0.00" | 1.16"
WEST YELLOWSTONE 0.00" | 0.00" | 0.61"
MOUNTAIN SNOWFALL THIS WEEKEND...
CONFIDENCE IS HIGH THAT THE MOUNTAINS, ESPECIALLY ABOVE 6500 FEET
ALONG THE CONTINENTAL DIVIDE NORTH OF THE MONTANA HWY 200 CORRIDOR,
WILL SEE SNOWFALL ACCUMULATIONS. HERE NBM5.0 10PCT VALUES GENERALLY
RANGE BETWEEN 0.5" TO 1", WITH SOME RIDGETOPS ACROSS GLACIER
NATIONAL PARK APPROACHING 3". WHERE UNCERTAINTY BEGINS TO GROW IS
WITH HOW LOW SNOW LEVELS WILL ULTIMATELY FALL WITH THIS FALL STORM,
ALONG WITH HOW MUCH PRECIPITATION WILL ULTIMATELY BE OBSERVED (SEE
EARLIER SECTION). SHOULD PRECIPITATION BE ON THE HEAVIER SIDE,
ESPECIALLY WITH THE INITIAL ONSET, IT IS LIKELY THAT SNOW LEVELS
WILL FALL SIGNIFICANTLY LOWER TO AROUND 5000 FEET. NOT ONLY WILL THE
HEAVIER PRECIPITATION LEAD TO HIGHER SNOWFALL TOTALS FOR ELEVATIONS
ABOVE 6500 FEET, WITH NBM90PCT SUPPORTING AMOUNTS APPROACHING 6" FOR
THESE ELEVATIONS, BUT MINOR ACCUMULATIONS UP TO 1" WOULD BE POSSIBLE
OVER THE HIGH PLAINS ADJACENT TO THE ROCKY MOUNTAIN FRONT. GIVEN THE
DEGREE OF UNCERTAINTY THAT STILL EXISTS WE WILL HOLD OFF ON ISSUING
ANY WINTER WEATHER HIGHLIGHTS, BUT SHOULD CONFIDENCE INCREASE OVER
THE NEXT 24 HOURS THEN A WINTER STORM WATCH MAY BE WARRANTED GIVEN
THE EARLY SEASON IMPACTS TO RECREATION (I.E. HUNTING SEASON). -
MOLDAN
AVIATION
11/06Z TAF PERIOD
VFR CONDITIONS ACROSS THE SOUTHWEST WITH MVFR TO IFR CONDITIONS TO
THE NORTH ARE EXPECTED. WIDESPREAD SHOWERS WILL CONTINUE TO MOVE
INTO CENTRAL AND NORTHERN TERMINALS BRINGING WIDESPREAD MVFR TO
IFR CEILINGS ACROSS TERMINALS KGTF, KCTB, AND KHVR THROUGH 11/19Z.
TERMINAL KLWT WILL FEATURE A LATER START TIME OF MVFR TO IFR
CONDITIONS BEGINNING AROUND 11/14Z AND LASTING THROUGH THE END OF
THE TAF PERIOD. MOUNTAIN OBSCURATION IS EXPECTED ACROSS CENTRAL
AND NORTHERN MONTANA LASTING THROUGH THE END OF THE TAF PERIOD AS
CLOUD BASES WILL BE SLOW TO RISE POST PRECIPITATION. SOUTHWESTERN
TERMINALS KBZN, KWYS, KEKS, AND KHLN ARE EXPECTED TO REMAIN VFR
THROUGH THE TAF PERIOD, WITH LIGHT WINDS BUT DENSE CLOUD COVER.
-JR
PRELIMINARY POINT TEMPS/POPS
GTF 81 49 57 44 / 0 90 90 20
CTB 73 43 50 40 / 0 80 80 30
HLN 84 50 62 45 / 0 40 60 10
BZN 84 47 69 44 / 0 0 20 10
WYS 72 36 68 31 / 0 0 10 10
DLN 82 45 72 38 / 0 0 10 0
HVR 82 46 61 38 / 10 70 70 10
LWT 84 47 54 39 / 0 20 90 30
TFX WATCHES/WARNINGS/ADVISORIES
NONE.
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