textproduct: Great Falls

KEY MESSAGES

- Showers and a few thunderstorms this evening

- Windy periods through Monday.

- After a cool start, a warming trend develops later this week through the weekend.

DISCUSSION

/Issued 530 PM MDT Sun Sep 13 2026/

- Meteorological Overview:

An upper level low positioned over eastern WA this afternoon shifts east across the Northern Rockies overnight, emerging along the AB/MT border Monday morning then continues east through Monday afternoon. Enhanced mid-level flow ahead of the trough and afternoon heating/mixing continues is promoting the downward transport of gusty south/southwest winds across portions of SW MT with sustained south winds in excess of 30 mph and a few gusts over 50 mph focused along the Madison River Valley, where terrain aligns with the mid-level flow and a High Wind Warning is in effect until 6 PM. Showers and a few thunderstorms develop ahead of the incoming upper level low late this afternoon with coverage increasing across central/north-central MT this evening. Gusty winds across SW MT will diminish early this evening as mixing decreases and an inverted surface trough and cold front begin to shift across the region. Gusty west winds, cooler temperatures and decreasing showers sweep east across the rest of central and north-central MT overnight behind the passage of these features. Another round of showers circulates around the mid-upper low as it emerges east of the Rockies Monday morning, mainly focused along the continental divide with a few showers tracking east across central and north-central MT through Monday afternoon as the upper level low tracks east. Snow levels still look to fall to around 6500 ft overnight across the Glacier NP and Rocky Mtn Front region and eventually across the rest of north-central and SW MT by Monday morning.

Northwest flow behind the departing upper low and a strong surface pressure gradient thanks to low pressure deepening across ND will support gusty winds across much of north-central MT on Monday with strongest winds across eastern portions of central MT Monday afternoon. Broad mid-level troughing and a lingering cool surface airmass will remain situated over MT through Tuesday prior to flow shifting south-southwesterly mid to late week as a weaker upper low lifts northeast out of the CA/Great Basin region. Temperatures return to near or slightly above normal values Wednesday through the weekend. Model guidance displays some variance regarding the timing and extent of moisture with the Great Basin feature; however, this system will bring warmer air alongside shower and potential thunderstorm activity, primarily impacting SW MT late Thursday into Friday before potentially spreading northward across central and north-central MT over the weekend.

- Forecast Confidence & Scenarios:

Although mid-level lapse rates in excess of 8C/km are present late this afternoon, the strength of convection through this evening may be somewhat constrained by CAPE values generally remaining below 500 J/kg. Nevertheless, mid-level wind speeds and shear increasing to 50 kt will sustain a threat for gusty winds and possibly even some small hail in stronger cells. High-resolution model ensembles target the Great Falls to Havre corridor for the highest concentration of showers and thunderstorms between 6 pm and 9pm, with weaker activity shifting east across JB, Fergus and Blaine counties by midnight.

Snow showers later tonight through Monday morning will primarily affect the higher peaks along the continental divide north of MT-200 with up to 1 inch of snow accumulation possible at Logan Pass in Glacier NP. Additional showers circulating across the central MT mountains Monday morning could see some enhancement across the Little Belts with a period of snow showers bringing some minor accumulation to the Kings Hill area as well.

High Wind Watches remain in effect for portions of Judith Basin and Fergus counties on Monday, where there is a broad 50-70% probability of gusts in excess of 55 mph with a 60-80% probability primarily across southeast portions of Fergus county. Hoenisch

AVIATION

14/06Z TAF Period

Showers and locally embedded thunderstorms will continue to push through the region bringing the potential for brief MVFR conditions to all terminals through 14/15z. VFR conditions are expected to prevail across terminals KEKS, and KHLN as cloud bases will be low-VFR but skirting criteria. Terminal KGTF is expected to be VFR conditions, but there is a 30% chance of showers that may drop cloud bases to near 1.5kft. Terminals KCTB and KLWT remain the problem children, with MVFR conditions expected for at least part of the TAF period. KCTB will struggle with low-VFR to MVFR conditions for most of the period with cloud bases hanging around 5kft, dropping as low as 1.5kft for several hours beginning 14/15z. KLWT will have multiple opportunities for MVFR conditions, beginning as early at 14/7z when light showers or thunderstorms will drop cloud bases down to 2.5kft lasting through 14/11z. Overall, wind will be the next biggest concern. Strongest across Central Montana with widespread gusts 30-45kts, with the greatest concern again being KLWT where a 50kt gust cannot be ruled out. -JR

FIRE WEATHER

A Red Flag Warning remains in effect for portions of Southwest MT through 9 PM this evening for low humidity and gusty winds.

PRELIMINARY POINT TEMPS/POPS

GTF 67 45 64 42 / 10 80 30 10 CTB 58 41 58 40 / 20 10 50 50 HLN 71 44 64 38 / 20 60 10 0 BZN 78 40 63 34 / 0 80 20 0 WYS 69 28 58 25 / 0 30 0 0 DLN 75 38 63 33 / 0 20 0 0 HVR 71 47 63 41 / 0 90 60 10 LWT 72 43 59 37 / 0 70 40 10

TFX WATCHES/WARNINGS/ADVISORIES

High Wind Watch from 9 AM MDT Monday through Monday afternoon for Fergus County below 4500ft-Judith Basin County and Judith Gap-Snowy and Judith Mountains.