textproduct: Great Falls

KEY MESSAGES

- Conditions remain dry through midweek for most of the region, with low end chances for showers in Southwest MT Tuesday and Wednesday.

- Better chances for precipitation across the region comes late Thursday into Friday.

DISCUSSION

/Issued 442 PM MDT Sun Oct 18 2026/

- Meteorological Overview:

Weak zonal flow aloft continues today, bringing benign conditions to the region with temperatures near normal. Zonal flow transitions to increasing southwest flow heading into the first half of the week as the next incoming trough comes onshore to the Western U.S. This next trough splits off into a cut off low down in CA/Great Basin region, which increases warm, southwest flow aloft and moisture. As a result, temperatures teeter to near to above normal through Thursday. The increased moisture also brings low end chances for showers in Southwest MT, particularly near the ID border Tuesday and Wednesday.

Better forcing and moisture along this cutoff system arrives late Thursday into Friday. At the same time, another shortwave trough dips down from Canada and into MT. These two systems interact and eventually merge into each other Friday, creating a broad wave. This helps bring better chances for precipitation across the region. A cold frontal passage Friday also help lower temperatures to below normal for the weekend. Snow levels also lower behind the front for light mountain snow. This trough also looks to bring breezy winds to North-Central MT Friday. Ensembles hint behind this system another incoming trough moving onshore at the beginning of next week, though models greatly diverge in amplitude and timing. However, below normal temperatures with slight chances of precipitation may continue into the beginning of next week.

- Forecast Confidence & Scenarios:

There remains a decent spread in moisture amounts with this system, which will depend on how these two waves evolve with each other. There are two forcings with this system currently, the incoming closed wave with the frontal passage and the trough from Canada into the Rocky Mountain Front and North-Central MT. Models have a decent range in how much precipitation is along and behind the front. Current probabilities gives a 40-70% chance for 0.5" of moisture for the Southwest Valleys and an 80% chance for the Gallatin Range. Probabilities drop farther north into North- Central MT, with a 20-40% chance for 0.5" of moisture. Snow levels falling behind the front gives moderate confidence for some light mountain snow to develop, with some model runs getting levels down towards 6,000ft Friday in Southwest MT. Depending how much cold air from the shortwave trough dipping down from Canada moves into the region, snow levels may lower to lower elevations late Friday night into Saturday morning, bringing a rain/snow mix. -Wilson

AVIATION

19/06Z TAF Period

VFR conditions will prevail through the TAF period. Winds will remain generally light, with gusts up to 20kts at terminal KEKS with other terminals remaining below that. Skies will remain fairly clear, with patchy high level clouds across Central and Southwest Montana. Denser cloud cover is moving in overhead across KCTB and eventually KHVR, that will stick around through the end of the TAF period. -JR

PRELIMINARY POINT TEMPS/POPS

GTF 60 38 71 40 / 0 0 0 0 CTB 57 31 61 36 / 0 0 0 0 HLN 62 33 68 35 / 0 0 0 0 BZN 60 33 67 36 / 0 0 0 0 WYS 57 22 59 26 / 0 0 0 0 DLN 60 33 64 35 / 0 0 0 0 HVR 62 35 65 35 / 0 0 0 0 LWT 58 36 71 41 / 0 0 0 0

TFX WATCHES/WARNINGS/ADVISORIES

None.