textproduct: Great Falls

KEY MESSAGES

- Mild and dry weather continues through Monday with breezy to locally windy conditions this afternoon.

- A cooler and active weather pattern begins Tuesday with a period of rain and snow developing Tuesday afternoon changing to snow Tuesday night.

- Cooler weather continues into next weekend with additional precipitation chances developing late in the work week.

DISCUSSION

/Issued 310 AM MST Sun Nov 15 2026/

- Meteorological Overview:

A mild and dry southwesterly flow aloft has reestablished across the Northern Rockies and MT and will remain in place through Monday. Starting Tuesday, a series of Pacific storm systems will push large-scale troughing inland, bringing a transition toward cooler and more active weather that persists into next weekend.

Well-above-average temperatures will persist through Monday. Breezy to locally windy conditions are anticipated across much of the region this afternoon, driven by a moderate surface pressure gradient combined with 30-40 kt 700 MB southwesterly flow. Peak afternoon atmospheric mixing will produce wind gusts near 30 mph in most areas. However, local terrain effects will enhance winds along the immediate eastern slopes of the Rocky Mountain Front and within terrain-aligned valleys of Southwest Montana, generating higher sustained winds of 30-40 mph and localized gusts reaching up to 50 mph.

As the initial upper-level trough moves inland early this week, it will slow and split. This split allows a surface low to track northeastward out of Wyoming late Tuesday, while the northern segment of the trough lingers over Western Montana. Consequently, a region of mid-level deformation and frontogenesis will develop and progress eastward across the region late Tuesday and Tuesday night. An accompanying plume of anomalous Pacific moisture will support locally moderate precipitation as the upper trough and frontogenic forcing cross the area late Tuesday and Tuesday night. The WY surface low will pull cooler low-level air southward along the Rocky Mountain Front on Tuesday, followed by broader large- scale cooling aloft as the main trough crosses the region Tuesday night, driving snow levels down below 4,000 feet across much of the area before precipitation winds down by Wednesday morning.

Large scale troughing lingers across the western US later this week into next weekend with another distinct upper low/trough moving inland and potentially affecting the area by Friday. Overall cooler/seasonal conditions will be maintained with precipitation chances increasing towards the end of the work week. Model ensembles lean toward higher precipitation chances across southern portions of the forecast area with this system but there is still a fair amount of uncertainty with details.

- Forecast Confidence & Scenarios:

Precipitation Potential (Tuesday & Tuesday Night): Recent model ensemble guidance maintains reasonable support for higher precipitation amounts focused along the I-15 corridor, where probabilities for exceeding 0.50" reach 40-50% (as well as across much of Southwest MT). High-resolution models indicate that initial frontogenic banding will develop further west near the Continental Divide during the day Tuesday. A secondary zone of frontogenesis is projected to consolidate over the I-15 corridor Tuesday evening before shifting eastward and diminishing overnight. Because this event remains over 48 hours out, additional minor adjustments to these spatial and timing details are likely.

Snow Levels & Accumulation: Snow levels will start out around 4,000- 6,000 ft across the region as precipitation begins Tuesday afternoon. They are expected to fall rapidly to near or below 4,000 ft along and west of the I-15 corridor in north-central MT as a narrow shallow surge of cooler air slides south along the Rocky Mountain Front. By Tuesday evening and overnight, snow levels will drop below 4,000 ft across most of the area. There is a 60-70% chance of snowfall totals reaching 2 inches or more across most mountain passes, with up to a 30% probability of amounts reaching 4 inches over Rogers and McDonald Passes where mesoscale banding is more likely to develop. Confidence in low- elevation snow accumulations remains lower given marginal surface temperatures and lingering uncertainty regarding the exact timing of the lower snow levels.

AVIATION

15/12Z TAF Period

VFR conditions will prevail across most of the region during the TAF period. MVFR ceilings are continuing to lift over KWYS and will become VFR for today. Breezy winds out of the southwest up to 25 KT this afternoon for central and north central terminals. KEKS will see up to 30 KT gusts out of the south today due to enhanced mixing and valley channeling however gusts will taper down tonight. Other hazards will include some early morning moutain obscuration due to stratus in Southwest MT as well as possible LLWS along and immediately downwind of the Rocky Mountain Front. -Akins

PRELIMINARY POINT TEMPS/POPS

GTF 57 38 54 37 / 0 0 0 30 CTB 55 36 50 32 / 0 0 0 30 HLN 55 32 51 34 / 0 0 0 40 BZN 52 29 53 32 / 0 0 0 10 WYS 41 22 46 27 / 0 0 0 20 DLN 48 30 49 33 / 0 0 0 30 HVR 59 33 55 32 / 0 0 0 10 LWT 57 36 57 33 / 0 0 0 10

TFX WATCHES/WARNINGS/ADVISORIES

None.