textproduct: Great Falls

KEY MESSAGES

- Isolated showers diminish this evening.

- Trending warmer and drier into the weekend.

- Unsettled again early next week.

UPDATE

The main changes to the update this evening was extending PoPs through the rest of the evening across North-Central MT. Northwest flow aloft has continued to develop isolated showers through the evening hours, with most showers winding down overnight into Friday morning before picking back up Friday afternoon. There is an isolated chance for patchy fog to develop along the Milk River Valley Friday morning, though confidence remains low. -Wilson

DISCUSSION

/Issued 548 PM MDT Thu May 21 2026/

- Meteorological Overview:

Upper level troughing pivoting through the Northern and Central Rockies is resulting in a cool northerly flow aloft this afternoon across the region. Given the combination of cooler air aloft and sufficient clearing, there is enough support for at least widely scattered showers through the remainder of the afternoon and early evening, primarily along and east of I-15. The shallow nature of the instability should keep the potential for lightning low, though a strike cannot be completely rules out in the strongest shower.

A brief stretch of ridging attempts to build in from the west tomorrow, though the northwesterly flow that develops still appears to have a marginally cyclonic nature to it. This looks to result in at least isolated showers developing in the afternoon and early evening, with greatest coverage near terrain.

A drier zonal flow then develops for the weekend. The main takeaway for Saturday and Sunday will be for a drier stretch with warming temperatures. The zonal flow aloft will also result in some gusty winds at times, most favored in the afternoon. Those recreating on the water should keep the gustier winds in mind. Additionally, even though the air temperatures will be quite warm by Sunday, water temperatures are still quite cool, which will also pose a risk to those not prepared for the conditions.

By Monday upper level troughing begins to nudge in from the eastern Pacific over the Pacific NW. There remains considerable uncertainty with respect to how quickly this troughing moves in, in addition to its progression once it does encroach upon the Northern Rockies. The main takeaway for Memorial Day through mid-week will be for active weather across the region. -AM

- Forecast Confidence & Scenarios:

The main, and most impactful source of uncertainty is related to the progression of upper level troughing across the Pacific NW and Northern Rockies early next week. The risk for thunderstorms will increase as early as Monday afternoon, as southwesterly flow ahead of the troughing overspreads the region.

Confidence decreases further into Tuesday, as there is a rough split between ensemble members that cutoff the trough, or at the very least allow it to dig significantly and slow its overall progression and members that keep an open wave and progress things through quicker. This plays a significant role in whether the risk for thunderstorms will linger into a second afternoon, or if precipitation across the region will be more stratiform in nature along and behind a cold front into Tuesday. Trends will be monitored for changes in confidence levels in either scenario. -AM

AVIATION

22/00z TAF Period

Isolated light shower activity clears out around 22/04Z with partial clearing taking place during the overnight hours. Northwesterly flow aloft will bring more low VFR clouds and a few isolated showers again on Friday, primarily along the Rocky Mountain Front and the plains between 22/18 and 23/00Z. - RCG

PRELIMINARY POINT TEMPS/POPS

GTF 36 68 41 76 / 20 10 10 0 CTB 34 67 39 74 / 20 20 20 0 HLN 35 68 40 75 / 0 10 10 0 BZN 29 65 36 74 / 0 10 10 0 WYS 22 59 29 68 / 0 20 20 0 DLN 31 65 37 76 / 0 10 20 0 HVR 34 70 39 79 / 20 0 0 0 LWT 33 63 38 73 / 20 10 10 0

TFX WATCHES/WARNINGS/ADVISORIES

None.