textproduct: Great Falls

KEY MESSAGES

- Record high temperatures possible on Tuesday.

- Strong thunderstorms Wednesday afternoon and evening.

- Rain changing to snow on Thursday, with heavy snowfall possible in the mountains.

- Much below normal temperatures expected from Thursday through Saturday.

DISCUSSION

/Issued 522 PM MDT Mon Apr 20 2026/

- Meteorological Overview: An upper level ridge of high pressure is currently over MT. This is resulting in warm air pushing northward into MT. By Tuesday afternoon, temperatures will be near record highs over the CWA. Additionally gusty southwest winds will allow for low humidity to develop. Elevated fire conditions are expected over Southwest MT, but with finer fuels beginning to green up, no fire statements will be issued at this time.

For Wednesday, an upper level trof will approach from the west, resulting in a strong Pacific cold front to move from west to east across the CWA Wed afternoon and night. An unstable southwesterly flow aloft will develop ahead of the cold front, resulting in a few strong thunderstorms over North Central MT Wed afternoon/evening. There is the potential that an isolated severe storm could also develop. The main threat from any stronger storms will be wind, but with cold temperatures aloft, hail can't be ruled out.

For Wednesday night into Thursday, expect temperatures to fall significantly over the CWA. Most areas will have a 30 degree drop, from the lower 60s to the lower 30s. This will result in the rain changing to snow for most elevations by Thursday morning. Snow accumulations are looking likely, especially in the mountains. Thus winter storm watches have been issued for portions of Southwest and Central MT for this event. It is likely that additional winter statements will be needed for this event. Strong north winds are also expected, with the strongest winds over the eastern portions of the CWA. Much colder temperatures are expected to arrive on Thursday, with afternoon temperatures averaging 10 to 15 degrees below normal.

For Friday through Monday...an unstable northerly flow aloft will reside over the CWA. This will result in low chances for daily light rain or snow showers, with the most favored areas being over the mountains. Overall below normal temperatures are expected through the weekend, with slightly warmer air returning to return by next Monday.

- Forecast Confidence & Scenarios:

There is around a 90 percent chance that afternoon temperatures could reach record highs over portions of the CWA tomorrow.

There is just enough cape/instability on Wed afternoon, that an isolated severe storm is possible over portions of North Central MT. It is possible that a marginal risk of severe storms could be introduced in later forecasts for portions of North Central MT.

The GFS model continues to be significantly higher with precipitation amounts for the Wed/Thu storm system. If snow levels end up being a bit lower than currently forecast, combined with the heavier QPF amounts the GFS model progs, a significant snowfall could unfold over portions of Central MT. For now, the current forecast is leaning more towards the average QPF amounts.

There is a 60 percent chance that strong winds could develop over the eastern portions of the CWA on Thursday. Thus there is the potential for high wind statements. Additionally, if the strong winds overlap when the snow is falling, there is the potential for near blizzard conditions over portions of Judith Basin and Fergus counties in Thu.

Much below normal temperatures are expected to end the work week. With overnight lows in the teens and 20s, some impacts are possible to new spring vegetation that has begun to bloom. Brusda

AVIATION

21/06Z TAF Period

VFR conditions prevail through the TAF period. Westerly flow aloft backs to southerly Tuesday afternoon with some increase in mid to high level cloud-cover. Generally light surface winds persist through Tuesday morning with breezy south winds developing at southwest MT terminals Tuesday afternoon. Hoenisch

PRELIMINARY POINT TEMPS/POPS

GTF 44 82 46 72 / 0 0 10 60 CTB 41 78 43 62 / 0 0 0 60 HLN 43 83 46 68 / 0 0 0 70 BZN 39 81 42 65 / 0 0 0 50 WYS 28 67 33 50 / 0 0 20 80 DLN 40 74 44 60 / 0 0 0 70 HVR 42 82 47 79 / 0 0 10 30 LWT 44 79 50 73 / 0 10 10 50

TFX WATCHES/WARNINGS/ADVISORIES

Winter Storm Watch from Wednesday evening through Thursday afternoon for Big Belt, Bridger and Castle Mountains-Gallatin and Madison County Mountains and Centennial Mountains-Little Belt and Highwood Mountains.

Winter Storm Watch from late Wednesday night through Thursday afternoon for Fergus County below 4500ft-Judith Basin County and Judith Gap-Snowy and Judith Mountains.