textproduct: Great Falls

KEY MESSAGES

- Scattered showers overnight tonight.

- Trending cooler and wetter for most areas Sunday night into Monday.

- After a brief lull Tuesday, another cooler precipitation producing system moves in Wednesday and Thursday.

UPDATE

Updated forecast is out. Main change was to adjust pops towards current trends. The threat for severe storms has ended, as more stable air has moved in from the west. Expect another round of showers/thunderstorms tomorrow, with the potential for a spring storm mid week. Brusda

DISCUSSION

/Issued 200 PM MDT Sat Apr 11 2026/

- Meteorological Overview:

A long fetch of southwesterly flow aloft is in place across the Northern Rockies this afternoon, ahead of an upper level low diving southeastward off the Northern California coast. The combination of warmer surface temperatures, sufficiently cool temperatures aloft, and a leading shortwave progressing across the region ahead of the upper low is resulting in a few showers and thunderstorms already early this afternoon. That trend looks to continue, with additional showers and thunderstorms developing and moving northeastward through the evening. While the overall magnitude of instability that develops isn't particularly high today, sufficiently deep mixing will result in a gusty wind threat in the most robust thunderstorms that do form. This activity wanes this evening as a cold front begins to work in across the plains.

Looking toward Sunday, the upper level low progresses inland across California. This positioning keeps a southwest to south flow aloft across the region. Another round of showers and thunderstorms is forecast as a result, though this time mainly across Southwest Montana and portions of Central Montana. The progression of the cooler air southward behind a front Sunday will ultimately determine the north/south extent of showery activity Sunday afternoon.

The core of the upper disturbance devolves into an open low with several embedded waves by late Sunday. One of these waves drifts northeastward toward the Northern Rockies Sunday night into Monday, which will keep at least spotty precipitation around through the day Monday. Snow levels look such that impacts from snow will be reserved for areas above most passes.

Zonal flow aloft then develops behind the departing wave and ahead of the next upper level system shifting southeastward from the Gulf of Alaska along the BC coastline Tuesday. While some spotty precipitation develops along the Continental Divide Tuesday, the main concern will be for gusty westerly to southwesterly winds developing ahead of the arrival of this system through Wednesday.

The main portion of the upper level system arrives Wednesday at some point, though there remains some uncertainty with exact timing. Additionally, there appears to be some splitting with this system as it moves inland, which brings about additional uncertainty with respect to where the best forcing for precipitation ultimately tracks. A transition toward cooler and wetter conditions is forecast late Wednesday into Thursday behind a cold front. Snow levels look to drop to all elevations behind this front, though given the aforementioned uncertainty with respect for the track of best forcing for precipitation, it is too early to mention any specifics for snow amounts.

Looking toward Friday and the weekend the main takeaway is for the system to begin its departure. How quickly it departs, and how quickly it warms back up as a result, depends on how much the troughing splits. A more consolidated system looks to progress quicker, while the more split scenario looks to linger across the west a bit longer. -AM

- Forecast Confidence & Scenarios:

Thunderstorms this afternoon and Sunday afternoon, along with overall precipitation amounts through Monday:

Latest mesoscale analysis favors the greatest DCAPE environment, and thus the area with the greatest risk for strong wind gusts from thunderstorm outflow, near and east of US-87 this afternoon, with decreasing risk for strong wind gusts the further you get from that area.

Cooler air moving in Sunday will keep the threat for gusty outflow winds across Southwest and portions of Central Montana Sunday. Forecast soundings in these areas mix a touch deeper Sunday compared to today, which would yield a slightly greater risk for gusty outflow compared to today in these areas.

Precipitation transitions to be more stratiform Sunday evening across the region, lasting into Monday. Areas with the greatest probability to exceed a half of an inch of liquid through Monday evening largely look to be north of the US-12 corridor and south of the MT-200 corridor. The probability for 3" snow at Kings Hill Pass over this timeframe is roughly 40%.

Winds Tuesday into Wednesday:

Westerly flow aloft approaching or briefly exceeding 50 kts look to develop Tuesday into Wednesday along the Rocky Mountain Front. Given the marginal winds aloft, confidence is not yet high in strong winds materializing at the surface. That said, both Tuesday and Wednesday do look to be breezy days.

Precipitation and colder temperatures Wednesday into Thursday:

A wide range of scenarios exists for precipitation amounts across the region for this event, largely related to the exact track and any splitting that occurs. The main takeaway at this range is that precipitation amounts trend higher from north to south across the region. -AM

AVIATION

12/00Z TAF Period

Main concern this evening is the potential for showers/thunderstorms. Most storms will diminish by 04z, with scattered showers continuing overnight. Showers redevelop on Sun afternoon over Central and Southwest MT, with more widespread rain/snow expected on Sun night. Mountains/passes will be obscured at times through the period. Brusda

PRELIMINARY POINT TEMPS/POPS

GTF 39 57 39 55 / 40 40 90 80 CTB 35 50 32 57 / 20 10 30 40 HLN 37 62 38 54 / 60 70 90 80 BZN 35 63 35 55 / 60 70 60 70 WYS 30 54 28 45 / 60 70 60 70 DLN 33 61 34 52 / 50 60 50 60 HVR 40 58 36 54 / 30 10 60 60 LWT 38 59 36 52 / 40 60 90 90

TFX WATCHES/WARNINGS/ADVISORIES

None.