textproduct: Great Falls

KEY MESSAGES

- Temperatures trend warmer through Tuesday.

- Wednesday looks to be a transition day, with afternoon showers and thunderstorms ahead of a cold front.

- Spring system brings much cooler temperatures with precipitation behind the cold front through at least Thursday.

DISCUSSION

/Issued 504 AM MDT Sun Apr 19 2026/

- Meteorological Overview:

Upper level ridging across the west will continue through the weekend into next week ahead of a slowly approaching upper level low across the eastern Pacific. Temperatures continue to trend warmer into the work week, peaking Tuesday as southerly flow ahead of the aforementioned upper low is maximized. This stretch also looks largely dry, though by Tuesday afternoon a few showers and thunderstorms near terrain cannot be ruled out.

The upper level low moves onshore across the west Tuesday evening, gradually devolving into several strong open waves by Wednesday morning. One of these waves looks to move from the Great Basin toward the Northern Great Plains through the day Wednesday into Wednesday night. All the while, additional troughing begins diving southeastward from Central BC toward southern AB through the day Wednesday into Wednesday night. This results in a complicated interaction between troughs and as a result, lends to lower confidence in specifics. The main takeaway at this point is for a transition cooler Wednesday into Wednesday night behind a cold front, with a few thunderstorms ahead of the front and a more widespread stratiform precipitation behind the front.

This complicated interaction results in continued lower confidence in specifics toward the weekend, though there is support for a cool northwesterly flow aloft continuing toward the weekend. At the very least the cooler temperatures look to persist, with opportunities for additional precipitation late week into the weekend. -AM

- Forecast Confidence & Scenarios:

Thunderstorms Wednesday:

Slightly cooler air aloft coinciding with warm afternoon temperatures ahead of the cold front will result in areas of instability Wednesday afternoon. Areas east of US-87 look to have the longest timeframe to destabilize ahead of the cold front and as a result have the greatest probability to see thunderstorms. The probability for at least 250 J/kg instability in areas east of US-87 is largely greater than 50% by the afternoon. Gusty winds look and lightning look to be the concern with the most robust thunderstorms that do form.

Precipitation behind the cold front into Thursday:

As mentioned prior, there are multiple waves involved with precipitation over this timeframe. How these waves interact will determine which areas see the greatest precipitation from this system. Given this system is still several days out and marginal shifts in track and timing result in large changes in outcomes, there is still a wide range of potential outcomes for any given area. For example in Great Falls the spread in potential amounts between the low-end scenario (10th percentile - ~0.15") and high-end scenario (90th percentile - ~ 1.8") over 48 hours ending Friday morning is greater than an inch and a half.

Snow levels look to fall sharply Wednesday night as the coolest air is ushered in by gusty northwesterly winds behind the departing surface low. Given the aforementioned wide range in scenarios in overall precipitation amounts, the uncertainty with respect to snow amounts is also quite large at this time. -AM

AVIATION

19/18Z TAF Period

VFR conditions will prevail across the CWA through the period. Do expect passing mid/high level clouds, but no aviation impacts are expected at this time. Brusda

PRELIMINARY POINT TEMPS/POPS

GTF 69 40 75 43 / 0 0 0 0 CTB 67 36 73 40 / 0 0 0 0 HLN 69 41 75 42 / 0 0 0 0 BZN 67 35 75 39 / 0 0 0 0 WYS 57 24 64 27 / 0 0 0 0 DLN 65 37 73 40 / 0 0 0 0 HVR 68 38 75 42 / 0 0 0 0 LWT 65 40 71 44 / 0 0 0 0

TFX WATCHES/WARNINGS/ADVISORIES

None.