textproduct: Great Falls

KEY MESSAGES

- Sunday will be breezy, warm, and generally dry across the region.

- Warm temperatures are expected through Tuesday before a brief cool down Wednesday and Thursday.

- Daily chances for showers and thunderstorms starting on Monday.

DISCUSSION

/Issued 1233 AM MDT Sun May 24 2026/

- Meteorological Overview:

Zonal flow aloft continues over Montana through Sunday with warm and generally dry conditions expected to persist through the day. By Monday morning an upper-level trough starts to come onshore along the PacNW. This switch to southwesterly flow will allow for some modest thunderstorm development in the afternoon, especially across Southwest Montana.

By Tuesday, the trough axis comes on shore and southerly flow starts to build across Montana. As the upper-level low continues to spin over CA/NV through Thursday, southerly flow will continue to funnel in moist air across the region. Combined with warm afternoon temperatures, there will be a daily chance for showers and thunderstorms through the rest of the week.

Towards the end of the week, the trough axis slowly moves northeast towards Montana, keeping temperatures near average for this time of the year and maintaining the daily chances for showers and thunderstorms through the weekend.

- Forecast Confidence & Scenarios:

Monday Thunderstorms:

Overall, these showers and thunderstorms look relatively mild compared to what is expected later in the week. With CAPE generally expected to stay below 1000 J/kg, there is not a lot to work with. Some isolated instances of strong, gusty winds are certainly possible across Southwest Montana but nothing reaching the level of concern compared to what arrives later in the week.

Tuesday Thunderstorms:

One of the limiting factors on Tuesday will be moisture. The 00Z run of the GFS has continued the trend of pushing back the timing for when the moist air gets pulled up into Central Montana. The Euro still has dewpoints getting close to 50 degrees starting at around 6 PM. Either way, the trend is that the moist air is not expected to arrive until much later in the day than what would normally be favorable for severe weather.

Which is not to say that severe weather is not possible. With highs across the Northern Plains in the mid 80s to mid 90s, there is still a potential for isolated, strong, diurnally-driven convection. Because moisture is going to be lacking, especially in the early afternoon hours, the main concern will be dry downbursts which could produce isolated instances of strong winds.

All things considered, if the moist air arrives earlier it will change the dynamics of the afternoon. If the moisture is able to arrive earlier in the day the chances for stronger convection increases. However, if the current trend of the GFS pushes the arrival further into the evening/overnight hours, then the threat lessens significantly. Despite only being a couple days out, there is still uncertainty as to how Tuesday will play out.

Wednesday Thunderstorms:

By Wednesday, moist air is expected to filter into Central and North- Central Montana with the latest GFS pushing afternoon dewpoints into the low to mid 60s across the Northern Plains. The current areas of concern are focused more on Central Montana, particularly around Judith Basin, Fergus, Chouteau, Hill, and Blaine counties. The latest model runs show a modest 1000-1500 J/kg CAPE across the region with some hints there could be pockets of higher CAPE further south towards Gallatin county although these are new compared to previous model runs. The limiting factor on Wednesday will be how warm temperatures get. Right now, east of a line between Havre and Lewistown, highs in the upper 70s to mid 80s are expected with locations to the west of that line only reaching the low to mid 70s. Widespread cloud cover is possible in the morning which could further limit afternoon instability.

Simply put, Wednesday is a day where afternoon thunderstorms are possible, it would not be unreasonable for a couple of them to be near-severe or severe. But right now there is too much uncertainty in the morning setup to make any deterministic calls on how widespread or significant the threat will be.

Thursday and Friday Thunderstorms:

While there is still a bit of uncertainty as to exactly how this upper level trough will set up across the western CONUS, there is increasing confidence with the latest model runs that both Thursday and Friday will be widespread thunderstorm days. As of now, the GFS is a lot more generous with CAPE than the Euro and the Canadian opted more for a confined area of higher CAPE across the central third of the CWA roughly between Great Falls and Townsend. Friday has more agreement amongst the models with higher CAPE and more moisture across the region. -thor

AVIATION

24/12Z TAF Period

VFR conditions will prevail across all terminals during this TAF Period with high-level clouds around. There will be gusty winds across all terminals during this TAF Period. -IG

PRELIMINARY POINT TEMPS/POPS

GTF 82 49 88 57 / 0 0 0 20 CTB 76 45 84 52 / 0 0 0 20 HLN 81 47 86 51 / 0 0 20 30 BZN 81 44 85 49 / 0 0 20 20 WYS 74 37 79 40 / 10 10 10 10 DLN 79 44 82 47 / 0 0 20 30 HVR 86 49 91 59 / 0 0 0 10 LWT 79 46 84 54 / 0 0 10 10

TFX WATCHES/WARNINGS/ADVISORIES

None.