textproduct: Great Falls

KEY MESSAGES

- A cold front will move across the region today bringing drier and breezy conditions.

- Scattered showers and thunderstorms are possible this afternoon with a chance a few may become severe.

- Cooler temperatures will persist over the next couple days before warming up towards the middle of the week.

DISCUSSION

/Issued 1207 AM MDT Sun Aug 23 2026/

- Meteorological Overview:

An upper-level trough will make its way into Montana today with the accompanying surface cold front expected to bring gusty winds to the region along with a chance for afternoon showers and thunderstorms. These thunderstorms will be drier in nature which will also increase fire weather concerns, particularly across Southwest Montana, through the evening.

Behind the trough, more zonal flow will set up allowing for temperatures to remain relatively cooler at least over the next couple days before upper-level ridging starts to build by the middle of the week. Lingering monsoonal moisture in the region along with the chance for some additional moisture towards the end of the week may provide daily chances for afternoon showers and thunderstorms, especially for Southwest Montana.

- Forecast Confidence & Scenarios:

Thunderstorms Sunday: With ample CAPE and shear in place and the cold front moving through, there is decent support for thunderstorm develop across the region this afternoon and evening. The remaining question is how this event will play out. The 00Z suite of hi-res models, particularly the HRRR, came in with much less coverage compared to previous runs and between the remaining hi-res models there is still some disagreement about whether there will be higher coverage in Southwest Montana or Central Montana. Some models like the NAM have pointed towards a threat of thunderstorms forming off the Little Belts and quickly becoming strong as they move into Judith Basin and Fergus county.

While uncertainty remains in who will get what, there is confidence that the majority of thunderstorm activity will move off into eastern Montana by 7 PM. Additionally the main hazards will be frequent lightning and strong, gusty winds with hail being a secondary hazard primarily with the initial storms that develop. -thor

AVIATION

23/12Z TAF Period

The primary concern for this morning is localized dense fog that has developed over the KWYS area. This should begin to thin out with clouds and spotty showers/thunder moving in from the southwest, but a tempo group was added through 15Z to cover the IFR/LIFR conditions there. The weak convective activity should slowly weaken as it moves into SW MT, so the mention of early day showers/thunder was left out of the SW terminals for now.

Otherwise, a trough will move northeastward out of the Pacific NW into S BC/AB and send a surface front moving through the Northern Rockies today. This will increase west/southwesterly winds by this afternoon, with gusts generally in the 20 to 35 mph range. There will also be widely scattered showers and thunderstorms developing this afternoon, mostly for locations east of I15. Some of these storms may contain wind gusts over 50 kts, brief downpours, and hail in addition to cloud to ground lightning. Primarily VFR conditions will prevail away from stronger convective cores.

For KGTF: Westerly winds increase to 10 to 20 kts with gusts up to 35 kts at times roughly between 23/16Z and 24/03Z. Afternoon convection looks to mostly stay east of the terminal but there is around a 30% chance for a shower or storm impacting the terminal. Thunderstorm hazards may include erratic wind gusts over 50 kts, brief downpours, and hail in addition to cloud to ground lightning. - RCG

FIRE WEATHER

A surface front will bring gusty westerly winds through the afternoon hours across the region. Widespread gusts over 35 mph are possible and will be enhanced by any thunderstorm activity that develops. Minimum RH values will be most critical in Southwest Montana where the RFW is currently in effect for Sunday afternoon and evening. Further north, conditions will be windy but not quite as dry. Additionally there is some disagreement in the latest models as to how the thunderstorms will develop and how widespread they will be. With this uncertainty in place the decision was made to hold off on issuing a RFW for North-Central Montana for now. But elevated to near-critical fire weather conditions will be a concern across the entire region. Where thunderstorms do develop, the concerns will be frequent lightning and gusty/erratic winds which may lead to new fire starts and make new and/or existing fires difficult to contain. -thor

PRELIMINARY POINT TEMPS/POPS

GTF 89 53 81 52 / 20 0 0 0 CTB 80 50 76 48 / 20 0 0 0 HLN 86 50 84 54 / 30 0 0 0 BZN 86 49 83 49 / 50 10 0 0 WYS 78 40 79 41 / 30 10 0 0 DLN 85 47 84 49 / 20 0 0 0 HVR 93 55 82 51 / 50 10 0 0 LWT 89 52 78 48 / 50 10 0 0

TFX WATCHES/WARNINGS/ADVISORIES