textproduct: Great Falls

KEY MESSAGES

- Temperatures warm close to average today despite some isolated shower activity this afternoon.

- Much warmer, drier, and eventually breezier conditions are in the forecast for most if not all of the holiday weekend.

- Breezy to windy conditions and increased shower and thunderstorm activity develop by late Monday into Tuesday.

- Cooler temperatures with periods of scattered to numerous showers move in for the latter part of next week.

UPDATE

Current forecast is on track. No morning update planned for today.

Afternoon temperatures should be a bit warmer than yesterday for most areas. Additionally, there is a small chance for an isolated shower/thunderstorm this afternoon, mostly over North Central MT. Still some cold air aloft, allowing for a bit of the instability. Brusda

DISCUSSION

/Issued 300 AM MDT Fri May 22 2026/

- Meteorological Overview:

Northwesterly flow aloft will maintain variable cloudiness and even some isolated shower activity today, although temperatures will warm to near average. Weak ridging develops over the weekend and warms temperatures well into the 80s by Sunday and Monday. Westerly flow aloft will also strengthen during the second half of the holiday weekend, which will combine with diurnal mixing for breezy to windy conditions, especially along the Rocky Mountain Front and the plains.

A deepening trough is now progged to move onto the Pacific NW coast on Monday with a more unstable south/southwesterly flow aloft developing over the Northern Rockies. Moisture, instability, and shortwave energy look to initiate a round of scattered showers and thunderstorms by Monday evening. Localized thunderstorm winds gusts and isolated lightning should be the primary hazards with dry sub- cloud layers and ML CAPE generally less than 500 J/kg.

The strengthening south/southwesterly winds aloft will also bring breezy to windy conditions, especially over southwest MT Monday night into Tuesday. The strongest brand of showers and thunderstorms also look to occur on Tuesday with trough and attendant cold front approaching the Continental Divide and eventually moving through the forecast area. ML CAPE increases to around 500 J/kg in the southwest and may approach the 1000 J/kg mark over the plains. This looks to be accompanied by bulk shear values above 40 kts, but note that both instability and shear will be highly dependent on the timing of the trough and cold front. Should they be favorably phased with diurnal heating, then there will be an expectation for a more robust brand of thunderstorms. Still thinking that strong wind gusts will be the primary hazard with limited moisture and dry surfaces resulting in DCAPE nearing 1000 J/kg. There will also be at least a period of cooler temperatures and increased shower activity on the backside of this system heading towards the latter part of next week. - RCG

- Forecast Confidence & Scenarios:

Early week thunderstorms and windy conditions followed by more widespread precipitation...

The concern for stronger non-thunderstorm winds continues to be primarily over southwest MT Monday night into Tuesday with some ensembles highlighting a higher amplitude trough and H700 winds approaching 50 kts. Strong to severe thunderstorms will also be a concern, especially if the cold frontal passage is in phase with diurnal heating and the trough sufficiently deepens. Strong, gusty winds near thunderstorms and occasional lightning look to be the primary concerns with this activity, which may result in blowing dust reducing visibility in addition to instances of tree and property damage, depending on how strong the winds get.

With all that being said, a lot can change between now and next Tuesday with ensembles continuing to highlight the closed circulation undergoing various means of shearing, a key factor in determining the timing and location of forcing. This maybe why both the winds and convection have been slow to show a strong signal on climate anomaly indices like the EC Extreme Forecast Index and the NAEFS.

There will also be at least a period of cooler temperatures and more widespread precipitation on the backside of this system heading towards middle and latter portion of next week; however, the latest suite of ensembles now favor the main low moving southward into the Great Basin for less precipitation and colder air availability for mountain snow. - RCG

AVIATION

22/12Z TAF Period

VFR conditions will prevail across all terminals during this TAF Period. Across North-central Montana isolated rain showers will develop after 22/18Z and continue through the end of the TAF Period. At the KCTB, KGTF, and KLWT terminals between 22/21Z and 23/03Z there is a 15 - 20% chance for a rain shower. At the KCTB terminal between 23/00Z and 23/03Z there is a 15% chance for thunder. During any rain shower there will be a brief period of mountain obscuration. -IG

PRELIMINARY POINT TEMPS/POPS

GTF 68 42 76 48 / 20 20 0 0 CTB 67 39 74 45 / 20 20 0 0 HLN 68 41 75 45 / 10 10 0 0 BZN 65 36 74 41 / 10 10 0 0 WYS 60 30 68 34 / 10 20 0 0 DLN 66 37 74 42 / 10 10 0 0 HVR 70 41 79 48 / 10 10 0 0 LWT 63 38 71 44 / 20 20 0 0

TFX WATCHES/WARNINGS/ADVISORIES

None.