textproduct: Great Falls

KEY MESSAGES

- Slightly cooler temperatures and scattered shower and thunderstorm activity will continue today, most numerous over central and north- central Montana.

- Very warm, mostly dry, and breezy to locally windy conditions develop late Sunday through mid- week.

- Shower and thunderstorm activity increases for the second half of the work week, along with more breezy to windy conditions.

- Next weekend looks to feature slightly cooler temperature with continued scattered shower and isolated thunder activity.

DISCUSSION

/Issued 243 AM MDT Sat May 9 2026/

- Meteorological Overview:

The shortwave trough responsible for the shower activity this morning will move southeast of the forecast area by around noon, though lingering instability behind this system will maintain widely scattered shower and thunder activity over central and north-central MT.

Transient ridging aloft quickly replaces the departing wave and brings much warmer and drier conditions by Sunday afternoon. Surface winds will begin increasing late Sunday through Monday in response to a another shortwave moving eastward along the Canadian border. The primary concern with the winds will be at least a brief period elevated fire weather conditions, particularly along the Hi-Line and down in the southwest where antecedent ground conditions are driest. The passing shortwave will have little impact on temperatures with afternoon highs continuing to run mostly in the 70s and 80s for lower elevation locations.

A closed mid-level trough moving onto the Pacific coast will bring a more unstable southeasterly flow aloft for the Wednesday through Friday period. This will introduce daily rounds of shower and thunderstorm activity, some of which maybe on the stronger side with CAPE values approaching 1,000 J/kg on some days. Windy conditions look to develop when the trough and attendant cold front approaches either Thursday or Friday. Ensemble guidance continues to display disagreements with the timing of the trough and this will have a significant impact on the timing of thunderstorm activity and the strongest winds. The overall unsettled weather pattern looks to continue heading into next weekend with more Pacific troughs approaching the Northern Rockies. - RCG

- Forecast Confidence & Scenarios:

Winds and fire weather concerns late Sunday and Monday...

A shortwave trough races eastward along the Canadian border Sunday night into Monday and brings breezy to windy conditions over much of the forecast area. Winds will increase along the Rocky Mountain Front and adjacent high plains late Sunday afternoon with gusts over 50 mph at times Sunday night through Monday morning. The remainder of the forecast are will generally see wind gusts mostly in the 25 to 40 mph range during the day on Monday. The exception to this will be over Hill and Blaine counties and again along the Rocky Mountain Front and nearby high plains. These areas currently have a 60 to 90% chance for gusts over 40 mph. The combination of winds, near or critically low minimum RHs, and dry antecedent conditions will bring the highest fire risk to Hill and Blaine counties on Monday. The one uncertainty that may preclude an extended period of elevated to critical fire weather conditions will be increasing humidities behind a surface front Monday afternoon. Held off issuing a fire weather watch for now given low confidence of an extended period of critical conditions, but the situation will continue to be monitored.

Increased shower and thunderstorm activity and winds Wednesday through Friday...

Ensembles continue to agree on a more unstable southwesterly flow developing and bringing multiple rounds of shower and thunderstorm activity during this timeframe; however, there are inconsistencies on which day will have the highest CAPE in the 500 to 1,000 J/kg range. Overall, there is an expectation for daily lightning and gusty wind threats given at least a few hundred joules of CAPE and very warm and dry sub cloud layers. The timing of the trough and associated shortwaves will ultimately determine which day will see the most robust convective activity and severe hail/wind threat.

Around a quarter of the ensembles were highlighting the trough ejecting eastward into the Northern Rockies as early as late Wednesday into Thursday and bringing widespread strong winds with it. The newer deterministic guidance seems to be backing off of this solution, though anomaly indices, including the ECMWF Extreme Forecast Index still have a weak signal for anomalously strong winds and NBM probabilistic guidance still paints a daily 20 to 30% chance for gusts over 55 mph for much of the forecast area Wednesday through Friday. Both the thunderstorm activity and wind situations will be monitored for this timeframe in the coming days. - RCG

AVIATION

09/12Z TAF Period

An area of concentrated showers and associated low VFR/MVFR conditions and mountain obscuration over and near the central island ranges will continue to move southeast and diminish as the morning progresses. There will be lingering instability for additional widely scattered showers and isolated thunder over central and north-central MT between 09/18 and 10/00Z. Partial clearing takes place tonight with some patchy fog development late tonight into Sunday morning, mostly over the river valleys. Confidence was too low to mention fog in any TAF for tonight. - RCG

FIRE WEATHER

Very warm, dry, and breezy to locally windy conditions develop late Sunday into early next week with the driest and windiest day looking to be Monday. Hill and Blaine counties currently have the driest antecedent ground conditions and will have over 70% chance for wind gusts over 40 mph. Dry fuels are also being observed over southwest Montana as well, but the stronger winds will be more localized in these areas. The one factor that may preclude an extended period of elevated to critical fire weather conditions along the Hi-Line will be increasing humidities behind a Canadian surface front Monday afternoon. Be mindful of the upcoming very warm and dry conditions and avoid activities involving sparks or open flames. - RCG

PRELIMINARY POINT TEMPS/POPS

GTF 66 43 82 55 / 80 10 0 0 CTB 65 41 78 51 / 30 10 0 0 HLN 69 41 81 50 / 10 0 0 0 BZN 66 36 79 46 / 10 0 0 0 WYS 61 30 72 39 / 0 0 0 0 DLN 66 37 80 47 / 0 0 0 0 HVR 69 40 82 52 / 20 10 0 0 LWT 59 39 77 50 / 90 20 0 0

TFX WATCHES/WARNINGS/ADVISORIES

None.