771 FXUS65 KTFX 211810 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 1210 PM MDT Mon Jul 21 2025 Aviation Section Updated. .KEY MESSAGES... - Scattered showers and thunderstorms this afternoon and evening with strong to severe thunderstorms possible in Central MT. - Another round of showers and thunderstorms Tuesday afternoon with an isolated chance for a few strong possible again in Central Montana. - A warm up in temperatures through the forecast period with low end chances for afternoon showers and thunderstorms through the weekend. && .UPDATE... /Issued 1008 AM MDT Mon Jul 21 2025/ Morning update has been published, with the main adjustment being to expand the areal coverage of 15-30% PoPs further south and east into Central Montana through the morning hours. Additionally, PoPs were raised through the afternoon and evening hours to match latest Hi-Res and NBM guidance, especially over the plains of Central and North Central Montana. Hi-Res model guidance continues to signal at a couple of supercells developing across Central and into portions of Southwest Montana early this afternoon, with this activity then lifting to the northeast through the remainder of the afternoon and evening hours. The "highest" window for severe thunderstorms, especially across Central Montana (generally along and north of I-90, south of MT Hwy 200, and east of the I-15), will be between 3PM and 9PM today. This severe weather threat will be conditional on sunny conditions across these areas, which so far this morning skies have remained clear along and southeast of a Helena to Lewistown. With this mind...all signs are pointing towards an active afternoon with respect to severe thunderstorms across portions of Southwest and Central Montana, with large hail, damaging winds, and even a isolated tornado (2-4% chance of occurring) being possible. - Moldan && .DISCUSSION... /Issued 1008 AM MDT Mon Jul 21 2025/ - Meteorological Overview: An upper-level trough will continue to dig along the Pacific Coast. This will keep showers continuing throughout the morning along the Continental Divide and North-Central MT. Late afternoon and evening, a more potent shortwave will pass through, bringing scattered showers and thunderstorms across the region. Good moisture, shear, and instability will bring the potential for strong to severe thunderstorms, primarily in Central MT. Precipitation coverage increases to more widespread throughout the evening and overnight hours into Tuesday. Precipitation continues off and on Tuesday, with another round of afternoon showers and thunderstorms expected. Favorable deep layer shear profiles as well will bring another risk for stronger thunderstorms across Central MT. A frontal passage will keep temperatures below normal today through Wednesday. On Thursday, we transition back to a zonal flow aloft pattern briefly before shift back to more southwesterly flow aloft Friday through the weekend. Moisture looks to be lower Thursday through the weekend, but embedded waves look to pass through daily. Weak instability suggests there is a low end chance for thunderstorms chances to continue through the weekend, but lower moisture suggests little rainfall amounts with them. Temperatures also warm back to near or slightly above normal by the weekend as well. - Forecast Confidence & Scenarios: Recent Hi-resolution models have been hinting at strong to severe thunderstorms this afternoon and evening in timing with the shortwave aloft. Modest CAPE of up to ~1,000 j/kg, deep layer shear of 50-60kts from 0-6km will provide for strong to severe storms, mainly in Central MT. The main hazards will be large hail and severe wind gusts. PWATS of 1" can also create brief heavy downpours with storms. The best area will be in Judith Basin and Fergus County, with an isolated risk mostly extending east of the Bozeman to Great Falls to Harlem line. Hodographs show favorable low level directional shear and helicity for an isolated rotating supercell or two as storms move off the Little Belts and Snowys. Tuesday's storms are more conditional depending on where the shortwave tracks. Currently, this risk resides just to the east of the CWA. However, there is good deep layer shear of 50-60kts from 0-6km. This will provide the environment again for strong to severe storms in Central MT if the shortwave moves farther west. North Central MT still looks favorable of getting the bulk of the precipitation Monday and Tuesday. The 25th percentile of the NBM shows lower end amounts of 0.1"-0.3" of rain and the 75th percentile shows the higher end of 0.4"-0.75" across North-Central MT. Though, those that get a good heavy shower from thunderstorms can see an isolated 1". Lower moisture content later this week will keep precipitation chances limited overall. However, southwest flow aloft bringing embedded waves will keep low end chances for precipitation through the weekend. -Wilson && .AVIATION... 21/18Z TAF Period. IFR conditions prevail across North-central MT with areas of light rain. Expect stronger and more widespread thunderstorms to develop this afternoon over Central MT, along and south of a line from KHLN to KLWT. Some storms will produce strong wind gusts and heavy rainfall. The thunderstorm activity will likely exit the northeast portions of the CWA after 06z Tue. Mountains/passes will be obscured at times by passing thunderstorms. Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .PRELIMINARY POINT TEMPS/POPS... GTF 70 55 74 51 / 70 80 40 20 CTB 58 51 63 45 / 90 90 70 20 HLN 76 55 77 52 / 90 60 50 30 BZN 87 52 79 49 / 50 50 70 40 WYS 81 45 79 41 / 30 20 30 20 DLN 84 49 77 44 / 40 30 50 10 HVR 72 55 72 51 / 30 100 60 20 LWT 75 52 69 49 / 50 90 70 60 && .TFX WATCHES/WARNINGS/ADVISORIES... None. && $$ http://www.weather.gov/greatfalls