textproduct: Great Falls

KEY MESSAGES

- Widespread moderate to locally heavy rain through Sunday morning.

- Isolated thunderstorms across eastern portions of north-central Montana through this evening.

- Minor flooding possible in areas of poor drainage with elevated streamflows across primarily western portions of north-central Montana.

- Unsettled weather with below average temperatures through Tuesday with warming temperatures and some drying mid to late next week.

DISCUSSION

/Issued 547 PM MDT Sat May 30 2026/

- Meteorological Overview:

An upper level low centered over SW WY this afternoon will slowly lift northward into MT Sunday and stall for a period before lifting north of the border early next week as the larger scale Omega blocking pattern of which it is a part of weakens. Showers already covering much of the area early this afternoon will continue to track northwestward in moist southeast to easterly mid-level flow through this evening with a few embedded thunderstorms possible through early this evening, mainly across eastern portions of central/north-central MT. Precipitation evolves into a more TROWAL- like feature later tonight through Sunday morning as the upper low lifts into the State and an area of widespread (non-convective) precipitation pivots around the low with an axis centered across western portions of north-central MT.

Gusty north to northwest winds increase tonight and continue through Sunday as surface low pressure lifts north into SK with cooler air and surface high pressure sliding south on its back side out of southern AB. This will also further cool temperatures across the area with most lower elevation locations holding in the lower 50s through Sunday. Snow levels are initially fairly high (8-10kft) tonight but lower to 7-8kft on Sunday, limiting chances for any accumulation or impacts to the highest terrain above passes.

The upper level low slowly lifts north into southern AB/SK early next week. While widespread precipitation diminishes to showers for most areas Sunday night, cyclonic flow around the low and cool air aloft will maintain below average temperatures and likely a daily risk for showers and possibly some afternoon thunderstorms through at least Tuesday. Temperatures warm back to near seasonal levels mid to late next week with some drying, but there is lower confidence in the timing of a weaker shortwave around Thursday as well as the arrival of the next trough into the Pacific NW next weekend, both of which could generate an increased chance for thunderstorms. Hoenisch

- Forecast Confidence & Scenarios:

An unstable airmass across northeast MT extends as far west as Hill and Blaine counties and may support the development of a stronger thunderstorm or two there through this evening. Otherwise, Thunderstorm activity tracking west/northwest out of eastern MT through this evening will weaken but bring the risk for embedded instances of heavier rainfall/rates.

Overall confidence in forecast precipitation amounts through Sunday night remains good with areas along and west of I-15 from Cut Bank south to Great Falls and the Little Belts west to the Continental divide and Helena and south through the Big Belts and much of northern Gallatin county having a 90% or higher probability for 1.00" or greater precipitation amounts. 2.00" or greater amounts will likely depend on where exactly the TROWAL feature sets up with areas from Glacier County southeast through Cascade county and the Little Belts most probable(40-60% chance). 3.00" or greater amounts will be limited and most likely to occur where upslope enhancement occurs Sunday. This includes areas near Highwoods and north slopes of the Little Belts where probabilities are as high as 60%, decreasing to around 30% at Great Falls. Hoenisch

AVIATION

31/06Z TAF Period

Widespread rain will continue through Sunday evening with most locations expected to stay within MVFR to IFR CIGs and VIS through the majority of the TAF period. Mountain obscuration will remain a concern throughout the period. West/northwest winds start to pick up after 31/04Z and will continue through the rest of the period with strongest winds expected along the Rocky Mountain Front into the Hi-Line. There is another chance for some isolated thunderstorms Sunday afternoon, however with even weaker instability expected compared to Saturday, confidence was not high enough to include it in the TAF. -thor

HYDROLOGY

Widespread rainfall amounts of the magnitude expected through Sunday night are not unusual for late spring weather systems and climate data shows a recurrence interval of about every 2-5 years. Recent dryness and lower than average streamflows during what would typically be peak snowmelt will help to mitigate some of the runoff from this precipitation as well. Some minor flooding/ponding of water in low-lying fields and urban areas with poor drainage is the main concern in areas that receive 2" or more rainfall through Sunday. Creeks emanating from the Rocky Mtn Front, Little Belts and Highwoods are likely to see increased volume and may exceed banks. The risk for intense precipitation rates is mainly with decaying convection through this evening, but this will be monitored for potential impacts to more sensitive areas including recent burn scars and areas of steep terrain. The risk for flooding along the Sun River and other rivers originating along the Rocky Mountain Front has decreased with newer forecast data, however a rise to around bankful is still expected and will continue to be monitored as well. Hoenisch

PRELIMINARY POINT TEMPS/POPS

GTF 42 59 40 63 / 90 60 30 30 CTB 37 52 36 56 / 80 90 60 70 HLN 42 63 42 67 / 80 50 30 30 BZN 36 64 37 69 / 50 40 40 10 WYS 29 63 30 67 / 30 20 20 10 DLN 37 63 37 69 / 30 50 30 10 HVR 39 59 38 64 / 90 80 30 40 LWT 37 59 38 64 / 80 50 50 50

TFX WATCHES/WARNINGS/ADVISORIES

Flood Watch through Monday afternoon for Cascade County below 5000ft-East Glacier Park Region-Eastern Glacier, Western Toole, and Central Pondera-Eastern Pondera and Eastern Teton-Gates of the Mountains-Northern High Plains-Southern High Plains-Southern Rocky Mountain Front.