textproduct: Great Falls

KEY MESSAGES

- Temperatures trend closer to average heading towards the end of the workweek.

- Daily rounds of showers and thunderstorms become more widespread by Thursday and Friday and will be most impactful for outdoor recreation.

- Breezy to windy conditions will also impact outdoor recreation across southwest Montana on Friday.

- Cool and wet conditions return this weekend into early next week with some instances of high mountain snow.

DISCUSSION

/Issued 514 AM MDT Tue Jun 23 2026/

- Meteorological Overview:

Weak ridging aloft will move over the Northern Rockies for the next few days and bring warmer temperatures and and at least a day with limited shower and thunderstorm activity. The primary concern for this morning will be low stratus and some patchy fog over central and north-central MT this morning and perhaps an isolated storm over the mountains this afternoon. A weak shortwave moves in and brings at least isolated showers and thunderstorms on Wednesday before a stronger shortwave moves in on Thursday and interacts with ML CAPE levels in the 400 to 600 J/kg range for increased thunderstorm coverage and intensity. Another wave of scattered to numerous showers and thunderstorms will move through the forecast area on Friday given southwesterly flow aloft becoming more established ahead of a larger scale trough moving into the Pacific NW. A slight increase in both ML CAPE and bulk shear from warming surface temperatures and the stronger flow aloft may encourage more of these storms to become strong to severe depending on timing. H700 to H500 winds will reach the 20 to 40 kt range by late Friday and will bring some gusty non-thunderstorm winds to the higher mountain peaks and the narrow south to north oriented valleys of southwest MT.

The aforementioned Pacific NW trough will move eastward and bring widespread rain showers and embedded thunderstorms for the first half of the weekend followed by general stratiform rain heading into early next week. This will be a slow moving trough with moisture levels about on par or slightly above climatology, but it's cold core aloft will have temperatures running 2 to 3 standard deviations below average for this time of year. Even though it appears the main area of forcing will be close enough to bring widespread rainfall to most locations, the shearing and transformation of this system makes it difficult to decipher the precise areas of heavier rainfall. Overall, expect a cool, wet weekend, especially Sunday into Monday. There will also be high mountain snow, primarily for elevations above 7000 ft during the overnight and early morning hours. Currently, this looks to set up over the southwestern mountains, but this may change if the positioning the cold core aloft changes and if other areas of dynamic cooling set up. Gusty winds may also develop on the back side of the system on Monday depending on the strength and position of the H700 low. - RCG

- Forecast Confidence & Scenarios:

Increased shower and thunderstorm activity Wednesday through Friday...

Shortwave energy interacting with a seasonably unstable atmospheric profile will result in increased shower and thunderstorm activity during the second half of the workweek. Wednesday's storms look to be the most benign of the three days with showers and storms mostly confined to and near the higher terrain of central and southwest MT. Instability increases on Thursday for more widespread showers and thunderstorms, but there are some disagreements on the strength and evolution of the shortwave and the shear it will bring to the table. Most members favor a weaker wave with less forcing and shear availability for widespread strong to severe storms, though the forcing looks sufficient for more widespread precipitation. On paper, Friday looks to have the best overall environment for stronger storms given increased instability and added shear/forcing from the approaching Pacific NW trough; however, there's nothing really standing out as unusually strong or intense for this time of year. Impacts for all three days will be mostly for those with outdoor recreation plans and will include localized strong gusty winds, hail, downpours in addition to lightning.

Strong and gusty winds over southwest MT on Friday...

The combination of deep layer mixing and the strengthening southwesterly flow may bring gusty to strong winds to southwest MT, particularly over the higher terrain and the south to north oriented valleys. Ensembles seem to be trending with the stronger winds aloft developing to the east of the forecast area, though the set up still favors breezy to windy conditions over the aforementioned areas. The latest NBM probabilities for wind gusts over 50 mph, for most areas south of the I-90 corridor, have fallen slightly to the 20 to 50% range and the probability for 40 mph + sustained winds have largely fallen below 15% at this time. This trend towards lighter winds is fairly new and will be monitored in the coming days. It is also important to note that any showers or thunderstorms that develop on Friday will help transfer stronger wind gusts to the surface. Given increased summer traffic across the area and more people recreating in the mountains, stronger winds will be more impactful than the winds normally observed during the cooler season.

Cool conditions with widespread precipitation and high mountain snow this weekend...

Widespread rain showers and embedded thunderstorms are in the forecast for the first half of the weekend with periods of moderate to heavy stratiform rain and even high mountain snow Sunday into Monday. The latest NBM probability for 1 inch of rain over the 72 hour period ending 6 am Tuesday is now running above 60% for virtually the entire forecast area with roughly 15 to 30% chances for 2 inches or more over most lower elevations during the same period. Mountain snow will depend on where the cold core aloft sets up and where any convective or heavier bands of precipitation artificially lower snow levels with dynamic cooling. The cold core looks to settle over the southwestern mountains Sunday into Monday, but the higher terrain along the Continental Divide and even the central ranges will need to be monitored for temporary lowering of snow levels from dynamic cooling. Snow levels during this entire event should range between 7000 to 9000 feet, lowest during the overnight and early morning hours Saturday night through Monday morning. Anyone with outdoor plans should plan for cool and damp conditions that may be dangerous to those not properly dressed. Also forest and rural roads may become muddy or even impassible from the wet conditions. - RCG

AVIATION

23/18Z TAF Period

Primary concern this TAF period will be for some early afternoon cumulus briefly resulting in isolated MVFR ceilings. As daytime mixing continues cloud bases slowly rise which will mitigate low cloud concerns. Winds will remain on the lighter side through the TAF period. -AM

PRELIMINARY POINT TEMPS/POPS

GTF 71 48 75 49 / 0 0 0 10 CTB 69 45 73 47 / 0 0 0 10 HLN 76 50 79 52 / 0 0 10 30 BZN 77 46 78 47 / 0 0 10 20 WYS 77 39 76 39 / 0 0 30 20 DLN 78 47 79 47 / 0 0 30 30 HVR 71 44 75 48 / 0 0 0 0 LWT 66 42 69 45 / 0 0 10 10

TFX WATCHES/WARNINGS/ADVISORIES

None.