textproduct: Great Falls

KEY MESSAGES

- Warm and windy conditions develop by this afternoon followed by showers and thunderstorms with localized strong winds, hail, and downpours moving southward through the plains this evening.

- Cooler, showery, and breezy to windy conditions move in on Wednesday, especially for central and north-central Montana.

- The workweek will finish with a warming and drying trend before shower and thunderstorm activity increases again and temperatures cool down this weekend.

DISCUSSION

/Issued 220 AM MDT Tue Jun 16 2026/

- Meteorological Overview:

A weak shortwave embedded within a northwesterly flow has brought some light shower activity to the Milk River Valley this morning. This activity should quickly move off to the east by dawn. Then the focus will shift to the 45 to 55 kt H700 jet streak that will pass through later this afternoon. The combination of this with deep layer mixing will result in windy, warm, and dry conditions for virtually the entire forecast area. Areas along the Rocky Mountain Front southward to MacDonald Pass, the plains west of I15, and portions of the central MT highway 87/200 will see the strongest winds for the longest period. There will also be some instances of gusts exceeding 50 to 55 mph over and near the Big Belt Mountains and some of the higher peaks in southwest MT. Relative humidities will fall to near critical levels while temperatures warm into the 80s. This will cause some localized fire weather conditions, mostly for southwest MT where the fuels are somewhat drier.

A Canadian cold front and associated showers and thunderstorms move southward through central and north-central MT late this afternoon through tonight. CAPE values for this time period still look to remain around 200 to 500 J/kg; however, bulk shear will generally be over 40 kts and will be supportive of localized strong wind gusts, hail, and downpours, especially during the evening hours.

Gusty northwesterly winds and scattered shower/thunderstorm activity linger on the backside of this system through Wednesday evening. General unsettled conditions continue for the remainder of the second half of the workweek, though it will be drier and warmer heading towards the first half of the weekend. There are some disagreements with the precise details for this weekend, but there is agreement with shortwaves interacting with ML CAPE values above 500 J/kg for increased shower and thunderstorm activity sometime Saturday into Sunday. Temperatures also look to warm closer to average Friday and Saturday before cooling off again Sunday into early next week. - RCG

- Forecast Confidence & Scenarios:

Windy, warm, and dry conditions today followed by evening thunderstorms...

Westerly winds increase significantly in advance of an approaching trough and cold front today. The NAEFS anomaly index has H700/H500 winds approaching three standard deviations above climatology and the EC EFI is now running between .7 and .9 for anomalously strong winds over the plains westward to the Rocky Mountain Front. Values approaching 1.0 suggest highly unusual strong winds for this time of year when compared to climatology. NBM probabilities are also increasing with the chance for 55 mph + gusts now running in the 70 to 90% range for areas along the Rocky Mountain Front southward to MacDonald Pass, the plains west of I15, portions of the central MT highway 87/200, and over the Big Belt/Bridger ranges.

There is still some uncertainty on whether these winds will persist for longer than a three hour period, but it's looking more like the answer to this question is trending towards yes given H700 winds ramping up by the early afternoon hours. Also model guidance continues to hold the Canadian front north of the international border through at least 6 pm this evening. It would take early thunderstorm initiation to bring it southward sooner which would result increased instances of convectively driven strong winds. Given these factors, I opted to go with a high wind warning for these aforementioned areas. Technically, I could leave the Rocky Mountain Front zones out of the warning since 75 mph gusts are not expected, but it's the warm season now and there will be more ongoing activities compared to the typical high wind season when winds gust in the 55 to 65 mph range occur regularly. Note that areas outside of these warnings will be windy as well and may even observe some isolated criteria gusts or sustained winds.

Showers and thunderstorms will move from north to south through central/north-central MT late this afternoon through the early overnight hours. Thunderstorm hazards may include localized strong wind gusts, hail, and downpours. This activity will be most widespread along the Hi-Line, especially over Hill and Blaine counties. With that being said any central/north-centgral location will be susceptible to isolated instances of these hazards.

The primary impact from today's winds and subsequent shower/thunder activity still looks be inclement outdoor recreation and difficult travel for those operating high profile vehicles. Also, it's important to note the combination of temperatures warming well into the 80s and RHs falling to near critically low levels this afternoon may result in localized elevated fire weather conditions, mostly for southwestern locations that have missed out on the rainfall or are having a poor greenup.

Gusty northwesterly winds and lingering scattered showers and thunderstorms on Wednesday...

The winds will shift to a more northwesterly direction on Wednesday and will generally be strongest over the plains east of I15, especially along the Hi-Line and over portions of Fergus County. Showers and thunderstorms will mostly be concentrated over central/north-central MT again and will generally be weak; however, they will be capable of transferring the stronger 40 to 50 kt winds aloft to the surface at times. - RCG

AVIATION

16/12Z TAF Period

Gusty to strong westerly winds develop by this afternoon for much of the forecast area. This will be accompanied by mountain wave turbulence and instances of low level wind shear. Scattered showers and thunderstorms will develop from north to south after 16/20Z and will mostly impact the plains terminals through around 17/08Z. Localized erratic wind gusts, hail, and brief downpours will accompany the stronger cells. General VFR conditions will prevail, but lower VFR and some MVFR clouds will become more widespread over the plains after 17/00Z. - RCG

PRELIMINARY POINT TEMPS/POPS

GTF 86 50 71 46 / 10 50 40 40 CTB 80 45 67 43 / 40 70 50 50 HLN 86 52 75 47 / 0 0 20 0 BZN 88 52 75 44 / 0 0 10 0 WYS 82 40 73 34 / 0 0 0 0 DLN 86 48 77 42 / 0 0 0 0 HVR 85 48 70 43 / 50 60 40 20 LWT 82 45 65 41 / 10 90 20 20

TFX WATCHES/WARNINGS/ADVISORIES

High Wind Warning from noon today to midnight MDT tonight for Big Belt, Bridger and Castle Mountains-East Glacier Park Region- Eastern Glacier, Western Toole, and Central Pondera-Judith Basin County and Judith Gap-Northern High Plains-Southern High Plains- Southern Rocky Mountain Front-Upper Blackfoot and MacDonald Pass.