textproduct: Great Falls

KEY MESSAGES

- A warming trend continues through Tuesday, although weak passing weather systems may bring a few isolated showers or storms for northern areas tonight through early Tuesday.

- Warm and windy conditions develop on Tuesday followed by periods of showers and thunderstorms and more gusty winds Tuesday evening through Wednesday.

- General unsettled conditions continue for the second half of next week with more opportunities for showers and storms.

DISCUSSION

/Issued 538 AM MDT Sun Jun 14 2026/

- Meteorological Overview:

Northwesterly flow aloft generally remains in place through the end of the workweek. The eastern periphery of a strengthening Pacific ridge will bring a warming trend over the Northern Rockies through Tuesday. Although dry conditions generally prevail, there will be a few weak shortwaves that bring a few isolated showers or storms, mostly along the Hi-Line tonight through Tuesday.

Westerly flow aloft increases late Monday into Tuesday in advance of an approaching shortwave and attendant cold front with H850/H700 winds increasing to the 40 to 50 kt range by Tuesday evening. This will bring windy and dry conditions Tuesday afternoon while temperatures surge well into the 80s. A Canadian cold front moves southward sometime Tuesday evening through early Wednesday and sends a wave of showers and thunderstorms through the forecast area, most numerous over central/north-central MT. CAPE values for this time period look to remain only around a few hundred J/kg; however, bulk shear will generally be over 40 kts so there will be at least localized strong wind gusts, some hail, and downpours with this activity.

Gusty northwesterly winds and scattered shower/thunderstorm activity linger on the backside of this system through Wednesday evening and general unsettled conditions continue for the remainder of the second half of the week. Shower and thunderstorm activity looks to ramp up again for the weekend with CAPE values approaching the 1,000 J/kg at times and subtle shortwaves providing sufficient forcing for stronger convective initiation. - RCG

- Forecast Confidence & Scenarios:

Windy conditions and thunderstorms Tuesday and Wednesday...

Westerly winds increase on Tuesday in advance of an approaching trough and cold front. The NAEFS anomaly index continues to advertise H700/H500 winds approaching three standard deviations above climatology. NBM probabilities for 50 mph + gusts continue to run in the 60 to 80% range along the Rocky Mountain Front/plains west of I15 Tuesday afternoon, but the swath of similar probabilities over central and southwest MT have become more widespread Tuesday evening/night.

The most relevant uncertainties continue to be the timing of the strongest winds aloft and whether they will move through during peak diurnal mixing or later in the evening with less momentum transfer. The Canadian cold front and any pre-frontal northerly winds shifts will also affect wind magnitude and duration for northern areas, especially areas along the Northern Rocky Mountain Front. The timing of showers and thunderstorms will also be highly dependent on the frontal passage. Thunderstorm hazards, including localized strong wind gusts, hail, and downpours will be most widespread over central/north-central MT Tuesday evening, especially along the Hi- Line.

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 H700 winds to the surface.

The primary impact from these winds and shower/thunder activity still looks be inclement outdoor recreation and difficult travel for those operating high profile vehicles. Also, the combination of temperatures warming well into the 80s and RHs falling to near critically low levels on Tuesday will also be monitored for fire weather concerns, although fuels will be less receptive given the recent rainfall and greenup. Areas that have missed out on the rainfall, like southwest MT, will be monitored for elevated fire concerns. - RCG

AVIATION

14/18Z TAF Period

VFR conditions prevail through the TAF period. Generally, a few passing high clouds through the TAF period with calmer winds. Monday morning, there will be a low end chance for light isolated showers along the Hi-line, but low confidence in impacting KHVR resulted in it being left out of the TAF. -Wilson

PRELIMINARY POINT TEMPS/POPS

GTF 71 45 78 55 / 0 0 0 10 CTB 71 45 78 57 / 0 0 10 30 HLN 73 44 80 55 / 0 0 0 10 BZN 70 39 77 48 / 0 0 0 0 WYS 68 32 75 38 / 0 0 0 0 DLN 69 40 79 48 / 0 0 0 0 HVR 74 46 78 52 / 0 10 20 30 LWT 68 41 71 49 / 0 0 10 20

TFX WATCHES/WARNINGS/ADVISORIES

None.