textproduct: Great Falls

KEY MESSAGES

- Scattered thunderstorms will develop this afternoon and evening, capable of producing strong wind gusts and large hail.

- After somewhat of a lull Sunday and Monday, showers and thunderstorms become more scattered again Tuesday onward.

- Near to above average temperatures this week.

DISCUSSION

/Issued 151 PM MDT Sat Jul 18 2026/

Meteorological Overview:

Southwesterly flow aloft ahead of compact upper troughing to the west and broad upper level ridging to the east will support another day of scattered showers and thunderstorms across the region. Deep mixing (Largely greater than 10k ft) and associated inverted-V profiles by mid-afternoon hours will support thunderstorms capable of strong wind gusts through the evening. While large hail cannot be ruled out, the primary threat today will be for wind gusts.

Aforementioned troughing lifts northeastward from WA tonight and then shifts east across AB/SK Sunday afternoon. A zonal flow aloft ensues as a result, with an ever so slightly anti-cyclonic nature to the flow developing by the afternoon. This looks to inhibit shower and thunderstorm formation in many areas by the afternoon. Areas near the Idaho border between Monida Pass and West Yellowstone will have the greatest probability to see a shower or thunderstorm Sunday afternoon.

Upper level ridging across the Central US extending northwestward toward the Northern Rockies looks to result in an anticyclonic flow aloft across the region much of the upcoming week. That said, monsoonal moisture rebuilds into the region through the western periphery of the ridging by Tuesday, which will result in at least scattered showers and thunderstorms each afternoon Tuesday onward through at least Friday. These looks to be initially terrain based before making inroads toward lower elevations. Gusty winds and heavy rain which could lead to localized flash flooding will be the primary concern with these thunderstorms.

Uncertainty grows for the upcoming weekend, though with at least some variety of southwesterly flow aloft favored, scattered showers and thunderstorms look to continue, primarily in the afternoon and evening hours. -AM

Uncertainty:

There is conditional risk for strong to severe thunderstorms Sunday afternoon, mostly across Central Montana and vicinity. This area looks to see the most robust combination of increased shear from the passing trough to the north as well as the best surface moisture which would result in increased instability and ability to break the cap. Although some weak capping looks to keep most of this thunderstorm activity at bay, should a thunderstorm develop in this environment (Perhaps initially forming over terrain), it would be capable of producing large hail and strong wind gusts. The risk for this scenario will largely depend on how well surface dew points are able to hold on into Sunday. Lingering higher dew points would favor a greater risk of breaking the cap while lower dew points would

AVIATION

19/06Z TAF Period

VFR conditions are expected to persist through the TAF period. There is around a 30% chance for some isolated showers and thunderstorms developing south of the I-90 corridor Sunday afternoon which may impact KWYS and KEKS. The main concern would be lightning and gusty, erratic winds. Across the rest of the region, winds are expected to pick up out of the west/northwest by late morning into early afternoon with widespread gusts up to 25kts possible and higher gusts possible along the Rocky Mountain Front. Minor amounts of wildfire smoke from the west may start to infiltrate into central Montana Sunday afternoon/evening. There may be some very minor reductions to slantwise visibility but overall no major visibility or air quality impacts are expected at this time. -thor

PRELIMINARY POINT TEMPS/POPS

GTF 61 93 57 84 / 10 0 0 0 CTB 57 85 56 80 / 0 0 0 0 HLN 60 93 57 87 / 40 20 0 0 BZN 57 93 57 91 / 30 20 10 0 WYS 49 87 49 91 / 20 40 20 20 DLN 55 90 55 88 / 20 20 10 10 HVR 63 93 58 87 / 40 0 0 0 LWT 57 89 55 82 / 20 20 10 0

TFX WATCHES/WARNINGS/ADVISORIES

None.