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

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 favor the cap remaining in place. -AM

AVIATION

18/18Z TAF Period

Initial concern this TAF period will be for development of showers and thunderstorms this afternoon and evening, capable of producing strong winds gusts, small hail, and lightning. Should any of these showers or thunderstorms produce briefly heavy rain, there will be the risk for some fog by Sunday morning. The confidence in this occurring was too low to warrant mention in any TAF at this point, however. Looking ahead toward Sunday during the day, breezy west to northwest winds look to develop in most areas by late morning. -AM

PRELIMINARY POINT TEMPS/POPS

GTF 61 93 57 85 / 20 0 0 0 CTB 57 85 55 80 / 10 0 0 0 HLN 60 92 56 87 / 50 20 10 0 BZN 57 94 56 91 / 30 20 20 0 WYS 49 88 49 89 / 30 20 20 0 DLN 55 90 54 88 / 30 20 20 0 HVR 63 93 57 87 / 40 0 0 0 LWT 57 89 54 82 / 20 20 20 0

TFX WATCHES/WARNINGS/ADVISORIES

None.