textproduct: Great Falls

KEY MESSAGES

- Mostly dry through Thursday, with thunderstorms returning to Southwestern Montana Friday.

- Additional thunderstorms expected Saturday, some of which could be strong and produce heavy rainfall.

- Temperatures will generally be seasonable, though above average temperatures are expected Friday and Saturday.

DISCUSSION

- Meteorological Overview:

Upper level ridging has continued to build across the Western US today, which has resulted in generally clear, albeit slightly smoky, skies across North Central and Southwestern Montana today. Aside from a low risk of a thunderstorm along the Hi Line tonight, expect the remainder of the day today to be dry and seasonably warm, which will continue into Thursday as well.

Although the ridge peaks Friday, monsoonal moisture will begin to work into the area Friday, which will help kick off a few afternoon/evening showers and thunderstorms, mainly across Southwestern and Central Montana. While these should dissipate with the loss of daytime heating, monsoonal moisture will remain in place on Saturday as the ridge wanes, resulting in a breezy day with widespread afternoon thunderstorms, some of which may produce some heavy rainfall and/or be on the strong side.

After the ridge weakens, zonal flow will set up briefly across the area before ridging returns early next week. Expect temperatures to remain around average for late August, with periodic chances for afternoon thunderstorms. Ludwig

- Forecast Confidence & Scenarios:

On Saturday there is a 30 - 45% chance for thunderstorms in Southwestern Montana. On Saturday there is a 15 - 30% chance for thunderstorms across North-central and Central Montana. On Sunday there is a 25 - 35% chance for thunderstorms across Central and Southwestern Montana. On Sunday there is a 15 - 20% chance for thunderstorms across North-central Montana. Saturday through Sunday there is a 25 - 50% chance for a quarter inch of rain or greater across Southwestern Montana. Precipitable Water (PWAT) will increase this weekend which has to potential to lead to localized flash flooding on burn scars with the stronger thunderstorms.

On Saturday there is greater than a 50% chance for wind gusts of 25 mph or greater across North-central, Central, and Southwestern Montana. On Saturday in northern Blaine County there is greater than a 70% chance for wind gusts of 40 mph or greater. On Sunday there is greater than a 50% chance for wind gusts of 30 mph or greater across North-central, Central, and Southwestern Montana. On Sunday there is a 50 - 75% chance for wind gusts of 40 mph or greater along the Hi-Line, Southern Rocky Mountain Front, and in Cascade and Judith Basin County. On Sunday afternoon across North- central Montana there is a 15 - 30% chance for wind speeds of 15 mph or greater combined with relative humidity of 20% or less (red flag criteria). On Sunday there is low confidence in relative humidity reaching critical levels and so at this time it appears on Sunday there will be at least elevated fire weather concerns due to gusty winds. -IG

AVIATION

20/00Z TAF Period

VFR conditions are expected across the CWA through the period. Areas of high clouds will affect North Central MT overnight. Additionally, smoke continues to move into the CWA from the west, reducing distant visibility and obscuring mountains/passes across the CWA.

For KGTF: Winds will generally be light over the next 24 hours. Variable winds this evening and overnight will generally become a southwesterly wind direction on Thursday morning. Brusda

PRELIMINARY POINT TEMPS/POPS

GTF 56 91 56 87 / 0 0 0 0 CTB 52 84 52 82 / 0 0 0 0 HLN 53 91 58 93 / 0 0 0 0 BZN 50 90 54 93 / 0 0 0 0 WYS 39 85 45 90 / 0 0 0 0 DLN 49 87 53 89 / 0 0 0 0 HVR 55 91 56 89 / 0 0 0 0 LWT 53 88 55 85 / 0 0 0 0

TFX WATCHES/WARNINGS/ADVISORIES

None.