textproduct: Great Falls

KEY MESSAGES

- Showers and thunderstorms will affect the area this afternoon/evening and Tuesday afternoon/evening.

- Temperatures will be around seasonal averages throughout this week.

- It will be dry Wednesday through Friday with thunderstorms returning this weekend with breezy conditions.

DISCUSSION

- Meteorological Overview:

Today there is an upper-level ridge with southwest flow aloft over North-central, Central, and Southwestern Montana. By this evening the upper-level ridge begins to break down and an upper- level trough begins to move over the area. This will bring breezy conditions to the area with isolated showers and thunderstorms this afternoon and evening. Temperatures will remain near seasonal averages on Monday. On Tuesday there will be zonal flow (west - east) over North-central, Central, and Southwestern. This will allow temperatures to remain near seasonal averages with breezy conditions due to modestly strong low and mid-level winds. There will also be showers and thunderstorms across North-central, Central, and Southwestern Montana on Tuesday.

On Wednesday and Thursday an upper-level ridge begins to build back in across North-central, Central, and Southwestern Montana. On Wednesday and Thursday temperatures will warm back up to around seasonal averages with dry weather. On Friday the upper-level ridge is over North-central, Central, and Southwestern Montana. This will bring hot and dry weather to the area. On Saturday an upper-level trough begins to move over North-central, Central, and Southwestern Montana. This will bring showers and thunderstorms back to the area. Due to modestly strong low-level and mid-level winds it will be breezy on Saturday. On Sunday the upper-level trough is over North-central, Central, and Southwestern Montana. This will cool down temperatures slightly and bring another round of showers and thunderstorms to the area. On Sunday due to modestly strong low and mid-level winds it will be breezy across North-central, Central, and Southwestern Montana. -IG

- Forecast Confidence & Scenarios:

This morning in any areas that clear fog has a high chance to form. The areas that have the greatest risk for fog forming this morning are the valleys of Southwestern Montana.

Today the Storm Prediction Center (SPC) issued a Marginal Risk for Severe Thunderstorms (5% chance for wind gusts of 58 mph or greater within 25 miles of a point) for Judith Basin and Fergus Counties. Today there is a 15 - 25% chance for thunderstorms across North-central and Central Montana. Today there is a 20 - 35% chance for thunderstorms in Southwestern Montana. On Tuesday there is a 20 - 30% chance for thunderstorms across North-central, Central, and Southwestern Montana. Winds will increase and relative humidity will decrease Wednesday through Friday which will lead to elevated fire weather conditions. -IG

AVIATION

17/06Z TAF Period

A few showers and weak thunderstorms are lingering across Central and Southwest MT but should move out by 09Z. There is a 40% chance for patchy fog and mist to set up again between 17/09 and 17/15Z in the KWYS area with MVFR to IFR ceilings and visibility. VFR conditions are expected throughout the rest of the terminals tonight into the morning. Tomorrow afternoon's thunderstorms will be less widespread and begin after 17/21Z over the Rocky Mtn Front and Southwest MT however some isolated cells may become severe between the KHVR and KLWT area from 18/00Z and 18/04Z. Model guidance on exact timing and coverage amount is still uncertain.

For KGTF: Prevailing winds tonight will be light and variable with VFR conditions. Winds will shift to the West after 17/20Z at around 12 KT predominantly. While confidence is still low, there is a 10% chance for an isolated thunderstorm to impact the terminal area tomorrow afternoon from 17/23Z to 18/01Z. - Akins

PRELIMINARY POINT TEMPS/POPS

GTF 82 55 83 52 / 20 20 20 10 CTB 76 50 77 50 / 30 20 10 10 HLN 83 57 82 53 / 20 20 30 10 BZN 81 53 80 48 / 30 30 20 30 WYS 75 43 73 35 / 30 30 30 30 DLN 79 51 78 46 / 30 30 30 20 HVR 82 53 83 53 / 20 20 10 20 LWT 77 52 77 50 / 20 30 40 20

TFX WATCHES/WARNINGS/ADVISORIES

None.