textproduct: Great Falls

KEY MESSAGES

- Shower and thunderstorms chances continue through Tuesday, with some of the stronger storms producing gusty outflow winds and heavy downpours.

- Temperatures near normal through much of the upcoming week.

- Gusty winds return from the middle of the work week through the upcoming weekend, which combined with dry conditions will lead to elevated fire weather conditions.

DISCUSSION

- Meteorological Overview:

Monsoonal moistures lifting north and east around upper level ridging centered over the Central Rockies through the Desert Southwest will support another day of scattered to numerous showers and thunderstorms across Southwest Montana, with isolated to widely scattered showers and storms over Central and North Central Montana. While showers and thunderstorms will decrease in coverage through the late evening hours tonight an isolated shower or storm can't be ruled out into the early morning hours on Monday, most notably over the plains of Central and North Central Montana where weak low level frontogenetic forcing will reside throughout the overnight hours. Partly clearing skies beyond midnight tonight combined with recent precipitation and light winds will support another opportunity for patchy fog across the Northern Rockies; most notably in the prone valleys of Central and Southwest Montana. - Moldan

By Monday 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 showers and thunderstorms Monday 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. 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 remain around seasonal averages. On Wednesday and Thursday it will be mostly dry across the area. 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 strong low-level and mid- level winds it will be breezy on Saturday. -IG

- Forecast Confidence & Scenarios:

Showers and Thunderstorms through Tuesday...

Sufficient shear, but marginal instability, will help to support continued chances for convection through the first half of the upcoming work week as monsoonal moisture continues to lift north and east around broad ridging centered over the Central Rockies and Desert Southwest. Inverted-V soundings and and tall skinny CAPE profiles support the potential for gusty outflow winds and the potential for periods of heavy rainfall, especially across Southwest Montana.

Gusty Winds from Wednesday through next Sunday...

Increasing zonal to southwesterly flow aloft will support gusty winds, most notably during the afternoon and evening hours, from the middle to the work week through next weekend with the exception of Thursday. These gusty southwest to west surface winds will initially occur along the Rocky Mountain Front on Wednesday, with a 20-30% chance that gusts exceed 35 mph. By Friday NBM5.0 probabilities for wind gusts exceeding 35 mph expand to all areas, with probabilities increasing to between a 20-60% chance for the upcoming weekend. While 35 mph wind gusts are not unusual, let alone noteworthy during the windy season, moderating temperatures and dry conditions will lead to increasing fire weather concerns given these speeds. - Moldan

AVIATION

16/18Z TAF Period

Another round of widely scattered showers and thunderstorms will move from southwest to northeast, generally between 16/20 and 16/06Z. Some storms will produce brief strong, gusty winds, cloud to ground lightning, and brief downpours. Brief low VFR /MVFR conditions may occur with the stronger cells. Patchy fog may develop again tonight between 17/09 and 17/16Z in the KWYS area, but confidence was too low to put in the TAF for now with less than a 10% chance for impactful fog.

For KGTF: Winds will generally remain light away from showers and storms during this TAF period. There is around a 20% chance for thunderstorms to affect KGTF between 16/22Z and 17/04Z. The primary risks from any thunderstorms will be gusty, erratic winds up to 35 kts and lightning. - RCG

PRELIMINARY POINT TEMPS/POPS

GTF 52 83 54 84 / 20 20 10 20 CTB 48 77 48 79 / 20 20 20 10 HLN 51 84 55 83 / 20 20 20 20 BZN 48 81 50 81 / 50 10 30 20 WYS 35 77 39 76 / 30 30 40 40 DLN 47 80 50 79 / 30 20 30 30 HVR 52 83 51 85 / 20 20 20 10 LWT 50 79 52 79 / 20 20 10 40

TFX WATCHES/WARNINGS/ADVISORIES

None.