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KEY MESSAGES

- A cold front will bring lower temperatures but continued chances for thunderstorms on Sunday. Some storms may produce severe wind gusts and brief heavy rainfall.

- A Lake Wind Advisory continues for Fort Peck Lake through 6 PM MDT Sunday.

- Temperatures will recover for the second half of the week with highs each day largely in the 80s.

DISCUSSION

WEATHER PATTERN OVERVIEW:

A cold front and upper trough will deliver a combination of lower temperatures, increasing west to northwest winds, and continued showers and thunderstorms for Sunday. SPC maintains a Marginal Risk for the east where severe wind gusts are a concern. These locations will see the warmest daytime temperatures and more unstable conditions. Overall, HREF shows timing as early as 18Z for the wind threat emerging, with activity evolving east by evening hours. A few of the storms may produce locally heavy rainfall as well.

As west winds ramp up on Sunday, a Lake Wind Advisory for Fort Peck Lake remains in effect until 6 PM MDT. Windy conditions will relax during the evening but ramp back up on Monday. That said, will defer headline decisions until later as trends have shifted winds to be more focused on the east side of the lake.

Upper ridging will then guide warmer and drier conditions to NE Montana for Tuesday. The ridge axis looks to slide east late in the week with diffluent southwest upper flow becoming established over the Northern High Plains. In short, the next round of thunderstorms may get underway as early as Wednesday evening.

FORECAST CONFIDENCE & DEVIATIONS:

NBM was given a modest blend with NBM90 for an upward nudge given the cold air advection. Pops were adjusted for near term collaboration and consistency. Otherwise there were no major deviations with model consensus lending to above average confidence this forecast cycle for cooler temperatures with thunderstorm chances on Sunday, followed by quiet weather on Tuesday. Confidence is also increasing on more active weather in the form of thunderstorms by midweek as the ridge translates downstream, supported by dynamic lift and increased instability.

AVIATION

LAST UPDATED: Sunday August 30 at 0630Z.

FLIGHT CAT RANGE: VFR, MVFR in thunderstorms.

DISCUSSION: An upper trough will help maintain shower and thunderstorm chances across area terminals for Sunday.

WINDS: Variable winds will become west to northwest at 10 to 20 kts, gusting to 30 kts. Winds look to diminish after 01Z Sunday.

GGW WATCHES/WARNINGS/ADVISORIES

Lake Wind Advisory from 7 AM this morning to 6 PM MDT this evening for Central and Southeast Phillips-Central and Southern Valley-Garfield-McCone-Petroleum.