Area Forecast Discussion

KEY MESSAGES

- Scattered showers and isolated thunderstorms develop mainly along and east of I-15 this afternoon.

- Another round of scattered to widespread showers with isolated thunderstorms expected on Sunday.

- Strong and gusty winds across Southwest Montana today, with gusty conditions expanding to all areas on Sunday.

- An active, cooler weather pattern is on tap Tuesday through the work week.

DISCUSSION

- Meteorological Overview:

Showers and thunderstorms will develop this afternoon across Southwest and Central Montana before lifting northeast across the remainder of Central and North Central Montana. Areal coverage of precipitation will be highest from the late afternoon through evening hours tonight, especially along northeast of a Ennis, to Helena, to Great Falls, to Havre line. A few of the thunderstorms over this timeframe could produce strong and gusty winds, especially across Southwest Montana and portions of Central Montana (Judith Basin, Fergus, and Blaine Counties). - Moldan

On Sunday, the main trough axis moves through the region. A cold front passage Sunday will bring better chances for scattered to widespread precipitation during the day. Weak instability will allow for some thunderstorms to develop, mainly towards Central MT. Snow levels falling to 6,000 to 7,000ft Sunday morning along the southern Continental Divide and down to 5,500ft towards the northern Continental Divide will allow for light mountain snow to develop. Below normal temperatures are expected Sunday. Stronger flow aloft with the trough passing through will slow bring another breezy to windy day, especially across Southwest MT.

With this trough exiting the region, Monday will be a drier day overall. Though Southwesterly flow aloft will continue to bring a low end chance for light showers during the day and breezy winds. The main closed 500mb low moves onshore Tuesday, and slowly make it's way east through eh week. This will bring another active, cooler pattern for the week. There are some differences in models with the amplitude and timing of this next trough, which will bring subtle differences in precipitation amounts. However, ensembles are in agreement for a wetter cooler pattern through at least next Friday. - Wilson

- Forecast Confidence & Scenarios:

Strong and Gusty Winds through Sunday

Strong and gusty winds initially over Southwest Montana today, mainly south of the I-90 corridor, will expand across the remainder of Southwest through North Central Montana for the day on Sunday. For areas along and southeast of a Dillon, to Ennis, to Big Sky there is a 50% or greater chance for wind gusts to exceed 40 mph through the remainder of the afternoon and into the evening hours, with even a 30-70% chance that gusts exceed 50 mph. Isolated higher wind gusts are possible through the afternoon and evening hours today beneath decay showers and thunderstorms given inverted-V soundings across the area. By Sunday increasing cross barrier flow associated with the upper level low moving overhead will help to support strong and gusty west winds across all areas, with a 40% or greater chance for wind gusts of 40 mph across any given area and a 60-80% chance for gusts of 50 mph along the Rocky Mountain Front and southeast of a Monida Pass to Big Sky line. - Moldan

Thunderstorm Risk through Sunday:

The main limiting factor Sunday is the timing of the cold front. The cold front is already reaching Fergus and Blaine County by 12pm, which does not support robust surface heating for thunderstorms. A little slower in the time of precipitation will increase the risk for stronger storms. With PWATs decreasing throughout the day, the heavy rainfall threat with storms are low. - Wilson

AVIATION

06/18Z TAF Period

Predominately low-VFR/VFR conditions are expected through the 0618/0718 TAF period, but low to mid-level cloud cover will be increasing from southwest to northeast throughout the next 24 hours. Additionally, showers and thunderstorms will spread from west to east across Southwest through North Central Montana throughout this timeframe, with the greatest risk for thunderstorms existing along and south of a KHLN, to KGTF, to KLWT line. Primary concern with any thunderstorm will be gusty and erratic winds, especially across the Southwest Montana terminals (i.e. KBZN and KEKS). Mountains will become increasingly obscured beyond 03-09z Sunday. - Moldan

PRELIMINARY POINT TEMPS/POPS

TFX WATCHES / WARNINGS / ADVISORIES

None.