Area Forecast Discussion

KEY MESSAGES

- Low pressure slowly moves east, with showers and thunderstorms ending tonight

- Patchy frost/freeze conditions tonight and Sunday night

- Showers and storms possible Tuesday/Wednesday and again late next week

DISCUSSION

Issued at 1154 AM MDT Sat Sep 19 2026

The low that has been plaguing the region the past few days, is finally moving across Idaho today. We will continue to see pockets of showers and storms through this evening. Rainfall amounts should not be terribly high, put we certainly could see some locally heavier rainfall rates and small hail in this situation. Overnight, the low continues to shift east of the Divide with some lingering showers around Island Park and Driggs. With cooler air filtering in, we will likely see some pockets of frost across the Snake Plain and Magic Valley as lows drop toward the mid 30s in more rural spots. Colder valley locations in the mountains will likely see frost or a light freeze. This potential also exists tomorrow night in the same locations. Otherwise we are dry until Tuesday and Wednesday.

The next closed low offshore shifts inland across California, then north across Utah and Idaho later Tuesday and Wednesday. Right now, the Blend of Models doesn't have a ton of moisture or a higher chance of showers and storms with the forecast. That seems to make sense based on a lack of significant tropical source from the Pacific, or at least one that will reach Idaho.We will need to see if that trend persists. We look dry again until next weekend, when the next storm develops offshore and shifts into the western U.S. Temperatures quickly jump 5-15 degrees on Sunday, but still not out of the 60s and 70s. After that, the warming trend continues but is much slower on a daily basis. By mid to late week, we will see a few more 80s for afternoon highs for our lower valleys.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/

Issued at 1138 AM MDT Sat Sep 19 2026

Upper low is shifting across East Idaho today. Radar shows batch of scattered SHRA working through the lower portions of the Snake Plain between BYI and PIH late this morning, with another pocket of isolated SHRA working north along the WY border through DIJ. Showers are very light, but have the potential to briefly bring CIGS down to MVFR. Additional light SHRA wrapping around the low toward SUN from the northeast. Will maintain VCSH or -SHRA at all terminals through the day, and PROB30 at DIJ where the best instability remains this afternoon. Precip ends this evening with VFR at all sites, though there is a 15-20% chance of MVFR CIGS developing overnight at DIJ.

FIRE WEATHER

Issued at 141 PM MDT Sat Sep 19 2026

The last gasp of the upper low shifts through East Idaho today. Isolated to widely scattered showers and thunderstorms remain in place today, giving way to dry conditions overnight. Rainfall amounts remain light, though gusty winds and small hail will be possible. Expect a gradual warming trend through the week, but humidities remain above critical thresholds through the week. A weak system passing through Tuesday and Wednesday may bring mainly isolated showers and thunderstorms to portions of East Idaho, otherwise dry conditions should prevail.

PIH WATCHES / WARNINGS / ADVISORIES

None.