Challis, ID Weather

Key Messages

- Mild temperatures through Thursday.

- Isolated showers and storms Today.

- Widespread rain arrives late Thursday.

- Much colder Friday.

Discussion

Issued at 111 AM MDT Wed Oct 21 2026

Low pressure off the coast of central California will remain in place today. It will start moving inland on Thursday, passing overhead Friday, before exiting the region on Saturday. Models show a batch of showers lifting northward through our area this morning but then clearing out for the afternoon with a few isolated showers developing late. We will probably see another wave of light showers Wednesday night into Thursday morning. But the main batch of precipitation will hold off until Thursday afternoon and evening. Models show a healthy band of showers and thunderstorms on the east side of the low as it moves northward. This is what will likely produce most of the precipitation over our area. There is also a good area of stratiform deformation zone rain on the north and northwest side of the low that will mainly pass through the central mountains into the Island Park region. Models are showing a good bit of dry air in the interior part of the low which could influence rainfall amounts. Forecast rainfall amounts remain relatively unchanged. The mean and 50th percentile qpf from the NBM shows 1.00 to 1.50 inches for east Idaho and across the Arco Desert into the Wood River and Lost River areas. The Magic Valley and central mountains look drier with around 0.50 inches. The 10th percentile is as low as 0.10 inches for the Magic Valley with 0.25 to 0.60 inches elsewhere. The 90th percentile is especially wet with amounts ranging from 1.25 inches to 2.00 inches. Both the operational GFS and NAM show this drier air in the reflectivity fields so the 90th percentile looks highly unlikely. But a drier than advertised system looks more plausible based on the dry air we are seeing in the models. The WPC forecast is just a tad under the 50% percentile. Snowfall with this system continues to look mostly unimpactful. Perhaps snow levels fall to some of our higher passes Friday night as the colder air settles into the area before the precipitation exits.

Cooler and drier air arrives for the weekend. We will notice about a 20 degree drop in temperatures from our highs on Thursday to highs for Friday. Temps will rebound slightly for next week, but remaining near or slightly below normal.

Aviation

Issued at 1141 AM MDT Wed Oct 21 2026

East Idaho on lee side of weak feature that brought SHRA to the region this morning. A few showers still in place on satellite/radar, but generally past terminals already so believe threat has been diminished for the remainder of today. High-res models show a weak feature working through East Idaho for a brief time this evening/overnight, which may be enough for a few SHRA at SUN, but should be no impact at the other terminals at this time. IDA and DIJ may be close, but not enough confidence to add to terminal forecast. Better confidence for increased coverage for SHRA and isolated TSRA at all terminals after 18Z Thursday. CIGS remain VFR for now, with light winds.

Fire Weather

Issued at 111 AM MDT Wed Oct 21 2026

A few spotty showers are expected today with little to no measurable rain. Wetting rains will likely hold off until late Thursday afternoon and Thursday night.