textproduct: Pocatello

KEY MESSAGES

- High elevation snowfall event through early Monday. Winter Storm Warnings and Winter Weather Advisories in effect for portions of East Idaho.

- Weather pattern remains active through Christmas week.

- Continued well above normal temperatures through Christmas. Slight cooling but still above normal next weekend.

SHORT TERM /THROUGH TONIGHT/

Issued at 116 PM MST Sun Dec 21 2025

Atmospheric river event ongoing across East Idaho per satellite and radar imagery, and surface observations. Temperature and snow level gradient is quite tight across the region, with the rain/snow line Hailey to Island Park. Surface freezing line is gradually shifting north as expected, albeit slightly slower than previously expected. Heaviest accumulations still expected above 7500 ft through tonight, with model means still supporting 24-hr liquid amounts exceeding 1.5" and 10th percentile amounts exceeding 1.0" liquid across higher elevations of the central mountains and the highest elevations along the WY border near and north of the Big Holes. Current range of winter headlines remain well supported, though could see southern zones canceling early overnight as the warm air mass becomes more entrenched and snow levels continue to rise.

Main shortwave drives east of the region during the day on Wednesday, leaving a broken deformation zone of precipitation across the region. Any orographic precipitation that can continue during the day should be much lighter, so a relative break is expected. Next warm surge late in the day re- consolidates the band into a new warm frontal feature, and lifts north during the overnight Monday night. Temperatures remain well above normal for the beginning of Christmas week with overnight lows around or above where normal highs should be.

LONG TERM /MONDAY THROUGH SATURDAY/

Issued at 116 PM MST Sun Dec 21 2025

We are still looking at a band of rain and snow to lift northwest out of our are Tuesday as another low helps reload the pattern to our west. For Christmas Eve day and night, we see a quick but potentially healthy shot of rain and snow across central and eastern Idaho. With strong southerly flow into our area, we are looking at fairly strong upslope into places like the Wood River Valley, Arco, Monida Pass, and Island Park. Meanwhile, downslope is likely along and south of the Snake River into the Teton Valley. We did knock down the precipitation amounts a bit as it appears the numbers might be influenced by some unrealistic amounts coming from the GFS. The latest precipitation amounts are in the 0.30-0.70" range where the bulk of the moisture falls. Places like the Challis and Pahsimeroi Valleys are looking at a major shadow effect and closer to 0.10" or less. Higher elevations are looking at upwards of 1" in favored areas. There are a few pockets of 1.0-1.25" currently in the forecast, which is somewhat backed up by probability forecasts that have a 20-40% chance of more than 1.0". If you took the GFS at face value, we COULD have another 0.20-0.50" across the area. Do expect these numbers to change as we get closer, but just beware that this time period could be another wet and impacted travel period for us. The ECMWF is a bit slower than other models, and actually holds on to heavier precipitation especially across the central mountains for Christmas. The rest of the model numbers point to keeping some showers around but nothing too crazy amount-wise. Our Blend of Models is NOT following the ECMWF's plan at the moment. The latest trends in the extended models and Blend of Models is to dry things out by the end of the extended holiday weekend. The GFS, earlier run of the ECMWF and Blend of Models close a low off well to our southwest over the weekend and pulls all of the moisture out of Idaho. Temperatures through Christmas remain well above average, with cooler temperatures returning as early as Friday. Even then, the current forecast has highs at or just above average.

AVIATION /18Z TAFS THROUGH 18Z MONDAY/

Issued at 1018 AM MST Sun Dec 21 2025

Needless to say, today's TAF forecasts have been very frustrating. The Blend of Models has been way too quick to changing any snow or mix to rain this morning in many areas. Eventually, this will happen but we are pushing that back to mid afternoon at the earliest. We currently are seeing mostly MVFR to LIFR weather, although BYI currently is MVFR and may actually be the only airport to remain mostly if not VFR through the forecast period. For PIH and IDA, we are forecasting mostly MVFR/high end IFR conditions. We may see a smaller window or two where condition may improve to VFR before going back to MVFR and/or IFR. For DIJ, we keep the forecast at MVFR or IFR. The main driver here is any downslope of the mountains, which seems to keep conditions more optimistic that what is forecast. If downslope loses out or we see little movement in snow levels, look for IFR and maybe LIFR conditions. At SUN, this is where the transition to a mix or rain is going to be key. They are currently at LIFR, and the latest forecast trends SHOULD be already IFR to MVFR and mixing out to all rain. We are keeping things LIFR/IFR until early Monday morning. Confidence on any improvement is low right now due to lack of confidence on when we warm up enough to go to at least -RASN or -RA. Even once that happens or we potentially go to VCSH conditions tomorrow, current forecasts keep ceilings MVFR/high end IFR.

PIH WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory until 11 AM MST Monday for IDZ060-064- 066-075. Winter Storm Warning until 11 AM MST Monday for IDZ071>074.