textproduct: Pocatello

KEY MESSAGES

- High elevation snowfall event arrives Sunday 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 SUNDAY NIGHT/

Issued at 151 PM MST Sat Dec 20 2025

Satellite imagery shows fast moving shortwave off the coast of California working toward the coast with ample moisture associated with it. Warm frontal boundary arrives overnight tonight, with temperatures and snow levels generally increasing after midnight. Although light precipitation will be possible in some areas prior to sunrise, most of the precipitation arrives during the day Sunday. Despite high confidence in this being another high elevation snow event for portions of East Idaho, there is still quite a bit of uncertainty with where snow levels land, and precisely what impact that will have on the forecast snow amounts. There is quite a bit of variation in model solutions: NBM appears to favor slightly higher snow levels, but HREF and REFS runs 06z and 12Z appear to keep temperatures slightly colder, implying slightly lower snow levels and thus higher accumulations. Considering a broad consensus of the highest accumulations above 6500 ft, and a steep gradient to minimal accumulations down the valley floors, the headlines were drawn up with this consensus in mind. For the Central Mountains, the greatest accumulations are expected across the Sawtooth Recreation Area and surrounding elevations. SH-75 will likely see a steep increase in accumulations north of Hailey (2-4") to Galena Pass (1-2'), with a steep drop off into the Stanley Basin (4-6"). Thus have issued a Winter Weather Advisory for the Wood River Valley, upgraded to a Winter Storm Warning north and east. Further east along the Wyoming border, the upslope component favors increased precipitation into the higher elevations, but the increased snow levels will drastically limit the impact. Thus a Winter Weather Advisory for the Island Park region, the Big Hole mountains, and the Bear River Range for 6-10" above 6500 ft, mainly impacting passes. Total liquid precipitation amounts range from under 0.25" (at 90th percentile range - 1 in 10 chance of exceedance) in normally shadowed areas such as the Pahsimeroi valley and the north end of the Lost River valley, to well over 1.5" of liquid in higher elevations (at the 10th percentile - 9 in 10 chance of exceedance). That is an incredible difference in precipitation amounts across East Idaho considering the percentile ranges. Any location above the snow level, regardless of where it falls, will likely see a very heavy wet snow.

LONG TERM /MONDAY THROUGH SATURDAY/

Issued at 151 PM MST Sat Dec 20 2025

As low pressure develops to our west for Tuesday, we will see a band of rain and snow lift northwest across central and eastern Idaho as high pressure builds. Snow levels rise to around 7000-8000ft during the day and 6500-7500ft Tuesday night. Higher elevations currently are looking at 0.20-0.50" of moisture, favoring the eastern highlands and the Sawtooths and surrounding ranges. This also favors again the Wood River Valley, even perhaps a bit more than the pattern for tomorrow and Monday. There is a 10-40% chance of exceeding 0.50" in those areas, and 15-30% across the Big Holes and higher elevations surrounding Island Park. This round though isn't producing as much moisture, however. The rest of the area across lower elevations are looking at anywhere from a few hundredths to around 0.20" depending on location. Snow-wise, we are only expecting 1-5" generally in the higher elevations with a few spots trying to "overachieve" that range.

Looking ahead to Christmas Eve and Day, current trends bring a healthy but quick shot of rain and snow through Christmas Eve Day into early Christmas morning. The rest of Christmas Day looks showery. In terms of a White Christmas, the potential at lower elevations is non existent unless you get up early to see snow falling...as temperatures should be warm enough to produce no accumulation. Current moisture numbers are 0.50-1.0" with locally higher numbers in the mountains, and 0.10-0.40" down low. The potential for more than 6" of snow at mid and upper slopes is really not there except where we see upslope possibly from around Galena Summit up through Lone Pine and the mountains surrounding Island Park. The chances are 30-60% there, but just beware we will likely see some adjustments in the coming days...so this forecast is just more of a "you may need to pay attention" one and definitely watch if you are going to be traveling during that period or out and about in the mountains. It will be breezy, but with warmer temperatures, any blowing snow potential may be limited to around higher pass level and well up into the backcountry. Precipitation will continue sporadically for the rest of the holiday weekend. We should see plenty of 40s and 50s through Christmas in the valleys, cooling off a bit heading into the last weekend of 2025.

AVIATION /00Z TAFS THROUGH 00Z MONDAY/

Issued at 451 PM MST Sat Dec 20 2025

Conditions start out solid VFR with unlimited CIG and VSBY, but it quickly deteriorates starting midnight 21/07Z at the earliest. A incoming warm front, rare except in these cases of atmospheric river events, will bring BR/FG and RA to lower elevation airports KIDA, KPIH, KBYI. Some of it reaching moderate rainfall rates with not only marginal VFR for CIG but for VSBY as well. The moderate to heavy precipitation for the higher elevation airdromes of KSUN and KDIJ will be heavily impacted for much of the day on Sunday. IFR for CIG is the primary impact at KSUN, although in the morning it will start as SN and reduce VSBY and shift over to BR and a RASN mixture that will continue the problems. KDIJ normally has only VSBY as an issue, but even there the amount of moisture coming into eastern Idaho will mean IFR for both CIG and VSBY that does develop a little later here, becoming impactful around 21/14Z.

PIH WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory from 2 AM Sunday to 11 AM MST Monday for IDZ060-064-066-075. Winter Storm Warning from 2 AM Sunday to 11 AM MST Monday for IDZ071>074.