textproduct: Pocatello

KEY MESSAGES

- Final Day of Quiet Warmth Today; Breezy Friday: Today brings one last afternoon of tranquil autumn weather. Friday remains warm but introduces gusty southwest winds of 25 to 35 mph across central and eastern Idaho, with mountain gusts reaching 40 mph.

- Tropical Moisture & Widespread Heavy Rain (SaturdayEarly Next Week): Split flow over the West will draw remnants of Tropical Cyclone Rachel northward, delivering a major rain event. Expect 1.0"2.0" across the southern/eastern highlands (2.25"2.5" on high ridges), 1.0"1.5" across the Snake Plain from Pocatello to Rexburg, and 0.10"0.30" in central mountain valleys.

- Potential Flood Headlines: High-end QPF totals over the eastern and southeastern highlands may require Flood or Flash Flood Watches in upcoming forecast updates as the west-east moisture placement locks in.

- High-Elevation Snow & Frost/Freeze Risks: Cold advection will lower snow levels to 7,000 feet, bringing several inches to high peaks and maybe into Island Park. Cooler temps early next week will bring widespread frost and freeze risks.

DISCUSSION

Issued at 217 PM MDT Thu Oct 8 2026

Today marks the final afternoon of tranquil, pristine weather across eastern Idaho before a major autumn storm system alters the regional pattern. Unseasonably mild temperatures and dry air will hold through Friday, with a few localized spots actually topping today's highs by a degree or two. The main change on Friday will be a tightening surface pressure gradient, which will drive breezy southwest winds across the forecast area. Wind gusts of 25 to 35 mph are expected across most lower elevations, with gusts topping 40 mph along central mountain ridgelines. While gusty, these speeds are anticipated to remain below advisory criteria outside of localized fire weather impacts. See fire weather discussion below.

A drastic synoptic transition unfolds Saturday as split flow establishes itself across the western United States. Global guidance (GFS and ECMWF) agrees on dropping a closed upper-level low south along and off the California coast before it tracks eastward. Out ahead of this system, tropical moisture associated with the remnants of Tropical Cyclone Rachel will be entrained northward directly into central and eastern Idaho.

Shower and thunderstorm coverage will surge Saturday and remain active into early next week. This rich moisture plume will support heavy rainfall totals as PWAT values are nearing climatological maximums. Current forecast calls for 1.0 to 2.0 inches forecast across the South Hills, Albion Mountains, and the southeastern/eastern highlands. Highest ridgelines east of I-15 could push 2.25 to 2.50 inches. Downstream QPF spillover will bring 1.0 to 1.5 inches to the Snake Plain from Pocatello northward through Rexburg. Farther west, central mountain valleys will see lighter amounts ranging from 0.25 to 0.75 inches. While these eastern highland totals represent the upper tier of model ensemble blends, they remain well within the realm of possibility given the tropical origin of the air mass. Because minor shifts in the track of Rachel's moisture axis could alter localized totals, Flood or Flash Flood Watch issuances have been deferred to Friday's forecast cycle but stay tuned.

Colder air wrapping into the system Sunday and Monday will drive snow levels down to around 7,000 feet across the central mountains and along the Continental Divide. While lower elevations will see mostly rain, several inches of wet snow are possible for high peaks and pass levels toward Island Park. A secondary upper-level trough is forecast to drop into the Intermountain West during the middle of next week, reinforcing cold air advection and keeping temperatures well below seasonal averages. Frost/Freeze headlines will likely be needed for a few days early next week before the "growing season" is officially declared over for the year.

AVIATION /18Z TAFS THROUGH 18Z FRIDAY/

Issued at 1016 AM MDT Thu Oct 8 2026

Light winds and VFR conditions remain likely over the next 24 hours.

FIRE WEATHER

Issued at 217 PM MDT Thu Oct 8 2026

Dry conditions continue into Friday, but conditions are beginning to change as a vigorous low pressure system works into the region. Winds will begin gusting across the region during the afternoon Friday. Along with the dry humidities, at least localized critical conditions are possible, becoming more widespread across the Southern Sawtooth Zone 427. Thus a Red Flag Warning will be in place for Zone 427 for Friday afternoon and early evening. Breezy winds continue into Saturday, but temperatures begin to slide as moisture shifts into the region, heralding a very quick transition to a wet fall system. Precipitation starts to expand across East Idaho Saturday and continues into early to mid week next week. 48 hour precipitation probabilities through Sunday night for totals over 1.0" exceed 60% for all but the central mountains and Eastern Magic Valley regions, and are 80+% for almost the entirety of the eastern and southern highlands. If the deeper moisture from remnants of tropical system Rachel work this far north, those 48 hr totals could range 1.5-2.5" for the eastern and southern highlands, possibly extending into the Snake River Plain. Exact totals will be dependent on the track of the system as it drops into the region, but the trend is clear. After a prolonged dry and unseasonably warm period, we will transition to much cooler and wetter. Temperatures will be cold enough by late in the weekend to see accumulating snow at higher elevations, briefly dipping closer to mid slope especially during the overnight periods. As of right now, there is potential for a relative break in the precipitation Tuesday, but another round is expected Wednesday into Thursday. The trend is toward the systems shifting east of Idaho late next week into the weekend, leading toward drier conditions and temperatures warming back to near normal.

PIH WATCHES/WARNINGS/ADVISORIES

Red Flag Warning from 2 PM to 8 PM MDT Friday for IDZ427.