textproduct: Pocatello

KEY MESSAGES

- Flash Flood Watch for Local Burn Scars: A Flash Flood Watch has been issued for the Wapiti, Ohio, and Big Rock burn scars from late Thursday through Friday, where incoming precipitation could trigger debris flows and rapid runoff.

- Main Rain Event Late Thursday & Friday: After a dry daylight lull on Thursday, widespread moderate-to-heavy rain will overspread the region late Thursday evening and peak on Friday as a closed Pacific low moves across the Great Basin. While models have nudged amounts upward around Sun Valley and slightly downward across the Snake Plain, the broader forecast remains unchanged: widespread soaking rain across all of eastern Idaho.

- Sharp Friday Temperature Drop: Daytime highs will tumble significantly on Friday, struggling to reach the lower 50s, before sunshine returns Saturday afternoon and Sunday with temperatures holding near or just below seasonal norms.

DISCUSSION

Issued at 124 PM MDT Wed Oct 21 2026

Afternoon satellite imagery reveals a mix of sun and clouds across eastern Idaho, while regional radar tracks light returns across parts of the Central Mountains up toward the Montana Divide. Areas farther south across the Snake Plain and Magic Valley remain mostly clear. Temperatures continue to run on the warm side of seasonal climatology, with lower elevations peaking in the upper 60s to lower 70s.

A pattern change is already underway to our southwest as an upper-level low moves onshore along the central California coast. Between now and the main event, most locations will stay dry. However, persistent southerly flow will allow high- resolution convective-allowing models (CAMs) to spark isolated showers and a few embedded thunderstorms through the early overnight hours tonight. A noticeable lull in precipitation will then take hold for much of the daytime hours on Thursday, providing a dry window ahead of the primary system.

The California upper low will track across the Great Basin over the next 24 to 48 hours, spreading deep moisture and strong synoptic lift directly into eastern Idaho. Widespread rainfall will begin moving into southern and western zones late Thursday evening, expanding areawide through the day on Friday.

While model guidance continues to exhibit minor spread on localized placementnudging rainfall totals upward in upslope- favored areas around Sun Valley and slightly downward across the Snake Plainthe big picture remains unchanged: widespread, soaking precipitation is imminent. Due to the total forecast precipitation, a Flash Flood Watch has been issued for the Wapiti, Ohio, and Big Rock burn scars given the elevated threat for flash flooding and debris flows over hydrophobic soils. More widespread areal flooding remains a low-end possibility if precipitation overperforms current consensus forecasts, but broad areal flood statements are not warranted at this time.

Strong cold advection and extensive cloud cover will result in a significantly colder Friday. Daytime maximum temperatures will struggle to climb into the 50s across lower elevations, though a few valley spots may briefly reach that threshold during brief breaks. Rain will steadily taper off from west to east late Friday evening and into the early morning hours on Saturday as the low center pulls eastward.

A much more pleasant weekend is in store once morning clouds exit on Saturday. While Saturday will remain on the cooler side, sunshine will break out during the second half of the day and continue into Sunday. Daytime high temperatures will hold at or slightly below seasonal averages in the 50s and low 60s. No widespread organized storm systems are projected behind this departing low, though isolated showers will remain possible across higher-terrain zones Monday and Tuesday under a cool, seasonable regime.

AVIATION /18Z TAFS THROUGH 18Z THURSDAY/

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.

PIH WATCHES/WARNINGS/ADVISORIES

None.