Area Forecast Discussion

KEY MESSAGES

- Return to winter weather in the high elevations. Winter Weather Advisories for portions of the central Idaho mountains and the highlands bordering Wyoming above 6500ft elevation.

- Cold front on Wednesday will bring wind strong enough to produce Wind Advisory criteria in Arco and Mud Lake Desert.

- Rain and occasional snow possible elsewhere starting late tonight and continuing through Wednesday night, changing to showery afterwards.

DISCUSSION

Issued at 206 AM MDT Tue Apr 21 2026

Today through Thu night. An approaching low will spread some clouds into the region today, which should make afternoon high temperatures level off compared to yesterday, which are close to records but likely to stay below that threshold. But this is the last of pleasant weather for a while as troughing along the west coast will be swinging a trough and associated cold front through central and eastern Idaho starting late tonight and continuing all day Wed and into Wed night. This cold front brings a threat of thunderstorms as well. There is little break as another low, this time approaching from British Columbia, digs southward and brings not quite as much precipitation, but will be remembered for its cold air. This second storm will focus more on the east and southeast highlands.

Temperatures will be going through the ringer. The middle to upper 70s today at low elevations will see a crash of 20 to 35 deg F to 45 to 55 deg F highs on Wed. On Thu, temperatures will longer about the same, plus or minus a couple of degrees due to thinning cloudiness and more showery precipitation. Overnight lows tonight will be mild due to cloud cover and the continued southwest flow bringing in warmer air. On Wed night temperatures will get down to with plus or minus a few degrees of freezing again. As the second low brings in more northerly air flow, overnight lows crash into the 20s in the lower elevations, especially the north end of the Snake River plain.

The Wed cold front brings a strong cold front, and this means some strong wind. At this time, it appears to be limited to Wind Advisory criteria to the Arco-Mud Lake Desert area, though ths Shoshone and Lava Beds will be close, along with a limited area east of Idaho Falls heading into the nearby highlands.

Fri through Mon. All clusters for all days indicate that this second low lingers with the troughing staying over eastern Idaho. This puts the region on the cold side of a slow moving low, so do not look for a quick warm up. Afternoon highs stay mostly in the 50s for the heavier populated cities, maybe breaking 60 by Mon. The lingering troughing means a chance of showers and thunderstorms, mostly in the slight chance to chance category for all of these days. Wind speed appears light to moderate with gusts to around 20 mph.

AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 1018 PM MDT Mon Apr 20 2026

Look for VFR conditions with only some few to broken high cloud cover up around 20 thousand feet until tomorrow afternoon. Will see an increase of southerly winds by tomorrow afternoon with gusts of 20 to 25 kts, especially for IDA, PIH, BYI and DIJ. Also, will see clouds to start to move into the area, mostly mid-level clouds. Expect an upper-level low system to move over the area starting early Wednesday, which will bring MVFR/IFR conditions with any showers on station along with continued breezy winds. By early tomorrow evening to midnight expect showers to start to move into SUN ahead of this upper-level low system. MVFR CIGS are possible for SUN with any heavier showers early tomorrow evening.

PIH WATCHES / WARNINGS / ADVISORIES

Wind Advisory from noon Wednesday to midnight MDT Wednesday night for IDZ052. Winter Weather Advisory from noon Wednesday to midnight MDT Thursday night for IDZ060-063-064-066. Winter Weather Advisory from midnight tonight to 6 AM MDT Thursday for IDZ069-071>074.