textproduct: Boise

UPDATE

Updated aviation discussion.

KEY MESSAGES

- Record high temperatures in the 90s are expected across the lower valleys Today before a sharp cooling trend arrives Wednesday.

- Becoming very windy and turning much cooler from west to east Wednesday, with showers and chance of thunderstorms along and behind a strong Pacific cold front.

- Slightly warmer Friday, then turning cooler again Saturday and Sunday, with light snow possible above 6000 feet in northern mountains.

SHORT TERM /Through Thursday Night/

Issued 310 AM MDT TUE MAY 12 2026 Upper level ridging remains the dominant feature across the western United States today. This will result in record breaking heat for many locations, with afternoon highs in the mid to upper 90s across the lower valleys. These temperatures are roughly 20 to 25 degrees above seasonal normals. High-res models indicate increasing mid-level moisture across south-central Idaho this afternoon, which will be enough for cumulus development but is unlikely (10% chance) to produce thunderstorms.

The weather pattern undergoes a significant shift Wednesday as a deep Pacific low pressure system moves toward the Oregon coast. As the ridge shifts east toward the Continental Divide, a steep thermal and height gradient will develop. This environment will support the formation of a strong surface cold front that is expected to sweep through the region from west to east on Wednesday. Expect strong winds to develop along and behind the front, particularly across southern sections of our area where a Wind Advisory has been issued. Sustained winds of 25 to 35 mph with gusts up to 55 mph are possible. The fast moving nature of the front and dry lower levels could lead to blowing dust and reduced visibility in areas that stay dry. While precipitation will be limited to the main low passage well north of the forecast area, there looks to be enough mid-level moisture for a slight chance of thunderstorms across south- central Idaho Wednesday afternoon. Temperatures will turn much cooler behind the front, dropping significantly from Tuesday's heat. Showers will continue Wednesday night, especially across the northern mountains where snow levels will begin to fall toward the higher peaks by Thursday morning.

On Thursday, the upper level trough moves east, leaving the region under a drier northwest flow. A 20 percent chance of showers will persist over the mountains of southwest Idaho. Breezy west to northwest winds will continue through Thursday, specifically across the Magic Valley, though wind speeds will be lower than Wednesday. Daytime highs on Thursday will return to near normal values.

LONG TERM /Friday through Tuesday/

Issued 310 AM MDT TUE MAY 12 2026 Come early Friday, there is strong guidance agreement that our area will remain under a dry west-northwest zonal flow, continuing a near- normal temperature trend. A shortwave trough will dig across the area from off the northwest coast Saturday through Sunday. This pattern will be mostly dry over our area, favoring some light isolated showers over the northernmost mountain areas of our CWA. A cooling trend from this pattern will drop daytime temperatures 5 to 10 degrees below normal over the weekend. Come Monday through Tuesday, there is some guidance disagreement over whether the area will stay under a west-northwest zonal flow or be under another dry shortwave trough. For now, dry conditions and a warming trend to normal temperatures are expected early next week.

AVIATION /12Z Tuesday through Wednesday/

Issued 530 AM MDT TUE MAY 12 2026 VFR with scattered high clouds. High density altitude possible due to high afternoon heat. Scattered showers over SE OR and west-central ID Mtns Wednesday early morning. Surface winds mostly variable less than 10 kt this morning, increasing to ESE 5-15 kt in the afternoon, with gusts 20-25 kt expected mainly over SE OR and Magic Valley.

KBOI...VFR. Winds SE less than 8 kt, increasing to SE 8-11 kt with gusts to 15 kt in the afternoon after 20Z. High density altitude possible 20Z-Wed/01Z due to high afternoon heat.

BOI WATCHES/WARNINGS/ADVISORIES

ID...Wind Advisory from noon Wednesday to midnight MDT Wednesday night for IDZ012-014>016-028>030. OR...Wind Advisory from noon MDT /11 AM PDT/ Wednesday to midnight MDT /11 PM PDT/ Wednesday night for ORZ063-064.