textproduct: Boise

KEY MESSAGES

- Chance of showers and thunderstorms late this afternoon and early this evening, mostly across the high terrain of southwest Idaho.

- Warm temperatures through Thursday, with values 10 to 15 degrees above normal Thursday along with increasing southerly winds. - Cold front passage Friday with cooler temperatures heading into this weekend and a chance of precipitation across northern portions of the forecast area Friday.

SHORT TERM /Through Thursday Night/

An upper level low over northern Nevada and Utah will aid in shower and isolated thunderstorm development late this afternoon. The best chance of showers and thunderstorms (20-40%) will be across eastern portions of the forecast area, mainly east of a line from McCall to Mountain Home. Gusty outflow winds up to 45 mph possible near showers and thunderstorms, alongside lightning, small hail, and brief moderate-heavy rainfall. Showers will diminish this evening with the loss of daytime heating while the low moves northeast across eastern Idaho.

Dry west to southwest flow will be over the area Wednesday with the flow aloft becoming more southwesterly by Thursday ahead of a strong longwave Pacific trough. Thus, temperatures will generally be on an upward trend Wednesday, and then warm sharply from Wednesday to Thursday. Temperatures will be 10-15 degrees above normal on Thursday, with many lower valleys forecast to see maximum temperatures in the low-mid 90s. Ahead of the approaching trough, winds in the Snake Plain will increase to SE 15 to 25 mph with gusts up to 35 mph. Elevated fire weather conditions will develop Thursday afternoon across SE Oregon and SW Idaho due to hot, dry, and windy conditions in southerly flow. Breezy to windy conditions will continue Thursday night ahead of the Pacific trough and approaching cold front.

LONG TERM /Friday through Tuesday/

The well advertised cold front is still on track to cross over the area come Friday afternoon into Friday night. This frontal passage will be mostly dry, with the wind being the main story. Southwesterly prefrontal winds will increase with gusts to 25-45 mph. The higher end of that range will be felt generally south and west of the Snake Plain and across ridgetops. As the front moves through the area, winds will switch to be out of the northwest, with post-frontal gusts remaining elevated at 25-40 mph. With the associated trough swinging north of our area, the best precipitation chances/totals remain on track to stay generally north of our area. For our area, the best chances of precipitation (20-40%) will be in northern portions of Baker and Valley Counties. The temperature effects of this front will be most felt in eastern Oregon, where it will move through earlier in the afternoon, with a nearly 20 degrees temperature difference between Thursday afternoon and Friday afternoon highs. Above normal temperatures will persist friday across SW- Idaho, with max temps in lower elevations reaching the low to mid-80s.

Temperatures will cool to 5-15 degrees below normal area-wide come Saturday. A trough digging off the west coast will pass-over the area late Sunday/early Sunday along with an associated cold front. While this trough and front will be weaker than that of Friday, it will help keep cooler conditions and breezy west/northwest winds in place into the start of the next week. Moisture availability is in question for this next system. With an active eastern Pacific, tropical moisture could work it's way back up to support precipitation chances. However, return flow will be limited with the quick one-two punch of these systems. Right now, am leaning towards another dry frontal passage with moisture remaining south and east of our area. Long-range guidance doesn't handle the energy transfer with tropical systems the best, but things should become more clear in the days to come.

AVIATION /18Z Tuesday through Wednesday/

Issued 1049 AM MDT TUE SEP 22 2026

VFR with high clouds. Isolated showers/thunderstorms this afternoon. Mainly near KTWF/KJER, over the Central ID Mtns, and SE Oregon highlands. Storms capable of outflows to 25-35 kt, lightning, and moderate rain. Surface winds: Becoming NW 5-15 kt this afternoon, then generally variable under 10 kt overnight. Winds aloft at 10kft MSL: Variable 5-10 kt.

KBOI...VFR with FEW/SCT high clouds. Surface winds: Becoming NW 5-10 kt this afternoon. then S-SE 3-8 kt overnight.

BOI WATCHES/WARNINGS/ADVISORIES

ID...None.

OR...None.