textproduct: Boise

UPDATE

Updated aviation discussion.

KEY MESSAGES

- Rain, mountain snow and gusty winds on Wednesday, then snow level lowering to valley floors tonight and Thursday morning.

- Subfreezing morning temperatures Friday and Saturday in the agricultural areas.

- Warmer and drier over the weekend, with another chance of precipitation early next week.

SHORT TERM /Through Friday Night/

Issued 322 AM MDT WED APR 15 2026 The next strong upper trough from the Gulf of Alaska and surface cold front were approaching our area this morning with another round of moderate to heavy rain and snow today and tonight. At 2 AM MDT the eastward-moving cold front was already onshore in western WA and OR, extending out into the Pacific along 42N. The supporting upper low was near 50/130 near the BC coast and moving southeastward. Radar was already showing areas of light rain and snow in eastern OR and western- most Idaho but little was reaching the ground. But pcpn will increase around sunrise and continue through the day and this evening. This system is colder than the previous one and will lower the snow level to valley floors late tonight and early Thursday morning, but by then most of the pcpn will be ending. The surface cold front is slated to pass through eastern OR this afternoon and western Idaho this evening. Ahead of the front, heaviest pcpn will fall in the Boise Mountains and west Central Idaho Mountains with snow level near 6000 feet, with rain heavy enough to loosen rocks and mud on steep slopes, so travelers should avoid the Banks-Lowman road and similar roads until rain changes to snow this evening. Total pcpn today through Thursday should be 0.75 to 1.25 inch in our northern mountains, and generally 0.25 to 0.75 inch elsewhere, except 0.15 to 0.25 inch in rain-shadowed southern areas. Total snowfall will be 8 to 15 inches above 6000 feet late today through tonight but only 1-3 inches near 5000 feet, including McCall/ID. Pre-frontal southwest to west winds will increase to advisory speeds in the southwest Idaho Highlands, southern Twin Falls County, and in southern Malheur and Harney Counties. A Wind Advisory has been posted for those areas this afternoon and early evening. The frontal passage itself will be marked by a short period of heavy showers and isolated thunderstorms. After that the snow level will lower rapidly and rain will change to snow, with up to an inch accumulation overnight in the Magic Valley but little or none in the Treasure Valley.

Thursday will be windy and cold with lingering snow showers as the upper low moves through, then clearing and quite cold Thursday night. A Freeze Watch has been posted for the Treasure Valley and western Magic Valley agricultural valleys for Friday morning and again Saturday morning, but Friday looks like the colder day. Low temperatures Friday will dip as low as 24 degrees in the western Magic Valley which would be a hard freeze, with 27 to 30 degrees in the Treasure Valley, again cold enough to damage young plants unless they are protected.

LONG TERM /Saturday through Wednesday/

Issued 322 AM MDT WED APR 15 2026 A ridge building in behind the system in the short-term period will allow for dry and milder conditions on Saturday, with temperatures near normal. Saturday morning will be the last morning (in this forecast period at least) with temperatures near or below freezing across the area. Temperatures come Sunday will warm to 5-10 degrees above normal.

This next week, guidance continues to resolve a low digging down from the Gulf Alaska and closing off from the main jet stream, but timing continues to be tricky. Over the past few runs, ensemble guidance has continually slowed the system, delaying its arrival into our area. With southerly flow ahead of this low, a slight warming trend would be able to sustain itself into early next week with a slower arrival. The current forecast carries slight precipitation chances come Monday, increasing to 20-40 percent area-wide Tuesday and Wednesday (where the consensus is starting to lean on the low's arrival). Temperatures should be able to maintain the slight warming trend and remain above normal through Tuesday in the southerly flow, before cooling to near normal behind the system. Breezy south/southwest winds are anticipated early next week as the low inches closer, becoming W-NW following its passage.

AVIATION /18Z Wednesday through Thursday/

Issued 1154 AM MDT WED APR 15 2026 Low VFR/MVFR ceilings in rain and IFR/LIFR in mtn snow. Snow levels 5-7kft MSL. A cold front will bring sharp wind shifts and intensify precip after 20Z, with MVFR/IFR in heavier rain showers. A 25% chance of thunder with small hail/graupel along the front. Snow levels rapidly lowering to valley floors following the front. Scattered light snow showers expected Thursday morning through afternoon. Surface winds: SE-SW 10-20 kt with gusts 20-35 kt, then W- NW 15-30kt with gusts up to 40 kt this afternoon with the frontal passage. Winds aloft at 10kft MSL: W-SW 25-40 kt.

KBOI...Showers continuing with periods of MVFR ceilings and reduced visibility this afternoon. A strong cold front will arrive this afternoon around 22Z. The front will bring a sharp NW wind shift, heavier precip, temporary MVFR/IFR, and potential for graupel/lightning. Conditions returning to VFR following the front. Surface winds: SE 10-15 kt this morning, then NW 15-25 kt with gusts up to 35 kt following frontal passage this afternoon/evening.

BOI WATCHES/WARNINGS/ADVISORIES

ID...Freeze Watch from late Thursday night through Friday morning for IDZ012-014-016. Wind Advisory until 8 PM MDT this evening for IDZ015-030. OR...Freeze Watch from late Thursday night through Friday morning for ORZ064. Wind Advisory until 8 PM MDT /7 PM PDT/ this evening for ORZ061-063.