textproduct: Boise

DISCUSSION

Dry northwest flow is bringing cool conditions and very low dew points to the region this evening. A few high clouds will linger overnight, but generally clear skies will dominate the area. Sheltered mountain valleys could see some patchy fog formation, but confidence is low (<30% chance) due to the generally dry conditions. High pressure will continue to develop through the weekend, continuing the warming and drying trend until cooler and wetter weather takes back over come late Saturday. A push of instability near the Nevada border could support a stray lightning strike on Saturday and Sunday afternoon, although forecast confidence is low (<10% chance). No forecast updates needed.

AVIATION

VFR. Surface winds: variable 10 kt or less overnight, then SW-NW 5-15 kt after Fri/17Z. Afternoon gusts around 20 kt for KTWF/KJER. Winds aloft at 10kft MSL: W-NW 15-30 kt.

KBOI...VFR. SE 3-8 kt overnight, becoming NW around Fri/17Z.

Weekend Outlook...Lowering clouds Saturday afternoon. Showers arriving in SE Oregon/SW Idaho from Nevada Saturday afternoon, bringing local MVFR ceilings and mountain obscuration. Showers expanding northward Sat night into Sunday. A 10% chance of lightning near NV border Sunday. Snow levels 5-6kft MSL near KBKE-KMYL, 7-8kft MSL near NV border. Surface winds Sat/Sun: variable 5-10 kt.

PREV DISCUSSION

SHORT TERM...Tonight through Saturday night...Dry air continues to move into the region this evening as a weak ridge builds over the area. Mostly clear skies expected which will lead to one more relatively cool night before a warming trend takes hold. Dry conditions will persist through Friday as the ridge shifts inland. Temperatures will warm several degrees, reaching near seasonal normals. West to northwest flow will remain in place, with just some high clouds streaming overhead.

A weak system will approach from the west on Saturday, bringing increasing clouds by the afternoon. This system is expected to track across Oregon and into the Great Basin, bringing a 30 to 50 percent chance of showers Saturday afternoon and evening. Snow levels will be quite high with this system, ranging from 5000 feet near Baker City and McCall to around 8000 feet near the Nevada border. Consequently, any snow accumulations will be limited to the higher mountain peaks. Precipitation chances will taper off late Saturday night as the weak trough moves east.

LONG TERM...Sunday through Thursday...The upper-level trough will move further inland into the Great Basin Sunday, keeping the region in southwesterly flow aloft and precipitation chances 30-50%. Precipitation chances remain elevated until late Monday. Some long range guidance, including the ECMWF EFI, REFS, LREF, and soundings hint at thunderstorms along the Nevada border Sunday afternoon. Chances at this time are quite low (5-10%), but mentionable. The highest PoPs and QPF totals for this system will be south of the Snake River Plain to the Nevada border, as well as SE Oregon. The main discriminator between models is the speed of this system, with some indicating precipitation lingering around until Tuesday morning. Brief upper-level ridging will build in Tuesday afternoon before another upper-level trough moves into the area early Wednesday. Elevated PoPs will be back in the picture with assistance from a weak cold front that brings temperatures back to near normal.

BOI WATCHES/WARNINGS/ADVISORIES

ID...None. OR...None.