textproduct: Boise

LONG TERM...Sunday through Thursday

A strong upper-level jet will ride overtop a strong upper-level ridge, existing in the Eastern Pacific, and into the Pacific Northwest. Pacific moisture and embedded upper-level shortwave disturbances amid the northwesterly flow will bring periodic rain and mountain snow. Our area will be on the edge of the storm track for much of the period, and a strong temperature gradient will exist over the area. This increases uncertainty in precipitation amounts and temperatures. However, overall the pattern strongly leans mild and wet with temperatures well above normal and periodic chances of precipitation.

A disturbance afternoon into evening Sunday will bring a 20-50% chance of valley rain and a 50-80% chance of mountain rain and snow. Snow levels will be around 4000-6000 feet, lowest in the morning across the north. Precipitation amounts should be light to moderate. Precipitation chances will dip briefly on Monday with the upper- level ridge axis building overhead before increasing once again Tuesday and Wednesday as an atmospheric river moves into the Pacific Northwest. Our area will be on the southern edge of the moisture, resulting in some uncertainty in precipitation amounts. However, moderate precipitation totals are possible, especially in the mountains, and the air mass is expected to be very mild with snow levels pushing up to 6500-8000 feet. By Wednesday, high temperatures are forecast to reach 15-20 degrees above normal. Strong westerly/northwesterly flow will also bring breezy to windy conditions. Forecast confidence is lower on Thursday, but strong, moist westerly/northwesterly flow will persist across the Pacific Northwest. Currently this forecast pattern looks to exist beyond the extended as well.

AVIATION

VFR. Clouds increasing today and gradually lowering, with widespread rain/snow arriving from the northwest this afternoon and evening. MVFR/IFR in rain and IFR/LIFR in snow. Snow levels 2.5- 3.5 kft MSL today, rising to 3-5 kft MSL across SW ID and 7-8 kft MSL across SE OR late tonight. Mountains becoming obscured. Surface winds: light and variable below 10 kts, except KTWF/KJER gusting near 25 kts overnight. Areas of low-level wind shear developing tonight. Winds at 10 kft MSL: NW 20-30 kt, increasing to 35-55 kt after Fri/00Z.

KBOI...VFR through mid-afternoon today. Increasing clouds with lowering ceilings later this afternoon, then rain developing around 22-01Z late this afternoon and continuing tonight. Around a 10% chance of rain mixing with snow to start, becoming predominantly rain later tonight. MVFR/IFR conditions in precipitation. Surface winds: variable around 5 kt or less.

Weekend Outlook...Widespread rain and snow on Friday with snow levels 6-8 kft MSL, except 4.5-6 kft across central Idaho. Lighter precipitation is expected Saturday and Sunday with snow levels 4-6 kft MSL. MVFR to LIFR conditions in precipitation with mountains obscured. Surface winds SW-NW 5-15 kt, except 15-20 kt with gusts 25- 40 kt late Friday into Saturday across higher terrain.

BOI WATCHES/WARNINGS/ADVISORIES

ID...Winter Weather Advisory from 5 PM this afternoon to 11 PM MST Friday IDZ011-013. OR...None.