textproduct: Boise

DISCUSSION

Water vapor satellite imagery showing a well defined closed low pushing onto the northern CA coast this evening. Showers will continue to develop out ahead of the low, tracking SW to NE. Heavier showers could drop brief heavy rain and gusty winds across SE Oregon. A rumble of thunder isn't out of the question (5-10%) as well. Snow levels will remain between 6500-8500 feet overnight limiting accumulation to higher peaks. Monday will see the focus of precipitation shift into SW Idaho zones as the low center tracks through northern NV. Current forecast is on track for this evening.

AVIATION

Numerous showers moving SW to NE through Monday morning, then NW to SE Monday afternoon. Snow levels: 6000-7500ft MSL. Heavier rain showers producing MVFR-IFR cigs/vis. IFR-LIFR in mtn snow. Isolated lightning near NV border. Mtns obscured. Conditions improving Monday eve, except lingering low stratus/fog for W Magic Valley and vicinity. Surface winds: variable up to 8kt, then W-NW 5- 15 kt with gusts to 20-25 kt Mon afternoon. Winds aloft at 10kft MSL: W-SW 10-20 kt, veering to N Monday afternoon.

KBOI...Periods of rain through Monday afternoon, creating low VFR to MVFR conditions at terminal. Temporary IFR possible mid to late Monday morning as winds shift to NW. Foothills obscured during precip. Surface winds: light and variable, then NW 5-15 kt after Mon/18Z.

PREV DISCUSSION

SHORT TERM...Tonight through Tuesday night...At 2 PM MST radar echoes were increasing in Malheur and Owyhee Counties, still well east of the supporting Pacific upper low off California 40/129. The low was moving eastward and has accelerated since this morning. It will pass through northern California tonight and northern Nevada Monday and bring widespread showers to our southern zones overnight through Monday evening, with fewer showers in northern zones. Rainfall during that time should total .20 to .50 inch in western Idaho, and .05 to .20 inch in eastern Oregon. We kept a slight (10-15%) chance of thunderstorms in southern Harney and Malheur Counties this evening. Showers will decrease from west to east late Monday and Monday evening as the weakening upper low exits eastward into Wyoming. Light winds tonight will become northwest 10 to 15 mph Monday behind the departing low. Clearing skies and diminishing winds will allow Monday night to be 8 to 14 degrees cooler than tonight, but Tuesday will warm rapidly into the 50s to lower 60s under temporary upper ridging, likely the warmest day of the week. The next upper trough will approach from the Gulf of Alaska Tuesday night and will be colder than Monday's trough. Rain and snow showers will reach Baker and Valley Counties toward Wednesday morning while clouds increase in our other zones from the west.

LONG TERM...Wednesday through Sunday...An upper level trough brings a cold front through the area Wednesday afternoon through Thursday morning. The frontal system will bring widespread precipitation, colder temperatures, and gusty winds. Precipitation chances peak Wednesday evening at 80-90% for the entire area. Snow levels at this time will be 5-6 kft MSL, before lowering to 3-4 kft MSL Thursday morning. Lower elevations will see 0.10-0.30 inches of rainfall, while mountainous areas see 0.40-0.80 inches of rain/liquid equivalent and 2 to 6 inches of snow. At the same time, wind gusts Wednesday evening reach 20-30 mph, focused along highlands and ridgetops. Showers will linger in the mountains Thursday and Friday as the flow turns northwesterly and high pressure builds in the North Pacific. Temps after the Wednesday night cold front drop to a few degrees below normal, and the building high pressure warms us back up to 5-10 degrees above normal come next weekend. While the main storm track will be north of the area, models have just enough moisture flux in our mountains to keep a 10-30% chance of precipitation through the weekend. Although, subsequent model runs, especially among ensembles seems to be reducing the amount of precipitation expected following the Wednesday front.

BOI WATCHES/WARNINGS/ADVISORIES

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