November 17, 2016 – Dry weather Thursday and Friday. Continued cooler but still near normal temperatures. Rain and higher elevation snow this weekend and early next week. A brief break Tuesday then another round of precipitation possible mid week.
Fair skies this morning under upper ridging over the west coast. These fair skies have allowed for much cooler temperatures this morning. Temperatures this morning are running anywhere from 5 to 15 degrees cooler across the CWA than 24 hours ago. Should see a few degrees of warming today as the airmass warms under the ridge but maximum temperatures are still expected to come in just below normal today. Temperatures warm just a bit more on Friday and although morning minimums tomorrow will remain cool they should at least not cool farther. Therefore, expect valley temperatures to remain above freezing Friday morning throughout the central valley.
A Pacific cold front moves onto the coast Friday evening bringing precipitation into the coast range and then across Norcal during the night. By Saturday afternoon this front is progged fairly closely by the models to have moved into the Sierra. Therefore, expect at least a chance of precipitation across the entire CWA by Saturday afternoon. GFS precipitable water values feeding this system forecast at about one and a third inches so this system could be a moderate rain producer at least across the north. The northern mountains could see up to 2 inches of rain while the northern San Joaquin valley may only see about 1/3 inch. Saturday afternoon and night could see enough snowfall at the passes for at least some minor impacts to trans Sierra travel. Lighter rain, mountain snow or showers will continue into Sunday as the upper trough pushes onto the coast. Clouds and a cooler airmass will keep daytime highs over the weekend back down below normal with overnight lows more mild under cloud cover.
Extended discussion (Monday through Thursday)
Lingering showers on Monday as upper troughing exits the area. Most showers expected over the mountains and foothills, with snow showers generally above 6000. Any rainfall and snow accumulations should be light. Monday night and Tuesday a brief period of upper ridging will bring dry weather across the area. Temperatures will start relatively cool Tuesday morning, a little below normal, especially in areas where skies clear overnight. Tuesday night the next frontal system begins to move in. Models have trended further south on Wednesday, with much of the area seeing the possibility of precipitation. Precipitation amounts do not look especially high with this system, especially if the GFS model is correct. The bulk of the precipitation is expected to be north of I80. Snow levels drop to 5000-6000 feet. The timing of this could mean snow bringing some impacts to a very busy Thanksgiving holiday travel period Wednesday and Wednesday night. Anyone planning to travel over mountain passes should closely monitor the forecast.
Models diverge some on Thursday (Thanksgiving), with the ECMWF bringing a weak system over the north, while the GFS brings a ridge. Will lean towards the ECMWF with a slight chance of some precipitation over the northern mountains and northern Sacramento Valley, and seasonably cool temperatures.