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April 18, 2017 – A series of weak storms expected into Thursday. Dry and warmer weather late in the week into the weekend.
Long wave trough continues in the EPAC with series of short waves moving through across Interior NorCal in moist SW flow aloft. Satellite imagery reveals main frontal band shifting east across southern portions of the forecast attm. 88-D mosaic showing scattered showers, mostly light, across the San Joaquin Valley, Motherlode, and west slopes of the Sierra. Water vapor indicating next short wave approaching. Models have taken a more southern track with this feature which would put best threat of showers over southern portions of the forecast area today. Progs continue to indicate widespread increased CAPE across Interior NorCal today to support deep moist convection, however main synoptic lift is focused more towards Central CA. Snow levels continue around 6500 feet today.
Decreasing threat of showers this evening with mostly dry weather expected overnight into Wednesday morning. Models spread leading edge of precip with next system across NW portions of the Interior NorCal by Wednesday afternoon. Mainly light precip spreads across most of the forecast area tomorrow night. Moderate precip possible across the west slopes of the Sierra Nevada due to orographic enhancement. Snow levels lower overnight with some accumulations at pass levels which could impact travel. Showery Thursday morning gives way to mainly dry conditions by the afternoon as subsidence spreads in from the west.
Dry weather expected Friday into the weekend as large scale upper ridging from the EPAC progresses over California. Around 10 degrees of warming expected Friday with highs in the upper 70s for the Central Valley with 50s to lower 70s for the mountains and foothills.
Extended discussion (Saturday through Tuesday)
Latest model runs continue to be consistent with placing an upper level ridge of high pressure across northern California for this coming weekend. The stable atmosphere will allow for temperatures to warm up to near or slightly above normal conditions. The main uncertainty remains as to the whether or not the upper level disturbance will create enough instability over the northern mountains to bring some light precipitation for Sunday night into Monday morning.
Although confidence is low at this point, the next weather making system may affect northern California starting Monday night into next Tuesday.