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Warm weather again today with 90s possible once again in the Valley with hazy conditions. Changes quickly come into the forecast starting Tuesday with a cooling trend into next weekend with chances for showers by mid to late week with breezy winds at times.
Light winds and mild temperatures are being observed over interior northern California this morning. As of 3:00 am temperatures are generally in the 50s – 60s in the Valley with many areas along thermal belts still in the 70s. Some lingering smoke is also being detected at the surface in the San Joaquin Valley with Modesto reporting degrading air quality. Hazy skies will likely continue today with much of the smoke remaining elevated. However, improving conditions are expected compared to yesterday. Increasing onshore flow into the afternoon should help to clear out some of the lingering wildfire smoke. Highs tomorrow are expected to be 5 – 10 degrees cooler as we start transitioning into a cooler, wetter pattern.
Ensemble guidance is in good agreement a deep trough will gradually work its way into our area bringing much cooler high temperatures and unsettled weather to the region. Cluster analysis has yet to come into good agreement about the timing of this approaching trough. However, there is some agreement that precip chances are expected to be minimal in the Valley with better chances over the mountains. There is also some agreement that amounts are are expected to be light with less than a half inch anticipated for the mountains. The most noticeable change will be the widespread cooler temperatures. High temperatures will fall to 10 to 20 degrees below climatology across the region. Breezy winds will also be possible at times along with cloudy skies.
Extended Discussion (Friday through Monday)
Ensemble guidance suggests the deep trough will continue to slowly move onshore late this week, bringing a chance of precipitation and continuing the cooling trend. Clusters still uncertain on exactly when the axis will move onshore, which is causing uncertainty in the precipitation timing and amounts. NBM continues to back off on precipitation chances in the majority of the Valley with just a slight chance on Friday. Otherwise, best chances for showers are for the mountains and foothills. Temperatures will continue to cool for Thursday and Friday with Valley highs in the 60s to low 70s and 30s to 50s in the mountains and foothills. With such cool temperatures in the mountains, snow levels could drop to around 7000 to 7500 feet, bringing a chance of light snow to the high Sierra and possibly the southern Cascades. Impacts are expected to be minimal. Also, expect breezy winds at times as the trough moves onshore.
Looking ahead to early next week, we could see another trough dig into the region bringing dry northerly winds to the Valley. Dynamic cluster analysis has some decent agreement about a possible trough over the West early next week, however a large amount of uncertainty exists with the details. We will keep an eye on this emerging feature as this pattern could produce elevated fire weather concerns.