November 16, 2018 – Dry with a little above normal daytime temperatures through early next week except near or cooler than normal in areas of heavy smoke due to the Camp Wildfire. Breezy northeasterly winds over the Sierra Nevada Saturday night into Sunday elevating fire danger. Cooler temperatures next week with increasing chances of precipitation across interior NorCal middle to end of next week. Fire Weather Watch from Saturday evening through Sunday afternoon for Northern Motherlode From 1000 to 3000 Ft.
High pressure over the eastern Pacific and western U.S. will keep the forecast area dry through the short term period. A light east flow out of the Sierra and a light northerly flow down the northern Sacramento valley combined with stable conditions under the ridge will again concentrate smoke from the Camp Fire into the central valley today.
Main concentration of smoke will be from southern Tehama county southward to Stanislaus county. In this region, daytime high temperatures will be limited by lack of sunshine keeping them near or even several degrees below normal. Other impact will be reduced visibilities in this region with current morning reports dropping visibility to 1/2 mile some local spots.
Only minor changes are expected in the weather pattern on Saturday so smoke is likely to remain concentrated into roughly the same areas. Although smoke seems to be blocking solar insolation enough to cool temperatures during the day, radiational cooling at night is allowing valley temperatures to drop down into the 30s or about 5 to 8 degrees below normal.
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Models in fairly good agreement in dropping a shortwave trough southeastward through the Pacific Northwest into the Central Great Basin on Saturday with high pressure rebounding over the west coast by Saturday night. The combination of northeast to easterly flow aloft and a tight northeast surface gradient across the Sierra will bring breezy northeast winds Saturday night through Sunday especially to the higher elevations and favorably oriented Sierra and foothill canyons. These breezy winds will bring elevated fire danger and a fire weather watch will remain in place for the Sierra and Foothills Saturday evening through Sunday afternoon. The breezy winds may bring enough vertical mixing to reduce the central valley smoke but the winds in the valley will not be all that strong so some of the smoke concentration is expected to remain. The main effect other than increased fire danger will be a little warming in formally very smokey areas Sunday where smoke amounts are reduced.
Upper ridge axis will shift just east of the forecast area by Monday afternoon bringing a slight cooling most areas. Central valley smoke will still be a wild card but with relatively light winds under the ridge believe that at least light smoke will remain in the valley. A few high clouds may start spilling into the region late Monday preceding a possible major change in the weather pattern coming mid week.
Extended Discussion (Tuesday through Friday)
Confidence in increase in a pattern change this week, bringing cooler temperatures and a chance of precipitation mid- to late- week. Models continue to show a split flow pattern Tuesday, with one upper level low moving over SoCal while a deeper upper low moves east over the eastern Pacific. The most recent GFS run is nudging closer to the Euro’s progression, though timing inconsistencies still remain. In general, a shortwave trough and associated cold front is forecast to move inland Wednesday, bringing with it a chance of precipitation and cooler daytime temperatures. Showers could linger behind the shortwave Thursday before another low pressure system moves onshore Thursday evening through Friday, bringing another wave of precipitation to NorCal. Precipitation timing and amounts are still uncertain at this time due to model inconsistencies this far out. Stay tuned to to the forecast for any updates.