October 18, 2018 – Warm and dry conditions through the weekend with daytime high temperatures a few to several degrees above normal. Cooler temperatures starting Monday with a chance of precipitation northern forecast area Tuesday through the end of the week.
High pressure aloft over the eastern Pacific and west coast will keep warm and dry conditions over Norcal today. Daytime highs are forecast to run between 5 and 10 degrees above normal. Afternoon humidity will remain fairly dry under light north to east winds dropping into the teens this afternoon many areas. Temperatures will warm a little more on Friday as the upper ridge axis centers over the region. A weak low, forming off the SoCal coast on Friday will open and drift over the state over the weekend. This will bring a slight cooling Saturday and Sunday and some breezy east winds over the Sierra Saturday morning but otherwise have little impact. Even with the cooler temperatures daytime highs over the weekend will remain a few degrees above normal.
Extended Discussion (Monday through Thursday)
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Weak upper low/trough shifts east into the Great Basin Monday as stronger short wave approaches the PacNW. Pac Frontal system moves inland Tue and weakens under diffluent upper level flow. EC showing stronger system and more widespread precip over CWA, while GFS indicating little if any precip spreading over Interior NorCal.
Given synoptic pattern, forecast leans more towards drier solution with low POPs mainly over the Coastal and Shasta mountains Tue into early Wed. Another disturbance moves into PacNW beginning late Wed. EC indicating less EPAC upper ridging and more widespread precip over CWA Thu, while GFS keeps precip focused north of a KUKI-KCIC line. Forecast attm blends more towards GFS. High temps near normal Monday, cool to below normal Tue into Thu.