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September 17, 2016 – High pressure over the west coast will bring fair skies and warm temperatures over the next few days. Daytime highs over the weekend are forecast to come in between about 5 and 10 degrees above normal but are not expected to get into record territory. Cooler temperatures are expected through most of next week.
Ridge from the eastern Pacific building into NorCal and will continue the warm and dry pattern into early next week. Active pattern just to our north with westerlies bringing bands of showers through the PacNW, and at least the northern half of the forecast area may see periods of high clouds.
High pressure ridge over the west coast brought fair skies and warmer temperatures on Friday with daytime maximum temperatures up a few to several degrees. These warmer temperatures have continued into this morning where current temperatures are still running a few to several degrees above 24 hours ago. Airmass continues to warm today with most locations expected to see highs at least a little warmer than on Friday. A weak system passing through the Pacific Northwest today will bring a few high clouds to the northern most CWA but otherwise have little impact. Most of forecast area will see a bit more warming on Sunday except for the far north where more systems passing to the north will keep daytime highs fairly level.
For most locations Sunday will be the warmest day of this warmer than average period. Things begin to cool off a bit on Monday as an upper trough begins to dig in offshore over the eastern Pacific. Temperatures will cool a degree or two but highs will still come in several degrees above normal for mid September.
Temperatures will see a much bigger drop on Tuesday as the upper trough continues to move inland. This will bring a cooler airmass and increased onshore flow with daytime highs coming in right around normal for this time of year. GFS and ECMWF keep moisture with this trough north of the forecast area but current GEM model indicates some moisture over the Sierra for some possible showers Tuesday afternoon or evening there. Will watch this area in subsequent model runs but for now, have left the forecast dry.
Extended discussion (Wednesday through Saturday)
An upper level trough extending from a low in the Pacific NW into NorCal will cause daytime highs to be 5-12 degrees cooler than normal on Wednesday and Thursday. Breezy conditions possible over mountains as this trough impacts the region. However, models show that the brunt of precipitation will stay north of our area. The ECMWF hints that there could be some areas of showers in our CWA, but in coordination with our neighbors, have kept the extended forecast dry at this point. The low moves southeastward and skirts far NorCal before tracking east of our region by Friday. This will allow temperatures to get back on a warming trend for the end of the week.