January 10, 2018 – Scattered showers today with shower threat shifting northward Thursday. Fair skies and warmer temperatures Friday through the weekend with some valley morning fog possible. Next chance of precipitation late Monday or Tuesday of next week.
Discussion
Upper low which moved through southern California over the last couple of days has now moved into Arizona and precipitation has ended nearly all areas. Upper ridge has begun to build over the eastern Pacific but a shortwave trough riding over this ridge will bring a threat of showers mainly over the mountains after mid day. For this morning, a fairly consistent low cloud deck should keep morning valley fog at a minimum. Snow levels today will come down a bit as cool air filters in behind the retreating low but precipitation amounts forecast to remain quite light so impacts will be minimal.
Some clearing tonight between systems will allow for a little more extensive valley fog to form. Another shortwave pushing through the Pacific northwest on Thursday afternoon will bring another chance of light precipitation north of about interstate 80. Again, snow levels will remain relatively high under the building upper ridge and QPF remains very light so impacts stay minimal.
Upper ridge finally builds enough over the west coast on Friday to end any precipitation threat over the CWA. Stable conditions and fair skies will bring a renewed threat of night and morning valley fog through the remainder of the week. Warming airmass will bring up daytime high temperatures to about 10 degrees above normal for this time of year.
Extended discussion (Sunday through Wednesday)
High pressure will continue to bring dry weather and seasonably warm weather through Sunday. Morning Valley fog will be a possibility through this timeframe.
Confidence continues to increase in a return to unsettled weather next week. The first shortwave trough is projected to arrive across the West Coast in the Monday-Tuesday timeframe. There are still some model differences, with the ECMWF projecting a stronger and wetter system than the GFS. Afterward, the GFS and ECMWF are in better agreement with a secondary, colder storm system mid to late next week. These details are in concurrence with the Climate Prediction Center’s 6-10 and 7-14 day outlooks. This gives us greater confidence in this pattern shift, and may continue beyond next week.