November 24, 2018 – Scattered showers this morning over the Sierra, then dry through early next week. Valley fog possible next couple of mornings. Next chance of precipitation next Tuesday. Heavier precipitation and lower snow levels possible next Thursday.
Discussion
One last shortwave trough dropping across northeast California bringing scattered light showers mainly to the Sierra. Plentiful residual moisture in the valley translating to some fog and low clouds there. Models indicating lower elevations should begin drying out by mid day today as winds transition to northerly behind the shortwave. Upper ridge builds over the west coast tonight and Sunday bringing a period of dry weather early next week. Stable conditions under the ridge will bring a continued threat of valley fog night and morning hours although light northerly breezes may limit area of fog coverage to the southern Sacramento and northern San Joaquin valleys.
Upper ridge axis shifts east of the forecast area on Monday as a Pacific frontal system approaches the coast. By Monday evening, cloud cover in advance of the frontal system should have spread over most of the forecast area with light rain hitting the northern zones. Models in fairly good agreement at dropping the front and associated precipitation southeast across the CWA on Tuesday. Relatively warm airmass will keep snow levels relatively high with this first system so snowfall impacts will be limited to the highest elevations.
Extended Discussion (Wednesday through Saturday)
Active pattern is expected during the second half of next week as a series of waves move across the region. Lingering shower activity is expected during the day on Wednesday ahead of an approaching Pacific system, which will move across interior NorCal late Wednesday into Thursday. However, models remain uncertain regarding storm strength, and timing, with the GFS being the most aggressive. Early precipitation estimates suggest about 1-2″ across the Valley, and 2-4″, locally higher, over the mountains. These amounts will likely change as we get closer to the event. The storm will push east of the forecast area on Friday, with lingering activity over the mountains. Another system could drop southeastward across the region late next week into early next weekend, but confidence is low. Temperatures will be running 5 to 10 degrees cooler than normal through the forecast period, with Valley highs in the low to mid 50s, and 30s and 40s over the mountains.