Warm conditions expected today with periods of weak to locally moderate northeast to east winds. Patchy dense fog is expected for the coast and western valleys tonight into Tuesday morning. Cooler conditions expected for the middle to end of next week. A windy and wet pattern is expected for the end of the week.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Areas of fog and dense fog were observed this morning within about 15 miles of the coast. As of 9 AM, visibility had improved rather significantly with just a few patches of low clouds lingering along the immediate coast. Areas of dense fog are possible again tonight into Tuesday morning from the coast into portions of the western valleys. The most likely locations for dense fog will be on the coastal mesas and near higher coastal terrain.
An area of low pressure currently 1400 miles west of San Diego will slowly begin to move east today. This slow eastward progression will begin to weaken the ridge of high pressure over the area by Tuesday. As the upper level pattern begins to shift, the surface offshore pressure gradient will weaken and begin to transition back onshore. Northeast to easterly winds this morning peaked at 30 to 40 mph. Winds will continue to weaken through the morning. With influence from the offshore flow and a fairly robust high pressure aloft high temperatures west of the mountains will be a few degrees warmer than yesterday. As the high weakens, conditions will begin to cool for Tuesday. Highs Tuesday will be 3 to 5 degrees cooler than today west of the mountains. Cooler conditions will continue to spread further inland Wednesday. As the onshore pressure gradient continues to increase for the middle of the week, dense fog will become less likely for coastal locations.
There is becoming better agreement in model guidance for the incoming low pressure system, particularly when it comes to the onset of the precipitation. Most guidance is indicating that precipitation will begin as early as Thursday afternoon and evening with decreasing chances for showers for Friday and Friday night. Through Friday, NBM has a 70 to 90 percent chance for one-quarter inch or more of rainfall from the coast to the mountains with a 25 to 45 percent chance of 2 inches or more for the mountains. Snow levels above 10000 feet will lower to 5500 to 6500 feet for Friday morning through Friday night. For early Friday, the NBM 25th percentile snow level is 4500 to 5500 feet with the 75th percentile snow level 6000 to 7000 feet. Nbm for Big Bear has a 42 percent chance for 1 inch or more of snowfall and a 9 percent chance for 6 inches or more. Winds are also expected to increase for Thursday into Friday. Gusts of at least 40 to 50 mph are looking likely over the mountains and into the deserts, with the potential for wind speeds to increase as we get closer.
NBM chances for precipitation are slow to taper off into Saturday, but any rainfall that lingers will likely be more scattered in coverage. Dry conditions are expected by Sunday, with high temperatures remaining around 5 degrees below average.
101630z, Coasts/western Valleys, VFR over land areas today but low clouds and FG will linger over nearshore waters through this afternoon. Clouds based 400-800 ft MSL return to coastal San Diego County 00-03Z, expanding later to include Orange County and pushing up to 10 miles inland. Bases may lower some overnight. Expecting dense FG (1/4 SM) along elevated coastal terrain and in western valleys with lesser vis reductions (1-3 SM) at sea level. However, patches of dense FG will remain possible at sea level. Clouds and FG retreat to the coastline 15-17Z Tue.
Inland Valleys/Mountains/Deserts, Clear skies and VFR conditions through Tuesday morning. Localized east to northeast winds 20-30 knots through passes and coastal slopes through 20Z.
Patches of low clouds and fog may linger over outer coastal waters this afternoon. FG expands in coverage once again this evening with areas of visibility less than 1 nautical mile through late Tuesday morning. A storm system is expected to bring stronger winds and higher seas for late Thursday through Friday. There is also a slight chance of thunderstorms Thursday evening.
Ca, None. PZ, None.
