Offshore winds arrived this morning and cleared out the low clouds. A moderate to strong offshore wind event will affect the region tonight and Tuesday, with weaker offshore flow Wednesday and another bump up in winds Thursday. Humidity levels will be low to very low. Frost or freezing temperatures are likely in wind-sheltered areas each night today through Thursday. There is a developing chance of rain next weekend.
High Wind Warnings and Fire Weather Concerns
High Wind Warnings are in effect for much of the region through early Tuesday afternoon due to the likelihood of widespread damaging winds in SoCal. Dangerous fire weather conditions are also expected today through Tuesday evening, with a high probability of continuing through Thursday. The Central Coast will not see winds anywhere near the 30-60 mph sustained winds with gusts past 70 mph in Southern California (gusts to 100 have been mentioned by NWS Los Angeles).
Offshore Winds on the Rise
The offshore wind event is well on track with 60 to 70 mph gusts in the mountains and 45 to 55 mph gusts across the coasts and valleys. Upper-level wind strength is still on track to increase along with a good shot of cold air advection which will help to drive the stronger winds down to the surface. All of these ingredients will combine to make the evening and early overnight hours the peak of this wind event with 80 to 90 mph gusts likely in the mountains and 55 to 65 mph in the warned sections of the coasts and valleys in Southern California.
The offshore gradients will relax a little on Tuesday, and the winds will decrease noticeably late in the morning and early afternoon. By mid-afternoon there may be some advisory level gusts remaining in the mountains of Southern California.
Continued offshore flow and low humidities are expected on Wednesday. There is negligible upper support, however, and there may only be a need for low end wind advisories in the morning in Southern California.
On Thursday, the offshore push is forecast to increase in Southern California. It's likely that there will be another round of wind warnings and advisories in the typical offshore windy areas. These winds will quickly subside in the afternoon.
It is important to note the Central Coast winds will also be offshore and dry in the night and morning hours, but the pace is generally just 10-20mph with local gusts to 25mph, but all of that doesn't trigger any advisories. That said, it doesn't take advisory-level winds to be concerned about fire. The local air is very dry, and short on rain, we should also be aware of the weather forecast challenges.
Temperature Fluctuations
Offshore flow can be tricky. The air is dry and the skies are clear so we are both potentially very cold to start and yet the highs can still be above average. That is exactly the condition we face this week. Thursday looks particularly warm with that offshore push, highs could be well into the 70s in a few places.
Frost and Freeze Conditions
With clear skies and very low humidity values, it will become very cold in wind-sheltered areas tonight and especially Tuesday night. Lows will drop to the lower to mid-20s in interior portions of the SLO valleys and the Cuyama Valley. Freezing temperatures are possible each night in wind-sheltered portions of coastal SLO and SBA Counties. Freezes are likely in the colder valleys, especially Tuesday night when there is less wind. Freeze warnings have been issued for many areas tonight with a freeze watch in effect for Tuesday night.
Looking Ahead to the Weekend
The upper high will be pushed to the south and west by a large trough moving out of the Pacific NW. More importantly the offshore flow will only about half as strong as it was Thursday morning and will turn onshore in the afternoon. There will be enough offshore flow in the morning to prevent the low clouds from forming, but the switch to onshore in the afternoon will bring a big 4 to 8 degree cool down across the coasts and valleys.
There is better but still not great agreement with the models and ensembles about the weekend forecast. Both now agree that the main weather player will be the cold long wave trough that will sweep through the state over the two day period. A cut off low will likely form at the base of the trough.
There is a 70 to 80 percent chance of rain over the area over the two day period with very low confidence on any given 6 hour period. Rainfall amounts should come in anywhere from light to .35 inches.
Snow levels will be quite low with this system, between 4000 and 5000 ft on Saturday and under 4000 ft on Sunday. Given the low amount of available moisture it does not look like there will be any significant accumulations below 6000 ft.
The cold core of the low will be over the forecast area. This will bring a 15 to 20 percent chance of a thunderstorm.
With good onshore flow and rapidly falling heights as the cold air from the interior moves in, max temps will plummet 12 to 18 degrees on Saturday and change little on Sunday. Max temps will almost all be in the mid to upper 50s or about 10 degrees under normals.
The upper low should slowly depart on Monday. Look for decreasing clouds, a decreasing chance of rain and a slight warm up.
