The weather in Anaheim this morning is much cooler than yesterday. The skies are partly cloudy and the wind is still. There is probably fog in some areas, though not here in Anaheim.
The National Weather Service (NWS) in San Diego forecasts patchy fog this morning and a partly cloudy day with a high of 67 F. This evening, there is a 30% chance of showers and a low of 54 F.
The visible satellite imagery shows light clouds over parts of southern California, with open cell convection off the California coast.
The enhanced infrared satellite imagery shows no thick clouds at all, so it has been omitted from this post.
The water vapor satellite imagery shows that the upper-level low pressure system is making landfall near the Oregon/Washington border. Notice the moisture wrapping around the center of low pressure in a cyclonic fashion.
The 12Z upper air sounding from San Diego shows a dry atmosphere, but notice the high dewpoint (and thus high humidity) near the surface. This is why there is patchy fog in many areas, as the humidity reaches nearly 100% right above the surface. Overall though, there is still only 0.34 inches of precipitable water present, and very little moisture until around 300 mb, where the dewpoint depression is low again. There was no Convective Available Potential Energy (CAPE) present this morning. There was also a strong radiational inversion, dropping the 0-3 km average lapse rate to 2.1 C/km.
The deep-layer shear was 38 kts, and the low-level shear was 17 kts. The higher shear values are due to the approaching shortwavge trough.
The surface observations (from the SPC Mesoscale Analysis Map) show the lower temperatures and still winds across the southern part of the state. There are no obvious frontal boundaries or drylines in my surface analysis.
The surface pressure map shows only a gentle pressure gradient over southern California, though a steeper one over the central part of the state.
The RAP shows this pressure gradient will intensify over the next six hours as the low pressure over Nevada drops from 1012 mb to 998 mb.
Synoptically speaking, the 300 mb NAM chart (from Unisys) shows that a closed low will continue to form in the end of the shortwave trough. This system has the potential to cause all sorts of holiday travel woes for the western part of the country. For southern California, it will likely bring some rainy weather.
The 500 mb NAM chart shows that there is strong vorticity associated with this low, though it will remain north of the LA metro area.
Associated with the strong Positive Vorticity Advection (PVA), the 700 mb NAM chart is showing rapidly rising air north of the LA Metro area.
The 850 mb NAM chart shows the Cold Air Advection (CAA) that pushed through the area last night. Notice how there are still winds blowing across the thermal gradient from cold to warm, meaning temperatures may drop again this evening.
Overall, I expect a few showers are possible this evening as the shortwave trough pushes onto land. I expect that there will be some moisture drawn into the upper level low, and that some of that moisture will fall over the LA Metro area. I also expect the winds to intensify near the Nevada and California border, based on the pressure map prediction from the RAP. I will enjoy as much of today as I can; so far, there has been no rain here in Anaheim.
Thank you for reading my forecast.
The upper air soundings and mesoscale analysis plots are from the Storm Prediction Center website.
The forecasted upper air soundings are from TwisterData.com.
The surface observation and upper level charts are from Unisys Weather.
The satellite data is from NASA – MSFC