textproduct: San Diego

SYNOPSIS

Widespread mid and high clouds today will clear from the west overnight. Low clouds and fog will become more widespread each night and morning through the week as the marine layer deepens. Temperatures will fluctuate a few degrees each day through mid- week, remaining around 5 to 10 degrees above normal. Much cooler with gusty onshore winds and chances of precipitation for Friday through the weekend.

..updated Aviation Discussion below

An upper level disturbance brought widespread mid and high clouds to the region today some of which produced rain. Most of the rain evaporated in the dry sub-cloud layer before reaching the ground, although a trace of rain reached the ground in a few places. The disturbance also weakened the marine layer inversion and mixed out the boundary layer so there has been no low clouds or fog to speak of today.

The disturbance will move east tonight taking the mid and high clouds with it and a transient ridge of high pressure will traverse the region through Wednesday. This will allow the marine layer to return, with low clouds and fog in the coastal areas and western valleys each night and morning. There will be only minor day-to-day variations in temperature, with daytime highs remaining about 5-10 degrees above normal each day.

Numerical models are in pretty good agreement through Friday with respect to the evolution of the synoptic pattern. A vigorous low pressure system, with a closed low at 500 mb, will likely impact the region from Thursday through the weekend. Temperatures will begin to lower, clouds increase and onshore flow strengthen on Thursday. Daytime high temperatures will be near or a few degrees above seasonal averages and westerly winds could be gusting to 35-40 mph in the mtns and on adjacent desert slopes.

For Friday through the weekend...model solutions begin to diverge and there is increasing uncertainty in the details of the forecast. In general, clouds will continue to increase through Saturday and temperatures will continue to trend lower. Sunday will likely be the coolest day, with high temperatures near or as much as 10-15 degrees below seasonal averages. This low pressure system will likely be vigorous enough to bring chances for widespread measurable rainfall and some mountain snow. Saturday will be the day with the best chances for precip and the greatest accumulations. Snow levels will start out above 7000 ft before lowering to around 6500 ft on Sunday as the precipitation begins to taper off. The National Blend of Models currently shows a 65% chance of 0.25 or more in the mountains, a 45%-55% chance in the valleys and coastal areas, about a 25% chance in the high deserts and a 10% or less chance in the lower deserts.

The low pressure system moves east by late Sunday and weak upper level troughing remains over the Western US into Monday, maintaining cool weather with highs near or a few degrees below seasonal averages.

AVIATION

070000Z...SKC across most of the region currently. Lack of high clouds should create better conditions for low cloud development this evening. Low clouds based 1000-1500 ft MSL develop first in San Diego County coastal areas around 02-05Z. Clouds slowly increase in coverage overnight to include Orange County, reaching 15-20 miles inland. Areas of minor vis reductions for elevated coastal terrain and western valleys (3-6SM). Slight chance for low clouds to reach the far western/southern Inland Empire (20% at KONT). Clouds scatter out 15-17z with SKC expected for Tuesday afternoon and early evening.

MARINE

Wind gusts in the outer waters could exceed 20 knots Wednesday night. Otherwise, no hazardous marine conditions are expected through Saturday.

SKYWARN

Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions.

SGX WATCHES/WARNINGS/ADVISORIES

CA...None. PZ...None.