textproduct: San Diego

SYNOPSIS

Well above average temperatures will continue through the weekend. Widespread marine layer low clouds this morning will become patchier over the weekend with increasing high clouds. Cooler Monday through Wednesday with high temperatures returning to normal. Breezy onshore winds and a chance of showers for the mountains westward Tuesday and Wednesday. Minor warming Thursday then more significant warming on Friday.

DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE

SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES...

Low clouds have spread into the coastal areas and have started to move into the far western valleys in San Diego County this evening. Otherwise skies are clear. Low clouds will clear back to the beaches by late morning. Another warm day is in store as upper level high pressure over the Southwest US expands slightly further west over So Cal. High temperatures will be as much as 15-20 degrees above normal inland, and around 5-10 degrees above normal near the coast. Several high temperature records are at risk of being broken, mainly in the mountains and low deserts. On Saturday, the marine layer will become more shallow, allowing for more warming in the inland coastal areas and valleys where high temperatures could be close to 25 degrees above normal. The shallower marine layer will also increase the risk of fog, potentially dense, in the coastal areas tonight into Saturday morning.

The upper level ridge begins to break down on Sunday, bringing minor cooling though highs will remain around 15-20 degrees above normal inland. Increasing high clouds late Saturday into Sunday may disrupt marine layer low clouds from redeveloping Saturday night. A weak upper level trough moves inland across the Pac NW on Monday with mostly zonal flow and continued cooling in So Cal. Monday is the first day in over two weeks that no record high temperatures are forecast to be broken.

Global ensembles are still struggling with the progression of an upper trough in the southern stream of the jet towards the middle of next week. Around 55% of the members are slower and keep the trough offshore into Tuesday, meaning less cooling and dry weather. The other 45% are more progressive for greater cooling and an earlier onset of precipitation. Uncertainty in the position and amplitude of the trough persists into Wednesday. All clusters show some form of troughing near the west coast with cluster means containing some precipitation. The most amplified and wettest cluster accounts for about 28% of the ensemble space, while 43% are lower amplitude/less wet and the remaining 29% is somewhere in between. While current forecast calls for at least a slight chance (15%) of precipitation Tuesday morning through Wednesday evening, this window will likely be narrowed and possibly shifted once the timing becomes more clear. Over a larger window (Tue morning through Thu morning) there is around a 50% chance of at least 0.01" for the mountains westward, and a 25-45% chance of at least 0.10", with the highest probabilities along the coastal mountain slopes. Ensembles have been trending drier overall the past couple days with means below 0.10", so not expecting much at this point. What is more certain is that it will be cooler and cloudier with breezy onshore winds in the mountains and deserts.

Whenever the trough decides to progress eastward later in the week (Thu-Fri), warmer and drier weather will follow with highs returning to slightly above normal.

AVIATION

270930Z...Low clouds and fog will continue to cover coastal areas this morning. Cigs will be 400-800 feet MSL with tops to 1100 feet, and vis reduced 0-5SM, lowest on mesas and higher coastal terrain. Scatter out 15-17Z. Low clouds will redevelop mainly near the coast, but will be more patchy and later after 06Z into Saturday morning. Random and intermittent cigs around 300-700 feet MSL.

Otherwise, mostly clear skies and VFR conditions today and tonight.

MARINE

No hazardous marine conditions expected through Tuesday.

SKYWARN

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

SGX WATCHES/WARNINGS/ADVISORIES

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