Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
195 FXUS66 KSGX 301118 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 418 AM PDT Tue Apr 30 2024 .SYNOPSIS... There will be slight differences in the marine layer depth and high temperatures for the coast and valleys through Thursday with Wednesday a little cooler with the marine layer a little deeper with coastal low clouds spreading a little farther inland into the valleys. Slow cooling will begin to spread inland on Friday as onshore flow begins to strengthen with greater cooling for Saturday and Sunday with Sunday the coolest day with the strongest west to southwest winds for the mountains and deserts. Then warming with weaker winds for early next week. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... .SHORT TERM (Today through Thursday)... The flow aloft across southern California will be weakly cyclonic through Thursday with weak low pressure systems moving eastward through the Great Basin modulating the strength of the onshore flow and marine layer depth for southern California. There will also be a weak coastal eddy at times for the next few days. The marine layer has deepened slightly overnight with satellite imagery showing coastal low clouds spreading northward along the coast and inland across much of the Orange County coastal plain and into portions of the western valleys in San Diego County. The marine layer is expected to be a little deeper for tonight into Wednesday morning, then a little shallower again for Wednesday night into Thursday morning. High temperatures for today near the coast are expected to change little from those on Monday with the inland valleys a little warmer. Then a little cooler on Wednesday for the coast and valleys, then a little warmer again on Thursday. Day to day changes for the mountains and deserts will be less with only slight changes for today through Thursday. && .LONG TERM (Friday through Monday)... A low pressure system will move inland along the West Coast for late Saturday and Sunday. This will begin to strengthen the onshore flow across southern California on Friday with the strongest onshore flow for late Saturday night and Sunday. This will begin to spread cooling inland on Friday with greater cooling for Saturday into Sunday as the onshore flow strengthens and the marine layer deepens. Cluster analysis for Sunday shows the cluster with greater potential for light precipitation is a little slower and more amplified with the low pressure system, something similar to the deterministic GFS. The drier solutions are less amplified and a little faster with the low pressure system and comprise a larger percentage of the ensemble members. While either of those outcomes is plausible, calibrated NBM guidance has the chance for measurable precipitation at less than 10 percent for Sunday. Then warmer with weakening winds for early next week as the low pressure system moves inland. && .AVIATION... 300910Z...Coasts/Valleys...Low clouds with bases 800-1200 FT MSL continuing to fill in through 12z Tue. Cigs may rise a few hundred feet after 12z Tue. Reduced vis of 1 SM or less where low clouds and terrain intersect. Scatter out 15-18z Tue. Otherwise, clear skies with unrestricted vis through tonight. && .MARINE... No hazardous marine conditions are expected through Friday. && .SKYWARN... Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...None. && $$ PUBLIC...17 AVIATION/MARINE...EA