textproduct: San Diego

SYNOPSIS

Slight chance of showers and thunderstorms over the mountains and high desert this afternoon. A deep marine layer this morning becomes more shallow tonight into Sunday and high temperatures remain below normal this weekend. A ridge of high pressure will expand by next week, leading to warmer and drier weather across Southern California.

..UPDATED AVIATION DISCUSSION

Marine layer low clouds have spread into parts of the valleys this morning with otherwise mostly clear skies. Low clouds will continue to move into the inland valleys through sunrise, then retreat to the coast by late morning. Mid-level flow turns slightly more southerly today, bringing a marginal increase in monsoonal moisture. There is a 15-20% chance of showers and a 10-15% chance of thunderstorms over the mountains and high desert this afternoon. Given how high based (700-500 mb) the moisture is, gusty outflow winds will be the primary threat. Otherwise, upper level troughing off the West Coast will maintain relatively cooler weather with high temperatures around 3 to 7 degrees below mid- August normals. Highs will be in the mid to upper 70s along the coast, low to mid 80s for inland Orange County and the western valleys, upper 80s to mid 90s for the inland valleys, mid 70s to upper 80s in the mountains, 90s in the high desert, and low 100s in the low deserts. High pressure begins to expand in from the east on Sunday for minor warming and more stable conditions, limiting the potential for any afternoon showers and thunderstorms over the mountains. This will also lead to a more shallow marine layer with low clouds not spreading as far inland Sunday morning.

The upper level ridge of high pressure continues to expand westward and strengthen through at least Thursday, bringing gradual warming and a shallower marine layer. High temperatures return to near normal by Monday, then rise to around 3 to 7 degrees above normal on Thursday. Though some mid-level moisture lingers in mostly southerly flow, the ridge axis will be overhead and the subsidence inversion will act as a lid on any potential convection. While there may be some shallow cumulus over the mountains in the afternoon, shower/thunderstorm chances are less than 10%. While air temperatures themselves are nothing notable for this time of year, muggy conditions and warm nights will push the HeatRisk into moderate for parts of the valleys, lower elevation mountains, and deserts Wednesday through Saturday, with locally high HeatRisk in the low deserts.

Ensembles begin to diverge on the position of the upper level high and a trough off the coast late in the week. Around 46% of the members have the trough further east (closer to the coast), which would provide some cooling, while the other 54% have the trough further off the coast with warmer weather here. The position of the trough and to a greater extent the upper high over the desert southwest will determine how much monsoon moisture hangs around. For now model consensus generally has the upper high in a more favorable position for convection Friday into next weekend.

AVIATION

151130Z....Coast/Valleys...Low clouds are fully into Orange County and into the San Diego valley with bases around 1,500-2,000ft MSL. clouds are teasing the edges of the IE but no longer look as if it will fill in. Vis restrictions 3-5SM will be possible in areas where clouds intersect terrain. Low clouds will begin to clear inland areas 15-16Z and inland OC 16-17Z. There is a 30-50% chance of patchy low clouds sticking to coastal SD through the TAF period. Low clouds return after 01-03Z Sunday.

Mountains/Deserts...VFR conditions prevail through the TAF period. SCT-BKN clouds AOA 10,000ft MSL expected to form after 18Z with a slight chance (10-20%) for TSRA over the Riverside County mountains and in the high deserts.

MARINE

Gusty northwest winds 20-23 knots near San Clemente Island expected Sunday and Monday afternoon. Otherwise, no hazardous marine conditions are expected through Wednesday.

SKYWARN

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

SGX WATCHES/WARNINGS/ADVISORIES

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