textproduct: San Diego

SYNOPSIS

Monsoonal moisture will decrease into the weekend with a slight chance of showers and thunderstorms for the mountains and high desert for this afternoon. Above average high and low temperatures will continue through next week. Slightly warmer high and low temperatures for the middle and latter part of next week will increase the HeatRisk with widespread moderate to locally major HeatRisk for the coast, valleys, and mountains except near the beaches and for the higher elevations in the mountains, with major to extreme HeatRisk for the lower deserts.

SHORT TERM (Today through Sunday)

A Mesoscale Convective Vortex that was initiated by thunderstorms over Arizona last night is now tracking toward the northwest and north in the southerly flow between the low pressure system off the West Coast and high pressure over the Rockies. Showers have developed over portions of western Riverside County and will spread northward into San Bernardino County for the remainder of the night. There is also a slight chance of thunderstorms.

Precipitable water values were forecast to peak over southwestern California on Thursday, then decrease into the weekend. Scattered showers and thunderstorms may develop this afternoon along convergence boundaries along the desert slopes of the mountains and northward across the Lucerne Valley in the high desert. Dry weather is then expected through the weekend.

High temperatures for the lower deserts will warm a few degrees today as drying of lower level moisture occurs. Otherwise, there will be slight day to day differences in high temperatures through the weekend. High temperatures for the weekend will be a few degrees above average near the coast to 4 to 8 degrees above average for inland areas. High temperatures for the weekend will range from the mid 70s to lower 80s near the coast to the upper 90s to 104 for the Inland Empire with 110 to 114 for the lower deserts.

LONG TERM (Monday through Thursday)

There may a brief increase in lower level moisture into the lower deserts around Monday with high temperatures for the lower deserts not quite as hot by a few degrees on Monday. Otherwise, high pressure to the east and low pressure over the eastern Pacific will maintain generally drier south to southwest flow aloft next week. High temperatures for next week will be around 5 degrees above average near the coast to 5 to 10 degrees above average for inland areas. High temperatures will range from around 80 near the coast to the upper 90s to 108 for the Inland Empire with 110 to 115 for the lower deserts and the upper 90s to 108 for the high desert.

Low temperatures will be around 5 degrees above average near the coast to 5 to 10 degrees above average for inland areas with the lower elevations of the mountains locally 10 to 15 degrees above average. For Wednesday through Friday, low temperatures will be mostly in the lower to mid 70s for the coast and valleys.

Major HeatRisk will continue for the lower deserts through next week with major to extreme HeatRisk for Thursday and Friday of next week. By Tuesday of next week, widespread moderate to locally major HeatRisk is expected for the coast, valleys, mountains, and high desert except near the beaches and for mountain elevations above 6500 feet, mostly due to the warmer nights. The Extreme Heat Warning for the lower deserts has been extended through Friday of next week, August 28th.

AVIATION

210930Z...Coast...Patchy low clouds based 800-1200 ft MSL over the coastal waters will remain patchy and intermittent at best for coastal areas through early this morning. Low clouds expand in coverage near sunrise with the best chance for cigs at coastal TAF sites 12-15z. VFR conditions expected this afternoon. Similar conditions expected tonight, with patchy low clouds generally remaining over the coastal waters with best chances for cigs at coastal sites Sat morning after 11z.

Otherwise...FEW to SCT clouds above 15 kft MSL through Friday. Slight chance (10-15%) for ISO SHRA/TSRA over mtns from 20z Fri to 01z Sat.

MARINE

No hazardous marine conditions are expected through Tuesday.

SKYWARN

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

SGX WATCHES/WARNINGS/ADVISORIES

CA...Extreme Heat Warning until 8 PM PDT Friday for Coachella Valley- San Diego County Deserts-San Gorgonio Pass near Banning.

PZ...None.