textproduct: San Diego

SYNOPSIS

Cooler this weekend with a return of the marine layer at the coast. Gusty west winds in the mountains and deserts this afternoon will transition to weak offshore flow Sunday through Tuesday. Significant warming Sunday through Friday with high temperatures of 20 to 30 degrees above normal and moderate to high heat risk.

DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE

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

Scattered high clouds are moving across the region this evening with no signs of marine layer clouds nearby. A weak upper level trough moving by to the northeast will bring an increase in onshore flow today. Breezy west winds will develop across the mountains and deserts this afternoon with gusts around 30-40 mph, locally higher below the San Gorgonio Pass. This trough and a developing coastal eddy will spread cooling inland today, though highs will still be around 10-15 degrees above normal. Marine layer low clouds are forecast to develop over the coastal waters this afternoon, spreading into the coastal areas this evening into Sunday morning. Fog may be dense at the coast when the marine layer first rebuilds, shifting onto the coastal mesas tonight as the marine layer deepens.

The trough makes a quick exit and surface pressure gradients turn offshore by Sunday morning. Winds will be confined to the usual passes and canyons with peak gusts around 25-35 mph. The big story is how this will begin our warming trend as offshore flow combines with the upper level ridge amplifying off the West Coast. For Sunday, high temperatures will increase to around 15-20 degrees above normal, with the greatest departure from normal in the valleys. Offshore flow weakens for Monday and Tuesday, but the ridge slowly shifts eastward over CA. This will result in warming for all areas, and by Tuesday highs will be approaching 30 degrees above normal in the Inland Empire, and around 20-25 degrees above normal elsewhere.

The ridge continues to slowly drift eastward for the latter half of the week, becoming centered near the lower Colorado River Valley and strengthening. Friday is currently forecast to be the hottest day of the week with high temperatures around 30 degrees above normal away from the coast, and around 20 degrees above normal at the beaches. This translates to highs in the mid 80s at the beaches, low 90s to 105 for the inland coastal areas and valleys, low 80s to low 90s in the mountains, upper 90s in the high deserts, and 109-112 in the low deserts. Moderate to locally high HeatRisk exists for most areas by Thursday and Friday, becoming High in the low deserts late in the week. Current Extreme Heat Watches may need to be expanded to include parts of the mountains and the low desert at least Thursday and Friday, possibly into Saturday. Many March temperature records are likely to be broken late in the week. See the CLIMATE section for more details.

AVIATION

141200Z...VFR conditions with SCT high clouds expected today. Satellite shows patchy low clouds (near 300-500ft MSL) out over the waters, but quite offshore and south of the International Border. Aided by a developing coastal eddy, guidance suggests these clouds will gradually increase in coverage and spread northward over the next several hours. This brings a window (14-17z) for CIGs and reduced VIS (down to 2-4 SM), mainly at KSAN, but there is only about a 20-30% chance of this occurring. Next to 0% chance for any impacts at KCRQ or KSNA.

Any clouds that may sneak ashore later this morning will retreat offshore by 17z, but the coastal eddy should continue to increase cloud cover over the waters into the afternoon. These clouds are expected to lift to around 400-800ft MSL this evening, pushing ashore after 02z Sunday.

MARINE

No hazardous marine conditions are expected through Wednesday.

CLIMATE

The following are the existing highest temperature records for March for selected locations along with the highest daily NBM probability to set a new March record for next week. This is not a comprehensive list, but the most likely locations to tie or set new monthly record high temperatures for March are in the deserts, valleys, and mountains.

Location March Record NBM Probability

Palm Springs 104 95-100 percent (Wed,Thu,Fri) Indio 104 100 percent (Wed, Thu, Fri) Thermal 103 100 percent (Wed,Thu, Fri) Ramona 94 92-97 percent (Thu, Fri) Big Bear 80 100 percent (Thu, Fri) Santa Ana 98 40-50 percent (Thu, Fri)

The existing highest 500 mb height for NKX for March is 590 DM. That could be exceeded for multiple days next week between Tuesday and Friday.

SKYWARN

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

SGX WATCHES/WARNINGS/ADVISORIES

CA...Extreme Heat Watch from Monday morning through Friday evening for Orange County Coastal Areas-Orange County Inland Areas- San Bernardino and Riverside County Valleys-The Inland Empire-San Diego County Coastal Areas-San Diego County Valleys-Santa Ana Mountains and Foothills.

PZ...None.