textproduct: San Diego

SYNOPSIS

High pressure off the coast will continue to pass over the region and strengthen through the week, bringing a long-duration and early season heat wave. Patchy low clouds and fog will occur once again near the coast on Monday morning before mostly clear skies take hold thereafter. This heat event will encompass temperatures up to 30 degrees above normal for this time of year, leading to moderate to high heat risk and record breaking temperatures. The area of high pressure will begin to weaken by next weekend, allowing for a gradual cooling trend.

DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE

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

Marine layer clouds have cleared out from this morning as the marine layer reached its max depth of the week near 1500-1800 feet. An area of high pressure off the coast will continue to strengthen, suppressing the marine layer into tonight and Monday morning. This will leave the chance for low clouds and fog to return closer to the immediate coast by Monday morning. The area of high pressure will strengthen into the upcoming week, with mostly clear skies expected across SoCal Tuesday onward.

High temperatures today will be fairly similar to yesterday across the region with the greatest warming of 3-5 degrees expected across the Inland Empire and Orange County. Upper level winds will be offshore on Monday and Tuesday as the high strengthens, which will contribute to a warming trend and long-duration heat wave across the region. The high will be centered over our area by Tuesday and Wednesday, becoming a very strong and hot air mass as models depict a ~594 dm high over the region. This will bring temperatures near 20 to 30 degrees above normal by this time period. Tuesday will be the first day of triple digit heat for some parts of the Inland Empire and lower deserts. Temperatures increase slightly on Wednesday, most notably over the mountains and deserts by another 3-5 degrees. 80s will be common across the mountains of RIV/SD Counties with 70s and lower 80s in the SBD mountains. The mountains will not be escaping the heat this week, so please limit outdoor recreation each afternoon in these areas.

Models continue to show the timing of the high peaking in strength on Thursday and Friday. This will bring the hottest temperatures of the week across the area as models show an unusual summer-like 595-597 dm high over our region as we enter the first days of spring. Our confidence is moderate on the exact strength of the high, which will dictate exactly how hot we get later this week. The average high in Julian in the SD County mts this time of year is 57 degrees but has around a 60-75% chance of seeing highs reach 90 by Thursday and especially Friday. Not only record temperatures for the month of March are expected to break, but also even for April. The record highs for the month of April at Indio and Thermal are 110 for both sites, where NBM indicates a ~70% chance of breaking this record. Triple digit heat has around a 50-50 chance of occurring across the inland San Diego valleys (Alpine, El Cajon, Poway, etc.) and northern Orange County (Lake Forest, Anaheim, etc.). Temperatures will likely surpass the 100 degree mark across the Inland Empire on Thursday and Friday, with areas around San Bernardino and Riverside seeing a 50-70% chance of temperatures reaching 105 degrees. March record highs for Big Bear (80 degrees) and Idyllwild (82 degrees) will likely be broken during this time period as well.

With moderate to high heat risk in the forecast, please check on family, friends, and neighbors this coming week! Make sure you have plenty of water and fans to cool off if there is no cooling system or cooling centers available near you. Outdoor activities should be limited as the duration of this early season heat wave will lead to increased risk of heat illness.

Models show fair agreement on the ridge slowly breaking down by next weekend. This will help spread onshore flow and subtle cooling first from the coast to the mountains on Saturday, then all areas by next Sunday. Models become more varied by early next week, but the warmer than average and dry weather pattern looks to continue as we head toward the end of March.

AVIATION

151800Z...Coasts/Western Valleys...Low clouds have cleared the coastal areas and have given way to VFR conditions through this evening. Expecting patchier low clouds around 300-800ft MSL to move in after 06z Monday, spreading up to 10-15 miles inland. Vis restrictions 4-6SM will be possible mainly across coastal mesas and inland valleys. Low clouds will scatter 15-18Z.

Inland Valleys/Mountains/Deserts...Breezy offshore winds are developing on the coastal mountain slopes, through mountain passes, and locally stretching into eastern valleys. North to northeast wind gusts of 20-25 kts expected, locally up to 35 kts in mountain passes. Gusts weaken after 03z Monday, increasing again towards the end of the TAF period.

MARINE

No hazardous marine conditions are expected through Thursday.

BEACHES

A long period (17-19 second) south-southwesterly swell (190-200 degrees) builds to 2-4 feet Monday afternoon into Tuesday. Breaking waves of 4-6 feet are expected, with sets up to 7 feet possible on south-facing beaches. This swell is expected to persist into Wednesday, waning Wednesday night.

SKYWARN

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

SGX WATCHES/WARNINGS/ADVISORIES

CA...Beach Hazards Statement through Wednesday evening for Orange County Coastal Areas-San Diego County Coastal Areas.

Heat Advisory from 10 AM Monday to 8 PM PDT Friday 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.

Extreme Heat Watch from Thursday morning through Friday evening for Coachella Valley-Riverside County Mountains-San Bernardino County Mountains-San Diego County Deserts-San Diego County Mountains-San Gorgonio Pass near Banning.

PZ...None.