textproduct: San Diego

SYNOPSIS

Strengthening high pressure aloft will bring a warming trend with a long-duration heat wave likely for this weekend through much of next week into the following weekend. The coastal basin will be particularly hot through this weekend as offshore flow reinforces hot and dry conditions. This will also produce elevated fire weather conditions for inland valleys and mountains through this weekend. Major HeatRisk is expected for most of the coastal basin from Friday through next week with areas of extreme HeatRisk for coastal zones and western valleys. Moderate HeatRisk through next week in the low deserts with minor HeatRisk elsewhere.

..UPDATED AVIATION DISCUSSION

A building strong high pressure today will center itself over southern NV and northern AZ this weekend. Easterly flow aloft will allow for periods of offshore winds through the weekend, especially in San Diego County. This will amplify already hot and dry conditions in the coastal basin. Model guidance suggests 500 mb heights will peak around 590 dm and 850 mb temps will reach 24-25 Celsius over the weekend. With offshore flow in place, this translates to surface temperatures well over 100 degrees through inland areas of the coastal basin Friday through Sunday. For western valleys, highs will locally reach 105 or higher, especially in San Diego County on Saturday and Sunday. This will combine with lows in the upper 60s to low 70s to create major HeatRisk throughout the coastal basin from Friday onward. Areas of extreme HeatRisk expected for coastal areas and western valleys.

Easterly flow of 10-20 kts at 700 mb through the weekend will support weak Santa Ana winds gusting 25-45 mph (locally higher) along west-facing slopes, adjacent foothills and locally into the inland valleys. The orientation of winds will favor San Diego County and downwind of the Banning Pass. Offshore winds in combination with heat and afternoon RH values of 15-25% will create elevated fire weather conditions for inland valleys and mountains through the weekend.

Outside of the coastal basin, heat will be less anomalous. High temperatures will range from the 70s in the mountains to near 100 in the low deserts, which is only about 5-10 degrees above normal. Thus, HeatRisk is minor outside of moderate risk in the low deserts.

Heading into early next week, the mean of model guidance backs off somewhat with the heat in the coastal basin as the high pressure weakens a touch and slides east. This will likely reduce or remove offshore wind potential for Monday and Tuesday. However, high temperatures in the 90s to near 100 inland from the coastline will keep major HeatRisk in place for most of the coastal basin. By mid to late next week, the general consensus is that upper ridging will strengthen slightly again, keeping this heatwave firmly in place.

AVIATION

020015Z...Coast/western valleys: low clouds based 400-800 ft MSL increase in coverage at the coast 03-06z over coastal SD County, then patchy coverage develops over coastal Orange County 09-12z. Visibility starts off 2-5SM at the immediate coast and 0-2SM (FG) over coastal mesas (including KCRQ where cigs are present), then bases fall to 100-500 ft MSL 10-14z, reducing VIS to 0-2SM with patchy fog at the immediate coast. Clouds scatter out 15-17z, then SKC.

Inland Valleys/Foothills/Mountains: East winds increase over west- facing foothills, inland valleys and in parts of the Inland Empire after 15z, gusting 25-40 kts Friday afternoon.

Otherwise...Clear skies through the TAF period.

MARINE

No hazardous marine conditions are expected through Monday.

SKYWARN

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

SGX WATCHES/WARNINGS/ADVISORIES

CA...Extreme Heat Warning from 10 AM Friday to 8 PM PDT Thursday 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.