textproduct: San Diego

SYNOPSIS

A moisture surge will bring scattered showers and thunderstorms to the mountains today with a slight chance of precipitation reaching into the lower elevations. Building high pressure will bring above average temperatures for midweek with highest temperatures on Wednesday. Widespread moderate to major HeatRisk is expected. This will also subdue thunderstorm coverage with only a slight chance of precipitation in the mountains. The high pressure breaks down by the weekend with temperatures returning to near normal along with increasing chances for monsoon storms once again. Coastal flooding will impact beaches through Tuesday with evening high tides exceeding 7 feet.

..UPDATED AVIATION DISCUSSION

Similar to last night, high clouds and scattered convection associated with a new moisture surge are currently situated over southern AZ and northern Mexico. High resolution models are in agreement that this will provide the forcing and mid-level moisture necessary for scattered showers and thunderstorms (30-60% chance) over the mountains and High Desert this afternoon. However, timing is essential as we saw today. An early onset of high clouds over the region may limit daytime heating and reduce thunderstorm potential, though this outcome appears less likely today. Heavy rainfall, lightning, and small hail will be possible with any storms that develop. Rain rates may reach up to 0.5"/hr for higher elevations. There is a slight chance (10-15%) for a storm to stray into the eastern valleys or low desert.

An upper ridge currently over the High Plains and intermountain west will build into the region for the middle of the week. This will act to warm temperatures and limit mid-level moisture starting Tuesday. Isolated showers and storms will remain possible along mountain ridges Tuesday through Thursday, but chances will be slim (15-25%). The ridge peaks in strength Wednesday, with 500 mb heights peaking around 593-594 dm over Southern California. Widespread moderate HeatRisk is expected below 6000 feet elevation Tuesday through Thursday with major HeatRisk expected through much of the coastal basin and locally into the lower deserts on Wednesday. There is still some uncertainty in exactly how hot temperatures will get, but current forecast highs on Wednesday range from the 80s for coastal areas and mountains above 6000 ft to 110-114 in the lower deserts. 100s expected for the Inland Empire, High Desert and eastern San Diego Valleys and 90s for the western valleys and lower elevations of the mountains. Additionally, humid conditions are expected along with low temperatures running 5 to 10 degrees above normal. There will be an increased risk for heat-related illness for vulnerable populations and anyone spending extended periods of time outdoors.

The ridge retreats back to the east late this week, allowing temperatures to return to near or slightly below average from Friday through the weekend. Additionally, southeasterly flow is expected to return along with increased mid-level moisture. This should increase chances for monsoon-related convection once again. However, as with any monsoon setup, coverage and location of thunderstorms are highly uncertain at the moment as this is dependent on the timing and location of any passing upper waves. At the very least, an uptick in activity over the mountains appears likely at this time.

AVIATION

141200Z....Coast/Valleys...Areas of low clouds with bases 600-1000 ft MSL clearing to the coast by 18Z. There is a 10-15% chance of showers moving off the mountains into the far inland valleys during the afternoon and early evening today. Coverage of low clouds Monday night will be much patchier with low confidence in timing of onset of any CIGS. Otherwise variable mid and high cloud cover at/above 10,000 ft MSL. Low clouds will redevelop and regather along the coastal areas beginning around 01-03Z Tue. and fill back into the inland areas through 09Z Tue, with slightly higher bases. This may be disrupted with patchy coverage locally at times due to passing mid and high level clouds overhead.

Mountains/Deserts...There is a 25-50% chance of thunderstorms over the mountains and high desert between 18Z and 02Z Monday afternoon and evening. Areas with highest probabilities of convection will be in the vicinity of the San Gorgonio and San Jacinto mountain areas. CB bases near 10,000 ft MSL with tops to 35,000 ft MSL. Thunderstorms will be capable of producing reduced visibility in RA and gusty outflow winds, and deadly cloud-to-ground lightning. Otherwise variable mid and high cloud cover at/above 10,000 ft MSL.

MARINE

No hazardous marine conditions are expected through Friday.

SGX WATCHES/WARNINGS/ADVISORIES

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

Extreme Heat Watch from Tuesday morning through Thursday evening for Orange County Coastal Areas-Orange County Inland Areas- Riverside County Mountains-San Bernardino County Mountains- San Bernardino and Riverside County Valleys-The Inland Empire-San Diego County Coastal Areas-San Diego County Mountains-San Diego County Valleys-San Gorgonio Pass near Banning-Santa Ana Mountains and Foothills.

PZ...None.