Cooler weather can be expected through Tuesday as onshore flow develops. The area of low pressure to south brought a few light showers to southern San Diego County earlier today but is now moving east northeast, reducing the chances for further shower activity. High pressure will move over the area for Wednesday into the first half of next week, bringing record setting heat and increased heat risk.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Today was much cooler than yesterday, as much as 20-23 degrees cooler in some locations. The low pressure system to our south brought a few light showers to southern San Diego County earlier today but is now moving east northeast, putting us in a more stable environment. As a result, the convection over AZ is unlikely to reach our area even with the easterly flow aloft. Onshore flow also returned today and brought with it some marine layer low clouds.
From previous discussion, Temperatures on Tuesday will be similar to today, with highs near to slightly above normal as the low pressure system continues to move east into Sonora/Chihuahua and eventually Texas. The marine layer will deepen over the next couple of nights to bring low clouds/fog from the coast to the coastal slopes each night/morning, where the most cloud coverage will be expected by Tuesday morning.
A ridge of high pressure to our west over the Pacific will begin to build over the west coast. By Wednesday, the ridge of high pressure will move eastward. This will increase high temperatures near 5-15 degrees from Tuesday to Wednesday, greatest change over the inland valleys with highs in the 80s and a chance to hit 90 across the Coachella Valley.
This will only be the start though, as the ridge becomes anchored just off the coast with 850mb temps rising near 20C (10-12C above normal). Another large increase in warming can be expected as the ridge strengthens, with higher temperatures expected by Thursday into at least the first half of next week, starting a period of prolonged heat. Wednesday to Thursday will see another large warm up with temperatures increasing 10-15 degrees for the coast into the western valleys, with a 5-10 degree warm up for the mountains and deserts. Nbm chances for reaching 100 degrees on Thursday are around 20-40% for northern Orange County and the eastern Coachella Valley.
By Friday, temperatures will increase further with some areas nearing not only daily record territory but for the entire month of March. Ramona's monthly record, for instance, is 94 degrees. Nbm model chances to break this record are quite good, around 75%. Nbm chances to see 100 degrees are near 25-50% for northern OC, western IE, parts of East County San Diego and likely triple digit heat across the entire Coachella Valley. Not even the immediate coast will retreat from the heat, with highs well into the 80s. The mountains will also continue to warm into the 70s and 80s. Please use this time to prepare for the heat if you work outdoors, have elderly neighbors or will be recreating outside.
The ridge will persist into the weekend, though a weak area of low pressure to southwest may provide a slight increase in greater onshore flow and cooling for areas mainly near the coast with areas staying in the 70s instead of 80s. All other areas will be with a couple of degrees of Thursday/Friday, so the heat will continue. By early next week, ensemble model clusters are in fairly good agreement on the ridge strengthening and slowly moving inland over the Desert Southwest. This will bring continued hot weather across the region into at least the first half of next week. As the dome of high pressure heats further, the chance grows for more of our climate sites to see record high temperatures for the month of March. To put this in perspective, the March record high for Palm Springs is 104 degrees, where NBM shows near a 70-80% chance to break this by next Monday. There is of course still room for modifications to the forecast, but the overall message is that very hot temperatures 15- 25+ above normal, so please take the precautions now so that you are prepared. As always, please keep up to date on the latest forecast on our social media pages and at weather.gov/sandiego.
100600z, VFR prevails this evening, with very patchy low clouds with bases varying from 1800-3000ft MSL. Confidence is low in how quickly these clouds will increase in coverage, but the window with the highest chances for CIGs at the coastal TAF sites will be between 12-16z Tuesday. 40% chance of CIGs reaching as far inland as KONT between 12-16z as well. Any CIGs will gradually scatter out between 16-19z Tuesday morning, with VFR expected to prevail thereafter. FEW-SCT marine layer clouds near 2500-3000ft MSL may stick around near the coast into the afternoon. Low clouds expected to re-increase in coverage for the coastal areas after 00-03z Wednesday.
No hazardous marine conditions are expected through Saturday.
Ca, None. PZ, None.
