Strengthening high pressure will bring warming this week. A long- duration heat wave, with widespread Major to locally Extreme HeatRisk for the coast and valleys, is likely for this weekend through much of next week into the following weekend. Record warm overnight temperatures are likely for the coast and valleys for Saturday through Monday.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Tonight through Wednesday,
An upper level low is continuing to exit the southwestern region, with northerly flow filtering in behind it. These winds will translate to weak off shore winds mixing in overnight, which will help to impede the development of the marine layer overnight. There may still be some patchy areas of low clouds, with the best probability for the coastal areas of San Diego County, due to the development of an eddy in close proximity of San Clemente Island. A few factors are also contributing to the lack of marine layer development overnight, given that there are relatively warmer sea surface temperatures currently, which has made it difficult for a good inversion to establish itself. This, in combination with weak offshore flow and drier air mixing into the boundary layer will likely give way to the marine layer struggling to form throughout the night.
High pressure is going to continue to build back in tomorrow, with a positively-tilted ridge axis extending up and over the region from the southwest. This will result in high temperatures further increasing. There will be better onshore flow for tomorrow, which may also help to advect in a little more moisture within the boundary layer, and aid in the development of better marine layer coverage for tomorrow night. It will also allow for westerly winds to increase and become gusty during the afternoon for mostly of the coastal and inland basin, with enhanced onshore flow as the compelling factor. Higher wind gusts are also expected for San Gorgonio Pass, near Banning, where there could be some gusts approaching 40-45 mph. For overnight, there may also be some patchy areas of fog developing within some of the higher inland valleys, also also where low level clouds intersect the west-facing slopes. As the ridge further expands and strengthens, heights will increase to values approaching 590 dm over the region, which will allow for the temperature warming trend to continue into Wednesday, with highs generally up to around 5 degrees above the seasonal average for this time of year.
Thursday through next Tuesday,
The ridge will further strengthen from Thursday into Friday, which will bring temperatures roughly around 5 to 10 degrees above average, and then 10 to 15 degrees above average for both days, respectively, for locations west of the mountains. For the deserts, temperatures will warm through Wednesday, and then plateau on Thursday. However, for locations west of the mountains, temperatures will be notably warmer on Thursday as the ridge expands back a little further to the west. By Saturday, some locations will for the coastal and inland basins will be around 20 degrees above average, with triple digit heat for most localities within the Inland Empire. At the moment, the highest probability for the warmest afternoon temperatures will be on Monday of next week, as heights top 590 dm over our deserts. Given the duration of the week, there will likely need to be some heat products warranted for issuance. There is one caveat, and that is overnight lows being well too mild towards the end of the week as a recent bias due to warmer nights with relatively higher moisture content under a more tropical environment in recent weeks, that is not reflected well within the national blend of models, as guidance has been overperforming. Because of this, the projected temperatures in the current forecast package might be a bit underdone with temperatures not being cool enough, as the pattern is showing a drier airmass mixing in, with better confidence of more efficient radiational cooling as a result. There will also likely be a better marine layer establishing itself, towards the end of the week, with a stronger inversion in place. This may also allow for there to be a higher probability of patchy fog developing for some of the coastal areas by this upcoming weekend. Only a slight weakening in the ridge will translate to slightly cooler temperatures for next Tuesday.
291745z, Coast/Valleys: SKC this afternoon and evening. Areas of low clouds based 1500-2000 ft MSL develop over coastal San Diego County starting around 06z Wed. As a coastal eddy takes shape overnight, clouds should spread northward into Orange County and reach 10-15 miles inland by 12z. Clouds scatter back to the coast 15- 17z.
Mountains/Deserts: FEW-SCT mid-level clouds at and above 9 kft through 01Z.
Otherwise, mostly clear skies today and tonight.
No hazardous marine conditions are expected through Saturday.
High tides will peak at 6.8-7.1 feet between now and noon today and again late Wednesday morning, leading to minor coastal flooding in low lying areas and coastal erosion. A Coastal Flood Advisory is in effect through Wednesday afternoon.
Please note - mentioned tide predictions in the Advisory have been adjusted to reflect actual measured tide observations.
Ca, Coastal Flood Advisory until 5 PM PDT Wednesday for Orange County Coastal Areas-San Diego County Coastal Areas.
PZ, None.
