Area Forecast Discussion

SYNOPSIS

Isolated light showers near the coast this morning, otherwise cool today with highs a few degrees below normal. Warmer and drier weather returns late week, with high temperatures increasing to 5 to 15 degrees above normal and weak to moderate Santa Ana winds, strongest on Saturday.

DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE

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

Isolated light showers have developed over the coastal waters this morning as an upper level trough continues to progress inland across the Western US. Latest hi-res guidance suggests most of these showers will move south and remain off the coast, with only around a 10% chance of these showers moving into the coastal areas. Any accumulation from these showers will be a couple hundredths of an inch or less. Otherwise cool today with highs around 3 to 7 degrees below normal.

Weak Santa Ana winds will develop tonight behind the departing trough. A second short wave trough is forecast to dig south across the Great Basin into Arizona Friday and Saturday, driving relatively stronger Santa Ana winds. Despite only being a few days away, there remains a sizable difference in the forecast pressure gradients between the GEFS and EC Ensemble, with the EC forecasting a stronger event. The CW3E ensemble currently shows a 40% chance of a weak-to-moderate event on Saturday (gusts around 25-40 mph in the wind prone areas), but only a 10% chance of a moderate event (gusts around 35-50 mph). For now winds do not appear to be much of a concern, but this offshore flow combined with an upper level ridge building in from the west will bring considerable warming. By Friday, highs will be anywhere from 5 to 10 degrees above normal west of the mountains with temps in the low to mid 80s for the coastal areas and valleys.

Warming continues into Sunday under upper level ridging and weak offshore flow with highs reaching the upper 80s for the inland coastal areas/western valleys and in general 5-15 degrees above normal for the coasts/valleys, but only a couple degrees above normal for the mountains and deserts. HeatRisk is forecast to reach Moderate for the coastal areas Saturday through Monday. Gradual cooling Tuesday and Wednesday as offshore flow weakens and eventual turns back onshore.

AVIATION

040530...SCT-BKN clouds around 2000 to 4000 ft MSL will continue to fill into the inland areas of Orange/San Diego and southern Riverside counties. Areas of -DZ/-RA are possible (15-25% chance) for coastal San Diego County through 07-15z Wednesday, most likely in south county, but aren't expected to lead to any decrease in VIS. There is a relatively high likelihood (70+% chance) that CIGs stay above 3000ft for the most part, but dips to 2500-3000 ft MSL are possible, especially in southern SD County where the -DZ/-RA may occur. Lower clouds start to scatter out around 15z Wednesday. Otherwise, VFR conditions prevailing into the afternoon and evening for tomorrow, with a low chance (less than 10 percent) of cigs based around 2000 to 2500 feet returning to the coastal areas of San Diego after 06Z Thursday and through the end of the forecast period.

MARINE

Northwesterly winds gusting in the outer coastal waters 20 to 25 knots through early Wednesday morning. Strongest gusts will be found near San Clemente Island and these winds will likely lead to rough, choppy seas. A Small Craft Advisory for this hazard remains through 4 AM Wednesday.

BEACHES

Tides will increase at the end of the week, reaching 7 ft as early as Thursday in Orange County and Friday in San Diego County. Tides will peak on Sunday/Monday at 7.4-7.6 ft. A northwest swell (from ~300 degrees) of 2-3 ft with a 14-16 second period is predicted to arrive on Friday, likely to persist into next week. If this swell materializes per the current forecast, max surf of 6-7 feet would occur. Between the high tides near 7-7.5 feet and the elevated surf, at least minor coastal flooding is expected during high tides Saturday-Tuesday, especially for more west-facing coastlines.

Reminder, tides mentioned have been corrected to reflect the current trends in actual tide observations.

SKYWARN

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

SGX WATCHES / WARNINGS / ADVISORIES

CA...None. PZ...None.