Marine Weather and Tide Forecast for March ARB, CA

DISCUSSION
FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES...

Updated Marine/Aviation Sections

Lots of high clouds above a very shallow marine layer. Some low clouds and patchy, dense fog made it to the coast last evening but are now being pushed offshore as the diurnal drainage winds and developing offshore flow combine. Sfc pressure gradients remain offshore with -8.8 mb SAN-TPH and -3.3 mb SAN-DAG. In the last hour, a handful of locations in the wind-prone locations reported wind northeast winds gusting to 40+ mph with one location reporting a gust of 54 mph. Low temps this morning are likely to be warmer than yesterday due to the high cloud cover.

Today and Sunday...
The offshore winds are peaking this morning but will then gradually weaken for this afternoon into Sunday morning as offshore pressure gradients weaken. The weakening offshore winds will allow a sea breeze to develop Sunday afternoon. High pressure aloft and the offshore winds will combine to produce daytime high temperatures 10-15 degrees above normal from the coast to the foothills. Elsewhere, high temperatures will be 5 to 10 degrees above normal. The National Blend Model indicate a 75-100% probability of 80+ degrees for the valleys and inland coastal areas today. Chances lower to 35-90% on Sunday as the weak sea breeze spreads marine layer air inland.

Weaker offshore flow will return for Monday and Tuesday mornings, with northeast to east winds gusting 35-40 mph in the passes and foothills. High-resolution models still show a weak, short-lived coastal eddy each of those mornings. Some of those high-res models also indicate that marine layer clouds and fog are likely to return to the immediate coast Monday and Tuesday mornings. The marine layer presence would also moderate temperatures in the coastal areas faster. The upper level ridge does begin to weaken during this period for gradual cooling even of the inland areas.
More persistent onshore flow returns for Wednesday and Thursday for a noticeable cooling trend and highs returning to within a few degrees of normal by Thursday.

Beyond Thursday, a closed low about 650 miles southwest of San Diego will be drawn into the mean westerly flow aloft by a shortwave trough moving southeast from the Pac NW and eventually moving across the region sometime Fri-Sat. A significant number of the Global Ensemble members indicate the potential for precipitation for next Fri-Sat but it's not yet a majority of ensemble members. As a result, much uncertainty remains as to the timing and amounts of any precipitation.



AVIATION
171630Z...SCT high clouds and VFR conditions prevail throughout most of the region through the period. Offshore winds will be elevated along coastal slopes and into adjacent foothills/parts of the Inland Empire through 06Z Sun with intermittent gusts 20-35 kts. Gusts locally to 40 kts through and just below wind prone passes, including the Cajon Pass. Winds decrease tonight. Isolated patches of dense fog are possible along the immediate coast 06-10Z Sun, but are unlikely (10% chance or less) to impact any TAF sites.

MARINE
Patches of fog in the coastal waters reducing visibility to 1 SM or less are possible tonight through early Sunday morning. Otherwise, no hazardous marine conditions are expected through Wednesday.

SGX WATCHES/WARNINGS/ADVISORIES
CA...None.
PZ...None.