Dry and warm today with weak offshore flow. Minor cooling Monday, then more significant cooling with chances of light precipitation and gusty southwest to west winds Tuesday through Thursday. Dry weather briefly returns on Friday before precipitation chances increase again late Saturday into Sunday.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
, New Aviation Discussion for the 18z TAF Package,
Skies are mostly clear this morning under weak offshore flow. Northeast to east winds are locally gusting to around 30 mph below the passes and on the coastal mountain slopes, and will begin to weaken late this morning. An upper level ridge of high pressure nudges in from the west today, bringing warmer weather with highs around 12 to 17 degrees above normal. Highs across the inland coastal areas and inland valleys will reach the low to mid 80s. The ridge weakens slightly on Monday with a return of weak onshore flow, allowing temperatures to lower a couple degrees. Monday will be the last warm day for at least the next week as a pattern change is in store.
A compact closed low moving towards the coast weakens and lifts north as it moves across Northern CA late Tuesday and Wednesday, with the tail end of the trough axis traversing So Cal. There is not much moisture with this system this far south, so while there is a 40-50% chance of precipitation late Tuesday afternoon into Tuesday night, amounts will be low. Through Wednesday afternoon, the NBM has a 35-55% chance of 0.10" or more for the coasts and valleys, a 50-70% chance along the coastal mountain slopes, a 15-20% chance over the high deserts, and less than 5% chance over the low deserts. This trough will also generate gusty southwest to west winds gusting to around 35-45 mph across the mountains and deserts Tuesday afternoon into Tuesday night.
A long wave positively tilted trough remains along the West Coast into Thursday, though with no discernible forcing, precipitation chances are low (10-20%) late Wednesday into Thursday. There is still uncertainly in the timing and track of the long wave trough finally progressing eastward sometime late Thursday into Friday. Moisture remains extremely limited with this trough, so any additional precipitation will be limited to a few hundredths of an inch west of the mountains with locally higher amounts on the coastal slopes. Snow levels will begin around 7500 ft Tuesday afternoon, then fluctuating between 6000-6500 ft Wednesday before falling to around 5500-6000 ft Thursday morning. Given the limited and shallow moisture, snow accumulations will be less than 1".
Weak transitory ridging follows the upper trough for Friday afternoon into Saturday, bringing a brief period of dry and slightly warmer weather. A more robust trough dropping out of the Gulf of Alaska will bring additional chances of precipitation and gusty winds beginning as early as Saturday evening. Wet and cool weather will likely continue into much of the following week with the potential for much higher rain and snow amounts.
081800z. VFR conditions expected through the TAF period. Northwesterly winds increase after 19z today for most locations, being replaced with weak offshore winds tonight after 02z Mon. Low clouds develop offshore after 06z, but are unlikely to reach the coast.
Northwest winds will gust to 15 knots in the outer coastal waters near San Clemente Island this afternoon and early evening. Otherwise, no hazardous marine conditions are expected through Friday.
Swell and associated elevated surf is winding down this morning, with most sites now reporting surf below 6 feet. Surf will continue to fall through tonight.
Ca, None. PZ, None.
