Warm weather will continue through Tuesday with highs around 5 to 15 degrees above normal. The marine layer will begin to slowly rebuild with the potential for patchy dense fog along the coast each night and morning through Tuesday, followed by more widespread low cloud coverage beginning Tuesday night. Offshore flow briefly returns Monday night into Tuesday morning with breezy conditions below the passes. A cooling trend begins on Wednesday into late week as a low pressure system moves closer to the region, helping build the marine layer even further. There is a 10-15% chance of precipitation late in the week.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Evening update, Scattered high clouds continue to move over the region this evening. Winds at North Island (Coronado) briefly turned southerly, ushering higher dew point marine air, but so far no fog has developed. Elsewhere along the coast dew points remain in the upper 30s to low 40s. The HREF is showing around a 35-45% chance of fog developing over the coastal waters tonight, but as long as there is enough drainage flow overnight the drier airmass should be able to hold at the coast, limiting the fog potential over land areas.
A weak upper level short wave will dig through the Great Basin on Monday, helping break down the nearby ridge. With the return of at least a weak sea breeze, expect a couple degrees of cooling west of the mountains with little change further inland. Marine layer low clouds and fog will have a better chance (40-50%) of developing along the coast Monday evening. Once the short wave passes, another round of offshore flow develops Monday night into Tuesday morning as surface high pressure strengthens over the Great Basin, helping clear out any low clouds overnight. This is currently forecast to be a weak event, with gusts around 30-40 mph below the passes and canyons prone to north/northeast winds. The upper level ridge will also rebuild, leading to another brief warm-up on Tuesday with highs in the valleys reaching the low 80s.
Previous discussion, Models show an area of low pressure moving closer to the region on Wednesday into later in the week. This will enhance onshore flow and build the marine layer with greater cloud coverage into the western valleys each night and morning. High temperatures will lower a few degrees each day starting Wednesday into Friday as the low pressure system moves closer. There is still great uncertainty on the path of this low pressure system. Model ensembles have decreased in total rain accumulations since yesterday, along with lower chances from the NBM, indicating less than a 15% chance of any measurable rainfall by Friday into next weekend.
By early next week, model guidance is fairly agreeable to weak high pressure moving back into the area with potentially more offshore flow. This pattern would give us warmer and drier weather as we head into the last full week of January.
190500z, FEW high clouds and VFR conditions prevail for inland areas through Monday night. North and east winds to increase after 00z Tue for the mountain passes and coastal slopes with gusts up to 35 kts.
At the coast, very localized FG with VIS < 1/2SM to develop after 11z, more likely off of coastal Orange County. Through 17z Mon, there is a 25% chance for brief FG impacts at KSNA and a 10% chance at KCRQ and KSAN. Greater coverage in FG is expected Monday evening, developing in patchy fashion along the immediate coast sometime between 02-06z Tue. 30-40% chance for FG impacts for the coastal TAF sites Monday evening.
Very localized dense fog to develop tonight into early Monday and more likely (35-45% chance) Monday night into Tuesday. Patchy fog can result in visibility dropping locally below 1 nautical mile. Otherwise, no hazardous marine conditions are expected through Thursday.
Ca, None. PZ, None.
