As San Diego heads into the final days of 2024, a high pressure ridge is bringing unusual warmth to the region, with temperatures climbing 5-12 degrees above normal inland and soaring 15-20 degrees above normal in the high desert, according to NWS San Diego. Despite the spike in heat, coastal areas have witnessed a marine layer each night and morning through Monday, with the potential for dense fog in some regions. At the same time, offshore flow is anticipated to escalate, ushering drier conditions as we welcome in the new year.
However, the heat won't linger everywhere, as Monday will see cooler temperatures in the high desert and mountains. Still, minor warming will persist west of the mountains, the National Weather Service's San Diego branch reports, and amid these fluctuating weather patterns, a short wave trough skirting by to the north will intensify onshore flow, leading to breezy conditions in the mountains and deserts by late Sunday with the strongest gusts reaching around 35 mph though their not much change in temperatures despite the upper high to the south strengthening slightly. A shallow marine layer is expected to materialize, bringing some relief to the coastal areas early in the week with an elevated chance of dense fog Monday night.
Attention turns to the Great Basin on Monday, dictating the development of weak Santa Ana winds across Southern California, as described by the Area Forecast Discussion. The winds will mostly buffet the passes, with localized gusts estimated around 30 mph. Though the surface high is projected to migrate eastward towards the Rockies on Wednesday, the weak offshore flow will sustain mild conditions into Thursday. Coastal residents and mariners should be mindful of the marine forecast, which warns of possible patchy fog into Sunday morning, and an advisory for elevated surf conditions through Sunday afternoon, with highs near 80 expected in valleys and low deserts by Thursday.
As the warm spell peaks into New Year's Eve, the fire weather forecast heightens concern; "Weak northerly Santa Ana winds will develop Monday morning with gusts to around 30 mph below the Cajon Pass," reports the NWS San Diego, while noting the relative humidity could plummet to 7-12 percent in mountain areas above 5500 feet elevation, presenting a narrow window for critical fire weather conditions, albeit localized, on Tuesday. Relief is on the horizon starting Friday as a low pressure trough ushers in onshore flow and a cooler trend, albeit with temperatures above normal inland.
