| Day | Date | High/Low | Forecast |
| Mon | 10th | 60/49 | Mostly cloudy morning; Partial afternoon clearing. Mostly cloudy evening. |
| Tue | 11th | 59/47 | Partly to mostly cloudy day. Mostly cloudy evening. |
| Wed | 12th | 55/51 | Mostly cloudy through the evening. Light rain likely during day. Chance of evening rain. |
| Thu | 13th | 57/50 | Rainy through evening and breezy at times. Rain, likely intense at times. |
| Fri | 14th | 58/47 | Rain tapering to a chance of showers in the afternoon; Possibly breezy at times. Partly cloudy evening. |
Synopsis
Marine layer clouds returned in earnest this morning. Yesterday’s weak, off-shore flow (reason for slightly warmer than normal weather most areas) turned to on-shore flow today (coastal eddy helped with forming low clouds west of the mountains). The on-shore flow should continue into tomorrow morning before weakening. The passage of an “inside slider” type trough early tomorrow may help trigger some marine layer induced drizzle/light rain (mainly western Riverside County southward and just in the morning).
Unlike what often occurs after an “inside slider” passage (clearing with off-shore flow), an approaching, Pacific storm will promote continued on-shore flow (just weaker than it is today). The various, computer models maintain a deep marine layer through the day. So, at best, partial clearing may occur in some areas west of the mountains (temperatures staying below normal).
The aforementioned, Pacific storm will bring into southern California a rare (for the region) warm front (more typical cold front will approach later in the week). This will take place on Wednesday. Light rain in L.A. County should begin no later than mid-morning and last a few to possibly several hours (latter more probable to the east and south of L.A. County). The predicted, low level winds (mainly northwesterly) shouldn’t favor any moderate or heavy rain in L.A. County. The presence of the warm front should produce a relatively low snow level at first (5000 feet or even slightly less). The snow level will rise by Wednesday evening with the passage of the warm front (some model solutions dissipate the front with time, but snow levels should nonetheless rise). Storm totals with this first wave should be under a quarter inch in L.A. County. Potentially, coastal facing foothills in San Diego County may receive up to half an inch (low level winds predicted to be more favorable for enhanced rainfall). Any snow at the local resorts should be minor (maybe on the slushy side).
All the models predict a major storm reaching southern California in the Thursday-Friday period. They do still disagree on details, however (once a day, weather reconnaissance flights scheduled this week can cover only so much territory on a single flight). Based on today’s model consensus, most of L.A. County should experience steady rain (snow levels rising for a time to 7000 feet) early Thursday morning (sunrise or slightly earlier). A period of steady rain should occur for a 12 – 15 hours. Good storm dynamics are predicted over much of southern California (late Thursday into the first hours of Friday). So, with a long fetch of atmospheric river, water vapor, an approaching cold front should produce periodic bursts of intense rain (snow lowering in the evening to around 6000 feet). While it’s not currently in the forecast, isolated thunderstorms are a possibility. Activity will turn showery once the cold front passes (early Friday in L.A. County), but some brief duration heavy precipitation is probable in places. Most showers should be winding down in the Southland by sunset Friday).
Unless the thrust of storm dynamics fail to reach L.A. County, rainfall from the second system (Thursday-Friday) should range from 2 to 3.5 inches in the lowland away from the mountains. Twice as much could fall in some favored, coastal facing foothills/mountains (significant flooding a concern). Snowfall at the local resorts may reach a foot to foot and a half (“wet” type). Even more is possible in spots above 7000 feet.
Dry, generally sunny weather is currently on tap for the Presidents’ Day weekend. A weak, off-shore flow should occur by Sunday (Saturday will be a transition day). Slightly warmer than normal may occur that day (similar to yesterday’s weather). Some models do show an “inside slider” trough passing nearby late Monday, but at this point, it shouldn’t pose any shower threat (just modest cooling and breezy conditions in the interior). Later next week, another off-shore flow may promote better warming (coastal plains temperatures well into the 70s around midweek). At this time, few model solutions show a relevant threat of additional wet weather next week (at least, in southern California).
Next issued forecast/synopsis may follow on Friday, 14 February.