| Day | Date | High/Low | Forecast |
| Mon | 3rd | 61/48 | Sunny day. Possibly breezy at times in the afternoon. Mostly clear evening. |
| Tue | 4th | 63/50 | Chance of some morning low clouds; Otherwise, mostly sunny day with scattered high clouds. Becoming partly cloudy in the evening. |
| Wed | 5th | 55/47 | Chance of morning rain; Rain likely in the afternoon. Decreasing chance of rain in the evening and becoming partly cloudy. |
| Thu | 6th | 56/45 | Partly cloudy with a chance of showers; Possibly breezy at times. Partly cloudy evening and possibly breezy at times with a slight chance of showers early. |
| Fri | 7th | 60/48 | Mostly sunny day and possibly breezy at times. Mostly clear evening. |
Synopsis
The storm that passed through southern California yesterday wasn’t much for L.A. County. Low level winds were more northerly than expected while the cold front passed through L.A. County. So, as the cold front rolled through the L.A. Basin early in the morning, it produced mostly, very light showers (not enough to produce puddles most areas away from the mountains). There were some cold air instability showers late in the afternoon, but those were mainly over/adjacent to the higher mountains and to areas east and south of L.A. County (latter produced about a tenth inch rain in some L.A. County, valley locales). Post-frontal wind was the more prominent, weather feature yesterday afternoon (UCLA recorded a peak gust to 29 mph; Some other coastal areas saw peak gusts into the mid-30s).
High pressure aloft will build into the Southwest for a short period (tonight through tomorrow). On-shore flow should weaken considerably tomorrow (no repeat of a “brisk” sea breeze expected), but the computer models aren’t forecasting any full fledged, off-shore flow (modest off-shore flow gradient toward the north but very weak, on-shore toward the east). So despite mostly sunny skies expected, daytime temperatures tomorrow should be only somewhat higher than it gets today (insufficient subsidence warming to modify significantly the current, polar air influx). At best, some inland locales may near seasonal normals for a day.
All the numerical models forecast a new storm passing through the state in the Wednesday-Thursday period (a two “wave” system). Some light showers may occur in L.A. County as early as mid-morning Wednesday. A period of mostly light rain should fall in the L.A. Basin in the afternoon to possibly early evening. A dry period should follow later in the evening (partial clearing possible). The cold core of the storm should pass through southern California on Thursday (showers and even isolated thunderstorms possible during the daylight hours though peak shower activity should be in the afternoon). Most model solutions show dry, mostly sunny weather returning on Friday.
Most of the models favor a decent precipitation producer (Wednesday-Thursday). Lowland storm totals away from the mountains may range from 0.50 to one inch (more than twice that for some favored, coastal facing, mountain slopes). Snow levels on Wednesday shouldn’t fall below 6000 feet, but with the cold core on Thursday, snow down to 3000 feet (for a short time) is possible. 6 – 12 inches of snow could fall at resort level. Any snow down to 3000 feet should be only a dusting.
I should state that recent ECMWF model forecasts don’t show much falling in L.A. County. It predicts low level winds being more northerly than westerly in the County (similar to what occurred with yesterday’s storm). If this scenario verifies, storm totals (at least, in L.A. County) should be well under a quarter inch in most locales (predicted, higher water vapor content should still promote widespread precipitation). More northerly winds should also restrict most showers/thunderstorms on Thursday to around the mountains and areas to the east and south of L.A. County. Since this is currently a minority model solution, I’m going with the higher storm total expectations. However, don’t be surprised if a storm forecast downgrade occurs in the next 24 hours or so.
Regardless of what type of storm occurs, the weekend weather should be mostly sunny, and temperatures should get slightly above normal. A weak, off-shore flow associated with high pressure aloft is expected. The high pressure should weaken on Sunday, but inland locales may remain warmer than normal that day (coast cooling back to seasonal normals).
Remarkably, the longer range models agree on a new storm for the state early next week. Details of the storm remain a little fuzzy, but wet weather could start in southern California by midday Monday (storm departs Tuesday). Many model solutions show good dynamics and available water vapor. So, there is potential for a good soaking storm (another cold storm favoring relatively low snow levels for a time). Other storms are possible later next week (“storm gate” may remain open though the end of next week). How wet those systems will be is still uncertain (greater range in possible outcomes but definitely some favor more good, soaking storms).
Next issued forecast/synopsis may follow on Friday, 7 March.