Weathernotes Archive February 2009

Rain Stays Mostly North of Pt. Conception. More Green in the Forecast.
Weathernotes for Wednesday, February 25, 2009.
(Any updates will be found at the end of this discussion. Last month's notes are archived here.)

As forecast by the computer models, most of the precipitation associated with a stream of sub-tropical moisture drawn into California by a large low off the West Coast occurred north of Pt. Conception. Here is an archived copy of a NWS Public Information Statement listing some rainfall totals for the period Saturday night to Monday afternoon. Downtown Los Angeles (USC) recorded only a trace of precipitation.

Both the 6-10 day and 8-14 day NWS Precipitation Outlooks continue to project above normal precipitation in California. At the moment, it looks like the next chance for some rain south of Pt. Conception may be in the Sunday to Monday timeframe, with another opportunity midweek. We'll see!

More information concerning Southern California weather can be found using our WEATHER LINKS page.

Rainfall Total Approaches Normal. Large Low Spinning Off the Coast.
Weathernotes for Wednesday, February 18, 2009.
(Any updates will be found at the end of this discussion. Last month's notes are archived here.)

Downtown Los Angeles (USC) recorded 1.40 inch of rain in our latest storm, bringing the water year total to 9.37 inches, which is only 0.8 inches below normal for the date. Rainfall totals generally ranged from 1.0 to 2.0 inches in the basin and valleys, with somewhat higher amounts recorded in favored foothill and mountain locations. There was heavy snow in the mountains. Here is an archived copy of a NWS Public Information Statement listing some rain and snowfall totals for the storm.

A large cut-off low pressure complex currently at about 140°W is forecast to spin tauntingly off the coast through Friday or Saturday. Pinwheeling low and vorticity centers, a building ridge, a 150 kt. jet, tropical moisture, and an upstream shortwave are in the forecast mix. At this point it looks like some form of the system moves onshore on Sunday, with most of the rain occurring north of Pt. Conception. However, the situation is extraordinarily complex, and we'll have to see how the forecast evolves.

Beyond next week it looks like there will be additional opportunities for rain in Southern California. Both the 6-10 day and 8-14 day NWS Precipitation Outlooks project above normal precipitation.

More information concerning Southern California weather can be found using our WEATHER LINKS page.

Rain Today. More On The Way.
Weathernotes for Friday, February 13, 2009.
(Any updates will be found at the end of this discussion. Last month's notes are archived here.)

Models have been trending somewhat wetter with the front approaching Southern California this morning. BUFKIT analysis of 12z data for Van Nuys generates about 0.4 inch rain, starting around noon and ending this evening. At Santa Barbara the generated total is about 0.5 inch, and at LAX about 0.25 inch. Locally higher amounts are possible in thunderstorms, and on southwest to west facing slopes.

This front is the first of several systems that have been forecast to affect the area over the next week. Model output has been variable regarding the timing and strength of these systems.

According to the models, the system originally forecast for Sunday is still in the works, but has been has been pushed back to Sunday evening or early Monday morning. The !2z NAM and GFS model runs forecast about 1.1 to 1.5 inch at Van Nuys from Sunday evening through Monday. Very strong southerly inflow is forecast with this system, so significantly higher totals are possible on south facing foothill and mountain slopes.

Beyond early next week, the models have been all over the place with some runs forecasting several inches of rain late in the week and other runs almost none at all -- the amount of rain being dependent on the proximity of a strong low to the coast. This morning's GEFS ensembles for next Thursday evening are indicative of the uncertainty. We'll see how the forecast evolves over the next few days.

Update 02/18/09. Here is an archived copy of a NWS Public Information Statement with some rainfall totals for Friday's storm.

More information concerning Southern California weather can be found using our WEATHER LINKS page.

Wet February to Follow Dry January?
Weathernotes for Friday, February 6, 2009.
(Any updates will be found at the end of this discussion. Last month's notes are archived here.)

The first of a series of upper lows, troughs and shortwaves expected to affect Southern California over the next several days has resulted in widespread rain, with storm totals in excess of 1.0 inch in many areas. Yesterday, new rainfall records were set for the date at Burbank and Lancaster. Many stations have recorded more rain in the past twelve hours than in the entire month of January.

Another Pacific system is working down the coast and is expected to result in periods of rain today, tonight and into Saturday. A break in the action is forecast on Sunday, but some showers are a possibility.

In a situation that has become too familiar this rain season, Sunday evening a trough is forecast to dig down the backside of a ridge along the West Coast. Model forecasts have varied from run to run, but the trough is expected to produce some rain in our area Sunday evening into Monday. A more westward track, over the Pacific, would likely produce more rain, and a more eastward track less.

This generally wetter pattern may continue into the 8-14 day period. The active phase of the Madden-Julian Oscillation (MJO) and the Global Wind Oscillation (GWO) are supporting a general circulation pattern that is favorable to West Coast troughs. In addition, a major Sudden Stratospheric Warming (SSW) event is underway and associated high latitude blocking might eventually result in a southward shift of the storm track over the U.S.

Both the 6-10 day and 8-14 day precipitation outlook from the CPC are indicate the possibility of above average rainfall in Southern California. We'll see!

Update 02/10/09. Here are the updated and corrected storm totals from the NWS for the period 4:00 a.m. Thursday to 4:00 a.m. Sunday. It looks like Wednesday's system should fall apart south of Pt. Conception, but if recent model runs hold true, Southern California is in store for more wet weather. Relatively weak shortwaves are forecast for Friday and Saturday, but these set the stage for more potent systems Sunday and mid-week. We'll see!

More information concerning Southern California weather can be found using our WEATHER LINKS page.