Weathernotes Archive September 2007

September Storm Socks Southland
Weathernotes for Sunday, September 23, 2007.
(Any updates will be found at the end of this discussion. Last month's notes are archived here.)

For a while it seemed the storm spinning off the coast would wait for Autumn to arrive, but late Friday afternoon the stubborn upper level low began to inch northeastward toward the coast. Around 9:00 p.m. a train of thunderstorms took aim at the Los Angeles area, and delivered a potent punch of heavy rain, thunder and lightning. Scattered heavy rain showers continued across the area into Saturday afternoon.

Rainfall amounts for the storm generally ranged from about 0.25 inch to about 1.0 inch in Los Angeles County. Several Southland locations recorded new rainfall records for the date on Friday and Saturday. Downtown Los Angeles set a new maximum rainfall record of 0.40 inch for September 22, exceeding the previous record of 0.15 inch set in 2000*. Here are archived copies of the NWS Public Information Statement with precipitation amounts for the storm, and the Record Event Reports for Friday and Saturday.

*Note: NWS climate and record reports issued 9/22 and 9/23 indicate the previous rainfall record for September 22 was 0.10 inch set in 1923. This appears to conflict with NWS data in the document 1921-2006 Sep KCQT DAILY EXTREMES. Here's the weather history for 9/22/2000 from the Weather Underground. In either case the previous record was broken.

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

Record Setting September Storm?
Weathernotes for Wednesday, September 19, 2007.
(Any updates will be found at the end of this discussion. Last month's notes are archived here.)

An unusually cold, deep and energetic upper level low is forecast to affect the area over the next 2-3 days. The system could set new rainfall and temperature records for Downtown Los Angeles (USC) and other Southern California locations.

Today's 12z runs of the NAM and GFS converged on similar solutions which forecast about 0.5 inch of rain at Los Angeles from midday or so on Friday into Saturday. The 18z run of the NAM is a little wetter, adding a chance of drizzle or light rain at times this evening, through Thursday.

Considering the energetic, convective nature of the system, the 0.5 inch forecast for Los Angeles should probably be considered an average value. Rainfall amounts around the Los Angeles area are expected to vary widely, and some areas could experience heavy rainfall. Depending on where, and how long, the low stalls off the coast some favored locations -- such as south to southwest facing mountain slopes -- might record substantially higher rainfall amounts.

According to NWS climate data, the rainfall record for Downtown Los Angeles for September 21 is 0.15 inch, set in 1887. The record for September 22 also appears to be 0.15 inch, set in 2000*. Both of these would appear to be in jeopardy, but like a child's top spinning on a hardwood floor, the behavior of an upper level low can be notoriously difficult to predict. We'll see!

*Note: NWS climate and record reports issued 9/22 and 9/23 indicate the previous rainfall record for September 22 was 0.10 inch set in 1923. This appears to conflict with NWS data in the document 1921-2006 Sep KCQT DAILY EXTREMES. Here's the weather history for 9/22/2000 from the Weather Underground.

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