Weathernotes Archive January 2006

Showers Saturday, Partly Cloudy Sunday. Is a La Niña Developing?
Weathernotes for Saturday, January 14, 2006
(Any updates will be found at the end of this discussion.)

GOES-10 water vapor image from 8:30 this morning shows upper level trough moving onshore in the West with associated baroclinic zone curving down from the Sierra into Southern California. Intellicast.com composite radar from 8:45 shows a band of light to moderate rain associated with the frontal zone as it was moving into the Los Angeles area.

The front generally resulted in about 0.1 to 0.2 inch of rain over a period of 2-3 hours as it moved through western Los Angeles county, with somewhat less rain recorded to the south and east. As of noon, the Malibu Hills RAWS has recorded 0.26 inch of rain; the Cheeseboro RAWS in the Topanga burn area 0.10 inch; and Los Angeles (USC) 0.10 inch. Daytime heating behind the front could trigger some convection and a chance of a shower. Sunday looks like it could be one of those post-frontal, partly cloudy, post card days. We'll see! (Link added 01/16/06.)

Is a La Nina in the works? Could be... the most recent value of the Multivariate ENSO Index (MEI) ranks the index just inside the threshold of a weak La Niña, and the MEI is the coolest it's been since February/March 2001. The CPC/NCEP ENSO Diagnostic Discussion issued January 12 points to atmospheric and oceanic anomalies and projects that "developing La Nina conditions" may continue into the northern hemisphere Spring and Summer. The January 6 ENSO Wrap-up from the Australian Bureau of Meteorology describes the current pattern as neutral, but "with some features of a weak La Niña." The Wrap-up goes on to say,"There is a chance that with further cooling, the pattern might develop into a La Niña for a brief period, although most computer predictions of ocean temperatures indicate a continuation of neutral conditions until the middle of 2006." This TAO/TRITON section plot of equatorial monthly averaged SSTs and anomalies shows the current cool conditions in the context of conditions from 1999 to the present.

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

Fast Moving Front Soaks Rose Parade. Strong Winds Blast Southland.
Weathernotes for Wednesday, January 4, 2006
(Any updates will be found at the end of this discussion.)

A fast moving cold front associated with a Pacific storm system roared through the Los Angeles basin Monday resulting in rain on the Rose Parade, and heavy rain and strong winds in many areas.

The LADPW rain gage at Flintridge recorded 1.03 inches from 7:21 A.M. to 10:45 A.M., the morning of the parade. JPL's weather station in Pasadena recorded about 1.7 inches of rain for the day.

The system was the second of two systems propelled into the west coast by strong upper level winds over the Pacific. The first system resulted in 0.88 inch of rain at Los Angeles (USC) on Saturday. As the second system moved into California New Year's Day, strong jet dynamics and diffluence ahead of its deepening trough resulted in moderate to heavy rain in the area Sunday afternoon. A final wave of moderate to heavy precipitation and strong winds occurred as the system's frontal band moved through the basin Monday morning.

It was this front, associated upper level winds and overhead 130 kt. jet that produced the high winds observed on Monday. Sustained winds of 56 mph and a gust of 101 mph were recorded by the Chilao RAWS at 5450 ft. in the San Gabriel mountains midday Monday.

Precipitation totals were a little less than expected, in part because of the speed at which the system moved through the area, and in part because of the relative lack of convective precipitation as the upper level trough moved through behind the front. Here is an archived copy of a NWS Public Information Statement listing rainfall totals from around the area for the 48 hour period ending 7:00 A.M. on January 3. Los Angeles (USC) recorded 2.84 inches for the period December 31, 2005 through January 2. 2006.

Over the holiday weekend, high snow levels and heavy precipitation brought rivers levels up in Northern and Central California, with some exceeding flood stage. Generally, coastal rivers with low elevation drainages such as the Smith, Russian, Klamath, and Eel were hit the hardest, but some middle elevation Sierra streams also peaked at high levels. Locally, Piru Creek above Lake Piru recorded a peak of over 7000 cfs, and Sespe Creek at Fillmore a peak of about 18,600 cfs.

Not all of the precipitation from the series of storms fell as rain. Mammoth Mountain reported 115 inches of snow over the 3-day holiday weekend, and snow sensors at higher elevations of the Sierra recorded 7 - 10 inches water equivalent of snow. This translates to 70 -100 inches of snow at normal snow densities. Tuesday's Regional Snowpack Summary from California Cooperative Snow Surveys reports the Southern Section of the Sierra at an astonishing 195% of normal for the date.

At the moment, the GFS computer model is saying no significant precipitation is in the works for Southern California for the next 6-10 days, and both the NWS 6-10 day and 8-14 day outlooks project below average precipitation for Southern California. A couple runs of the GFS have hinted at the possibility of something happening around mid-month, but it is really way too early to tell. We'll see!

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