Weathernotes Archive February 2008

Pacific Storm Soaks California -- Dumps More Snow in Sierra.
Weathernotes for Monday, February 25, 2008.
(Any updates will be found at the end of this discussion. Last month's notes are archived here.)

Weather conditions were tough for the Amgen Tour of California cyclists cranking over Mill Creek Summit yesterday. The Mill Creek RAWS recorded an average temperature of 35°F, with winds of 25 mph, gusting to 40 mph, at about the time the peloton cleared the summit. The Clear Creek RAWS, where riders turned right onto Angeles Crest Highway, recorded about 0.20 inch of rain during the afternoon, with the temperature hovering at around 40°F.

As bad as it was for the tour cyclists, the system was generally not as wet as expected -- particularly in the Los Angeles County mountains, where precipitation amounts ranged from about 0.25 inch to about 1.0 inch. Similar rainfall amounts were recorded in the Los Angeles basin and valleys.

Downtown Los Angeles (USC- KCQT) recorded 0.07 inches of rain Saturday, and 0.46 inches Sunday, bringing the water year total (since July 1) to 13.37 inches, which is about 3.1 inches above normal for the water year to date.

Since mid-week last week some Sierra snow sensors have recorded as much as 8 or 9 inches snow water equivalent of precipitation -- the rough equivalent of 6 or 7 feet of snow. Today's Statewide Summary of Snow Water Equivalents, provided by the California Cooperative Snow Surveys, reports the Sierra snowpack at 119% of normal for the date and 101% of the average April 1 seasonal total.

It looks like most of the west coast weather action will be shifting to the Pacific Northwest for the next week or so. Today's NWS 6-10 Day and 8-14 Day Precipitation Outlooks for Southern California continues to indicate Below Normal precipitation. We'll see!

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

Intense Pacific Storm Approaching West Coast.
Weathernotes for Friday, February 22, 2008.
(Any updates will be found at the end of this discussion. Last month's notes are archived here.)

Rapidly intensifying Pacific low pressure system approaching the west coast looks very impressive on satellite images this afternoon, with strong upper and low level jet dynamics, a good moisture feed, and a classic baroclinic leaf.

The system is forecast to be filling as it moves onshore, but a very strong jet max moving through the base of the trough should keep the dynamics interesting. In any case, significant rain is expected throughout much of California over the weekend, with heavy snow in the Sierra.

Southern California is forecast to be on the southern margin of the action, however in keeping with the wet trend this rain season, the 18z GFS is forecasting about 1.5 inches of rain at Los Angeles from midday Saturday through Sunday afternoon, and the 18z NAM about 1.0 inch. A moderately strong mid-level southerly to southwesterly inflow should increase precipitation amounts in favored foothills and mountain locations.

Precipitation totals resulting from the passage of the second trough yesterday afternoon into this morning have ranged from about 0.25 to 0.75 inch in the Los Angeles area, with up to about 1.0 inch recorded at some locations. Here is an archived PDF of a NWS Public Information Statement with some preliminary rainfall totals as of 4:00 p.m. Isolated showers have continued to pop up around the Los Angeles area much of the day, but are forecast to be ending in most areas this evening.

Downtown Los Angeles (USC- KCQT) recorded 0.19 inches of rain Thursday, bringing the water year total (since July 1) to 12.84 inches. We're still at a deficit for the month of February, but remain above normal for the water year to date. Much of the February deficit may be erased by Monday. We'll see!

Following this series of systems, a ridge is forecast to build in, resulting in generally fair, Spring-like weather for at least several days. Today's NWS 6-10 Day and 8-14 Day Precipitation Outlooks for Southern California continues to indicate Below Normal precipitation.

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

Extended Pacific Jet Sends Us Some Rain!
Weathernotes for Thursday, February 21, 2008.
(Any updates will be found at the end of this discussion. Last month's notes are archived here.)

Precipitation totals from the first of a series of shortwaves associated with a extended Pacific jetstream produced rainfall amounts ranging from about 0.1 to 0.25 inch in the Los Angeles area yesterday, with up to about 0.5 inch recorded in some mountain locations.

Downtown Los Angeles (USC- KCQT) recorded 0.14 inches of rain Wednesday, bringing the water year total (since July 1) to 12.27 inches -- still about 2.5 inches above normal for the date. Here is an archived PDF of a NWS Public Information Statement with some preliminary rainfall totals as of 4:00 p.m. yesterday afternoon.

There were a few sprinkles this morning, and Intellicast composite radar shows some shower activity around the area at 12:30 p.m. this afternoon. More general rain is expected to develop this afternoon or evening. Today's 12z NAM projects about 0.6 inch at Los Angeles between now and mid-morning Friday. Over that same period, a BUFKIT analysis of 12z NAM data for Van Nuys projects about 0.75 inch, but an analysis of 12z GFS data generates only about 0.25 inch.

A third system is forecast for the Saturday afternoon into Sunday timeframe and is expected to produce similar amounts of precipitation. However, the upper level flow will be transitioning to a more amplified pattern, so the computer models may have some difficulty with the forecast. We'll see!

Following this series of systems, a ridge is forecast to build in, resulting in generally fair, Spring-like weather for at least several days. Today's NWS 6-10 Day and 8-14 Day Precipitation Outlooks for Southern California are indicating Below Normal precipitation.

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

Trough Wetter Than Expected. Pattern Change Next Week?
Weathernotes for Thursday, February 14, 2008.
(Any updates will be found at the end of this discussion. Last month's notes are archived here.)

Today's trough was supposed to be an inside slider that stirred up some strong winds, and perhaps some drizzle. A more westward position of the upper low than forecast by yesterday's 18z GFS and NAM, has resulted in a more vigorous system that has produced rain in several areas of the Southland and snow in the mountains.

As of 11:00 a.m. the California Nevada River Forecast Center Los Angeles Area Precipitation Map shows 24 hour precipitation amounts ranging from 0.1 to 0.2 inch, generally south of the Los Angeles basin.

The last few runs of the GFS have been indicating a transition back to a wetter pattern around mid-week of next week, when a strong Pacific jet and a series of shortwave troughs are forecast to target the west coast. It appears that there is the possibility of a significant precipitation event in California, but it's too early to say where, when and how much rain may occur. We'll have to see how things develop over the next few days!

Today's NWS 6-10 Day and 8-14 Day Precipitation Outlooks for Southern California are indicating Above Normal precipitation.

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

Western Drought Severity Lessens. More Rain For Los Angeles, More Snow For The Sierra.
Weathernotes for Tuesday, February 5, 2008.
(Any updates will be found at the end of this discussion. Last month's notes are archived here.)

Sunday's storm added more rain to Southern California's unexpectedly wet water year totals, and more snow to the Sierra snowpack. This rain season western storms have reduced drought classifications by as much as three steps in some areas of California and four in Arizona.

As of February 4, Downtown Los Angeles (USC- KCQT) has recorded 12.13 inches of rain since July 1-- about 4.5 inches above normal for the date. Here is an archived PDF of a NWS Public Information Statement with some preliminary rainfall totals for Sunday's storm.

Sierra snow course measurements for February 1 are coming in and manual measurements are confirming what automatic snow sensors have already reported -- that the Sierra snowpack is well above normal for the date.

Will the wet western weather continue? The GFS and ECMWF medium range models, and NCEP and PSD ensembles are forecasting a generally quiescent, rain free period for Southern California over the next several days, and into the extended period. Today's NWS 6-10 Day and 8-14 Day Precipitation Outlooks for Southern California are indicating Below Normal precipitation.

However, there are suggestions (see Atmospheric Insights) that sometime around February 15-20, the currently active MJO may more or less phase with the GWO, and amplify La Nina to produce a energetic, extended Pacific jet and west coast trough, similar to what occurred around January 3, 2008. We'll see!

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