Induced by MJO enhanced convection in the West Pacific, a change in pattern is underway which is expected to produce significant rainfall in California over the next week.

The first shortwave is forecast to ride down the east side of a very high amplitude blocking ridge along the West Coast, dig offshore on Sunday evening, and merge with another shortwave as the westerlies try to undercut the ridge on Monday.

It's an extraordinarily complex scenario, and just how it will play out is hard to say. A BUFKIT analysis of 18z NAM data generates about 1.2" at LAX and about 1.5" at VNY. Relatively strong south to southwest inflow is forecast and would be expected to produce higher precipitation amounts in favored foothill and mountain locations.

Mid-week the westerlies are forecast to break through underneath the ridge, opening the door to more wet weather.

Update 12/08/09 5:00 p.m. The best dynamics worked out to be south and east of Los Angeles county, and as this AHPS graphic shows that's where the most precipitation was recorded. But the Los Angeles area still received it's fair share of precipitation and managed to do so without inundating the areas burned in the San Gabriel Mountains by the Station Fire. This was due in part to the generally moderate rainfall rates and the low snow level. This Intellicast.com composite radar image from 2:30 Monday afternoon shows the jet enhanced precipitation to the south of the Los Angeles basin, and the frontal band north of the basin.

Over the course of the storm Downtown Los Angeles (USC) recorded 0.95 inches, bringing the water year total to 2.28 inches, which is about 0.75 inches above normal for the date. Here's an archived copy of a NWS Public Information Statement with rainfall -- and snowfall -- totals from around the area.

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

Drier than average weather in the Southwestern U.S., and wet weather in the Pacific Northwest in recent weeks has some folks wondering if the 2009-2010 El Niño is going to be another one of the quirky, underachieving El Niños we've been seeing this decade.

For much of September and October, the primary area of equatorial convection in the Eastern Hemisphere was in the Central Pacific, just west of the dateline. Convection was suppressed in the Indian Ocean. Such a pattern is consistent with El Niño.

Enhanced convection centered at about 160E in early October may have helped to extend the Pacific jet following an East Asian mountain torque event around October 5. This in turn may have contributed to an atmospheric river precipitation event in California October 13-14, 2009.

At that time it looked like we might finally be off and running with a "real" El Niño event. Particularly because during October equatorial Pacific SSTs and heat content anomalies increased dramatically. Theses increases were the result of of a strong Westerly Wind Burst (WWB), an associated downwelling Kelvin wave, and diminished tradewinds,

However -- and I think I hear Ed Berry's Rottweiler growling -- beginning in mid October, strong convection developed in the Indian Ocean. This essentially neutralized El Niño, and perhaps contributed to the La Nina like precipitation pattern we've been experiencing along the west coast of the U.S.

Indicative of the ocean-atmosphere issues, relative Atmospheric Angular Momentum (AAM) has been negative since early September, and the Global Wind Oscillation (GWO) has remained on the La Nina side of the GWO phase space.

Does this mean we've had an El Niño false alarm?

I wouldn't put away my rain gear just yet. Although November rainfall for Downtown Los Angeles is about 0.6 inch below normal, we usually only get about an inch of rain in November. And don't forget, because of the big storm in October, we are still about 0.6 inch ABOVE normal rainfall for the water year.

Update November 24, 2009. Current equatorial heat content anomalies are about the same as in 2006, not greater. See this composite TAO/TRITON section plot comparing equatorial heat content in 2006 and 2009.

And there are some positive signs. Equatorial Pacific SST and heat content anomalies are much greater than in the short-lived 2006 El Niño, and are more along the lines of those observed in the 2002-2003 El Niño. In addition, a strong MJO has developed. It has remained coherent, and is propagating eastward into the Western Pacific. It already appears to be helping to enhance convection in the Western and Central Pacific, and could kick-start the El Niño engine over the next week or two. We'll see!

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

A potent early season Pacific storm carrying the remnants of West Pacific typhoon Melor has hammered California, setting numerous rainfall records, increasing stream flows, and producing heavy snow at the higher elevations of the Sierra.

Several stations, including some in Southern California, recorded precipitation totals exceeding 10 inches. In Santa Barbara County, San Marcos Pass recorded 10.32 inches. In Ventura County Nordoff Ridge recorded 10.04 inches and White Ledge Peak 10.87 inches. Precipitation amounts in Los Angeles County generally ranged from 1 to 3 inches, with orographically favored foothill and mountain locations receiving the higher amounts. Little rain fell in Palmdale and Lancaster because of a pronounced rain shadow effect. Downtown Los Angeles (USC) received 2.03 inches. Here's an archived copy of a NWS Los Angeles/Oxnard Public Information Statement with some rainfall totals for the storm from around the area.

A number of rainfall records for October 13 and 14 fell to the storm, including those for Paso Robles, Santa Maria, Santa Barbara Airport, WFO Oxnard, Burbank Airport, Pierce College in Woodland Hills, LAX, Santa Monica Pier, San Gabriel, and Long Beach Airport. Many of the records broken were set in 1957 and 1968 -- both El Niño years with above average rainfall at Los Angeles.

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

Los Angeles Temps Continue Below Normal.

Downtown Los Angeles (USC) ended the water year on June 30th having recorded 9.08 inches of rain, which is 6.06 inches below the 1971-2000 norm of 15.14 inches. Some additional water year rainfall totals:

According to the El Nino/Southern Oscillation (ENSO) Diagnostic Discussion issued July 9 by the Climate Prediction Center/NCEP/NWS, "During June 2009, conditions across the equatorial Pacific Ocean transitioned from ENSO-neutral to El Niño conditions." According to the report, El Nino conditions are expected to continue to develop, and last through the NH Winter.

The May-June Multivariate ENSO Index (MEI) value, reported July 6, has increased by 0.51 to +0.85. As was the case last month, the 3-month rise of the MEI (since February-March) is the 4th highest on record for this time of year, and was last exceeded by the strong El Niño of 1997. According to the MEI's originator, Dr. Klaus Wolter, "the combination of already border-line moderate El Niño conditions along with such a big rise in the MEI at this time of year has always been followed by continued El Niño conditions through the remainder of the calendar year, at least in the modern MEI record (since 1950)."

However, as the truncated 2006-07 El Niño event demonstrates, an El Niño is more than just warm Pacific equatorial SSTs. Through complex forcing and feedback mechanisms, the atmosphere and oceans have to cooperate on a global scale. As climate scientist Ed Berry cautions in his July 3rd Atmospheric Insights post, "Should total AAM departures become comparable to that observed during this past January and February, my concerns of an El-Nino 'false alarm' for the weather-climate dynamical system will be significantly raised."

Generally speaking, the momentum of the atmosphere increases when there is an El Niño, and decreases during a La Niña. Over the past 40 days the Global Wind Oscillation (GWO) has retreated from the higher AAM (El Niño) side of the GWO phase space to the lower AAM (La Niña) side. One concern is that two areas of tropical forcing (Indian Ocean and Pacific) may interact in such a way as to quash the El Niño engine. We'll see!

Closer to home, although temps in Southern California have recently been more seasonable, particularly in the Valleys, the last time the average daily temperature in Downtown Los Angeles was above normal was back on May 21 -- 48 days ago.

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

Instability and moisture associated with a very late season upper level low produced more rain in Southern California Friday, setting a record for June rainfall at Santa Barbara Airport.

Downtown Los Angeles (USC) recorded a total of 0.13 inch of rain Friday. The rainfall increased the water year precipitation total for Los Angeles to 9.08 inches, which is 6.05 inches below normal. Santa Barbara Airport recorded 0.51 inch, setting not only a new record for the date, but for any day in June, as well as for the total amount of rain in June. Here's an archived copy of a NWS Public Information Statement with some preliminary rainfall totals from around the area as of 5:00 p.m. Friday.

The April-May Multivariate ENSO Index (MEI) value (released today) has increased by 0.54 to +0.34. As discussed by MEI originator, Klaus Wolter, the 3-month rise of the MEI since January-February is the 4th highest on record for this time of year, exceeded last by the strong Niño of 1997. According to Dr. Wolter, if next month's MEI rank is at least the same as this month (37th), "it would be unprecedented for it to drop below that high-neutral ENSO-phase range by the end of 2009, virtually excluding a return to La Niña, based on the MEI record since 1950." We'll see!

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

Unusual weather for June. Not so much that there were thunderstorms, but that the thunderstorms were in part the result of an unseasonably strong jet embedded in the base of an offshore upper level low.

It's a bit of a stretch, but an argument could be made that these storms were a calling card of an increasingly energetic atmosphere, and a developing El Niño.

Downtown Los Angeles (USC) recorded a total of 0.02 inch of rain Wednesday. The rainfall increased the water year precipitation total for Los Angeles to 8.95 inches, which is 6.16 inches below normal.

It's not often that a trace of rainfall sets a record, but that was the case at Camarillo Airport and Palmdale, which had not previously recorded precipitation on June 3. The 0.03 inches recorded at Sandberg was also a record. Here's a CNRFC graphic with some 24 hour rainfall totals in Los Angeles County.

Several factors point to an increased probability of El Niño conditions developing over the next few months. Among them, Equatorial Pacific SSTs have increased, and the subsurface heat content is the highest it's been since the El Niño of 2006-07.

But as the short-lived 2006-07 El Niño event demonstrates, an El Niño is more than just warm Pacific equatorial SSTs. Through complex forcing and feedback mechanisms, the atmosphere and oceans have to cooperate on a global scale. Generally speaking the momentum of the atmosphere increases when there is an El Niño, and decreases during a La Nina.

And it looks like the atmospheric momentum may be increasing. Orbits of the Global Wind Oscillation (GWO), a measure of atmospheric momentum, have been shifting upward, in the direction of more energetic values usually associated with an El Niño.

However, an El Niño is not a done deal. The climate system is just leaning in that direction. As climate scientist Klaus Wolter has previously pointed out, in a similar situation in 1973-1975, the climate fell back into a La Niña for another year. But at this point it appears we may be diverging from that analog case. (See June 6 Weathernotes.) We'll see!

Update 06/05/09. Unseasonably strong 110+ kt jet overhead as upper low center moves onshore in Central California. At 7:15 this morning, Intellicast composite radar showed most of the shower activity occurring to the north of Los Angeles, but there has been scattered showers in the Los Angeles area as well, with measurable rain recorded at a number of stations. Here's an archived copy of a NWS Public Information Statement with some preliminary rainfall totals as of 5:00 p.m.

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

Upper low off the coast of Southern California this morning is forecast to track into Northern Baja by Saturday, and then continue east into Texas Easter Sunday. There's a chance of a shower, or possibly a thunderstorm, over much of Southern California today, diminishing tonight. Tomorrow is expected to be partly cloudy, with mostly sunny skies forecast for Easter Sunday.

Downtown Los Angeles (USC) recorded at total of 0.03 inch of rain Tuesday into Wednesday as a weak front associated with an upper level low moved through the basin. The rainfall increased the water year precipitation total for Los Angeles to 8.93 inches, which is about 5.5 inches below normal. Here is an archived copy of a NWS Public Information Statement, with some precipitation totals from around the area.

A warming trend is expected over the next several days, with high temperatures near 90 by the end of the week.

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

Compared to last week, GFS and ECMWF runs this week have been much drier in Southern California, with most of the activity focused on the Pacific Northwest. No significant rain is forecast here next week, and both the 6-10 and 8-14 day forecasts project below average precipitation for Southern California.

Recent runs of the GFS show the East Asian jet pumping up a huge, high amplitude ridge in the central Pacific around the dateline, but the resulting downstream trough, jet energy and storm track are forecast to remain above about 40°N.

Model performance has not been the best in recent weeks, and generally suffers during seasonal transitions. However, if the 12z GFS forecast is on the mark, March rainfall for Downtown Los Angeles (USC) would fall well below the 3.14 inch norm. Since normal April rainfall is 0.83 inches, and May only 0.31 inches, beyond March it becomes increasingly unlikely that a big rain event will significantly boost our rainfall total.

Since November 1, Downtown Los Angeles has recorded 8.80 inches of precipitation. This is consistent with the mean November-March precipitation for coastal Southern California during 9 La Niña events from 1948 to the present. (See the composite precipitation map in Weathernotes for October 31, 2008.) The water year total for Los Angeles is now 3.32 inches below normal.

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

The precipitation total for Downtown Los Angeles (USC) for February was a little above normal, but not enough to offset January's dry weather. We started out March with a water year rainfall total about 2.4 inches below normal, and as of today we're about 2.73 inches behind.

Tuesday's frontal passages helped a little. Here's a GOES-11 water vapor image from 2:30 in the afternoon, and an Intellicast.com composite radar image from 2:45 p.m. Downtown Los Angeles (USC) recorded 0.25 inch of rain for the storm, and rainfall totals generally ranged from about 0.25 to 0.50 inch. Here is an archived copy of a NWS Public Information Statement listing some rainfall totals.

It looks like our rain season may not be over. Recent runs of the GFS have been hinting at some rain in the 8-10 day timeframe, with a series of systems following. This is consistent with Ed Berry's Atmospheric Insights post today. In response to increased subtropical westerly wind flow, he suggests the possibility of an extended East Asian jet in the week 2-3 timeframe, with possible western USA impacts. We'll see!

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

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.

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.

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.