# Tuesday, April 01, 2008

GOES-11 Water Vapor 4/01/08 10:00 am PDT Click!
GOES-11 Water Vapor 4/01/08 10:00 am PDT.

A blustery Spring storm is expected to produce measurable rain over much of Southern California tomorrow. As has often been the case this year, the 12z NAM and 12z GFS are at odds, with the NAM generating less than 0.25 inch at Los Angeles, and the GFS more than 0.5 inch.

Today's NWS Precipitation Outlooks for Southern California indicate normal precipitation in the 6-10 day period and below normal for the 8-14 day period. We'll see!

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

Tuesday, April 01, 2008 3:50:14 PM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Sunday, March 30, 2008

LAX Precipitation Last 90 Days Click!
LAX Precipitation Last 90 Days

A weak cold front held together a little better than expected, producing a few showers in the Los Angeles area early Sunday morning. Here is an archived PDF of a NWS Public Information Statement with some preliminary rainfall totals as of 5:00 p.m. No measurable rain was recorded at Downtown Los Angeles (USC- KCQT).

Only 0.01 inch of rain was recorded at Downtown Los Angeles (USC- KCQT) the entire month of March, pulling the water year rainfall total more than a 0.5 inch below normal for the first time this rain season. It looks like there's a pretty good chance of some rain Wednesday. We'll see!

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

Sunday, March 30, 2008 3:46:00 PM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Monday, February 25, 2008

AHPS 7 Day Precipitation Analysis - Ending February 25, 2008 4:00 a.m. PST Click!
AHPS 7 Day Precipitation Analysis
Ending February 25, 2008 4:00 a.m. PST

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.

Monday, February 25, 2008 9:11:50 PM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Friday, February 22, 2008

UW GOES-11 Water Vapor February 22, 2008 1:00 pm PST Click!
UW GOES-11 Water Vapor
February 22, 2008 1:00 pm PST.

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.

Friday, February 22, 2008 9:15:18 PM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Thursday, February 21, 2008

UW GOES-11 Water Vapor February 21, 2008 11:00 am PST Click!
UW GOES-11 Water Vapor
February 21, 2008 11:00 am PST.

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.

Thursday, February 21, 2008 9:21:09 PM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Thursday, February 14, 2008

Click!
Upper Level Low Digging Southwestward
GOES-11 Water Vapor 2/14/08 6:30 am PST.

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.

Thursday, February 14, 2008 9:25:20 PM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Tuesday, February 05, 2008

Drought Monitor Classification Change for Water Year Ending January 29, 2008 Click!
Drought Monitor Classification Change
Water Year Ending January 29, 2008

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.

Tuesday, February 05, 2008 9:30:08 PM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Monday, January 28, 2008

AHPS 7 Day Precipitation Analysis - Ending January 28, 2008 4:00 a.m. PST Click!
AHPS 7 Day Precipitation Analysis
Ending January 28, 2008 4:00 a.m. PST

According to NWS Preliminary Climatology Data (CF6), Downtown Los Angeles has recorded measurable rain on each of eight days from January 21 to January 28, 2008. This puts it in the top six of the station's wettest periods from 1921-2007.

Downtown Los Angeles (USC-KCQT) has recorded 5.78 inches of rain over the period, bringing its water year total to 11.73 inches -- nearly 5 inches above normal for the date. Even if Los Angeles were to receive no rain through the entire month of February, we would still go into the month of March ahead of normal.

And it doesn't look likely that we'll have no rain this February. Today's NWS 6-10 Day Precipitation Outlook for Southern California is Above Normal, and the 8-14 day outlook is Normal. We'll see!

Here is an archived PDF of a NWS Public Information Statement with some preliminary rainfall totals for our most recent storm -- from 4:00 p.m. Saturday to 10:00 a.m. this morning.

Update 01/29/08. Early this morning the NWS released a Public Information Statement (PDF) with the rainfall totals for the eight day period from January 21 to January 28.

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

Monday, January 28, 2008 7:27:35 PM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Friday, January 25, 2008

UW GOES-11 Water Vapor Image - January 25, 2008 9:00 a.m. PST Click!
UW GOES-11 Water Vapor Image
January 25, 2008 9:00 a.m. PST

Computer weather simulations can be impressive, but sometimes the models just don't get it. That was the case overnight and into this morning as the Los Angeles area was hit by thunderstorms, heavy rain, and hail. Rainfall totals around the area generally ranged from about 1.5 to 3 inches, with some foothill and mountain location recording much more. OPIDS Camp, near Mt. Wilson in the San Gabriel Mountains recorded 6.27 inches for the 24 hour period ending at 8:00 this morning.

As has been the case several times this rain season, the GFS provided a better rainfall guesstimate than the NAM, forecasting 1.5 inches at Los Angeles through today, compared to the NAM's paltry 0.5 inch. Here are a CNRFC graphic of 24 hour rainfall totals in the Los Angeles area, a PDF of some preliminary Los Angeles County rainfall totals, and another PDF of a NWS Public Information Statement with some preliminary rainfall totals for the ongoing rain event. Several stations have recorded more rain since Monday than during all of last year's rain season.

Now attention turns back to the large upper level low spinning off the coast. The extensive circulation around this low is forecast to interact with the southern branch of the jet stream and an associated plume of sub-tropical moisture, and draw the jet and moisture into Southern California overnight on Saturday. According to NAM, GFS and high resolution NMM and ARW, the strongest dynamics and precipitation are forecast for Northern and Central California, however heavy precipitation is also expected in Southern California.

The 12z NAM and GFS are in better agreement than in recent days, projecting about 2.5 inches at Los Angeles from early Saturday morning to early Monday morning, with peak rain rates around 1:00 a.m. on Sunday. A BUFKIT analysis of 12z VNY data shows a strong, saturated, veering, southeasterly to southerly inflow, turning southwest over a six hour period from about 9:00 p.m. Saturday to 3:00 a.m. Sunday. This could produce significant orographic enhancement of precipitation on favored foothill and mountain slopes. Wet antecedent conditions at the lower elevations, and the possibility of rain on snow at the middle elevations, could increase runoff.

Update 01/26/08. Today's models appear to be indicating stronger dynamics in the south with more embedded vorticity, more diffluence aloft, and more favorable jet stream dynamics, but the 18z NAM and GFS are still cranking out about 2.3 inches at Los Angeles, beginning this evening, continuing through Sunday night, and tapering off Monday morning. Strong southerly inflow could produce much more than this in the foothills and mountains, particularly on south facing slopes. As the upper level low moves onshore on Sunday afternoon, thunderstorms could produce very heavy rain in areas where the soil iis already saturated.

Here is a NWS Public Information Statement with the preliminary rainfall totals for the period 4:00 p.m. Monday afternoon, to 4:00 p.m. Friday afternoon.

Please refer to your local NATIONAL WEATHER SERVICE FORECAST OFFICE for official forecasts and warnings.

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

Friday, January 25, 2008 7:31:50 PM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Thursday, January 24, 2008

WSI 24 Hr. Precipitation Estimate Ending January 24, 2008 4:00 a.m. PST Click!
WSI 24 Hr. Precipitation Estimate
Ending January 24, 2008 4:00 a.m. PST

You can see why the weather models had such a tough time with yesterday's forecast for Los Angeles. Much of the day the main rain band associated with the upper level low spinning off the coast was stalled and producing moderate to heavy rain in areas of Ventura, Santa Barbara and San Luis Obispo counties. New daily rainfall records were set at Santa Barbara, Santa Maria, and Paso Robles airports.

With just a slight change in the position of the low, that rain band might have spent the day over Los Angeles instead. As it was, the rain did finally move into the area during the afternoon, resulting in an inch or more of precipitation in many areas, and snow in the mountains -- closing I-5 over the Grapevine. Here are PDFs of some preliminary Los Angeles County rainfall totals, and a NWS Public Information Statement with some preliminary rainfall totals for the ongoing rain event.

As wet as it's been, it could get wetter. This morning's 12z NAM shows the upper low currently off the coast being replaced by another -- stronger -- upper level low. The new low is forecast to tap into an area of high precipitable water in the tropics and draw that moisture into Southern California Saturday night. The result could be copious rainfall. The wet antecedent conditions would likely increase runoff. In addition, thickness values and 850 mb temps are forecast to rise, which could result in a higher snow level, with rain on snow a possibility.

But keep in mind we're dealing with another upper level low. The models continue to have difficulties with the forecast. The 12z GFS is astronomically wet, generating 6 inches of rain at Los Angeles between early this morning and Sunday afternoon. A BUFKIT analysis of 12z GFS data for Van Nuys shows a peak rain rate of 1.5 inch/hour Saturday night! The GFS is also wetter in the short term, producing about 2 inches over the next 36 hours. In comparison the 12z NAM generates only about 2.75 inches at Los Angeles through Sunday, and less than an inch through Friday. We'll see!

Update 01/24/08 4:00 p.m. The 18z NAM and GFS are not as wet as the 12z runs. The 18z GFS generates about 4 inches through Sunday evening, and 1.5 inches through Friday evening. The 18z NAM produces about 1.75 inches through Sunday evening, and 0.4 inches through Friday evening.

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

Thursday, January 24, 2008 7:36:30 PM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Tuesday, January 22, 2008

GOES-11 Water Vapor Image - January 22, 2008 6:30 a.m. PST Click!
GOES-11 Water Vapor Image
January 22, 2008 6:30 a.m. PST

In a rain season characterized by upper level lows, yet another one has set up shop off the coast and has been sending some showers our way. As of 8:00 a.m. this morning rainfall totals around the Los Angeles area have generally ranged from a few hundredths of an inch to as much as about 0.25 inch in a few locations. Here is an archived copy of a NWS Public Information Statement with some preliminary rainfall totals.

As is often the case with this kind of scenario, the models have been having a difficult time handling the situation, and there has been a lot of variation from run to run. The 12z NAM and GFS remain at odds. The GFS is much wetter at Los Angeles through early morning Thursday, generating about 1.3 inches vs. the NAM's 0.5 inch. From early Thursday through Friday afternoon the NAM is a little wetter, generating 1.6 inches of rain at Los Angeles vs. the GFS's 1.2 inches.

In any case it looks like the water year rainfall total at Downtown Los Angeles has a good chance of remaining above normal as we head into February. We'll see!

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

Tuesday, January 22, 2008 7:40:38 PM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Monday, January 07, 2008

HPC 5 Day Precipitation Forecast for the period ending January 8, 2008 4:00 a.m. PST Click!
AHPS 7 Day Precipitation Analysis
Ending January 7, 2008 4:00 a.m. PST

The last of a series of storms that have been producing rain and snow in the western U.S. the past several days moved eastward and (mostly) out of the region today. According to preliminary NWS data, Downtown Los Angeles (CQT) recorded 2.00 inches of rain in the course of the event, bringing its water year total to 4.41 inches -- 1.54 inches above normal.

Precipitation totals in the Los Angeles area from Friday morning to this morning generally ranged from 2-5 inches in the basin and valleys, and from 5 to 10 inches or more in the local foothills and mountains. San Marcos Pass, near Santa Barbara recorded nearly 11 inches of rain, and OPIDS Camp, near Mt. Wilson, recorded nearly 13 inches of precipitation. Here is an archived copy of a NWS Public Information Statement with preliminary rainfall totals for the rain event, and an AHPS Precipitation Analysis of California precipitation for the 7 day period ending 4:00 a.m. this morning.

According to today's Summary of Snow Water Equivalents from California Cooperative Snow Surveys, the series of storms increased the Sierra Snowpack to 111% of normal for the date -- up from 60% at the end of 2007.

Another fast moving shortwave is forecast to primarily affect areas north of Pt. Conception Tuesday into Wednesday, with only a small chance of showers in the Los Angeles area.

So far this rain season, Southern California has dodged a La Nina bullet. This AHPS Precipitation Analysis for the water year to date indicates much of the area having received near normal to above normal precipitation. Even though the Climate Prediction Center's revised precipitation outlook for January, issued December 31, indicates above normal precipitation in the western U.S., the JFM Precipitation Outlook, issued December 20, remains pessimistic. We'll see!

Updated January 10, 2008. The ESRL-PSD Composite ENSO plots page was updated today to correct an issue that resulted in the wrong set of years being used for its Winter La Nina composites. As a result the La Nina composite precipitation map in the October 9, 2007 Weathernotes has been updated. Note that the average La Niña rainfall indicated for coastal Southern California is in the 7.0-10.5 inch range, rather than the 10-15 inch range previously indicated in the ESRL-PSD graphic.

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

Monday, January 07, 2008 7:44:55 PM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   |