# 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  |   | 
# Thursday, January 03, 2008

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

Forecast details have changed, but the main message is the same regarding a deep trough and 504 mb H5 low developing off the west coast. Strong, deep-layered, moist southwesterly flow is forecast to produce copious precipitation Friday night into Saturday, with lesser amounts preceding and following this period.

HPC's quantitative precipitation forecast issued this morning for the 5 day period ending Tuesday morning indicates totals as high as 11 inches (water equivalent) in the Sierra Nevada, and up to about 8 inches in the mountains of Ventura and Los Angeles. The 12z runs of the NAM and GFS generate about 3 inches of rain at Los Angeles between now and Sunday afternoon -- a little more forecast by the NAM and a little less by the GFS.

BUFKIT analysis of 12z NAM data for Van Nuys continues to indicate a low level jet of approximately 50 kts developing overnight Friday, with precipitable water values of 1.2 inches and cloud velocities exceeding 60 kts. Such a scenario -- if the forecast verifies -- could produce extraordinarily heavy, orographically enhanced rainfall in the foothills and mountains, with flash flooding and debris flows possible, particularly in areas that have been recently burned.

A new wrinkle, just introduced by the 12z GFS, is a more southerly track of a shortwave progged for mid-week next week, with a chance of rain developing Wednesday into Thursday. We'll see!

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

Update 01/06/08 1:00 P.M. Archived copy of a NWS Public Information Statement with preliminary rainfall totals for the ongoing rain event.

Update 01/05/08 9:00 A.M. Rain event progressing more or less as expected with storm totals so far generally ranging from about 1 to 5 inches in the basin and valleys, to 3 to 7 inches or more in the foothills and mountains. San Marcos Pass, near Santa Barbara has recorded nearly 9 inches of rain, and OPIDS Camp, near Mt. Wilson, has recorded about 8 inches of rain. Here is an archived copy of a NWS Public Information Statement with preliminary rainfall totals for the storm, and an AHPS Precipitation Analysis of California precipitation for the 24 hr. period ending 4:00 a.m. this morning.

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

Thursday, January 03, 2008 7:49:35 PM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Monday, December 31, 2007

12z GFS Forecast 60 Hr. Precipitation Total For the period ending January 7, 2008 4:00 p.m. PST Click!
12z GFS Forecast 60 Hr. Precipitation Total
For the period ending January 7, 2008 4:00 p.m. PST

Los Angeles will end 2007 with precipitation for the water year close to normal, and with the Sierra snowpack at about 60% of normal. However the first week of 2008 may usher in one of the strongest Pacific storms to affect California in some time, and by Monday of next week, precipitation and Sierra snowpack totals may have increased dramatically.

If recent runs of the GFS and ECMWF verify, California -- including much of Southern California -- will be deluged with heavy precipitation in the Thursday to Sunday timeframe. A BUFKIT analysis of 12z GFS data at Van Nuys indicates rain rates of over 0.7 inch an hour Friday night, and a rainfall total for the period of more than 4 inches. A second impulse Sunday is forecast to add about another 1.0 inch to the total.

CIRA Blended TPW loops show energy and moisture associated with tropical forcing in Indonesia being transferred into the the mid-latitudes, priming the system. Additional moisture is being drawn into the system from the tropics near Hawaii, and the GFS indicates a tropical connection as the system moves into California.

Details are likely to change as the week progresses, but at this point the storm's forecast parameters are impressive. At its peak, the Van Nuys BUFKIT analysis indicates a low level jet of approximately 50 kts developing, with precipitable water values of 1.2 inches and cloud velocities exceeding 60 kts. Such a scenario -- if the forecast verifies -- could produce extraordinarily heavy, orographically enhanced rainfall in the foothills and mountains, with flash flooding and debris flows possible, particularly in areas that have been recently burned.

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.

Monday, December 31, 2007 4:06:36 PM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Thursday, December 20, 2007

Intellicast Composite Radar - December 18, 2007 3:00 p.m. PST Click!
Intellicast Composite Radar
December 18, 2007 3:00 p.m. PST

According to preliminary NWS data, Downtown Los Angeles (CQT) recorded 1.24 inches of rain as a result of Tuesday night's storm, bringing the water year total to 3.69 inches. This amount is about 3/4 inch above normal for the date, and exceeds the 3.21 inch total recorded at Los Angeles during the record setting dry water year of 2006-2007.

Rainfall totals around the Los Angeles area generally ranged from about 0.75 to 1.25 inch in the basin and surrounding valleys, with as much as 1.5 to 3.0 inches (or more) recorded in some foothill and mountain locations. Here's a copy of a NWS Information Statement listing some rainfall totals for the storm.

In terms of percent of normal rainfall over the past 90 days, Southern California and the Desert Southwest have fared better than might be expected during a La Niña. The snowpack distribution in the Sierra is also somewhat unusual for a La Niña. Today's Summary of Snow Water Equivalents reports that the Sierra Southern Section snowpack is at about 77% of normal for the date, while the Central and Northern sections are at 53% and 61% of normal.

Today's NWS 6-10 Day Outlook projects above normal precipitation in Southern California, while the the 8-14 Day Outlook projects normal precipitation. We'll see!

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

Thursday, December 20, 2007 7:59:18 PM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Monday, December 17, 2007

18z NAM 48 hr. Total Precipitation December 17, 2007 Click!
18z NAM 48 hr. Total Precipitation
December 17, 2007

SREF Ensembles have been trending wetter south of Pt. Conception over the next 36 hours with each run. The 15z run indicates >90% chance of the rainfall total exceeding 0.1 inch in the Los Angeles area for the 24 hr. period ending 7:00 a.m. Wednesday.

The last couple of runs of the NAM have also been wetter. An ARL analysis of 18z NAM data generates about 3/4 inch of rain at Los Angeles over the next 48 hours, and a BUFKIT analysis generates about 2/3 inch at Van Nuys. According to these analyses light rain is forecast to begin about 10 p.m. this evening, increase in intensity during the day tomorrow, and taper off early Wednesday morning. We'll see!

Today's NWS 6-10 Day Outlook projects above normal precipitation in Southern California, while the the 8-14 Day Outlook projects normal precipitation.

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

Monday, December 17, 2007 8:05:41 PM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Saturday, December 08, 2007

NRL GOES Composite Visible/IR Satellite Image December 8, 2007 1:30 p.m. PST Click!
NRL GOES Composite Visible/IR Satellite Image
December 8, 2007 1:30 p.m. PST

Model performance hasn't been the best this Autumn. Sometimes this has worked in our favor, and sometimes not. The elements of Thursday night's system came together a little differently than projected and it wasn't as strong as expected.

Given the flash flood and debris flow potential in recently burned areas, the amount of rain was probably about as much as could be handled without causing too many problems. Downtown Los Angeles (CQT) recorded 0.41 inch of rain, bringing the water year total (since July 1) up to 2.44 inches -- still 0.16 inch above normal for the date. Last year at this time only 0.50 inch had been recorded.

Rainfall totals around the Los Angeles area generally ranged from about 0.25 to 1.00 inch, with as much as 1.0 to 2.0 inches (or more) recorded in some foothill and mountain locations. Here's a copy of a NWS Information Statement listing some rainfall totals for the storm.

An NRL GOES composite visible/IR satellite image from 1:30 p.m. PST this afternoon shows a strong vorticity max and upper low center near Pt. Conception, embedded in very strong north-northwesterly flow associated with a digging trough. The upper low is somewhat moisture starved, but very energetic. GOES soundings around the base of the trough indicates precipitable water values on the order of 0.50 to 0.75 inch. Radar shows some convective shower activity associated with the disturbance.

The 18z models project that the low will continue to dive south down the coast before moving onshore in northern Baja Mexico. Both the NAM and GFS generate about 0.1 inch at Los Angeles over the next 24 hours, with somewhat more to the south -- about 0.4 inch at San Diego according to the NAM. Because of the convective nature of the system, precipitation may be widely scattered and variable. Some areas may record no rain and others significantly more (or less) than the projected values. Here's the Day 1-2 QPF forecast from the HPC.

Today's (un-interpreted) NWS 6-10 and 8-14 day outlooks call for above normal precipitation in Southern California. In support of this notion, the 12z run of the ECMWF develops a full latitude trough around December 17, and the 18z GFS brings a strong system into California around December 19. A lot could change between now and then, but we'll see!

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

Saturday, December 08, 2007 8:14:26 PM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Saturday, December 01, 2007

Intellicast Composite Radar November 30, 2007 10:30 a.m. PST Click!
Intellicast Composite Radar
November 30, 2007 10:30 a.m. PST

In a November where the other 29 days were bone dry, the 30th was surprisingly wet, with downtown Los Angeles (CQT) recording 0.56 inch of much needed rain. The storm brought the water year total (since July 1) for Los Angeles to 2.03 inches, which is a deceptive 0.15 inch above normal for the date.

Rainfall totals generally ranged from about 0.25 to 1.00 inch, with well over an inch recorded in some foothill and mountain locations. Here's a copy of a NWS Information Statement listing some rainfall totals for the storm.

Although today's (uninterpreted) NWS 6-10 and 8-14 day outlooks call for below normal precipitation in Southern California, the 12z runs of the GFS and ECMWF suggest there might be an opportunity for some wet weather towards the end of the work week. We'll see!

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

Saturday, December 01, 2007 8:24:38 PM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   |