# Wednesday, February 18, 2009

RAMDIS IR3 Water Vapor Image February 18, 2009 6:30 a.m. PST Click
RAMDIS IR3 Water Vapor Image
February 18, 2009 6:30 a.m. PST

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.

Wednesday, February 18, 2009 8:48:22 AM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Friday, February 13, 2009

Intellicast.com Composite Radar February 13, 2009 9:15 a.m. PST Click
Intellicast.com Composite Radar
February 13, 2009 9:15 a.m. PST

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.

Friday, February 13, 2009 8:50:41 AM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Friday, February 06, 2009

CPC 8-14 Day Precipitation Outlook Click
CPC 8-14 Day Precipitation Outlook

The first of a series of upper lows, troughs and shortwaves expected to affect Southern California over the next several days has resulted in widespread rain, with storm totals in excess of 1.0 inch in many areas. Yesterday, new rainfall records were set for the date at Burbank and Lancaster. Many stations have recorded more rain in the past twelve hours than in the entire month of January.

Another Pacific system is working down the coast and is expected to result in periods of rain today, tonight and into Saturday. A break in the action is forecast on Sunday, but some showers are a possibility.

In a situation that has become too familiar this rain season, Sunday evening a trough is forecast to dig down the backside of a ridge along the West Coast. Model forecasts have varied from run to run, but the trough is expected to produce some rain in our area Sunday evening into Monday. A more westward track, over the Pacific, would likely produce more rain, and a more eastward track less.

This generally wetter pattern may continue into the 8-14 day period. The active phase of the Madden-Julian Oscillation (MJO) and the Global Wind Oscillation (GWO) are supporting a general circulation pattern that is favorable to West Coast troughs. In addition, a major Sudden Stratospheric Warming (SSW) event is underway and associated high latitude blocking might eventually result in a southward shift of the storm track over the U.S.

Both the 6-10 day and 8-14 day precipitation outlook from the CPC are indicate the possibility of above average rainfall in Southern California. We'll see!

Update 02/10/09. Here are the updated and corrected storm totals from the NWS for the period 4:00 a.m. Thursday to 4:00 a.m. Sunday. It looks like Wednesday's system should fall apart south of Pt. Conception, but if recent model runs hold true, Southern California is in store for more wet weather. Relatively weak shortwaves are forecast for Friday and Saturday, but these set the stage for more potent systems Sunday and mid-week. We'll see!

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

Friday, February 06, 2009 8:52:41 AM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Monday, January 26, 2009

GEFS Ensemble Forecasts - For February 4, 2009 4:00 a.m. PST Click
GEFS Ensemble Forecasts
For February 4, 2009 4:00 a.m. PST

Weather is by nature chaotic, and not perfectly predictable. From a given starting point, small variations in initial temperature, pressure, moisture, and other factors in the weather system can lead to dramatically different outcomes. In addition, interactions of earth's oceans and terrain with the atmosphere further complicate predictability.

Two periods of rain were recently forecast in Southern California -- one from Wednesday into Saturday, and another from Sunday evening into Tuesday. Model projections varied from day to day and run to run. At one time it looked like the Los Angeles area might get about an inch or rain out of both systems. So what happened?

Considering the first period, Wednesday into Saturday, here are the preliminary rainfall totals from the NWS. Note how much the rainfall varies. In the Los Angeles basin, Downtown Los Angeles (USC) recorded 0.34 inch, LAX recorded 0.51 inch and Santa Monica recorded 0.76 inch. Locations that benefited from orographic enhancement recorded higher totals. For example. Pacioma Dam recorded 1.11 inch, Warm Springs 1.31 inch, and OPIDS Camp 1.54 inch. Some stations in Santa Barbara and San Luis Opisbo counties received as much as 2-3 inches of rain. A slight change in the position of low to the south on Wednesday and Thursday, or the low to the west on Friday and Saturday could have easily resulted in much more rain.

We're in the middle of the second period now. Instead of an over the ocean path forecast a couple of days ago, the cold trough and upper low that is over the southwest took a drier overland course down the West Coast. Nonetheless, there has been scattered showers in Southern California, and even isolated thunderstorms, lightning and hail. It's not a huge step to speculate the rainfall would have been more widespread if the system had taken a more westward path, and picked up additional moisture.

So what's next? Globally, some interesting things are occurring that could impact our weather over the next few weeks. The MJO and GWO are expected to continue their circuit into phase 3-4. This might open the door to more West Coast troughs, or MJO enhanced rainfall. A Sudden Stratospheric Warming (SSW) event appears to be underway and may result in polar air outbreaks that would affect the mid-latitude circulation.

However, in the short term Los Angeles rainfall remains below normal. As of January 25, Downtown Los Angeles (USC) has recorded 5.00 inches of rain this water year, which is 1.38 inches below normal. Last year, the water year total on January 25 was 9.35 inches. The ECMWF and GEFS ensembles suggest the possibility of a strong trough affecting California around February 4th or 5th, but that is a long way out, and we'll have to see!

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

Monday, January 26, 2009 8:55:48 AM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Tuesday, January 20, 2009

HPC QPF Forecast - 48 hrs. Ending 4:00 pm 01/22/09 Click
HPC QPF Forecast
48 hrs. Ending 4:00 pm 01/22/09

Including today, Los Angeles has enjoyed an unprecedented ten straight January days with highs in the eighties. In the yin yang of weather, the western half of the U.S. has been enjoying unusually warm temps, while the eastern half of the country has shivered.

Since the start of the water year on July 1, Downtown Los Angeles (USC) has recorded 4.66 inches of rain. Just 10 days ago, 4.66 inches was almost exactly normal rainfall for the date. However, as is so often the case in Southern California, this apparent normality was the sum of offsetting wet and dry periods. December's precipitation was generally well above normal, but January has been dry, dry, dry. Today, the Los Angeles rainfall total is about 1.10 inch below normal, and every day it doesn't rain, our deficit increases by about 0.10 inch.

Our warm temperatures and dry weather have been the result of a high amplitude ridge, pushed up over the West Coast by a very strong and extended Pacific jet stream. Big upper level ridges such as this are consistent with La Nina, and have been a recurring theme this Fall and Winter. Much of our rainfall and cold weather this season has occurred when an extended Pacific jet collapses or contracts -- as is occurring now -- and the blocking ridge shifts westward, opening the door to cold storms plunging down the backside of the ridge from the north.

This time there is a wildcard in the mix. One of the reasons the Pacific jet has been extended is the active phase of the Madden-Julian Oscillation (MJO) has recently propagated from west to east, across the Pacific. The system that is forecast to affect Southern California Wednesday night into Thursday looks like it might be enhanced by an inflow of moisture from an area of tropical convection that may be associated with the MJO.

How much might it rain? A BUFKIT analysis of 12z NAM data generates 1.3 inches of rain at Van Nuys for the period Wednesday evening through Thursday afternoon. The HPC 2 Day forecast is not so bullish, indicating about 0.50 inch to 0.75 inch over the area. We'll see!

Medium range models suggest the weather in the West could remain unsettled into next week and beyond. Of particular interest is this morning's 12z ECMWF forecast for mid-week next week, which projects the retrogression of the West Coast ridge to 150-160°W, with a cold, wet pattern similar to what we saw in December. That would be quite a change!

Update 01/22/09. It seems the NAM and GFS models can't get a handle on the system currently affecting our area. The 12z NAM generates 1.6 inches (!) of rain at Van Nuys and the 12z GFS 1.2 inches at LAX from this morning into Saturday afternoon. On the other hand the 09z SREF Ensembles puts the probability of more than 0.25 inch of rain for the 24 hr. period ending mid-morning Friday at about 50%, and then only about 10-30% for the following 24 hr. period. Upslope enhancement may produce higher totals on south facing foothill and mountain slopes. The GFS continues to advertise the possibility of a significant rain event Monday afternoon into Tuesday or Wednesday, but given recent model performance, we'll wait and see!

Update 01/21/09. The 12z models now extend the rainy period for the first system into Saturday. The 12z NAM generates about 1.0 inch of rain at Van Nuys, beginning Thursday morning and ending Saturday midday. The 12z GFS also produces about 1.0 inch, beginning Wednesday evening and ending Saturday afternoon. The GFS adds another 0.9 inch from Sunday morning to Monday night. Somewhat higher amounts would be expected in some foothill and mountain locations. As always, we'll see!

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

Tuesday, January 20, 2009 8:57:46 AM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Thursday, December 25, 2008

Intellicast.com Radar Precipitation Estimate for the Click
Intellicast.com Radar Precipitation Estimate
24 hrs. Ending 4:00 am 12/25/08

A Pacific storm system -- which at one point was expected to be the wettest of the rain season thus far -- took a more westward track and skirted the coast of Southern California on Christmas Eve, generally producing only modest rainfall across the area.

Today, the trough digging down the coast is further west that forecast. (In retrospect this might have been foreseen taking into account the GWO phase 1-2 transition.) In any case, the flow into California has been moist and cyclonic, and rain has continued in many areas, with snow at the higher elevations.

A front associated with this trough is working its way down the coast, and early this afternoon is just north of Los Angeles. This could add a little more to our rainfall totals as it moves through later today. We'll see!

Update 12/26/08 10:30 am. Here are some preliminary storm totals from the NWS Los Angeles/Oxnard and storm totals from the NWS San Diego.

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

Thursday, December 25, 2008 5:55:42 PM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Tuesday, December 23, 2008

NRL VIS/IR Satellite Image - December 23, 2008 10:30 a.m. PST Click
NRL VIS/IR Satellite Image
December 23, 2008 10:30 a.m. PST

A potent appearing Pacific storm system is developing off the coast of Oregon and Northern California and headed our way. Significant rain, with snow at the higher elevations, is expected over much of the state.

Rain associated with this system is forecast to begin in Northern California this evening. At the moment, it looks like prefrontal rain could develop in the Los Angeles area tomorrow morning. Rainfall rates are forecast to increase Christmas Eve, and then taper off during the day on Christmas.

Although the models appear to be converging on similar solutions, there has been a lot of variability from run to run. This is due in part to the difficulty of the forecast. The intensity of the low, the path of the low center, the amount of moisture available to the system, the upper and lower level jet dynamics and other factors could change the amount of rainfall.

The HPC QPF forecast for the period Tuesday afternoon to Friday afternoon shows about 1.25 to 1.50 inches along the coast with up to about 3 inches in the mountains. These amounts could be somewhat understated. We'll see!

The system that moved through the Los Angeles area Sunday night into Monday was a little stronger than expected, with rainfall amounts generally ranging from about 0.1 inch to 0.25 inch. Here are some preliminary rainfall totals from the NWS.

Update 12/24/08 11:00 am. 12z NAM and GFS forecast a more westward track of the low and have backed off precipitation amounts forecast for the Los Angeles area. The 12z NAM generates about 0.6 inch at Van Nuys and the 12z GFS only about 0.26 inch for the storm. HPC's latest 2-day Quantitative Precipitation Forecast indicates precipitation amounts ranging from about 0.75 inch to 1.50 inch in coastal Southern California. On the other hand, the 06z high resolution WRF-NMM was quite wet, with precipitation amounts in our area ranging from 1.0 to 4.0 inches.

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

Tuesday, December 23, 2008 6:00:05 PM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Thursday, December 18, 2008

TerraModis West 1km True Color - December 17, 2008 10:30 a.m. PST Click
TerraModis West 1km True Color
December 17, 2008 10:30 a.m. PST

A cold upper level low produced widespread rain and snow in Southern California, closing highways, fouling traffic, and chilling Southlanders. As much as a foot of snow was reported in the Antelope Valley and the snow level dropped to near 2000 ft in the foothills and mountains of Ventura and Los Angeles counties.

As forecast by the NAM/WRF, the precipitation totals were higher to the south of the Los Angeles basin. This Intellicast.com animated loop shows the pattern of rain and snowfall from Tuesday evening to Wednesday evening. Here are some preliminary storm totals from the NWS Los Angeles/Oxnard and storm totals from the NWS San Diego.

Downtown Los Angeles (USC) recorded 0.51 inch for the storm, bringing the water year rainfall total at Los Angeles to 2.79 inches. As of December 17, this is 1.41 inches above normal, and 0.34 inch more rain than we had last year on this date.

What's next? RAMDIS 4km water vapor animation shows a weak disturbance northwest of Pt. Conception, moving east toward the Central Coast. Although today's 18z NAM/WRF is dry overnight south of about Monterey, this area of vorticity could produce a shower north of Pt. Conception. After that, things should stay dry in Southern California until around Monday, when a fast moving front sweeps through the state. Later in the week, sometime around Christmas, the models are suggesting the possibility of a major system impacting California. We'll see!

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

Thursday, December 18, 2008 6:03:32 PM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Tuesday, December 16, 2008

AHPS Precipitation Analysis For Week Ending 12/16/08 4:00 a.m. Click
AHPS Precipitation Analysis
For Week Ending 12/16/08 4:00 a.m.

An intense upper level low, fed in part by moisture that originated in the subtropical mid-Pacific, produced widespread rain in Southern California, with snow at the higher elevations. Precipitation totals generally ranged from about 1 to 3 inches, and new rainfall records for December 15 were set at LAX, UCLA, Long Beach, San Gabriel and Santa Barbara. Here are some preliminary rainfall totals from the NWS.

A very cold core upper level cutoff low is currently spinning off the California coast. A GOES sounding from this afternoon indicated a temperature of -33°C at the 500 mb level and significant instability. The low is forecast to move onshore over the next 24 hours, and slight changes in its trajectory could have a big impact on precipitation amounts and intensity.

The NAM/WRF has been quite a bit drier in the Los Angeles area than the GFS, with the heaviest precipitation occurring south of the basin. The latest (00z) run of the NAM appears to be wetter in the Los Angeles area than runs earlier today. With such cold temperatures aloft, heavy rain and strong thunderstorms are a possibility, particularly wherever the low moves onshore. BUFKIT analysis of PMD and VNY data suggests the snow level could drop to 2000-2500 ft., perhaps lower in heavy showers. We'll see!

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

Tuesday, December 16, 2008 6:58:38 PM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Friday, December 12, 2008

Forecast 24 hr. Precipitation (18z NAM 12/12/08) 10 PM Sunday to 10 PM Monday Click
Forecast 24 hr. Precipitation (18z NAM 12/12/08)
10 PM Sunday to 10 PM Monday

It's been a couple of weeks since an upper level low set rainfall records for the date at several Southern California locations, and pushed water year rainfall totals above normal at Los Angeles. Since then we've had almost no rain, and as of yesterday, Downtown Los Angeles (USC) rainfall has dropped to about six-tenths of an inch below normal. If a storm later this weekend works out as expected, we could be back above normal by Monday night.

Several factors could affect the forecast. As we've seen earlier this season, the computer models don't do a particularly good job with high amplitude flows, retrograding ridges and digging troughs. Throw into the mix a strong 150-170 kt. jet stream, sub-tropical moisture being advected from Hawaii (nearly) to the Aleutians, and cold air being drawn down from Canada and Alaska, and there is the potential for high impact weather.

A chance of showers is forecast Saturday into Sunday, but at the moment, the main event is forecast for Sunday evening through Monday. HPC's QPF for that period indicates rainfall amounts ranging from about 0.75 inch to 2 inches or more in the mountains. We'll see!

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

Friday, December 12, 2008 7:02:58 PM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Thursday, November 27, 2008

NRL NEXSAT 24 hr. Blended Precipitation) for the period ending 11/26/08 - 4:00 p.m. PST Click!
NRL NEXSAT 24 hr. Blended Precipitation)
Period Ending 11/26/08 - 4:00 p.m. PST

Happy Thanksgiving! Our record-setting upper low system is slowly moving east out of the area, but this morning there's still some shower activity occurring south and east of the Los Angeles basin. The best chance of showers today is in the mountains, and areas south and east of the basin, but a shower could pop up just about anywhere in Southern California.

Rainfall totals for the storm have generally ranged from 1.0 to 2.0 inches in the coastal and valley areas, with some higher amounts recorded in foothill and mountain locations. Rainfall records for November 26th were broken at several locations, including Lancaster, Palmdale, Sandberg, UCLA, Burbank, Woodland Hills, and San Gabriel. OPIDS Camp, in the San Gabriel Mountains has recorded 3.29 inches. Here are some preliminary rainfall totals from the NWS.

Through yesterday, Downtown Los Angeles (USC) has recorded a storm total of 1.60 inches, bringing the water year total to 1.87 inches, which is 0.17 inches above normal for the date.

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

Thursday, November 27, 2008 5:49:22 PM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Monday, November 24, 2008

GOES-11 Water Vapor (UW-MAD)  Monday, November 24, 2008 - 4:30 p.m. PST Click!
GOES-11 Water Vapor (UW-MAD)
Monday, November 24, 2008 - 4:30 p.m. PST

In the past week the weather models have been all over the map -- and sometimes off of it -- trying to come up with a forecast for this week and the Thanksgiving holidays. Now that a potent looking upper level low system is bearing down on the Southland, the 18z NAM and 18z GFS both agree we are going to get drenched.

The Hydrometeorological Prediction Center (HPC) is projecting from one to two inches of rain over a large area of Southern California. BUFKIT analysis of 18z data for Van Nuys generates rainfall totals of in excess of 2 inches for the storm. Depending on the strength of the southerly inflow, rainfall totals could be higher on south facing foothill and mountain slopes.

Radar is already showing some echoes aloft, and some showers could occur overnight and into tomorrow. Rain is expected to begin in earnest during the day tomorrow, perhaps as late as tomorrow afternoon or evening, and taper off late Wednesday night into Thursday morning.

NOAA has just released their 2008-2009 Winter Outlook. The precipitation outlook for December through February indicates an equal chance of below normal, near normal, or above normal precipitation for California. The IRI Multi Model Seasonal Forecast for Dec-Jan-Feb indicates below average precipitation is slightly more likely in southern third of California.

Update 11/25/08. BUFKIT analysis of 12z NAM and GFS data for Van Nuys isn't quite as wet as yesterday's 18z run. Over the next 36 hours, the 12z GFS generates about 0.8 inch, and the 12z NAM about 1.7 inch of rain, with maximum rain rates of about 0.4 inch/hour. Rain is expected to move into the Los Angeles area later this afternoon or evening.

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

Monday, November 24, 2008 5:52:49 PM (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   |