cw3e-web - Center for Western Weather and Water Extremes

Setting the Stage for a Global Science of Atmospheric Rivers

January 25, 2016

The above image, from the EOS article, is a depiction of an atmospheric river, interacting with West Coast mountains and a midlatitude cyclone over the northeast Pacific on 5 February 2015. This image provides an example of approximate locations of associated tropical moisture exports and a warm conveyor belt (WCB). Credit: Adapted from NOAA/ESRL Physical Sciences Division

An EOS article from CW3E scientists Dettinger, Ralph and Lavers summarizes key outcomes from a unique workshop held at Scripps Institution of Oceanography in June 2015. The Workshop brought together leading scientists and users of scientific outputs to discuss emerging advances in Atmospheric River (AR) science and applications. A “Meeting Report” about the workshop appeared in print in the EOS issue published on 1 January 2016: Click here to acccess the report.

Points of contact: F.M. Ralph (mralph@ucsd.edu), M.D. Dettinger (mddettin@usgs.gov), and D. Lavers (dlavers@ucsd.edu) at the Scripps Institution of Oceanography, UCSD.

AR storms impact northern California: January 12-15

January 15, 2016

DRI/CW3E researcher Nina Oakley, CW3E researcher Scott Sellars and other CW3E team members evaluate two storms that had an impact on northern California as well as the Pacific Northwest from 12-15 January 2016. Fresh Sierra snow can be seen in the cover satellite image from Friday, January 15 (courtesy NWS Sacramento). The approaching clouds from the next series of storms can be seen approaching the coast as well as valley fog in the Sacramento region. The first storm event leading to this fresh snow was a moderate atmospheric river (AR) storm with 1 to over 4 inches of precipitation from northern California to the Canadian border. The second storm event was weaker and ahead of a larger scale AR that will impact the same region from 15-18 January 2016. The weaker event spun off the Aleutian Low and produced some areas of heavy snowfall in the Sierra Nevada. An outlook for the upcoming AR event for 15-18 January is also briefly examined.

Click here for a pdf file of this information.

Above is a sequence of SSMI water vapor imagery from 10-13 January 2016 which shows the AR propagating towards northern California and making landfall.

Above is a sequence of SSMI water vapor imagery from 12-15 January 2016 which shows the first AR making landfall and the dissipation of the second AR as it approaches land.

Recent Rainy Week in San Diego County

January 8, 2016

El Nino-fueled storms over the last few days, including a land-falling atmospheric river on 5 January (see cw3e.ucsd.edu for more details), have brought San Diego county’s accumulated winter precipitation to well above normal for this time of year. These numbers are tracked by the California-Nevada Applications program (cnap.ucsd.edu) and the Center for Western Weather and Water Extremes (cw3e.ucsd.edu) at UCSD’s Scripps Institution of Oceanography, in association with KPBS. The precipitation tracking tool shows the impact of the recent storms on the accumulated winter precipitation:

In the last three days, San Diego county has received almost 17% of the amount of precipitation it receives in an entire year, on average.

Precipitation gauge records compiled by the California Nevada River Forecast Center show accumulations of 3-5″ over much of the Los Angeles basin in the 72 hour period, reaching 7″ in some locations in the surrounding mountains. San Diego county accumulations are 1-3″ over much of the city, and 4-5″ in the North County interior:

These storms bring San Diego county’s running total accumulated precipitation so far this winter to 42% of the total typically received over an entire average year. This is an above-average value for the first time since the winter started; typically, by this point in the winter, San Diego will have accumulated 32% of the average year-end total precipitation.

Before the recent storms hit, the accumulated precipitation in the Los Angeles region since the winter started was only 11% of the typical end-of-winter total, far below the average value of 29%. In three days the accumulation has jumped to 27%. This rapid increase is more than is experienced in 95 out of 100 wet periods of 3-day duration in the region, leading to strong flows in the normally quiescent Los Angeles river and localized flooding in Southern California coastal areas.

Precipitation during the week was widespread, with rain and snow delivered from Washington to Northern Mexico. California statewide totals also were boosted during the Jan 4-7 period (cnap.ucsd.edu), although amounts were not as heavy in Northern California as they were in Southern California.

These accumulated precipitation totals can be tracked in real time from the California-Nevada Applications Project (CNAP) and Center for Western Weather and Water Extremes (CW3E)’s “San Diego Precipitation Page”. This includes monitoring of how current winter precipitation compares to that during the last 5 strongest El Nino winters (1982-83, 1997-98, 1957-58, 1972-73, and 1965-66), shown as the colored lines in the upper panels:

The current El Nino event is is one of the three strongest in records that go back to 1950, with a broad area of unusually warm ocean surface waters in the tropical Pacific ocean and highly anomalous winds and other atmospheric conditions in the region. El Nino events can alter the North Pacific winter storm track, producing unusually wet winters in Southern California about 60% of the time, compared to about 11% of the time during years when no El Nino or its opposite, La Nina, is present. Forecasts indicate that El Nino conditions are likely to persist through the spring of 2016, before fading in the early summer of 2016.

Points of contact: David Pierce (dpierce@ucsd.edu), Dan Cayan (dcayan@ucsd.edu), and Marty Ralph (mralph@ucsd.edu) at the Scripps Institution of Oceanography, UCSD.

For a PDF version of this information click here.

California Storm of 5 January 2016: A Preliminary Synopsis of a Marginal Landfalling Atmospheric River

January 5, 2016

CW3E researchers Brian Kawzenuk and Scott Sellars and DRI researcher Nina Oakley provide a preliminary analysis and synopsis of a weak Atmospheric River that made landfall over southern California on 5 January 2016. The AR was the first event in what will be an active week over the North Pacific and brought significant precipitation throughout central and southern California. The AR initially developed near Japan and propagated across the entire North Pacific Ocean before making landfall. A brief forecast for the rest of the week is also provided by the San Diego National Weather Service Forecast Office, courtesy Roger Pierce.

Click here for a pdf file of this information.

Above is a sequence of SSMI water vapor imagery from 01-05 January 2016 which shows the Atmospheric River propagating towards California and making landfall.

-Atmospheric River intially developed over the northwestern Pacific Ocean
-AR propagated eastward and strengthened
-AR became disconnected with its parent low and began to dissipate prior to landfall
-Secondary cyclogenesis occurred just off the California/Oregon coast north of the AR shortly before landfall
-AR made landfall over southern California at ~0600 UTC 5 January 2016

Above is a sequence of integrated vapor transport (IVT) from the GFS analysis during 31 December 2015 to 5 January 2016 which shows the Atmospheric River propagating towards California and making landfall.

Above is a sequence of Jason Cordeira’s AR Landfall tool initialized between 0600 UTC 29 Dec 2015 and 0600 UTC 5 Jan 2016. The sequence shows how the forecast developed over the previous eight days and shows the skill this tool had in forecasting the AR. For more information on this product visit the AR Forecast page.

– Greater than 50% of ensemble members predicted the landfall of the AR ~8 days in advance
– Greater than 85% of ensemble members predicted the landfall of the AR ~3 days in advance
– AR conditions were not forecasted over southern CA until ~5 days in – advance
– Between days 8 and 3 duration of AR conditions forecasted ranged from ~18–48 hours
– Duration and location of AR conditions remained constant and accurate during days 0–3 forecasts

The following forecast is from the San Diego National Weather Service Forecast Office

The weather pattern in SoCal will be very active this week with several storm systems moving through the region. This afternoon through Wednesday morning will bring moderate to heavy rainfall over the coast, valleys, foothills and deserts, with heavy snowfall occurring in the mountains above 5,500 ft. Total snowfall for the through Wednesday morning will be around a foot for elevations above 5,500 ft, with lesser amounts between 4,500 and 5,500 ft. Rainfall totals through Wednesday morning will be 1 to 1.5 inches west of the mountains with local amounts near 2 inches in the foothills. If you have travel plans at anytime during the week, especially in the mountains, check local conditions and be prepared for inclement weather. Another storm with moderate to high impacts will affect the region Wednesday afternoon through Wednesday night. A third system on Thursday will bring additional rain and mountains snow, but it appears to be less intense than the first two.

Pacific Northwest Storm of 13-15 November 2015: A Synopsis of Landfalling Atmospheric River Conditions

November 25, 2015

CW3E researcher Brian Kawzenuk provides an analysis and synopsis of an Atmospheric River that made landfall along the U.S. Pacific Northwest over the 13-15 November 2015 period. The AR made initial landfall along the Washington coast and lead to significant precipitation for nearly three days throughout western Oregon, Washington, and British Columbia. The AR initially developed near Japan and propagated across the entire North Pacific Ocean before making landfall.

Above is a sequence of 30-minute NEXRAD radar composite imagery from 12-15 November 2015 which shows precipitation throughout the Pacific Northwest during nearly the entire period.

The above loop shows SSMI Integrated Water Vapor during 10-15 November 2015.

A Preliminary Summary of Highway 58 and I-5 Flooding Event of October 15, 2015

October 27, 2015

Nina Oakley (WRCC/DRI), Jeremy Lancaster (CGS), John Stock (USGS), Brian Kawzenuk (CW3E), and Mike Kaplan (DRI) provide an analysis and synopsis of the meteorological and geological conditions that produced alluvial fan flooding over portions of Highway 58 and Interstate 5 in southern California. A weakening cutoff low that had entrained subtropical moisture moved onshore over southern California, initiating convection and localized heavy precipitation. Hillslope runoff concentrated in steep valleys where it entrained debris. The debris then flowed onto steep alluvial fans at the base of these valleys, inundating portions of I-5 and State Hwy 58.

Click here for pdf file of this information.

Improving Understanding of Atmospheric Rivers: Legislation Authorized by California Governor Brown

October 12, 2015

The Center for Western Weather and Water Extremes (CW3E) is grateful for the approval of legislation that will improve California’s ability to respond to major precipitation episodes. This legislation, recently approved, will aim to allow the state of California to better manage water supplies by expanding climate and weather research that is focused on the causes of drought and flood.

The two images below show an example of research aimed at improving forecasting ability. The two maps show the integrated water vapor (IWV) forecast from February 9, 2014. The top panel shows a CW3E simulation by a regional model (called West-WRF). The bottom panel shows a national forecast by the Global Forecasting System (GFS). The CW3E simulation offers a resolution of 9km while the national forecast is at 0.5 degrees (approximately 100km). This improved model forecast horizontal resolution will allow forecasters to better pinpoint heavy precipitation events aimed at the west coast.

Please find more at the Scripps Institution of Oceanography news page: https://scripps.ucsd.edu/news/legislation-improve-understanding-atmospheric-rivers-authorized-governor

Southern California Storm of 18-20 July 2015: A Synopsis of Record Breaking Precipitation

California Storm of 5 January 2016: A Preliminary Synopsis of a Marginal Landfalling Atmospheric River

July 24, 2015

CW3E researcher Brian Kawzenuk provides an analyis and synopsis of an extreme precipitation event over the Southwestern United States during the 18-20 July 2015 period. Former Hurricane Dolores provided high amounts of atmospheric moisture to the Southwestern United States with allowed for multiple showers and thunderstorms to develop on 18 and 19 July 2015. Monthly precipitation records were broken in 48 hours throughout Southern California, which caused multiple landslides and flash floods.

The above loop shows MODIS (Moderate Resolution Imaging Spectroradiometer) true-color during 15-22 July 2015.

Above is a sequence of 30-minute NEXRAD radar composite imagery from 18-20 July 2015 which shows the development of multiple thunderstorms.

Please click here for pdf file of this information.

California Storm of 10-12 December 2014: A Synopsis Including Landfalling Atmospheric River Conditions

July 10, 2015

CW3E researcher Brian Kawzenuk provides an analysis and synopsis of an Atmospheric River that made landfall along the U.S. West Coast over the 10-12 December 2014 period. The AR made initial landfall along the Oregon coast and propagated south before dissipating over southern California. Up to 350 mm of 72-hour precipitation was produced in northern California representing up to 45% of total water year to date precipitation. The precipitation from this event provided many drought-stricken California reservoirs with significant amounts of water supply and improved drought conditions throughout northern California.

Above is a sequence of 30-minute NEXRAD radar composite imagery from 10-13 December 2014 which shows the penetration of the heaviest precipitation.

The above loop shows the strong atmospheric river making landfall and the associated integrated water vapor (color bar in cm).

Please click here for pdf file of this information.

Climate change intensification of horizontal water vapor transport in CMIP5

CW3E Publication Notice

Climate change intensification of horizontal water vapor transport in CMIP5

June 25, 2015

Lavers, D.A., F.M. Ralph, D.E. Waliser, A. Gershunov, and M.D. Dettinger, 2015: Climate change intensification of horizontal water vapor transport in CMIP5. Geophys. Res. Lett., 42, doi:10.1002/2015GL064672.

Projected multimodel mean changes in the mean, standard deviation, and 95th percentile of winter water vapor transport (over 2073-2099) in the RCP4.5 and RCP8.5 scenarios. The multimodel mean percentage changes are shown in the right column. From Lavers et al. (2015).

Research over the last decade has shown that the majority of heavy precipitation and flood events on the western edges of mid-latitude land masses are connected to intense water vapor transport. This vapor transport is found within the atmospheric river region of extratropical cyclones. As climate change is expected to create a warmer atmosphere capable of supporting more water vapor, it is also thought that the global water cycle will intensify leading to more vapor flux and hydrological extremes, such as floods and droughts. Any changes to the water vapor transport by the atmosphere are likely to have hydrological ramifications of great significance to hydrometeorological applications.

The research presented in Lavers et al. (2015) investigates the historical and projected changes to water vapor transport in the latest Climate Model Intercomparison Project Phase 5 archive. Using output from 22 models, robust increases in vapor flux by the end of the 21st Century are found, which suggests the likelihood for larger precipitation and floods in the future. This research was a collaborative effort led by CW3E, with the aim of ascertaining the projected global water cycle changes that may need to be considered in the future.

Abstract

Global warming of the Earth’s atmosphere is hypothesized to lead to an intensification of the global water cycle. To determine associated hydrological changes, most previous research has used precipitation. This study, however, investigates projected changes to global atmospheric water vapor transport (integrated vapor transport (IVT)), the key link between water source and sink regions. Using 22 global circulation models from the Climate Model Intercomparison Project Phase 5, we evaluate, globally, the mean, standard deviation, and the 95th percentiles of IVT from the historical simulations (1979–2005) and two emissions scenarios (2073–2099). Considering the more extreme emissions, multimodel mean IVT increases by 30–40% in the North Pacific and North Atlantic storm tracks and in the equatorial Pacific Ocean trade winds. An acceleration of the high-latitude IVT is also shown. Analysis of low-altitude moisture and winds suggests that these changes are mainly due to higher atmospheric water vapor content.