CW3E AR Update: 17 November 2017 Outlook and Summary

CW3E AR Update: 17 November 2017 Outlook and Summary

November 17, 2017

Click here for a pdf of this information.

Strong AR recently made landfall over northern California

  • The AR reached its strongest magnitude of ~750 kg m-1 s-1 at ~6 PM PST over northern California making this a strong AR
  • IWV values within the AR ranged from 34–40 mm during the event
  • A second AR is forecast to make landfall over the USWC between 19 and 21 November 2017
  • The AR is currently over Southern California bringing precipitation to the Los Angeles area
  • Another AR is forecast to impact the USWC in the next several days

SSMI/SSMIS/AMSR2-derived Integrated Water Vapor (IWV)

Valid 0000 UTC 15 November – 1600 UTC 17 November 2017

Images from CIMSS/Univ. of Wisconsin

Click IVT or IWV image to see loop of GFS Analysis

Valid 0000 UTC 15 November – 1200 UTC 17 November 2017


 

 

A potentially extreme AR is forecasted to make landfall over the U.S. West Coast next week

  • The current AR impacting Southern California is forecast to end by later tonight
  • Multiple systems are forecast to bring potentially strong to extreme and prolonged AR conditions to the USWC
  • As much as 19 inches of precipitation could fall over the Olympic Mountains over the next week
  • Multiple rivers in Washington are currently forecast to rise above flood stage

Click IVT or IWV image to see loop of 0-180 hour GFS forecast

Valid 1200 UTC 17 November – 0000 UTC 25 November 2017

 

 

 

 

 

 

Summary provided by C. Hecht, B. Kawzenuk, J. Kalansky, and F.M. Ralph; 3 PM PT Friday 17 November 2017

*Outlook products are considered experimental

CW3E AR Update: 8 November 2017 Outlook

CW3E AR Update: 8 November 2017 Outlook

November 8, 2017

Click here for a pdf of this information.

Two ARs Forecasted to Make Landfall over the U.S. West Coast in the Next Week

  • A strong AR is currently making landfall over the U.S. West Coast
  • This AR is expected to produce up to 6 inches of precipitation over northern CA
  • The southerly orientation of this AR will result in the heaviest precipitation over the north Central Valley
  • A second, moderate strength, AR is forecasted to make landfall over northern CA, OR, and WA on 12 November 2017
  • The second AR is expected to make landfall further north resulting in the highest precipitation over the Olympic and Cascade

Click IVT or IWV image to see loop of 0-168 hour GFS forecast

Valid 1200 UTC 8 November – 1200 UTC 15 November 2017


 

 

 

 

 

Summary provided by B. Kawzenuk, J. Kalansky, and F.M. Ralph; 12 PM PT Wednesday 8 November 2017

*Outlook products are considered experimental

Atmospheric Rivers Highlighted in the U.S. Fourth National Climate Assessment

Atmospheric Rivers Highlighted in the U.S. Fourth National Climate Assessment

November 6, 2017

Click here for a pdf of this information.

The Fourth National Climate Assessment, released last week, highlights atmospheric rivers as a key topic of its chapter on “Extreme Storms.” The other storm types addressed in this section are “tropical storms (hurricanes and typhoons),” “severe convective storms (thunderstorms)” and “winter storms.

The “Key findings” on atmospheric rivers are: “The frequency and severity of landfalling “atmospheric rivers” on the U.S. West Coast (narrow streams of moisture that account for 30%–40% of the typical snowpack and annual precipitation in the region and are associated with severe flooding events) will increase as a result of increasing evaporation and resulting higher atmospheric water vapor that occurs with increasing temperature. (Medium confidence).”

This major report further highlighted the atmospheric river topic by using a satellite image of an atmospheric river hitting the U.S. West Coast in February 2017 for the cover page of the entire report.


 

 

Contacts: Duane Waliser, F. Martin Ralph

CW3E AR Update: 3 November 2017 Outlook

CW3E AR Update: 3 November 2017 Outlook

November 3, 2017

Click here for a pdf of this information.

Two systems expected to produce precipitation over the U.S. West Coast in the next week

  • AR conditions (IVT >250 kg m-1 s-1 and IWV >20 mm) are expected over most of CA over the next four days
  • While AR conditions are forecast for some locations of the USWC, this event is not necessarily an AR due to geometric and spatial structure, but could produce up to 5 inches of precipitation and some snow over the Sierra Nevada
  • A potentially strong AR is expected to make landfall over CA, OR, and WA on 8 November 2017
  • The highest amounts of precipitation are expected over the coastal ranges of CA and OR
  • The AR is currently expected to have a southerly orientation which will result in less extreme precipitation

Click IVT or IWV image to see loop of 0-180 hour GFS forecast

Valid 1200 UTC 3 November – 0000 UTC 11 November 2017


 

 

 

 

 

 

 

Summary provided by B. Kawzenuk, J. Kalansky, C. Hecht, and F.M. Ralph; 3 PM PT Friday 3 November 2017

*Outlook products are considered experimental

CW3E AR Update: 31 October 2017 Outlook

CW3E AR Update: 31 October 2017 Outlook

October 31, 2017

Click here for a pdf of this information.

Atmospheric River to potentially make landfall over California

  • A weak to moderate AR is predicted to make landfall over California during 3-8 November 2017
  • Current forecasts indicate the geometry of the AR conditions may not meet standard criteria to be considered and AR by AR conditions (IVT >250 kg m-1 s-1 and IWV >20 mm) are expected to impact the majority of CA
  • Precipitation amounts up to 5 inches are expected over the Sierra Nevada with the majority of CA receiving at least 0.25 inches of precipitation
  • Forecast certainty is currently low on timing and strength of AR conditions but confidence of at least weak AR conditions over central and southern CA is high

Click IVT or IWV image to see loop of 72-180 hour GFS forecast

Valid 1200 UTC 3 November – 0000 UTC 8 November 2017


 

 

 

 

 

Summary provided by B. Kawzenuk, J. Kalansky, C. Hecht, and F.M. Ralph; 3 PM PT Tuesday 31 October 2017

*Outlook products are considered experimental

CW3E AR Update: 18-23 October 2017 Summary

CW3E AR Update: 18-23 October 2017 Summary

October 26, 2017

Click here for a pdf of this information.

Two Early Season Atmospheric Rivers Make Landfall over the Pacific Northwest

  • The first AR made landfall over WA and OR ~1200 UTC 18 October 2017
  • This AR produced >300 mm of precipitation over the Olympic Mountains in 72 hours (R-Cat 2)
  • The second AR made landfall over OR ~0600 UTC 21 October 2017
  • This AR produced >400 mm of precipitation over the Cascade Mountains in OR in 72 hours (R-Cat 3)

Click IVT or IWV image to see loop of GFS analysis

Valid 0000 UTC 18 October – 0000 UTC 24 October 2017

SSMI/SSMIS/AMSR2-derived Integrated Water Vapor (IWV)

Valid 0000 UTC 18 October – 0000 UTC 24 October 2017

Images from CIMSS/Univ. of Wisconsin

 

 

 

 

Summary provided by B. Kawzenuk, C. Hecht, and F.M. Ralph; 1 PM PT Thursday 26 October 2017

CW3E Graduate Student to Participate in United Nations Convention Next Month

CW3E Graduate Student to Participate in United Nations Convention Next Month

October 23, 2017

Tashiana Osborne, a graduate student within CW3E, will be attending the 23rd United Nations Framework Convention on Climate Change in Bonn, Germany next month. During the convention, Tashiana will lead a press conference centered on oceanic and atmospheric phenomena with another Scripps student. Her attendance at the Convention along with two other Scripps graduate students was highlighted in a recent San Diego Union Tribune article. Tashiana was interviewed about atmospheric rivers and their importance to California’s water supply as well as their potential to lead to flooding. Read more here about Tashiana and other graduate students heading to the Convention on Climate Change.

CW3E AR Update: 18 October 2017 Outlook

CW3E AR Update: 18 October 2017 Outlook

October 18, 2017

Click here for a pdf of this information.

Multiple ARs forecast to Impact U.S. West Coast

  • A potentially extreme AR is forecast to make landfall over the Pacific Northwest today
  • NWS precipitation forecasts show accumulations of ~10 inches for the Olympic Mountains in northwest Washington
  • A second AR is forecast to make landfall on Saturday, though forecast uncertainty is currently high
  • Total 5-day precipitation accumulations could be as high as 15.5 inches
  • Current soil conditions are dry which could lead to less runoff and lower flooding potential

Click IVT or IWV image to see loop of 0-141 hour GFS forecast

Valid 0600 UTC 18 October – 0300 UTC 24 October 2017

For more information on the satellite imagery and the configuration click here

 

 

 

 

 

 

Summary provided by C. Hecht, B. Kawzenuk, and F.M. Ralph; 1 PM PT Wednesday 18 October 2017

*Outlook products are considered experimental

CW3E Releases New Interactive Geospatial Observation and Forecast Maps

CW3E Releases New Interactive Geospatial Observation and Forecast Maps

Spetember 18, 2017

CW3E has released a new interactive mapping tool that takes advantage of “web mapping services”, GIS-based coding/thinking, and interactive technologies in order to provide dynamic weather analysis graphics in support of the CW3E mission. These interactive maps allow the user to display and interact with numerous variables from a synoptic to a watershed scale with the goal of providing insight into potential impacts of landfalling atmospheric rivers over California.

This interactive tool was developed as a means to geospatially visualize meteorological and hydrologic observations on a new platform and from a new perspective. This first set of maps/webpages illustrate the utility of the tool in displaying atmospheric river related forecast products and CW3E will continue to build upon the tool. As we continue to experiment in improving and expanding the tool, we encourage any feedback or suggestions. Please contact the website creator or the CW3E Webmaster with any questions or feedback you may have.

The development of the tool and maps/webpage is supported by the California Department of Water Resources. The page was created and developed by CW3E collaborator Dr. Jason Cordeira and CW3E Director Dr. F. Martin Ralph with input from CW3E researchers Brian Kawzenuk, Chad Hecht, and Dr. Julie Kalansky.

Click here to view the new interactive geospatial observation and forecast maps.

CW3E Publication Notice: Dropsonde Observations of Total Integrated Water Vapor Transport within North Pacific Atmospheric Rivers

CW3E Publication Notice

Dropsonde Observations of Total Integrated Water Vapor Transport within North Pacific Atmospheric Rivers

Spetember 14, 2017

F. Martin Ralph, director of CW3E, along with collaborators, recently published a paper in the American Meteorological Society’s Journal of Hydrometeorology: Ralph, F. M., S. Iacobellis, P. Neiman, J. Cordeira, J. Spackman, D. Waliser, G. Wick, A. White, and C. Fairall, 2017: Dropsonde Observations of Total Integrated Water Vapor Transport within North Pacific Atmospheric Rivers. J. Hydrometeor., 18, 2577-2596, https://doi.org/10.1175/JHM-D-17-0036.1

This study uses vertical profiles of water vapor, wind, and pressure obtained from 304 aircraft dropsondes across 21 ARs, in the midlatitudes as well as the subtropics, which were deployed during various experiments since the winter of 1998, including CALJET (Ralph et al. 2004), Ghostnets (Ralph et al. 2011), WISPAR (Neiman et al. 2014), CalWater-2014, CalWater-2015 (Ralph et al. 2016), and AR Recon-2016. Dropsondes provide the best measurements to date of horizontal water vapor transport in atmospheric rivers (ARs) and can document AR structure. Different methods of defining AR edges, using either integrated vapor transport (IVT) or integrated water vapor (IWV), were compared.

The study found that total water vapor transport (TIVT) in an AR averaged nearly 5×108 kg s-1, which is 2.6 times larger than the average discharge of liquid water from the Amazon River. The mean AR width was 890 ± 270 km. Subtropical ARs contained larger IWV but weaker winds than midlatitude ARs, although average TIVTs were nearly the same. Mean TIVTs calculated with an IVT-threshold versus an IWV- threshold produced results that differed by only 4% on average, although they did vary more between midlatitudes and subtropical regions. In general, important AR characteristics such as width and TIVT are less dependent on latitude when the IVT-threshold is used, and the IWV threshold often was not crossed on the warm side of subtropical ARs, so IVT represents a more robust threshold across a wider range of conditions than IWV.

Results were summarized in a schematic to illustrate the AR structure in 3 dimensions (see below). This schematic was used in the AR definition that was recently published in the American Meteorological Society’s Glossary of Meteorology.

Figure 1: Schematic summary of the structure and strength of an atmospheric river based on dropsonde measurements analyzed in this study, and on corresponding reanalyses that provide the plan-view context. (a) Plan view including parent low pressure system, and associated cold, warm, stationary and warm-occluded surface fronts. IVT is shown by color fill (magnitude, kg m-1 s-1) and direction in the core (white arrow). Vertically integrated water vapor (IWV, cm) is contoured. A representative length scale is shown. The position of the cross-section shown in panel (b) is denoted by the dashed line A-A’. (b) Vertical cross-section perspective, including the core of the water vapor transport in the atmospheric river (orange contours and color fill) and the pre-cold-frontal low-level jet (LLJ), in the context of the jet-front system and tropopause. Water vapor mixing ratio (green dotted lines, g kg-1) and cross-section-normal isotachs (blue contours, m s-1) are shown. Magnitudes of variables represent an average mid-latitude atmospheric river with lateral boundaries defined using the IVT threshold of 250 kg m-1 s-1. Depth corresponds to the altitude below which 75% of IVT occurs. Adapted primarily from Ralph et al. 2004 and Cordeira et al. 2013.