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.

CW3E Publication Notice: Characterizing the Influence of Atmospheric River Orientation and Intensity on Precipitation Distribution over North-Coastal California

CW3E Publication Notice

Characterizing the Influence of Atmospheric River Orientation and Intensity on Precipitation Distributions over North-Coastal California

Spetember 12, 2017

Chad Hecht, a CW3E staff researcher, and Jason Cordeira, a CW3E affiliate and professor at Plymouth State University, recently published an article in AGU Geophysical Research Letters: Hecht, C. W., and J. M. Cordeira, 2017: Characterizing the Influence of Atmospheric River Orientation and Intensity on Precipitation Distribution over North-Coastal California. Geophys. Res. Lett., 44, doi:10.1002/2017GL074179. click here for personal use pdf file.

The key result of the study found that south-southwesterly oriented atmospheric rivers (ARs) produce significantly more Russian River watershed areal-average precipitation compared to westerly ARs (median areal-precipitation of 13 mm vs. .5 mm). This difference in precipitation accumulations is attributed to both the orientation of water vapor flux relative to the watershed topography and large-scale forcing that results in ascent.

The study uses clustering to objectively identify different orientations and intensities of ARs that make landfall over the California Russian River watershed (Fig. 1). Daily averaged IVT was calculated using 11-years of National Centers for Environmental Prediction (NCEP)–Climate Forecast System Reanalysis (CFSR) data spanning from 1 January 2004 to 31 December 2014. The paper analyzed the synoptic-scale flow configurations and resulting precipitation accumulations and distributions of westerly and south-southwesterly oriented ARs (Orange and Blue clusters in Fig. 1b).

Figure 1. (a) Domain averaged daily IVT direction (angular coordinate) and magnitude (kg m/s ; radial coordinate) for all days from 1 January 2004 to 31 December 2014 that data were available. Markers are color-coded based on 24-h accumulated precipitation (mm). The colored lines illustrate the average IVT for days with precipitation >10 (black), >25 (blue) and >50 mm (red). The 200 kg/m/s threshold that was applied in this study is shown by the black circle. (b) As in (a) except for days with daily average IVT ≥200 kg/m/s and color-coded based on K-means cluster.

Composite analyses illustrate the vastly different synoptic-scale characteristics associated with westerly and south/southwesterly ARs (Cluster 2 and Cluster 3). These different synoptic-scale flow configurations result in differences in synoptic scale forcing co-located over the composite AR and the Russian River watershed (Fig. 2).

Figure 2. (a, b) Composite mean IVT (kg/m/s ; plotted according to the reference vector in the upper right), SLP (hPa; contoured), and IWV (mm; color-coded according to scale), (c, d) composite mean 250-hPa geopotential height (dam; contoured), wind speed (m s–1 ; colorcoded according to scale), and IWV (mm; dashed blue contour), and (e, f) composite mean 700-hPa geopotential height (dam; solid contours), Q-vectors (1011 K/m/s ; plotted according to the reference vector in the bottom right), Q-vector divergence (1016 K/m/s ; color-coded according to scale) and potential temperature (K; dashed red contours) at t–12 h during (a,c,e) westerly and (b,d,f) south–southwesterly ARs.

The large difference in Russian River watershed area-averaged precipitation between westerly and south-southwesterly ARs (Fig. 3a) is not likely explained by statistically similar cluster IVT magnitudes (i.e., AR intensity; Fig. 3b) and IWV values (Fig. 3e) but likely a combination of a more favorable southwesterly IVT direction (i.e., AR orientation) relative to the orientation of the local topography and favorable synoptic-scale forcing for ascent (Fig. 2) illustrated by Q-vector convergence (Fig. 3d). While both AR types exhibit significantly statistically similar mean IVT, south-southwesterly ARs are associated with statistically significantly higher mean low-level IVT (1000–850 hPa; Fig. 3c).

Results from this study suggest that extreme precipitation produced by ARs is the result of both upslope moisture flux and quasi-geostrophic forcing for ascent.

Figure 3. Box and whisker plots of Russian River Watershed (a) area-average 24-h precipitation (mm), (b) domain average IVT (kg/m/s ), (c) domain average lower tropospheric (1000–850 hPa) IVT (kg/m/s ), (d) domain average Q-vector divergence (1016 K/m/s ), and (e) domain average IWV (mm) for westerly (orange) and south–southwesterly (blue) ARs. The boxes represent the interquartile range of the data and the whiskers represent upper and lower quartile of the data. The horizontal line within the boxes is the median value. The colored dots represent outliers and the asterisks represent extreme outliers. The box in the upper-left corner of each panel indicates the result of the independent samples t-test with 95% confidence (white indicates significantly statistically similar means and black indicates significantly statistically different).

Support for this project was provided by the State of California-Department of Water Resources and the U.S. Army Corps of Engineers, both as part of broader projects led by CW3E. A majority of this work was conducted while Chad was a graduate student at Plymouth State University. Dr. Cordeira and his graduate students at Plymouth State University actively collaborate with CW3E on topics related to atmospheric rivers, such as analyzing, understanding, and forecasting their impacts along the U.S. West Coast.

CW3E Publication Notice: Hourly Storm Characteristics along the U.S. West Coast: Role of Atmospheric Rivers in Extreme Precipitation

CW3E Publication Notice

Hourly Storm Characteristics along the U.S. West Coast: Role of Atmospheric Rivers in Extreme Precipitation

July 10, 2017

Fifty-five years of gridded hourly precipitation observations (CPC Hourly U.S. Precipitation) are used in this study to identify storm characteristics which most strongly modulate extreme storms along the U.S. West Coast. By investigating storms at fine (hourly) time scales, we showed that U.S. West Coast storm total precipitation is more strongly modulated by storm durations than by storm intensities, whereas in the Southeast U.S., storm intensities more strongly dictate the storm total precipitation (Figure 1, presented as Figure 2 in Lamjiri et al. [2017]). This study also showed that the most extreme precipitation events along the U.S. West Coast are associated with the most persistent atmospheric rivers, rather than the high intensity ARs. Therefore, it is of high importance to improve forecast skill of the duration of storms over the U.S. West Coast, which provides valuable information that could be used to mitigate flood risks and enhance water reservoir management. More details are provided in the full manuscript, which was published in the AGU journal Geophysical Research Letters: Lamjiri, M. A., M. D. Dettinger, F. M. Ralph, and B. Guan, 2017: Hourly storm characteristics along the U.S. West Coast: Role of atmospheric rivers in extreme precipitation, Geophys. Res. Lett., 44, doi:10.1002/2017GL074193. click here for personal use pdf file

Figure 1 Correlation coefficient of storm-precipitation totals with storm durations (a), maximum intensities (b), and average intensities(c) based on hourly precipitation observations from 1948-2002.


Abstract

Gridded hourly precipitation observations over the conterminous US, from 1948 to 2002, are analyzed to determine climatological characteristics of storm precipitation totals. Despite generally lower hourly intensities, precipitation totals along the U.S. West Coast (USWC) are comparable to those in Southeast U.S. (SEUS). Storm durations, more so than hourly intensities, strongly modulate precipitation-total variability over the USWC, where the correlation coefficients between storm durations and storm totals range from 0.7 to 0.9. Atmospheric rivers (ARs) contribute 30-50% of annual precipitation on the USWC, and make such large contributions to extreme storms that 60-100% of the most extreme storms, i.e. storms with precipitation-total return intervals longer than two years, are associated with ARs. These extreme storm totals are more strongly tied to storm durations than to storm hourly or average intensities, emphasizing the importance of AR persistence to extreme storms on the USWC.

CW3E Undergraduate Researcher, Cody Poulsen, Awarded a SDEP Excellence Award

CW3E Undergraduate Researcher, Cody Poulsen, Awarded a SDEP Excellence Award

June 28, 2017

Cody Poulsen, an undergraduate student at UC San Diego pursuing a degree in Environmental Chemistry in the Environmental Systems (ESYS) Department and a minor in Digital Media, has collaborated on a research project with CW3E post-doc Scott Sellars. The project began during the summer of 2016 and was focused on using a program created by the Monterey Bay Aquarium Research Institute (MBARI) named Video Annotation Reference Systems (VARS) to produce useable meteorological metadata. VARS was created by MBARI to aid researchers in cataloguing the occurrences of biological species and geological formations in the large amounts of underwater footage collected by their ROVs. The research continued as part of Cody’s senior thesis during which he created an Atmospheric River metadata set with VARS. During the process, he learned more about the system and its capabilities. The metadata set is comprised of annotations for the location of AR landfall and center of AR events during the Water Years (WYs) 2001 and 2011. In addition, annotations for ARs with an associated Lower Level Jet (LLJ) structure where produced for both WYs. In the case study of WYs 2001 and 2011, the metadata depicted an anomalously high amount of landfalling AR events in California/Oregon for December 2010 juxtaposed to zero landfalling events along the North American West Coast excluding Alaska for December 2000. 500-hPa average wind speeds, heights, & direction plots for the two months where created to discern the general first principal flow that might explain the different AR trajectories. With these plots, it was found that a high-pressure ridge at 180° and low pressure trough at 140°W funneled ARs onto the California/Oregon coast for December 2010. Where December 2000 had a slight high pressure ridge along the coast to produce an insignificant blocking action leading to the assumption that some other synoptic features must be at play to produce the zero-event period.

For his senior thesis, Cody produced a poster on the VARS research project and presented it at the ESYS senior symposium. The symposium was comprised of poster presentations from each of the ESYS seniors that participated in research projects/ internships over their senior year. Cody and his research were selected by San Diego Environmental Professionals (SDEP) as one of the two projects to win an excellence award.

CW3E undergraduate researcher, Cody Poulsen, presents his research using VARS at the ESYS senior symposium.

CW3E AR Update: 06 June 2017 Outlook

CW3E AR Update: 06 June 2017 Outlook

June 06, 2017

Click here for a pdf of this information.

Update on Late Season AR Forecast to Impact West Coast This Week

  • Little change from yesterday’s forecast
  • Ensemble GFS members are still in good agreement of the onset, duration, and maximum magnitude of coastal IVT
  • NOAA WPC precipitation forecasts are predicting as much as 4.2 inches over the Coastal Mountains of Northern CA and OR
  • A few rivers in the Cascade Range of WA and OR are forecast to rise to action or flood stage due to melting snow and the landfalling AR

Click IVT or IWV image to see loop of 0-114 hour GFS forecast

Valid 1200 UTC 06 June – 0600 UTC 11 June 2017


 

 

 

 

 

 

Summary provided by C. Hecht and F.M. Ralph; 12 PM PT Tuesday 06 June 2017

CW3E AR Update: 05 June 2017 Outlook

CW3E AR Update: 05 June 2017 Outlook

June 05, 2017

Click here for a pdf of this information.

Late Season AR Forecast to Impact West Coast

  • An unseasonably strong AR is forecast to impact the Pacific Northwest and Northern CA over the next couple of days
  • As much as 4.1 inches of precipitation is forecast to fall over the higher elevations of the Coastal Mountains in CA and OR over the next week
  • With higher freezing levels forecast during landfall, there is a potential for rain on snow and increased runoff
  • Due to the combination of snowmelt and the landfalling AR, several rivers in the Pacific Northwest are forecast to rise above flood stage

Click IVT or IWV image to see loop of 0-114 hour GFS forecast

Valid 1200 UTC 05 June – 0600 UTC 10 June 2017


 

 

 

 

 

 

Summary provided by C. Hecht and F.M. Ralph; 1 PM PT Monday 05 June 2017