CW3E Fieldwork Season Begins

CW3E Fieldwork Season Begins

January 10, 2018

A team of CW3E postdocs, students, staff, and collaborators headed to Northern California on Sunday, 7 January to begin the winter 2018 fieldwork campaign. Throughout this winter season, CW3E plans to release radiosondes, conduct stream surveys, and collect isotope samples. The campaign aims to continue efforts in understanding atmospheric rivers (ARs) and their impacts on the Russian River Watershed. In support of the Forecast Informed Reservoir Operation (FIRO), hydrometeorological data from the campaign will be used to enhance water resources and flood control operations.

The team is launching from two sites: a coastal site, the UC Davis Bodega Bay Marine Laboratory and an inland site in Ukiah, CA, southwest of Lake Mendocino. These launches are being shared with National Weather Service Weather Forecast Offices in Eureka, Sacramento, and Monterey. Peak launches recorded 511 units integrated water vapor transport (IVT) at Bodega Bay (0000Z 9 January 2018) and 389 units IVT at Ukiah (2100Z 8 January 2018).

A radiosonde launch completed in Bodega Bay (0259Z 9 January 2018) shows a sounding with typical AR conditions.


Note: no orographic enhancement present (NOAA Earth System Research Laboratory)


The Regional and Mesoscale Meteorology Branch (RAMMB) of NOAA/NESDIS and Cooperative Institute for Research in the Atmosphere (CIRCA)


Leah Campbell and Anna Wilson, Postdocs, prepare to release radiosondes from Bodega Bay


Photograph taken at the mouth of the Russian River after the storm.

Other members of the team have been working on stream installations and measurements, along with isotope sampling. Working with the Sonoma County Water Agency (SCWA), CW3E has begun inventorying supplies to continue using the stream gauges that were installed during the previous fieldwork season. They have completed discharge measurements at five of the six streams where gauges are deployed, and will complete measurements at the remaining site today.

The team will continue collecting data and releasing radiosondes throughout this event with plans to return to sample ARs as they occur in the coming months. CW3E will also be partnering with NOAA and the U.S. Air Force, as part of the field campaign, for a series of Reconnaissance (Recon) flights into AR events. The AR Recon missions will start on 25 January, and continue through 28 February. In addition to the NOAA G-IV aircraft, flying out of Seattle for three storms, the campaign will also include two Air Force C-130s that will fly through a total of six storms, overlapping with the NOAA G-IV for three storms. These flights are a valuable method in improving the forecasting of AR conditions offshore and can provide enhanced prediction of AR landfall duration and intensity.

Odds of Reaching 100% Water Year Precipitation – Jan Update

Odds of Reaching 100% of Normal Precipitation for Water Year 2018 (January Update)

January 8, 2018

Contribution from Dr. M.D. Dettinger, USGS

The odds shown here are the odds of precipitation in the rest of the water year (after December 2017) totaling a large enough amount to bring the water-year total to equal or exceed the percentage of normal listed. “All Yrs” odds based on monthly divisional precipitation totals from water year 1896-2015. Numbers in parenthesis are the corresponding odds if precipitation through December had been precisely normal (1981-2010 baseline).

Click here for a pdf file of this information.

 

 

 

How these probabilities were estimated:

At the end of a given month, if we know how much precipitation has fallen to date (in the water year), the amount of precipitation that will be required to close out the water year (on Sept 30) with a water-year total equal to the long-term normal is just that normal amount minus the amount received to date. Thus the odds of reaching normal by the end of the water year are just the odds of precipitation during the remaining of the year equaling or exceeding that remaining amount.

To arrive at the probabilities shown, the precipitation totals for the remaining months of the water year were tabulated in the long-term historical record and the number of years in which that precipitation total equaled or exceeded the amount still needed to reach normal were counted. The fraction of years that at least reached that threshold is the probability estimate. This simple calculation was performed for a full range of possible starting months (from November thru September) and for a wide range of initial (year-to-date) precipitation conditions. The calculation was also made for the probabilities of reaching 75% of normal by end of water year, 125%, and 150%, to ensure that the resulting tables of probabilities cover almost the full range of situations that will come up in the future.

[One key simplifying assumption goes into estimating the probabilities this way: The assumption that the amount of precipitation that will fall in the remainder of a water year does not depend on the amount that has already fallen in that water year to date. This assumption was tested for each month of the year by correlating historical year-to-date amounts with the remainder-of-the-year amounts, and the resulting correlations were never statistically significantly different from zero, except possibly when the beginning month is March, for which there is a small positive correlation between Oct-Mar and Apr-Sept precipitation historically.]

Contact: Michael Dettinger (USGS)

Odds of Reaching 100% Water Year Precipitation – Dec Update

Odds of Reaching 100% of Normal Precipitation for Water Year 2018 (December Update)

December 8, 2017

Contribution from Dr. M.D. Dettinger, USGS

The odds shown here are the odds of precipitation in the rest of the water year (after November 2017) totaling a large enough amount to bring the water-year total to equal or exceed the percentage of normal listed. “All Yrs” odds based on monthly divisional precipitation totals from water year 1896-2015. Numbers in parenthesis are the corresponding odds if precipitation through November had been precisely normal (1981-2010 baseline).

Click here for a pdf file of this information.

 

 

 

How these probabilities were estimated:

At the end of a given month, if we know how much precipitation has fallen to date (in the water year), the amount of precipitation that will be required to close out the water year (on Sept 30) with a water-year total equal to the long-term normal is just that normal amount minus the amount received to date. Thus the odds of reaching normal by the end of the water year are just the odds of precipitation during the remaining of the year equaling or exceeding that remaining amount.

To arrive at the probabilities shown, the precipitation totals for the remaining months of the water year were tabulated in the long-term historical record and the number of years in which that precipitation total equaled or exceeded the amount still needed to reach normal were counted. The fraction of years that at least reached that threshold is the probability estimate. This simple calculation was performed for a full range of possible starting months (from November thru September) and for a wide range of initial (year-to-date) precipitation conditions. The calculation was also made for the probabilities of reaching 75% of normal by end of water year, 125%, and 150%, to ensure that the resulting tables of probabilities cover almost the full range of situations that will come up in the future.

[One key simplifying assumption goes into estimating the probabilities this way: The assumption that the amount of precipitation that will fall in the remainder of a water year does not depend on the amount that has already fallen in that water year to date. This assumption was tested for each month of the year by correlating historical year-to-date amounts with the remainder-of-the-year amounts, and the resulting correlations were never statistically significantly different from zero, except possibly when the beginning month is March, for which there is a small positive correlation between Oct-Mar and Apr-Sept precipitation historically.]

Contact: Michael Dettinger (USGS)

CW3E Publication Notice: Flood runoff in relation to water vapor transport by atmospheric rivers over the western United States

CW3E Publication Notice

Flood runoff in relation to water vapor transport by atmospheric rivers over the western United States

December 1, 2017

CW3E long-time collaborator, Mike Dettinger, and USGS colleague, recently published a paper in Geophysical Research Letter titled: Flood runoff in relation to water vapor transport by atmospheric rivers over the western United States.

In the study they analyzed historical flood flows at over 5000 streamgages across the western US in relation to landfalling atmospheric-river storms. Specifically, they focused on the probabilities of floods flows occurring as conditioned by the presence of an atmospheric river and by the water vapor-transport rates in the atmospheric river. Through this analysis they were able to show that stronger the atmospheric river, the more likely are flood flows to develop.

Along the west coast, these peak flows coincide with atmospheric rivers about 80+% of the time, falling off to about 40-50% of the time in southern California, and falling off the farther inland the river basin (with notable regional anomalies, e.g., around Phoenix and in northern Idaho).

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 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: The Chiricahua Gap and the Role of Easterly Water Vapor Transport in Southeastern Arizona Monsoon Precipitation

CW3E Publication Notice

The Chiricahua Gap and the Role of Easterly Water Vapor Transport in Southeastern Arizona Monsoon Precipitation

Spetember 13, 2017

Click here for personal use pdf file

This study is a collaborative effort between CW3E and University of Arizona that identifies a terrain feature along the Arizona-New Mexico border just north of Mexico that is potentially important to the weather and climate of the southeast Arizona summer monsoon. The terrain feature is a “gap” that is approximately 250 km across and 1 km deep and represents the lowest terrain elevation along the 3000-km length the Continental Divide from 16-45°N. The name “Chiricahua Gap” is introduced to identify this key terrain feature, which reflects the name of a nearby mountain range in southeast Arizona and the region’s Native American history. The importance of the Chiricahua Gap is that it represents the primary pathway in which low altitude atmospheric water vapor is transported across the Continental Divide.

Motivated by identification of the Chiricahua Gap, upper-air observations from a wind profiling radar in Tucson, model reanalyses (Climate Forecast System Reanalysis), and gridded daily precipitation data (NCEP Stage-IV) are used to construct a case study and 15-year climatology to link summer monsoon rainfall events in southeast Arizona to low-altitude water vapor transport within the Chiricahua Gap. The results show that 76% of the wettest summer monsoon days in southeast Arizona during 2002-2016 occurred in conditions of low-altitude easterly water vapor transport in the Chiricahua Gap on the previous day. This result highlights how low-altitude water vapor associated with the wettest summer monsoon days in southeast Arizona originates from the east side of the Continental Divide, which differs from previous studies published since the 1970s. Much of the recent scientific literature points to southwesterly surges of low-altitude water vapor from over the Gulf of California as the primary driver of rainfall over southern Arizona during the summer monsoon. The current study by F. M. Ralph and T. J. Galarneau shows that the source region of low-altitude water vapor in southeast Arizona during the summer monsoon is potentially more complex, and is significantly influenced by source regions east of the Divide.

The paper is an example of CW3E expanding its research to examine the dynamics of the North American monsoon. Because monsoon is an important source or water for the US southwest and can cause flooding events, particularly flash floods, better understanding and improving forecasts of the North American monsoon is and important component of CW3E achieving its goal of revolutionizing the physical understanding, observations, weather predictions, of extreme events in Western North America and their impacts on floods, droughts, hydropower, ecosystems and the economy.

Figure 1: Terrain height (shaded in m) over Arizona, New Mexico, western Texas, and northern Mexico. Key terrain features are labeled in black. The location of Tucson, Arizona, is labeled by the black-filled circle. Low-altitude easterly water vapor transport through the Chiricahua Gap is shown by the blue arrows. This figure is modified from Fig. 1b in Ralph and Galarneau (2017).

CW3E Field Team Beats the Heat, Installs Meteorology and Hydrology Instruments in Russian River Watershed

CW3E Field Team Beats the Heat, Installs Meteorology and Hydrology Instruments in Russian River Watershed

September 6, 2017

A group of CW3E graduate students, postdocs, and staff worked to install soil moisture, meteorology, and streamflow instruments in the Lake Mendocino watershed August 28 – September 1. Taking extra precautions and shifting work schedules due to California’s triple-digit heat wave, the team installed three soil moisture and surface meteorology arrays and a stream gauge on ranchlands representative of the hilly topography draining into Lake Mendocino. CW3E thanks the landowners who have volunteered to have instruments installed on their properties, as well as Steve Turnbull of the U.S. Army Corps of Engineers for participating in the installations. Two more soil moisture and meteorology arrays and three more stream gauges are planned to be installed in the watershed prior to the 2017-18 AR season for a total of six soil moisture and meteorology arrays and six stream gauges. The data from these sites will be used to better understand AR meteorological and hydrologic impacts in this region and improve streamflow forecasts on the Russian River.

The field team after completion of the Potter Valley North site: Lindsey Jasperse, Steve Turnbull, Will Chapman, Maryam Asgari-Lamjiri, Douglas Alden, Anna Wilson and Xin Zhang. Not pictured: Julie Kalansky and Brian Henn

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.