CW3E AR Update: 19 March 2018 Outlook

CW3E AR Update: 19 March Outlook

March 19, 2018

Click here for a pdf of this information.

Update on Atmospheric River Forecast to Impact California Next Week

  • Several changes have occurred in the forecast for the AR that may impact CA this week
  • GFS Ensemble members have continued to converge on Coastal AR conditions
  • While there is more agreement between GFS Ensemble members there are still numerous changes from model run to model run, introducing several uncertainties in the impacts associated with this event

Click IVT or IWV image to see loop of 0-102 hour GFS forecast

Valid 1200 UTC 18 March – 1800 UTC 23 March 2018

 

 

 

 

 

 

 

 

Summary provided by C. Hecht, F.M. Ralph, and B. Kawzenuk; 1 PM PT Monday 19 March 2018

*Outlook products are considered experimental

CW3E AR Update: 16 March 2018 Outlook

CW3E AR Update: 16 March Outlook

March 16, 2018

Click here for a pdf of this information.

Update on Atmospheric River Forecast to Impact California Next Week

  • Several changes have occurred in the forecast for the AR that may impact CA later next Week
  • GFS Ensemble members have started to converge on coastal AR conditions
  • While there is more agreement between ensemble members, there is still considerable uncertainty in onset, duration, and magnitude of AR conditions

Click IVT or IWV image to see loop of 18-180 hour GFS forecast

Valid 0600 UTC 17 March – 0000 UTC 24 March 2018

 

 

 

 

 

 

 

Summary provided by C. Hecht, F.M. Ralph, and B. Kawzenuk; 3 PM PT Friday 16 March 2018

*Outlook products are considered experimental

CW3E AR Update: 15 March 2018 Outlook

CW3E AR Update: 15 March Outlook

March 15, 2018

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A potentially moderate strength atmospheric river is forecast to impact Southern California

  • An AR is currently forecast to impact Southern California on 21 and 22 March 2018
  • Some GFS ensemble members are indicating that this AR could be moderate strength (IVT >500 m-1 s-1)
  • There is currently large uncertainty pertaining to the magnitude and duration of this event
  • CW3E’s high resolution West-WRF model suggests this event is capable of producing 2-4 inches of precipitation over portions of Southern California

Click IVT or IWV image to see loop of 48-180 hour GFS forecast

Valid 0600 UTC 17 March – 1800 UTC 22 March 2018

 

 

 

 

 

Summary provided by C. Hecht, F.M. Ralph, B. Kawzenuk, and J. Cordeira; 12:30 PM PT Thursday 15 March 2018

*Outlook products are considered experimental

CW3E AR Update: 7 March 2018 Outlook

CW3E AR Update: 7 March Outlook

March 7, 2018

Click here for a pdf of this information.

Weak Atmospheric River expected to impact the U.S. West Coast this week

  • A weak or potentially moderate AR is expected to make landfall over northern CA and the Pacific Northwest on 8 March 2018
  • This AR will produce precipitation over the Pacific Northwest and northern CA over the next three days
  • Precipitation amounts during this event are not expected to be extreme, with the highest accumulations predicted to be less than 3 inches

Click IVT or IWV image to see loop of 0-78 hour GFS forecast

Valid 0600 UTC 7 March – 1200 UTC 10 March 2018

 

 

 

 

 

A second AR is expected to make landfall this weekend

  • A second weak Atmospheric River is expected to make landfall over southern CA and Baja CA on 10 March 2018
  • This AR is expected to produce precipitation over the southern CA with two day accumulations of less than 1 inch

Click IVT or IWV image to see loop of 60-120 hour GFS forecast

Valid 1800 UTC 9 March – 0600 UTC 12 March 2018

 

 

 

 

 

Summary provided by B. Kawzenuk, J. Kalansky, and F.M. Ralph; 12 PM PT Wednesday 7 March 2018

*Outlook products are considered experimental

CW3E Publication Notice: High-Elevation Evapotranspiration Estimates During Drought: Using Streamflow and NASA Airborne Snow Observatory SWE Observations to Close the Upper Tuolumne River Basin Water Balance

CW3E Publication Notice

High-Elevation Evapotranspiration Estimates During Drought: Using Streamflow and NASA Airborne Snow Observatory SWE Observations to Close the Upper Tuolumne River Basin Water Balance

March 5, 2018

CW3E postdoc Brian Henn has published a study on estimating evapotranspiration (ET) in California’s Sierra Nevada in Water Resources Research titled High-Elevation Evapotranspiration Estimates During Drought: Using Streamflow and NASA Airborne Snow Observatory SWE Observations to Close the Upper Tuolumne River Basin Water Balance. The study leveraged NASA Airborne Snow Observatory (ASO) and distributed streamflow observations and a basin-scale mass balance approach to estimate ET across the upper Tuolumne River watershed region over three warm seasons (2013-2015), showing spatially coherent totals of about 200 mm per year of ET for these high-elevation areas during California’s recent drought. This represents a novel application of ASO and mass balance approaches to estimate ET at the watershed scale, which is difficult to observe directly. The Tuolumne watershed and others like it the Sierra Nevada are critical water supply areas for California, and changes in ET in the future could impact the reliability of major reservoirs.

The paper was written in collaboration with Tom Painter and Kat Bormann of the NASA ASO team, Bruce McGurk of McGurk Hydrologic, Lorraine and Alan Flint of the USGS, Vince White of Southern California Edison, and Jessica Lundquist of the University of Washington. Please contact Brian at bhenn@ucsd.edu with inquiries.

Figure 1. Figure (1) from Henn et al. (2018): (a) ASO lidar-derived 50 m SWE map for 3 April 2013, over the basin of the Tuolumne River at Highway 120. (b) Example plot for this ASO flight, showing how the basin’s water balance is quantified. All SWE from the 3 April flight is assumed to melt by 30 September ( math formula); cumulative streamflow ( math formula) and precipitation ( math formula) between the flight date and 30 September are then calculated. Uncertainty bounds at 95% confidence are shown for each variable.

Henn, B., Painter, T. H., Bormann, K. J., McGurk, B., Flint, A. L., Flint, L. E., White, V., Lundquist, J. D. (2018). High-elevation evapotranspiration estimates during drought: Using streamflow and NASA airborne snow observatory SWE observations to close the upper tuolumne river basin water balance. Water Resources Research, 54. https://doi.org/10.1002/2017WR020473

CW3E Publication Notice: Global Assessment of Atmospheric River Prediction Skill

CW3E Publication Notice

Global Assessment of Atmospheric River Prediction Skill

February 27, 2018

CW3E collaborators Michael DeFlorio (NASA/JPL), Duane Waliser (NASA/JPL), and Bin Guan (UCLA), along with CW3E director Marty Ralph and colleagues David Lavers and Frederic Vitart of the European Centre for Medium-Range Weather Forecasts (ECMWF), recently published a paper in the Journal of Hydrometeorology titled Global Assessment of Atmospheric River Prediction Skill (early online release; doi:10.1175/JHM-D-17-0135.1). The study introduces the Atmospheric River Skill (ATRISK) algorithm, which is an object-based approach used to quantify atmospheric river (AR) prediction skill using Subseasonal to Seasonal (S2S) Project global hindcast data from ECMWF. Two decades of data from this ensemble hindcast system were used in this work. The ATRISK algorithm determines the distance between the centroids of observed and forecasted ARs (an adjustable parameter; see Fig. 1), which can be used to compute relative operating characteristic (ROC) curves. DeFlorio et. al (2018) shows that climate variability conditions modulate regional AR forecast skill. In particular, over the US West Coast, AR forecast utility (defined as the ratio of hits to false alarms) decreases at 10-day lead during negative Pacific-North America (PNA) conditions, and increases at 10-day lead during positive El Nino and Southern Oscillation (ENSO) conditions, with an even larger increase in AR forecast skill during phase-locked El Niño and positive PNA conditions (Fig. 2).

Figure 1: Figure (2) from DeFlorio et al. (2018): Method of determining if a predicted atmospheric river (AR) is a “hit” or a “miss” relative to an observed AR. Predicted and observed ARs are shown as shaded light and dark shaded ovals, respectively. Their IVT-weighted centroids are shown as black dots, and the distances D1 and D2 between each predicted AR and the observed AR are shown as black arrows. The distance threshold DT, which indicates the acceptable horizontal distance between an observed and predicted AR for a prediction to be considered skillful, is shown as a black arrow. In this example, the prediction of AR1 is considered skillful (a “hit”) since its centroid falls within the distance threshold of the observed AR, while the prediction of AR2 is not considered skillful (a “miss”) since its centroid falls outside the distance threshold of the observed AR.

Figure 2. Figure (10a) from DeFlorio et al. (2018): Relative operating characteristic (ROC) curves composited on positive (red) and negative (blue) phases of the combined El Niño-Southern Oscillation (ENSO) & Pacific-North America teleconnection (PNA) modes in December-January-February (DJF) over the North Pacific/Western U.S. region. The 1000 km distance threshold is used, and positive and negative phases are defined using +/- 0.5 standardized values of the climate index for each mode. 3-day (solid), 7-day (dashed), and 10-day (dotted) lead times are shown. The number of positive and negative phase days for each combined mode phase are listed above the legend. Area under ROC curve distributions for both region/mode/lead times of relevance, calculated from a bootstrap process that was repeated 1000 times by using resampling of the composite positive and negative mode days (red and blue, respectively) and all days (white) distributions with replacement, are included beside the ROC curves.

Deflorio, M., D. Waliser, B. Guan, D. Lavers, F.M. Ralph, and F. Vitart, 2018: Global assessment of atmospheric river prediction skill. Journal of Hydrometeorology, early online release, doi:10.1175/JHM-D-17-0135.1

CW3E Welcomes Dr. Nora Mascioli

CW3E Welcomes Dr. Nora Mascioli

February 20, 2018

Dr. Nora Mascioli joined CW3E as a Post-Doctoral Scholar in February of 2018, after completing her PhD in Earth and Environmental Science from Columbia University. At Columbia, Nora worked with Dr. Arlene Fiore and Dr. Michael Previdi studying aerosol impacts on regional climate. Using a global climate model, Nora demonstrated that aerosols have a significant effect on the frequency and magnitude of extreme temperature and precipitation events in the U.S. historically, and that future declines in aerosol emissions will likely have a large impact on temperature extremes. Using a combination of observations and a suite of CMIP5 models, Nora demonstrated that aerosols contributed to the southeastern U.S. “warming hole” in summer, although internal variability also played a large role. Nora also found that aerosols drove changes in atmospheric stagnation, a meteorological phenomenon associated with extreme temperature and pollution events, and that impacts on stagnation were largely independent of the aerosol source region. At CW3E, Nora will be studying the impacts of ice-nucleating aerosols (e.g. dust) on extreme wintertime precipitation in California. Ultimately, she hopes to help design and implement an improved representation of aerosols in West-WRF to support better forecasts of extreme precipitation events.

CW3E Post Event Summary: Arizona AR

CW3E AR Update: 16 February Post Event Summary

February 16, 2018

Click here for a pdf of this information.

Atmospheric River Impacts Southern Arizona

  • An AR made landfall over the Mexican Baja peninsula on 14 February 2018
  • Due to the favorable orientation of IVT relative to gaps in elevation along the Baja, the AR was able to penetrate inland and bring AR conditions and precipitation to Southern Arizona
  • Tucson, Arizona received ~1.3 inches of precipitation in 24 hours, ~10% of the average annual precipitation total, with storm total precipitation reaching ~1.5 inches
  • Precipitation from this event more than doubled the water year precipitation to date for the City of Tucson
  • Mt. Lemmon, to the northeast of Tucson, received 8.66 inches of precipitation over the course of the event

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

Valid 0600 UTC 13 February – 1700 UTC 16 February 2018

Images from CIMSS/Univ. of Wisconsin

Click IVT or IWV image to see loop GFS Analysis

Valid 0600 UTC 12 February – 0600 UTC 16 February 2018

 

 

 

 

 

 

 

 
 

Summary provided by C. Hecht, F.M. Ralph; 2 PM PT Friday 16 February 2018

*Outlook products are considered experimental

CW3E Launches Near Real-Time AR and QPF Forecast Verification Website

CW3E Launches Near Real-Time AR and QPF Forecast Verification Website

February 13, 2018

CW3E has developed a new suite of tools designed to quickly evaluate the performance of forecasts for the U.S. West Coast. Tools are now available to verify forecasts of precipitation and integrated vapor transport (IVT), a proxy for atmospheric rivers. The verification method is based upon identifying contiguous regions, called objects, in the forecast that meet the requirements for an impactful precipitation or atmospheric river event. For example, in the below Figure, the forecasted AR (blue shading) is an IVT object (proxy for AR) because it exceeds the threshold 500 kg m-1 s-1 and has geometry consistent with an atmospheric river. The blue shaded forecast IVT object has a location, size and other characteristics that can be compared to an analysis object (blue outline) at the matching forecast valid time. To visualize this process, see the overlap of the two objects in the Figure’s middle panel. On the CW3E website, users may choose to examine precipitation and IVT fields for the previous week; choose one of several forecast sources – including several well-known numerical models; choose a range of forecast lead times; and choose one of several object thresholds. For IVT objects that exceed 500 kg m-1 s-1, additional statistics are provided. The tools are designed to inform operational stakeholders of model performance for key precipitation events and atmospheric river landfalls.

The new verification website is created using NCARs Method for Object-Based Diagnostic Evaluation (MODE) software. These tools were developed by Laurel DeHaan, Andrew Martin, Rachel Weihs, Brian Kawzenuk and Chad Hecht of CW3E and David Reynolds of CIRES. They can be accessed from the CW3E forecast verification webpage. A more complete explanation of the verification and the methodology is provided on the website.

Additional forecast verification tools are in development at CW3E and will be posted to the website as they become available.

(Left) Forecasted IVT from the NCEP GFS, initialized 1200 UTC 24 January 2018 and valid 1200 UTC 29 January 2018.
(Middle) Forecasted (shading) and observed (contour) IVT objects identified by MODE using a 500 kg m-1 s-1 threshold.
(Right) GFS analysis (0-hr forecast) IVT valid 1200 UTC 29 January 2018.

CW3E Publication Notice: Genesis, Pathways, and Terminations of Intense Global Water Vapor Transport in Association with Large-Scale Climate Patterns

CW3E Publication Notice

Genesis, Pathways, and Terminations of Intense Global Water Vapor Transport in Association with Large-Scale Climate Patterns

February 13, 2018

CW3E researchers Scott Sellars and Brian Kawzenuk and director Marty Ralph in collaboration with Phu Nguyen (UC Irvine) and Soroosh Sorooshian recently published a paper in Geophysical Research Letters titled Genesis, Pathways, and Terminations of Intense Global Water Vapor Transport in Association with Large-Scale Climate Patterns (http://onlinelibrary.wiley.com/doi/10.1002/2017GL075495/full). The study uses the CONNected objECT (CONNECT) algorithm applied to integrated water vapor transport (IVT) data for the period of 1980 to 2016 calculated from Modern-Era Retrospective analysis for Research and Applications version 2 (MERRA-2) to identify objects associated with extreme moisture transport (Sellars et al., 2013, 2015).

The algorithm generated a global dataset of life-cycle records in time and space of evolving strong water vapor transport events. Each object was associated with distinct physical and climatological features such as object size, location, and intensity, various climatological teleconnection patterns, and many other characteristics. This algorithm identified various weather phenomena associated with strong moisture transport such as atmospheric rivers, hurricanes and tropical cyclones, monsoon transport, and various other systems that produced extreme moisture transport. It was illustrated that these events typically occurred in five distinct regions located in the midlatitudes (off the coast of the southeast United States, eastern China, eastern South America, off the southern tip of South Africa, and in the southeastern Pacific Ocean) (Figure 1a). Additional analysis showed distinct genesis and termination regions and global seasonal peak frequency during Northern Hemisphere late fall/winter and Southern Hemisphere winter (Figure 1c and d). In addition, the frequency and location of these events were shown to be strongly modulated by the Arctic Oscillation, Pacific North American Pattern, and the Quasi-Biennial Oscillation. Moreover, a positive linear trend in the annual number of objects was reported, increasing by 3.58 objects year-over-year. The vast dataset produced in this study will be used for various future research opportunities focused on extreme moisture transport and its connection to large-scale climate dynamics.

Figure 1:(a) Total number of IVT objects from January 1980 to August 2016. (b) Average duration in hours of object at each grid cell. (c) The number of objects at genesis (starting) locations for all IVT objects. (d) The number of objects at termination (ending) locations for all IVT objects. The gray areas represent landmass.