Winter Weather

IDAHO POWER PROJECT

BACKGROUND

Figure 1. Terrain map of the SNOWIE project domain north of Boise, Idaho, illustrating the sites of ground-based instrument locations (see legend) as well as an example flight track for the Seeding Aircraft and University of Wyoming King Air, assuming conditions with westerly winds.  The Payette River Basin is outlined in thick gray, and was the target region for the SNOWIE field campaign.  From Tessendorf et al. (2019).
Figure 1. Terrain map of the SNOWIE project domain north of Boise, Idaho, illustrating the sites of ground-based instrument locations (see legend) as well as an example flight track for the Seeding Aircraft and University of Wyoming King Air, assuming conditions with westerly winds.  The Payette River Basin is outlined in thick gray, and was the target region for the SNOWIE field campaign.  From Tessendorf et al. (2019).

Idaho Power Company (IPC) conducts a winter cloud seeding program to augment snowfall along the Snake River Basin and its tributaries for hydroelectric generation. The program has been focused in Payette River basin in western Idaho and the upper Snake River system in eastern Idaho, and has recently expanded into the Boise and Wood basins in western Idaho.  RAL has been working with IPC since 2011 to develop model-based forecasting and evaluation tools for their cloud-seeding program.  In 2017, IPC, RAL and several universities collaborated on a field project called SNOWIE—Seeded and Natural Orographic Wintertime clouds: the Idaho Experiment.

The SNOWIE project aims to study the impacts of cloud seeding on winter orographic clouds.  The field campaign took place in Idaho between 7 January–17 March 2017 and employed a comprehensive suite of instrumentation, including ground-based radars and airborne sensors, to collect in situ and remotely-sensed data in and around clouds containing supercooled liquid water before and after they were seeded with silver iodide aerosol particles (Figure 1). Seeding material was released primarily by a seeding aircraft, which produced zig-zag lines of silver iodide as it dispersed downwind.  In several cases, unambiguous zig-zag lines of radar reflectivity were detected by radar, and in situ measurements within these lines have been analyzed to examine the microphysical response of seeding the cloud (Figure 2).  The measurements from SNOWIE aim to address long-standing questions about the efficacy of cloud seeding, starting with documenting the physical chain of events following seeding.  The data is also being used to evaluate and improve computer modeling parameterizations, including the cloud-seeding parameterization developed in RAL that will be used to further evaluate and quantify the impacts of cloud seeding.  

Figure 2. PPI scans (0.99-degree elevation angle) at 0109 UTC (left) and 0137 UTC (right) from the Packer John DOW radar. The red line denotes the track of the seeding aircraft. The track was repeated 8 times between 00:03 and 01:29 UTC. The wind barbs indicate mean flight-level winds. From Tessendorf et al. (2019).
Figure 2. PPI scans (0.99-degree elevation angle) at 0109 UTC (left) and 0137 UTC (right) from the Packer John DOW radar. The red line denotes the track of the seeding aircraft. The track was repeated 8 times between 00:03 and 01:29 UTC. The wind barbs indicate mean flight-level winds. From Tessendorf et al. (2019).

In FY19, RAL worked on a “Phase Eight” study for IPC to conduct data analysis and modeling research from SNOWIE. This has included specific investigation on quantifying the amount of precipitation produced by cloud seeding in three SNOWIE cases with unambiguous seeding lines using SNOWIE observations, simulating those cases to compare the model with the SNOWIE observations, studying ice generating cells in SNOWIE data, and the evaluation of the ability of model re-analysis and high-resolution simulations to replicate the layered clouds observed in SNOWIE.

FY2019 ACCOMPLISHMENTS

In 2019, RAL conducted SNOWIE modeling and data analysis on the effectiveness of cloud seeding and precipitation formation processes in the clouds observed over Idaho.  Components of this effort included:

  • analyzing snow gauge data and radar data in cases from SNOWIE where unambiguous seeding lines were observed;
  • running model simulations of cases from SNOWIE where unambiguious seeding lines were observed;
  • comparing model simulation results with observations, such as radiometer, sounding, snow gauge, and aircraft data from SNOWIE;
  • analyzing the in situ aircraft data and airborne W-band cloud radar data for the presence and characteristics of ice generating cells and layered cloud structures,
  • evaluating the ability of the WRF model and ERA-5 reanalysis to resolve the observed layered cloud structures, and
  • collaborating with the RAL In Flight Icing team to use SNOWIE data for evaluation of the HRRR forecast model.

 

These efforts have yielded several publications to date, with several more in preparation. In FY19, an article summarizing the SNOWIE field campaign, led by Dr. Sarah Tessendorf, was published in the Bulletin of the American Meteorological Society (BAMS).  Another collaborative manuscript, led by Dr. Bob Rauber, was published in FY19 in the Journal of Applied Meteorology and Climatology entitled “Wintertime Orographic Cloud Seeding--A Review”.  It provides a modern review of the science regarding cloud seeding, including the latest advances from SNOWIE. A third paper, led by Dr. Katja Friedrich, was submitted to Proceedings of the National Academy of Science (PNAS) shows results that quantify the impact of cloud seeding using snow gauge measurements and radar derivations of precipitation rates.  A fourth paper was also written and will be ready for submission in early FY20 on the detailed microphysics of the three cases with unambiguous seeding lines, which builds upon French et al. (2018), which was published in PNAS last year.

Figure 3. The observed cloud droplet concentration (top) and liquid water content (bottom) for SNOWIE IOP9 on 31 January 2017 compared to 3 model simulations: Climatology uses the climatology background aerosol, 01CCN uses 0.1 times the climatology for CCN, and CTRL is the control simulation that uses 0.15 times the climatology for CCN.
Figure 3. The observed cloud droplet concentration (top) and liquid water content (bottom) for SNOWIE IOP9 on 31 January 2017 compared to 3 model simulations: Climatology uses the climatology background aerosol, 01CCN uses 0.1 times the climatology for CCN, and CTRL is the control simulation that uses 0.15 times the climatology for CCN.

The SNOWIE modeling simulations conducted in FY19 continue to reveal a strong sensitivity of the simulated cloud microphysical characteristics to the amount of background ice produced by the model as well as to the background aerosol in the model (Figure 3). Analyses to improve the model in this regard is underway and will be a major focus for FY20 and going forward.  A simulation of one seeding case with unambiguous seeding lines was conducted with temporal model output being generated every 5 minutes to better resolve the temporal evolution of the observed seeding lines.  Analysis is underway to evaluate this simulation compared to the observations and run it at even higher horizontal grid spacing using Large Eddy Simulation (LES).

FY2020 PLANS

  • Conduct additional data analysis and model simulations from the SNOWIE field project and collaborate with SNOWIE university PIs to perform analysis on high priority cases
  • Simulate SNOWIE cases at even finer resolution with Large Eddy Simulations (LES) to evaluate the impacts of grid resolution on the resulting cloud characteristics
  • Perform detailed case study data analyses and model simulations to improve the production of supercooled liquid water and ice in the model, as well as improve the cloud seeding model, especially with regard to ice production and dispersion of seeding material in the seeding model compared to the observations from SNOWIE
  • Work with IPC to develop new and/or augmented observational networks for continued monitoring, forecasting assistance, and evaluation of their cloud-seeding program
  • Publish journal papers on the major findings from these studies.

 

Education and Outreach on the State of Cloud Seeding Science

In FY19, the U.S. Bureau of Reclamation (USBR) sponsored RAL scientists to develop training material on the latest state of science regarding cloud-seeding research, evaluation capabilities, and understanding of relevant processes.  The training material consists of presentation slides and a 1-page fact sheet handout.  The trainings will be held at each of the five USBR regional offices over the course of the next year.

The training material consists of a historical background of cloud seeding research, as well as background material on the conceptual model of cloud seeding, with recent results from the research coming out of SNOWIE and other advances in the field that NCAR is leading. 

FY2020 PLANS

  • Finalize training material
  • Conduct training sessions at five USBR regional offices

 

Measurements of snow at the Marshall Field site

A long term snow measurement site has been maintained at the NCAR Marshall field site since the early 1990’s.  The site was used to support research related to ground deicing in the 1990’s and 2000’s, and supported the Solid Precipitation Inter-Comparison Experiment (SPICE) in the 2010’s.   NOAA supported the SPICE effort as well as testing and developing new instruments for its Climate Reference Network (CRN).  This year NOAA supported testing efforts regarding a new wind shield design for CRN.  The NCAR Water System program is supporting testing and evaluation of a new hotplate sensor built and designed by Pond Engineering.

This site is able to serve as a reference site due to the deployment of a WMO standard snow reference system called the Double Fence Intercomparision Reference (DFIR) system.  The main features of this system are the use of double fences of outer diameter 40 feet and inner diameter 25 feet, with an automated gauge in the center.  The automated gauge used is an Alter shielded GEONOR.   A key aspect of this site is the archival of the data on an efficient database and the ability to examine the data in real-time based on a web based graphical interface.