CW3E Publication Notice: Evaluation of Atmospheric River Predictions by the WRF Model Using Aircraft and Regional Mesonet Observations of Orographic Precipitation and Its Forcing

CW3E Publication Notice

Evaluation of Atmospheric River Predictions by the WRF Model Using Aircraft and Regional Mesonet Observations of Orographic Precipitation and Its Forcing

April 16, 2018

CW3E project scientist Andrew Martin and co-authors have published a study characterizing predictability limits in Atmospheric River (AR) forecasts and apportioning Russian River precipitation forecast errors among vapor transport and orographic precipitation components. The article, titled Evaluation of Atmospheric River Predictions by the WRF Model Using Aircraft and Regional Mesonet Observations of Orographic Precipitation and its Forcing, is now in early online release at the Journal of Hydrometeorology.

This study leveraged airborne dropsonde observations of offshore Atmospheric Rivers completed during the CalWater experiment and the Atmospheric River Observatory at Bodega Bay and Cazadero, CA to verify forecasts of AR properties and their resulting precipitation. Forecasts were created by CW3E’s numerical weather prediction model, West-WRF, and compared to Global Forecast System reforecasts (GFSRe) valid for the same events. Forecast skill in AR properties and precipitation was evaluated at lead times up to 7 days ahead. Notably, the study found that deterministic skill in integrated vapor transport and other related fields degrades (meaning that forecasts created from climatology perform just as well or better) more than 4 days ahead for both models. However, West-WRF improves upon GFSRe skill in IVT at days 1, 2 and 3 ahead (see Fig. 1c).

Figure 1. a) Value added by GFSRe over GFSRe climatology validated against 145 CalWater dropsondes for the variables z500 (blue), IVT (black), IWV (green) and e925 (red). b) as in a, except for West-WRF value added over GFSRe climatology. c) as in b, except reference forecast is GFSRe.

The study also employed a novel forecast error separation technique to apportion precipitation forecast errors among the component caused by vapor transport simulation and orographic precipitation process simulation. Data from the Atmospheric River Observatory was used to demonstrate that West-WRF forecasts of orographic precipitation during landfalling AR are more accurate in simulating both components; but also that West-WRF forecasts of precipitation can be improved by improving the vapor transport component because its orographic precipitation process is accurate. This lends confidence that CW3E’s effort to improve west coast precipitation forecasts by assimilating offshore observations into West-WRF analyses can yield successful results.

Co-authors include Dr. F Martin Ralph, Reuben Demirdjian, Laurel DeHaan, and Dr. Rachel Weihs of CW3E with Dr. David Reynolds of the Cooperative Institute for Research in Environmental Sciences and Dr. Sam Iacobellis of Scripps Institution of Oceanography. The study was funded by the US Army Corps of Engineers, the California Department of Water Resources, and the National Science Foundation XSEDE program.

CW3E AR Update: 04 April 2018 Outlook

CW3E AR Update: 04 April Outlook

April 04, 2018

Click here for a pdf of this information.

Atmospheric river forecast to impact California over the next four days

  • Forecast confidence is increasing for a moderate or strong AR to strike the U.S. West Coast between this Thursday and Saturday
  • This will be the strongest AR of the season for this region, with total water vapor transport greater than approximately 25 Mississippi Rivers worth of water
  • Heavy precipitation is predicted over the CA coast and Sierra Nevada, with accumulation up to 7 inches possible
  • High freezing levels during the heaviest precipitation will result in rain at high altitudes over the Sierra Nevada leading to potential flooding

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

Valid 0600 UTC 04 April – 1200 UTC 08 April 2018

 

 

 

 

 

 

 

Summary provided by B. Kawzenuk, F.M. Ralph, and C. Hecht; 10 AM PT Wednesday 04 April 2018

*Outlook products are considered experimental

CW3E AR Update: 03 April 2018 Outlook

CW3E AR Update: 03 April Outlook

April 03, 2018

Click here for a pdf of this information.

Atmospheric river forecast to impact Northern California later this week

  • GFS Ensemble members are currently forecasting a potentially strong to extreme AR over northern and central California later this week
  • Forecast certainty has increased since yesterday but there is still some uncertainty in the onset, duration, and strength of the AR
  • Up to 7 inches of precipitation is forecasted to fall over the Coastal and Sierra Nevada Mtns in CA, OR, and WA
  • The GEFS is currently suggesting high freezing levels for most of this event, which may lead to most of the precipitation falling as rain

Click IVT or IWV image to see loop of 0-126 hour GFS forecast

Valid 0600 UTC 03 April – 1200 UTC 08 April 2018

 

 

 

 

 

 

 

Summary provided by B. Kawzenuk, F.M. Ralph, and C. Hecht; 11 AM PT Tuesday 03 April 2018

*Outlook products are considered experimental

CW3E AR Update: 02 April 2018 Outlook

CW3E AR Update: 02 April Outlook

April 02, 2018

Click here for a pdf of this information.

Atmospheric river forecast to impact Northern California later this week

  • GFS Ensemble members are currently forecasting a potentially strong to extreme AR over Northern California later this week
  • There is currently large uncertainty in the onset, duration, and magnitude of AR conditions, creating uncertainties in the potential impacts of this event
  • >5 inches of precipitation could fall during this event over the high elevations of the Coastal and Sierra Nevada Mountains in Northern California
  • The GFS is currently suggesting freezing levels >8,000 feet for most of this event, which may lead to most precipitation over the high Sierra falling as rain

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

Valid 1200 UTC 02 April – 0900 UTC 08 April 2018

 

 

 

 

 

Summary provided by C. Hecht, F.M. Ralph, and B. Kawzenuk; 1 PM PT Monday 02 April 2018

*Outlook products are considered experimental

CW3E AR Update: 23 March 2018 Post Event Summary

CW3E AR Update: 23 March Post Event Summary

March 23, 2018

Click here for a pdf of this information.

A strong AR made landfall over southern California this week

  • The atmospheric river made initial landfall over Big Sur around 1800 UTC Wednesday, 20 March 2018
  • AR conditions were present over southern California about ~1200 UTC Friday, 23 March 2018
  • This was an R-Cat 1 event as over 200 mm of precipitation was observed just south of Big Sur and over the northern Sierra Nevada over 72 hours
  • This event produced nearly 7 percent of normal annual precipitation over all of California and the Northern Sierra 8 Station Index

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

Valid 0000 UTC 19 March – 1200 UTC 23 March 2018

Images from CIMSS/Univ. of Wisconsin

Click IVT or IWV image to see loop of 0-48 hour GFS forecast

Valid 1200 UTC 22 March – 1200 UTC 24 March 2018

NEXRAD Radar Reflectivity
Valid 00 UTC 20 March – 12 UTC 23 March 2018

  • Precipitation began over central CA early morning on 20 March 2018
  • Moderate to heavy precipitation occurred over central and Southern CA for nearly 72 hours during 20–23 March
  • The highest precipitation amounts occurred over the Coastal Mts. between Santa Barbara and Big Sur and over the southern Sierra Nevada
  • Several thunderstorms also occurred during this event on 22 and 23 March as evident by the highest reflectivity values observed by radar


 

 

 

 

 

 

Summary provided by C. Hecht, B. Kawzenuk, and F.M. Ralph; 3 PM PT Friday 23 March 2018

*Outlook products are considered experimental

CW3E AR Update: 22 March 2018 Outlook

CW3E AR Update: 22 March Outlook

March 22, 2018

Click here for a pdf of this information.

Update on Atmospheric River Currently Impacting California

  • Precipitation continues to fall across portions of California
  • The AR will begin to propagate southward bringing moderate AR conditions to Orange and San Diego Counties
  • As much as 9.5 inches of precipitation has fallen over the Coastal Mountains of California during the last 48 hours
  • ~3.75 inches of precipitation has fallen over the high elevations of Santa Barbara and Ventura Counties and 3.5 more inches could fall during the remainder of the storm
  • AR conditions are expected to end at ~11 pm PDT (+/– 3 hours) tonight over Southern California

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

Valid 0000 UTC 19 March – 1600 UTC 22 March 2018

Images from CIMSS/Univ. of Wisconsin

Click IVT or IWV image to see loop of 0-48 hour GFS forecast

Valid 1200 UTC 22 March – 1200 UTC 24 March 2018

 

 

 

 

 

 

 

 

Summary provided by C. Hecht, F.M. Ralph, and B. Kawzenuk; 3 PM PT Thursday 22 March 2018

*Outlook products are considered experimental

CW3E AR Update: 21 March 2018 Outlook

CW3E AR Update: 21 March Outlook

March 21, 2018

Click here for a pdf of this information.

Update on Atmospheric River Currently Impacting California

  • Light to moderate precipitation has begun falling over portions of California
  • GFS Ensemble members have continued to converge on coastal IVT forecast for the remainder of the AR
  • Portions of Southern California are forecast to experience Strong AR conditions between 2 and 5 AM on Thursday 22 March
  • ~1–2 inches of precipitation has fallen over the Santa Ynez Mountains over the past 24 hours
  • An additional 10+ inches of precipitation are forecast to fall over the higher elevations of Santa Barbara and Ventura Counties during the remainder of this AR

National Weather Service Composite Radar Reflectivity

Valid 1748-1858 UTC 21 March 2018

Images from weather.gov

Click IVT or IWV image to see loop of 0-72 hour GFS forecast

Valid 1200 UTC 21 March – 1200 UTC 24 March 2018

 

 

 

 

 

 

 

 

Summary provided by C. Hecht, F.M. Ralph, and B. Kawzenuk; 1 PM PT Wednesday 21 March 2018

*Outlook products are considered experimental

CW3E AR Update: 20 March 2018 Outlook

CW3E AR Update: 20 March Outlook

March 20, 2018

Click here for a pdf of this information.

Update on Atmospheric River Forecast to Impact California This Week

  • The terminus of the atmospheric river plume is approaching coastal CA and precipitation will begin today
  • Models are suggesting potentially strong (IVT >750 kg m-1 s-1) AR conditions over San Luis Obispo and Santa Barbara Counties
  • Locations further south may experience moderate strength AR conditions (IVT >500 kg m-1 s-1)
  • AR conditions are forecast to peak over portions of SoCal between Midnight and 11 AM PDT on Thursday, 22 March 2018
  • As much as 10 inches of precipitation may fall over the higher elevations of Santa Barbara and Ventura Counties
  • The National Weather Service has issued numerous Flash Flood Watches and Winter Weather Warnings in California

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

Valid 0000 UTC 18 March – 1600 UTC 20 March 2018

Images from CIMSS/Univ. of Wisconsin

Click IVT or IWV image to see loop of 0-72 hour GFS forecast

Valid 1200 UTC 20 March – 1200 UTC 23 March 2018

 

 

 

 

 

 

 

 

 

 

Summary provided by C. Hecht, F.M. Ralph, J. Rutz, and B. Kawzenuk; 1 PM PT Tuesday 20 March 2018

*Outlook products are considered experimental

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: 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