Potential Use of the NOAA G-IV for East Pacific

Atmospheric Rivers

Marty RalphDave Reynolds, Chris Fairall, Allen White, Mike Dettinger, Ryan Spackman

15 August 2013

• SSM/I satellite data shows atmospheric river• Stream gauge data show regional extent of high stream flow covers 500 km of coast

Russian River floods are associated with atmospheric rivers

- all 7 floods over 8 years.

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Flooding on California’s Russian River: Role of atmospheric rivers

Ralph, F.M., P. J. Neiman, G. A. Wick, S. I. Gutman, M. D. Dettinger, D. R. Cayan, A. White

Geophys. Res. Lett., 2006

Flooding in Western Washington: The Connection to Atmospheric Rivers

Paul J. Neiman, Lawrence J. Schick, F. Martin Ralph, Mimi Hughes, and Gary A. Wick

J. Hydrometeorology (2011)

Of 48 annual peak daily flows on 4 watersheds, 46 were associated with the land-fall of atmospheric river conditions.

• West coast flooding can be severe and is usually the result of land-falling ARs (e.g., Howard Hanson dam experience and ARkStorm)

• Errors in predicted AR landfall position averages 500 km at 5 day lead time (Wick et al. 2013)

• Extreme QPF is often seriously in error (Ralph et al. 2010; HMT), partly due to the AR forecast position errors

• CalWater 2 field experiment is focusing heavily on ARs• CalWater 2 involves NOAA’s Ron Brown and P-3 (both formally requested), DOE facilities, and

the 100-station HMT-West meso network in California• CalWater 2 will have a major field effort in winter 2014/15, for which the G-IV could provide

vital dropsonde and tail radar data• A CalWater 2 early start deployment of the G-IV in Jan-Feb 2014 will exercise the use of both

the dropsondes and tail Doppler radar for AR measurements offshore• Key science problems, e.g., could measure the water budget in ARs and explore

aerosols

G-IV for atmospheric rivers (AR) in Eastern Pacific:Major drivers

AR Landfall Position Forecast ErrorsWhile overall occurrence well forecast out to 10 days, landfall is less well predicted and the location is subject to significant errors, especially at longer lead times

• Errors in location increase to over 800 km at 10-day lead

• Errors in 3-5 day forecasts comparable with current hurricane track errors

• Model resolution a key factor

• Models provide useful heads-up for AR impact and IWV content, but location highly uncertain• Location uncertainty highlights limitations in ability to predict

extreme precipitation and flooding• Improvements in predictions clearly desirable

RMS Error in Forecast AR Landfall Location

From Wick et al., 2013 (submitted to Weather and Forecasting)

500 km forecast error at 5-day lead

time

G-IV for atmospheric rivers in Eastern Pacific:Major monitoring gaps and possible role of G-IV• Winds in ARs offshore are not observed (key region is 0-3 km MSL)

• Dropsonde system on the G-IV is ideally suited to help fill this gap as demonstrated in a WISPAR mission in 2011 (paper in preparation; Neiman et al.)

• Tail Doppler radar could be a significant new source of wind information in ARs

• AR water vapor transport is key factor in determining impacts and is not observed using current satellite systems• The duration of an AR at a given location at landfall determines much

of the flood risk (Ralph et al. 2013, JHM)• Mesoscale frontal waves are a key phenomena determining if and

where an AR will stall, but measurements offshore are sorely lacking

G-IV has been used to sample an AR (in March 2011)

Neiman et al paper in preparation documenting G-IV use in an AR near Hawaii

We need corollary to Land Falling Hurricanes in West for AR Landfall

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25 Million at Risk

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G-IV

G-IV for atmospheric rivers in Eastern Pacific:A new targeting concept for AR monitoring• Data assimilation

• New method of targeting would emphasize the AR itself, rather than the traditional WSR approach which used a very large area unrelated to the AR

• Focus demonstrations entirely in west coast extreme event predictions, rather than on storms elsewhere in the nation

• Focus on key AR characteristics in evaluating impact of assimilating G-IV data, especially precipitation at landfall, and AR intensity and location at land-fall

• Watches and warnings• Much like the hurricane recon program, the ability to accurately monitor AR intensity and location offshore

12-24 hours before landfall has potential benefits to the NWS watch-warning program (new paradigm for this is possible)

• Key parameters in an AR offshore that could be monitored with the G-IV• Exact position and intensity• Total water vapor transport• Orientation of the AR winds relative to coastal terrain (determines which watersheds are most vulnerable)• Detection of a mesoscale frontal wave that could portend a stalling AR