Background What is an atmospheric river? Atmospheric Rivers (AR) are relatively narrow regions in the atmosphere that are responsible for most of the horizontal transport of water vapor outside of the tropics. ( Provide necessary rainfall to places like CA but can also cause flooding events and general damage when they are too strong. Ex: Pinapple Express

History The ‘Great Flood’ of 1862 “largest flood in the recorded history of Oregon, Nevada and Califo rnia, occurring from December 1861 to January 1862” ( /Great_Flood_of_1862) /Great_Flood_of_1862 “The entire Sacramento and San Joaquin valleys were inundated for an extent of 300 miles (480 km), averaging 20 miles (32 km) in breadth. “( /Great_Flood_of_1862) /Great_Flood_of_1862 The flooding was so bad that the governor had to go to his inauguration on a rowboat

History The New Year’s Flood of square miles inundated by flood waters 2 fatalities, 50 injuries. 120,000 people displaced by flooding. $1.6 billion in damages Disaster areas declared in 43 counties in CA. Multiple levees along the Sacramento and San Joaquin Rivers broke due to extremely high runoff from melting snow and heavy rainfall. ( ivers/events/) ivers/events/

October 13-15, 2009 Event Synopsis: Widespread rainfall totals >2 inches throughout central and northern CA Maximum 24-h rainfall totals near 19 inches along central CA coast Maximum 24-h rainfall totals >10 inches in the southern Sierra Nevada ( atmrivers/events/) atmrivers/events/ (flood warning sign in Santa Cruz, CA; bsnews.com/ pictures/calif ornia- storms /) bsnews.com/ pictures/calif ornia- storms / (Clearing a storm drain in Ben Lomond, CA; ) (Flooding in Downtown Sacramento; storms /13/ ) storms /13/

October 13-15, 2009 Event Synopsis: No fatalities reported. Landslides reported in the Santa Cruz Mountains and in Sequoia National Park in the Sierra Nevada. Estimated $10 million in damages. High wind gusts (>50 mph) downed trees and power lines. s/ (Wind damage in Healdsburg, CA; california-article ) california-article (Wind damage in Sacramento, CA; ) (High winds and rains in downtown Sacramento; com/pictures/califor nia-storms /3/ ) com/pictures/califor nia-storms /3/

October 13-15, 2009 Event Daily precipitation totals over California during the AR event ( )

October 13-15, 2009 Event In this gif you can see the precipitable water hitting the west coast of the US in a concentrated stream, as well as the strong jet in the height contours. The high winds and water content in the low level jet are forced up by the Sierra Nevada mountains and there is extreme precipitation in the mountains and further west because of this

October 13-15, 2009 Event Cap of the stream of the PW in the jet hitting California

October 13-15, 2009 Event Unfortunately, the gif of these parameters was too large to fit in the powerpoint, however the screen caps show large negative omega values (indicating upward motion) where the largest precipitation values are (rates not acccumulation) Red indicates negative and the more blue the values become the more positive they become The most negative values can also be seen where there are mountains, whether the coastal range or the Sierras, indicating the upward motion in the system caused by orographic lifting.

October 13-15, 2009 Event The wind vectors in the program don’t show up over land in this case, however, even with the ones present you can see that values were at least 35mph off the coast. Actual recorded values reached over 50mph You can also see a wind shift between the 15 th and 16 th indicating the final passage of the entire system.

Summary In comparison to some storms, there was no catastrophic damage or flooding. Most of damage was related to wind Trees falling onto houses, etc. Lack of flooding due to dry conditions previously Despite the damage caused, brought much needed snowfall to the area California depends on snowmelt during the summer months for additional water supply as there is usually much less rainfall during the summer seasons