CW3E Atmospheric River Update Update on ARs Currently Impacting and Forecast to Impact West Coast Precipitation continues to fall over a majority of California The Transverse Mountains (north of Santa Barbara) have received over 3.5 inches in the last 24-hours SoCal is forecast to receive another 2 6 inches in the next 24-hours, raising concerns for flooding and landslides Forecast confidence for this weekends landfalling AR has increased over Northern California NWS NEXRAD RADAR
Over the last 24 hours (ending at 10:30 AM PST), some coastal locations of Southern CA received 1.5 to 3.7 inches of precipitation The high elevations of the Northern Sierras and southern Coastal Mts. have received.5 1 in. over the last 24 hours For official NOAA-NWS observed precipitation see cnrfc.noaa.gov/rfc_guidance.php Ending 10:30 AM PST 17 Feb
Weekend AR Current AR AR conditions associated with the current AR are forecast to last until ~11 PM PST tonight Probability of reaching AR conditions (IVT >250 kg m 1 s 1 ) has increased to 90 100% in association with the third AR, but there is large uncertainty associated with start time and duration of AR conditions
High confidence that moderate AR conditions (IVT >500 m 1 s 1 ) will last for 3 6 hours over coastal Southern CA The probability of moderate AR conditions has increased to 90 100% in association with the AR forecast for 19 21 Feb There is still higher uncertainty in onset and duration of moderate AR conditions for this weekends AR
IVT magnitude over Santa Barbara could reach strong AR conditions later today Forecast certainty has increased since yesterdays outlook Maximum possible IVT ~ 900 kg m 1 s 1 Mean IVT ~ 800 kg m 1 s 1 Uncertainty ~ +/ 13% High confidence that AR conditions will end at ~8 PM PST 17 Feb Duration of AR conditions Weak: ~22 hours Moderate: ~8 hours +/ 2h Strong: ~3 hours
Another AR is forecast to make landfall over Northern California from 19 to 21 Feb Forecasts of IVT ranges from moderate to extreme AR conditions over the Russian River Watershed Maximum possible IVT ~ 1100 kg m 1 s 1 Mean IVT ~ 850 kg m 1 s 1 Uncertainty ~ +/ 30% There is still a large amount of uncertainty in onset of AR conditions. The mean start time is ~2 PM 19 Feb Duration of AR conditions Weak: ~30 hours +/ 20 h Moderate: ~16 hours +/ 12h Strong: ~12 hours +/ 12 h
The Transverse Mts. are forecast to receive another 6.22 inches of precipitation from 4 PM 17 Feb to 4 PM 18 Feb The lower elevations of Los Angeles and San Diego are forecast to receive 1.5 4.5 inches over the next 72-hrs For Official NOAA-NWS and CNRFC Precipitation Forecasts see wpc.ncep.noaa.gov/qpf/qpf2.shtml Or cnrfc.noaa.gov/rfc_guidance.php
There are 19 total river gauges that are currently at or forecast to rise above flood stage in California and Nevada As of 11:30 AM PST There are an additional 37 gauges that are currently at or expected to rise above monitor stage For official NOAA-NWS CNRFC Streamflow Forecasts see cnrfc.noaa.gov/rfc_guid ance.php Since yesterday s update, the forecast stage of the Ventura River at Foster Park, CA has decreased to 17.6 ft (flood stage) The Russian River at Guerneville is now forecast to rise to 32.5 feet at 11 am on 21 Feb. due to the precipitation produced by the next AR
Primarily due to the AR that is forecast to make landfall later this weekend, the Russian River Watershed is forecast to receive 4.5 8.25 inches of precipitation over the next 6 days The high forecast precipitation is causing the forecast stage height of the Russian River at Guerneville, CA to rise to ~32.5 ft,.5 feet above flood stage
The Lake Oroville Watershed is forecast to receive 5.6 12 inches of precipitation over the next 6 days The Middle Fork Feather river at Portola, CA is forecast to rise to a height of 9.6 feet, 1.1 feet above flood stage