CW3E Atmospheric River Update Update on AR Currently Impacting CA, OR, and WA Precipitation continues to fall over portions of Northern California, Washington, and Oregon 6 10 inches of precipitation has fallen over some locations over the last 72-hrs AR conditions continue to persist over Northern CA, OR, and WA as the second AR made landfall this morning Another 5 8 inches are forecast for the higher elevations of Northern CA, OR, and WA as flooding remains a concern NWS Radar Loop as of 2:20 PM GFS IVT Forecast for 4 pm PST 8 February
24-hr QPE Over the last 24- hrs, the central Sierras saw 3 5 inches of precipitation while lower elevations and the Coastal Mts. saw.5 3 inches 72-hr QPE Ending 4 AM PST 8 Feb This brings the total 72-hr precipitation to over 10 inches over the Sierras and 6 inches over the Coastal Mts. Note: Change in Color Scale For official NOAA- NWS observed precipitation see cnrfc.noaa.gov/rfc _guidance.php
There are currently 6 river gauges that have risen above flood stage and an additional 27 above monitor stage CURRENT River Stage Heights (as of 1:45 PM PST) For official information on point specific flood warnings and watches visit weather.gov At ~5 am PST, the Russian River at Guerneville, CA rose to ~34 feet See NWS/CNRFC (cnrfc.noaa.gov) for potential impacts associated with a 34 ft stage height
The southwesterly oriented AR is forecast to bring IVT magnitudes as high as 1000 kg m 1 s 1 and IWV values as high as 28 mm to the West Summary by C. Hecht 4 PM PT Wednesday 8 Feb. 2017
There is high confidence that AR conditions (IVT >250 kg m 1 s 1 ) will last until 4 pm PST on 9 February 2017 over Northern CA, OR, and WA before the AR propagates southward Southern CA is expected to see weak AR (IVT 250 500 kg m 1 s 1 ) conditions for ~6 12-hrs as the AR propagates southward
There is high confidence that Moderate AR conditions (IVT >500 m 1 s 1 ) could last until 7 am PST on 9 February 2017 over portions of Northern CA, OR and Southern WA Summary by C. Hecht 4 PM PT Wednesday 8 Feb. 2017
For the Russian River Area (North of San Francisco) Forecasts of IVT magnitude peak around 7 AM on 9 February 2017: Maximum possible IVT ~ 950 kg m 1 s 1 Mean IVT ~ 850 kg m 1 s 1 Minimum possible IVT ~ 750 kg m 1 s 1 Uncertainty ~ +/ 12% AR conditions are forecast to last until 4 PM PST 9 February 2017 with high confidence (+/- 3 hrs) Summary by C. Hecht 4 PM PT Wednesday 8 Feb. 2017
NWS/WPC forecasts an additional 6 9 inches of precipitation is forecast to fall over the high elevations of the Sierras, Trinity Alps, and the Coastal, Cascade, and Olympic Mts. Over the next 3 days Lake Oroville and the Feather River Watershed could potentially receive another 3 9 inches For Official NOAA-NWS and CNRFC Precipitation Forecasts see wpc.ncep.noaa.gov/qpf/qpf2.shtml Or cnrfc.noaa.gov/rfc_guidance.php Summary by C. Hecht 4 PM PT Wednesday 8 Feb. 2017
There are 22 total river gauges that are currently at or forecast to rise above flood stage in Northern California As of 2:40 PM PST There are an additional 34 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 of stage height of the Middle Fork Feather River at Portola has risen to 11.6 feet at 10 pm on 10 Feb., which would be the flood of record For potential impacts of an 11 ft. stage (height) visit NWS/CNRFC (cnrfc.noaa.gov) for more information
Rainfall Category (R-Cat) was developed to identify and compare extreme precipitation using 3-day precipitation accumulations from rain gauges across the U.S. (Ralph and Dettinger 2012) R-Cat 1: 200-299 mm (roughly 8-12 inches) / 3 days R-Cat 2: 300-399 mm (roughly 12-16 inches) / 3 days R-Cat 3: 400-499 mm (roughly 16-20 inches) / 3 days R-Cat 4: >500 mm (more than roughly 20 inches) / 3 days From 12 AM PST 5 to 12 AM PST 7 February, 12 rain gauges experienced extreme precipitation of R-Cat 1 magnitude. The Four Trees rain gauge experienced the largest 3-day total: 10.16 inches (258.1 mm) To subscribe to this automated CW3E R-Cat Extreme Precipitation Alert via email: just email a message with subject subscribe to rcatalert@cirrus.ucsd.edu.