####018006537#### FGUS75 KREV 051611 ESFREV CAZ070>073-NVZ001>005-NVZ030>031-NVZ033>041-122300- Spring Flood Potential Outlook National Weather Service Reno NV 810 AM PST Tue Mar 5 2024 ...Above normal threat of snowmelt flooding along the Humboldt River and tributaries, and from watersheds draining far northern Nevada, including the Owyhee, Jarbidge, Bruneau, and Salmon Falls Creek.. Normal threat of flooding from rivers that drain from the eastern Sierra... There is an above normal threat of spring snowmelt flooding along the Humboldt River and its tributaries due to an above normal snowpack throughout northern Nevada. There is a typical threat of spring snowmelt flooding for areas along the Carson and Walker rivers where snowpack conditions have recently climbed to near normal conditions. Flooding on rivers can occur from heavy rainfall at any time, or combined with snowmelt during the spring. Observations and forecast runoff predictions reported here may change significantly with additional storms this spring. Please visit the CNRFC webpage (http://www.cnrfc.noaa.gov) for the latest information. Current basin conditions: Snowpack: After a dry start to the water year in the Sierra, numerous storm systems have moved across the region the past two months, greatly improving the snowpack conditions throughout California and Nevada. Early March Storms added 4 to 12" of snow water equivalent (SWE) gains throughout the Sierra, and more modest gain elsewhere. As of March 4th, the eastern Sierra snowpacks are near to slightly above normal and well above normal in the remainder of northern and northeastern Nevada. The Humboldt Basin and other far northern Nevada basins have already exceeded their median seasonal peak snowpacks about three to four weeks early. Snowpacks in the Owyhee, Bruneau, Jarbidge and Salmon Falls Creek all exceed last year's snowpack at this time. The early March storm brought snow to all elevations boosting the low elevation snowpack and vastly expanding the snow covered area. The eastern Sierra snowpack is currently 108% of median to date, and 94% of the median seasonal peak. The snowpack in the Humboldt watershed is currently well above normal at about 150% of median to date and 120% of median seasonal peak. Soil moisture is near to slightly above normal in the eastern Sierra and well above normal throughout the Humboldt and far northern Nevada. Near normal base flows have been observed from the east Sierra, and above normal along the Humboldt and northern Nevada. Accumulated volume on the lower Humboldt at Imlay is nearly double the to-date median. Precipitation: Precipitation totals across northern Nevada are now near normal in the Sierra and above normal in northern Nevada. Precipitation outlooks from the Climate Prediction Center currently show near normal precipitation across California and Nevada during the 1 to 2 week timeframe. No clear signals for above or below normal precipitation exist for the week 3-4 timeframe and into April-May. Temperatures are projected to lean above normal this spring but confidence is mixed. Seasonal (April - July) runoff forecasts: The seasonal April-July runoff forecasts are above average throughout the Humboldt watershed. Forecasts range from near 135% to 170% of average along the mainstem of the Humboldt River. In the Carson and Walker basins, seasonal forecasts are near normal at around 80-100% of average. These seasonal forecasts may change significantly with spring storms, or lack thereof. Please check cnrfc.noaa.gov for updates. Flood exceedance probabilities: The risk of flooding during the spring is elevated in the Humboldt basin due to the above normal snowpack and elevated baseflow. With a shallow, low elevation snowpack in place across the northern Humboldt watershed, the flooding potential is further elevated due to the potential for a late season rain-on-snow event or an early heat wave. Models currently show a near 75% chance of minor flooding on the Marys River and along the Humboldt River at Comus. There is also an elevated flood risk for the Owyhee, Bruneau, Jarbidge, and Salmon Falls Creek in far northern Nevada. There is a slight risk of flooding on the Carson and Walker rivers, as the snowpack in these watersheds is now near normal with significant low elevation snow. The flood risk is low for the Truckee, Susan and Middle Fork of the Feather from snowmelt alone. These drainages and others are all susceptible to flood risk in the event of a warm and strong late season atmospheric river event. Consult the AHPS long-range flood risk map for the latest point exceedance probabilities for the March through May time period: https://water.weather.gov/ahps/region_long_range.php?rfc=cnrfc Summary: The risk of flooding during the spring is elevated along the Humboldt River and its tributaries, as well as the Owyhee, Jarbidge, Bruneau, and Salmon Falls Creek, due to the above normal snowpack, low elevation snow, and above average baseflow and soil moisture. The flood threat is near normal along the Carson and Walker rivers, where the current snowpack is near average. Flooding can occur from snowmelt, rain, or a combination of both. Refer to the long range outlook product for updates to flood exceedance probabilities at specific locations throughout the spring. For short term hydrologic forecasts and general water resource information, please see the CNRFC webpage at: http://www.cnrfc.noaa.gov For more detailed water supply and streamflow forecast information for Nevada and eastern California, please refer to the following web sites, NWS California-Nevada River Forecast Center... http://www.cnrfc.noaa.gov/water_supply.ph NWS Reno for weather updates along with watches and warnings for hazardous weather and flooding conditions... http://weather.gov/reno Nevada Natural Resources Conservation Service... http://www.nv.nrcs.usda.gov/snow/ California Department of Water Resources... http://cdec.water.ca.gov/ NWS Climate Prediction Center Long Range Outlook Maps... http://www.cpc.ncep.noaa.gov/products/forecasts/ U.S. Drought Portal...Including U.S. Drought Monitor... http://drought.gov/ TB/MI