Flood Risk High and Flooding Imminent for the Red River of the North Basin; Above Average Risk for Upper Midwest and from the lower Great Lakes to Illinois and part of New England (March 13, 2009)   General Assessment Copious precipitation during the fall, wet soils before freeze-up, and areas of substantial water in the snow pack have produced an imminent risk of major flooding along the Red River of the North and a risk of minor to moderate flooding in much of eastern North Dakota and northern Minnesota. Major overland flooding is expected in eastern North Dakota and northwest Minnesota beginning the week of Sunday, March 22. This will subsequently lead to major, and possibly record, flooding along the Red River of the North and its tributaries. During the previous 6 months numerous locations have received above normal precipitation. Heavy rainfall (in February and early March) falling on already saturated soils caused recent flooding and very high flows on rivers across southern Michigan, northern sections of Ohio, Indiana and Illinois.  These conditions make future flooding more likely in this area.  Areas of the Nation suffering from drought with accompanying low soil moisture and sub normal to non existent snowpack have a below average risk of flooding this Spring. The risk of flooding is gauged by assessing the cumulative impact of hydrometeorological factors such as precipitation, groundwater conditions, streamflow, snow conditions, river ice, and reservoir storage. Areas of the West, with sub normal snowpack and dry soils, are expected to have below normal streamflows, negatively affecting the water supply across the region. It is important to remember that heavy rainfall at any time can lead to river flooding, even when overall river flood potential is considered below average and ice jams can cause rapid water level rises on rivers with significant ice accumulation. Special note: After the end date of this assessment, temperatures across the upper Midwest rose significantly, resulting in numerous flood advisories for melting snow and potential ice jams. Specific Areas of Above Average Flood Risk Upper Midwest Based upon forecasts produced by National Weather Service field offices using the Advanced Hydrologic Prediction Service (AHPS), significant spring flooding is expected across the upper Midwest, including the Red River Basin . A sharp cold snap immediately following late fall rains, which produced 200 to 400% of normal precipitation for October and November, created saturated soils and a deeply frozen surface before winter snows fell. The water content of the snow pack ranges from 3 to 6 inches across much of the region. These conditions will enhance runoff when the snow pack melts, increasing the risk of flooding. Major flooding is expected along the entire Red River of the North, with major to near record flooding expected at Fargo, ND and major flooding in the Grand Forks area. With flood severity in the basin contingent upon the timing and rate of snow melt, tributaries such as the Sheyenne River and Wild Rice River in North Dakota are expected to have major to near record flooding. Major flooding also remains likely along the James River in northern South Dakota.The temperature of the snow pack is still very cold, which indicates that it has not yet ripened, delaying the onset of snowmelt. As Spring progresses, the chances of a rapid warm up increase, thereby increasing the likelihood of a rapid and continuous melt and the risk and severity of flooding. Colder than normal temperatures this winter along with high river flows at the time of freeze-up have generated a thick ice cover which heightens the risk of ice jam flooding on the Red River and its tributaries. In addition, widespread overland flooding is expected due to frozen drainage networks.   Extended-range AHPS-based forecasts indicate that Devils Lake has a nearly 100% chance of establishing a new record high water level, exceeding the record of 1,449.2 feet set in May, 2006.  Moreover, there is a 65% chance the water level at Devils Lake will reach 1,451.2 feet. The permanent dike that protects the city of Devils Lake provides protection up to a lake level of 1,454 feet. At Fargo , ND , there is a 100% chance the Red River will exceed the major flood level of 30 feet, which is 12 feet above flood stage. There is also close to a 25% chance of exceeding 40.1 feet, the record flood level set at Fargo on April 7, 1997. At Grand Forks , the Red River has a 100% chance of exceeding the major flood level of 46 feet or 18 feet above flood stage. The top of the Grand Forks dike system, built after the 1997 Red River flooding, is at a level of 60 feet. The Red River at Grand Forks has a 10% chance of exceeding 54.35 feet, the record flood level set on April 22, 1997. These outlooks are subject to change based on the timing of the Spring melt combined with future precipitation and any river ice-jam flooding. Lower Great Lakes to Illinois and part of New England Wet soils combined with up to 150% of normal winter precipitation, sub normal winter temperatures and frozen grounds have produced an area with an above average risk of Spring flooding from  the southern Great Lakes into Illinois.  Streamflows are running well above historical averages and a number of locations are already near or above flood stage, setting the stage for additional flooding. A significant snowpack still exists across much of northern New York and the rest of New England. An above average area of flood risk exists across a portions of east central New York into southern Vermont and New Hampshire.    Alaskan Potential The flood potential from snowmelt and ice jams this spring breakup season throughout Alaska is currently rated as average. The March ice thickness data are available for a limited number of observing sites in Alaska. Measurements indicate that ice thickness ranges from below normal on the the Yukon at Nulato and the Tanana at Fairbanks to above normal at the Yukon River at Eagle. Accumulated freezing degree days are generally between 100 and 120 percent of normal over most of mainland Alaska. On the North Slope they are around 84 percent of normal while southeast Alaska has values ranging from 146 to 164 percent of normal. An analysis of the March 1 snowpack by the Natural Resources Conservation Service (NRCS) indicates an above normal snowpack throughout much of mainland Alaska. Exceptions include below normal snowpack in Southwest Alaska, the Matanuska/Susitna basin and the North Slope drainages while the Kenai Peninsula is below to well below normal. Above normal snowpack is reported in much of southeast Alaska. There is enough snow in most areas to produce significant snowmelt runoff peaks and potential flooding if subjected to a rapid warming pattern.   Temperature and Frost Depth Temperatures this winter have been variable across the United States.  The north central states saw temperatures 5 to 6 degrees below normal in December and January, with the deep cold extending eastward across the northeastern quarter of the Nation in January. Above average temperatures across the West, High Plains and into the central and southern Plains reached as much as 4 degrees above normal for the winter.  February warmth across the Northeast reduced the amount of snow cover in southern New England and western and southern New York. It also contributed to melting much of the snowpack across the southern Great Lakes into the Midwest, generating the ongoing minor to moderate river flooding and creating an above average risk for Spring flooding. The warm temperatures from parts of Montana through the central and southern Plains have reduced the extent of snow cover and the amount of water held in the snow, contributing to the lower than average risk of flooding. Frost depths across the north central U.S. range from 2 to more than 3 feet deep in eastern North Dakota as a result of saturated soils preceding the freezeup in November and December. Depths run from 1 to 2 feet in parts of the southern Great Lakes states to 2 to 4 feet in northern sections. Frost depths in southeastern Michigan are less than a foot due to early season snow insulating the ground.  Precipitation and Snow Conditions Precipitation across the U.S. has varied from 50% or less of normal during the past 90 days across the central and southern Plains and Southeast to in excess of 150% of normal in parts of the northern and central Rockies  and the upper Missouri Valley. Substantial Fall precipitation across the northern and central Plains into the Great Lakes resulted in very wet soils which froze going into the winter.  Several warm, wet storm systems in mid February through early March brought heavy rainfall across Illinois, Indiana, northern Ohio, northwest Pennsylvania and western New York. These systems, with accompanying snow melt and ice jamming, produced widespread flooding across the region. A late season storm in early March deposited from 4 to 6 inches of precipitation across the Midwest and  southern Great Lakes. Winter storms during March also deposited substantial amounts of precipitation across parts of northern California. A preliminary graphic of the 5 month precipitation (October 2008 - February 2009) across the West shows above normal precipitation throughout the higher elevations of southeast California, southern Nevada and over the western High Plains including much of Montana.  Precipitation is well below normal across much of central and northern California, eastern Oregon, southwestern Idaho, southeast Arizona, and southern New Mexico.      Snowpack as of March 1st across the West is above the long term average over much of the Rockies and below normal across much of the west coast states.  Although some basins in the Sierra Nevada Mountains saw impressive gains to the snowpack from a wet storm system that lasted from March 1st through March 4th, snowpacks remain below average. Across the northern tier of states, snowpack  is substantial with 4 to 6 inches of water held in the snowpack.  In the Northeast, substantial snowpack is confined to a portion of eastern New York, New Hampshire and Vermont where the risk of flooding is above normal.   Soil Moisture and Drought Conditions Plentiful rainfall has resulted in very wet soils from the northern and central Plains, across the middle Mississippi Valley and across the southern Great Lakes as well as parts of northern New England. The wetness is reflected in the Palmer Drought Severity Index as well as soil moisture conditions. This wetness can enhance runoff, especially in areas with ample snowcover. Dry soil conditions across the southern Plains to the Southeast as well as areas west of the Rockies combined with above normal temperatures and substantially below normal precipitation to create a reduced flood risk. Drought conditions have contributed to the below average flood risk across the southern tier of states and much of the West.     River Conditions Rivers in a swath from New England across the southern Great Lakes into Illinois and eastern Iowa and Missouri are running above normal as of March 13th. Warm temperatures combined with rain from the Midwest to the mid Atlantic and southern New England caused snow melt in mid February which generated above average streamflows across this area.  River ice in much of southern New England and the Midwest was eliminated due to these recent warm temperatures and rainfall.  However, river ice is expected to be a problem in the Upper Midwest as ice is unusually thick this Spring due to the colder than normal Winter. This will lead to increased chances of ice jam flooding on the Red River of the North and its tributaries. River ice also persists across northern New York and northern New England, creating the potential for ice jam flooding in the region.    Water Supply The water supply outlook as of March 1st across the West is significantly lessened from that of the same time last year. Mountain snowpack is variable, with significant surpluses in scattered basins across the West and over the interior and panhandle of Alaska.  Large deficits dominate much of the Upper Columbia River basin and the southern Arizona-New Mexico border.  Precipitation during fall and winter was generally below normal. The map of water contained in the snow  shows large areas of sub normal content.  Reservoir storage as of March 1st shows the effect of persistent drought, with most levels below average. The anticipated sub-average streamflows will not improve the drought situation.  Most of the annual streamflow in the western U.S. originates as snowfall that accumulates in the mountains during the winter and early spring. This snow accumulation can continue into April. If March and early April have below normal precipitation, the snowpack could fall back to sub normal levels.  As a result of the plentiful precipitation this winter across the Northeast, water supply reservoirs across the region are generally at or above target levels for mid March. Groundwater monitoring wells across New England and New York state show levels near to above normal. Lakes and reservoirs are near or above target levels for mid March. As of March 3rd, the New York City water supply system was at 85.8 percent of capacity, which is 1.6 percent above normal. Water supply is not anticipated to be an issue going into spring for this area. Across the Mid Atlantic, water supply conditions are generally close to average. In the Southeast, reservoir conditions are near normal except for portions of northeast Georgia and western South Carolina. Lake Lanier, Lake Hartwell and Lake Thurmond are running very low even though they have seen some beneficial rainfall lately.   Summary Early season heavy rain saturated soils which froze deeply before snow fell across the northern Plains, combined with substantial snowpack, has created an area of above average flood risk. Major overland flooding is expected in eastern North Dakota and northwest Minnesota beginning the week of Sunday, March 22. This will subsequently lead to major, and possibly record, flooding along the Red River of the North and its tributaries.  There is a 100% chance that the Red River at Fargo ND will exceed the major flood level of 30 feet, and close to a 33% chance of exceeding 39.57 feet, the record flood level set on April 17, 1997. At Grand Forks, the Red River has a 100% chance of exceeding the major flood level of 46 feet. The top of the permanent Grand Forks dike system, built after the 1997 Red River flooding, is at a level of 60 feet. The Red River has a 10% chance of exceeding 54.35 feet, the record flood level set on April 22, 1997.  Deeply frozen rivers in the region have created an above average risk of ice jam flooding. Major flooding also remains likely along the James River in northern South Dakota. Heavy rains and saturated soils has caused flooding on rivers from Illinois to the lower Great Lakes region.  Additional heavy spring rainfall is likely to cause renewed flooding.  Elsewhere, substantial snowpack across an area of eastern New York and southern New Hampshire and Vermont has created a greater than average risk of flooding this Spring.  Ongoing drought conditions and below average snowpack led to a below average risk of flooding across portions of the West, as well as portions of the Southwest into southern New Mexico and Texas . In addition, generally dry conditions have yielded a lowered risk of flooding across parts of the Southeast and upper Great Lakes.   For current flood information: http://www.weather.gov/ahps http://www.noaawatch.gov/floods.php Joanna Dionne Hydrologic Information Center