National Weather Service United States Department of Commerce
WATER RESOURCES OUTLOOK NATIONAL WEATHER SERVICE OHIO RIVER FORECAST CENTER WILMINGTON OH 1150 AM EDT Tuesday April 27 2021 THE FOLLOWING IS THE 30-DAY WATER RESOURCES OUTLOOK FOR THE MONTH OF MAY .WATER RESOURCES STREAMFLOW OUTLOOK... The Ohio River Forecast Center Water Resources Outlook for the month of May calls for Below Normal streamflows for roughly the northern third of the basin. The rest of the basin, particularly locations lying south of the mainstem Ohio still look to remain more in the Normal range when all is said and done with the month. ..................................................................... .HYDROLOGIC FLOOD AND DROUGHT POTENTIAL... As we begin to really get into the heart of the warm season in May, the existing drier than normal conditions of the far northern basin certainly have the potential for "true" drought and the possibility of expanding a bit southward from the current swath. The latest drought monitor (see https://droughtmonitor.unl.edu) indeed does show the beginning of some D1 drought, particularly up by the lakefronts. So to start to make a dent in any precipitation deficit we need to see some signs of slightly to above normal rainfaill in the guidance/models. As of this writing, the models and longer term guidance do not show much of a signal for that. As far as any flood potential for the month of May...precipitation in the month begins to often make a turn to the more convective. Meaning, heavier amounts come a bit more quickly and through localized anomalously heavy swaths. Certainly, there is a chance anytime for these kind of mesoscale and "training" events, but for the scope of this middle to longer range outlook, any potential does not look enhanced. ..................................................................... .PAST 30 DAY HYDROLOGICAL AND METEOROLOGICAL REVIEW... RAINFALL DEPARTURES... The April precipitation was below normal for nearly the entire Ohio River forecast basin, save for a few small areas in the far southeast. Percents of normal ran about 65-90 percent for the southern half of the basin while the northern basin ran roughly 25-50 percent of normal April precipitation. https://www.weather.gov/ohrfc/images/dynamic/latest30day.jpeg SOIL MOISTURE CONDITIONS... Antecedent soil conditions by the end of April were below normal to normal... naturally due to the below normal precipitation mentioned above. As a general rule, areas north of the Ohio River mainstem are below normal, increasing in deficit the more northward, with the southern half still hanging on to normal. https://www.cpc.ncep.noaa.gov/soilmst/w.shtml STREAMFLOW CONDITIONS... Again, north of the Ohio mainstem is by April month's end running roughly 10 to 30th percentile when it comes to streamflow...even slightly below 10th percentile for northwestern PA. The southern half is more in the 50th to 60th percentile range. https://watermonitor.gov ..................................................................... .ATMOSPHERIC TELECONNECTION AND OSCILLATION FORECASTS FOR THE NEXT MONTH... TELECONNECTION/OSCILLATION PATTERN ARCTIC OSCILLATION Trending Normal = Normal NORTH ATLANTIC OSCILLATION Trending negative = Normal for southern basin PACIFIC/NORTH AMERICAN TELECONNECTION Trending Normal = Normal ENSO - EL NINO/LA NINA OSCILLATION Transitioning from La Nina to Neutral = Normal https://www.cpc.ncep.noaa.gov ..................................................................... .TECHNICAL DISCUSSION... The upcoming month of May finds an Ohio River basin that is generally a bit below normal in precipitation. This is particularly the case for the northern tier of the Ohio Valley as the current rainfall is in a bit of deficit for the season and drought monitors are already tagging this area as abnormally to moderately dry. There does seem to be some indication in the nearer term models that the beginning of May could be a bit more active when it comes to systems traversing the Ohio Valley. However, at current time, there is nothing showing the period being much more than normal to slightly above normal precip-wise and placement still looks more south of the Ohio mainstem, where antecedent conditions are normal. Certainly, the month of May typically brings the chance of more convective type events which can make an area "whole" in a hurry. However, for the scope of this Monthly-scale outlook, any potential of this does not look enhanced. Given this, the overall streamflow outlook for May remains and expands a bit below normal for the northern third of the forecast basin, with the southern half of the basin looking and staying normal. ....................................................................... VISIT OUR WATER RESOURCES WEBSITE AT http://www.weather.gov/ohrfc/WRO IN ADDITION TO A 30-DAY STREAMFLOW OUTLOOK...YOU CAN ALSO OBTAIN A 60- AND 90-DAY OUTLOOK AT THE WEBSITE $$