Winter/Spring River Flood Potential Outlook
NWS Middle Atlantic River Forecast Center (MARFC)
State College, PA
3:35pm EST Wed, Jan 8, 2020
Outlook Number 20-01 - January 8, 2020
This Winter/Spring River Flood Potential Outlook is valid for the two-week period January 9-23, 2020.
This outlook estimates the potential for river flooding (not flash flooding) to develop during the next two weeks across the Middle Atlantic River Forecast Center`s (MARFC) area of responsibility (Mid- Atlantic Region) based on a current assessment of hydrometeorological factors which can contribute to river flooding. Across the MARFC area these factors include future weather conditions, recent precipitation, soil moisture, snow cover and snow water equivalent, river ice, streamflow, and others. This outlook does not address the severity/extent of any future river flooding.
Remember, in the Mid-Atlantic region heavy rainfall is the primary factor which leads to river flooding. Heavy rainfall can rapidly cause river flooding any time of the year, even when overall river flood potential is considered to be low or below average.
TWO-WEEK RIVER FLOOD POTENTIAL - AVERAGE
The river flood potential during the next two weeks (through January 23, 2020) is about average. Factors which contribute to this assessment of river flood potential are discussed below.
CURRENT RIVER FLOODING - NONE
There is currently no river flooding occurring within the MARFC service area.
RECENT PRECIPITATION - VARIABLE
During the last 30 days (December 9, 2019 - January 7, 2020) observed precipitation has been rather variable across the MARFC region, but fairly close to normal for most of the area. Exceptions include portions of southwestern PA and much of NJ which have been somewhat wetter than normal. To view precipitation departure data please visit https://www.weather.gov/marfc/Precipitation_Departures.
SNOW CONDITIONS - BELOW AVERAGE/AVERAGE
While much of the MARFC region has snow on the ground as of this morning (January 8, 2020), all of the snow is essentially insignificant hydrologically. Within the MARFC service area, there is little/no snow across southeast VA, the Delmarva region, and along coastal NJ. This is normal or about average. Otherwise, generally 1-5 inches of snow covers the ground, with a few locally greater depths. The water equivalent of the snow is mostly less than a half inch, again except for a few locally higher amounts. Snow conditions are below average (in some areas much-below average) for the date across about the northwestern half of the region, and about average elsewhere. Even if all the snow melted in a short time frame, the snow is currently not a significant factor in terms of its ability to produce river flooding. Snow information can be found at https://www.weather.gov/marfc/Snow and https://www.nohrsc.noaa.gov.
RIVER ICE - BELOW AVERAGE/AVERAGE
Very little river ice currently exists within the MARFC service area. This is below average for roughly the northwestern half of the region, and about average for the southeastern half.
STREAMFLOW CONDITIONS - VARIABLE
The latest data from the United States Geological Survey (USGS) indicates streamflow conditions are somewhat above median across NY and portions of PA, then gradually decrease to average/below average heading south into VA. For current streamflow conditions please visit https://waterdata.usgs.gov/nwis/rt.
SOIL MOISTURE CONDITIONS - VARIABLE
The long-term Palmer drought severity index is useful to estimate deep soil moisture conditions. The January 4, 2020 chart (found at https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/regional_ monitoring/palmer.gif) suggests deep soils are unusually moist to extremely moist across much of NY, PA and northern NJ. Further south, the index suggests near normal to somewhat below normal values across VA and the Delmarva region. Additional more detailed soil moisture information also suggests that soils are somewhat wetter than normal across portions of NY and northern PA, while soils gradually dry heading south. Soils in MD, VA and DE are drier than normal for the date. Go to https://www.cpc.ncep.noaa.gov/products/Soilmst_Monitoring/ and then click on U.S. Monitoring to view this soil moisture information.
GROUNDWATER - NEAR NORMAL
Within the MARFC service area, real-time USGS groundwater monitoring wells indicate groundwater levels are generally fairly close to normal. Please visit https://groundwaterwatch.usgs.gov.
RESERVOIR CONDITIONS - AVERAGE/ABOVE AVERAGE
Most major reservoirs within the MARFC region are holding storages that are average to somewhat above average for this time of year.
FUTURE WEATHER CONDITIONS - MODERATE RAIN EVENT THIS WEEKEND
After a seasonably chilly start, another warm up quickly begins in what has thus far been a rather mild winter. By Saturday, January 11, temperatures are currently predicted to range from the mid-50s in NY to the mid-70s in southeast VA. This will effectively melt nearly all of the snow on the ground within the MARFC region. Periods of rain will accompany the mild temperatures this weekend. Presently moderate rainfall is anticipated, with amounts generally in the 0.25-1.00 inch range ending Sunday. However, it is worth mentioning that there is a limited risk that heavy rain (1-2 inches) could fall across portions of NY and PA this weekend. Additional light-moderate rain is possible around next Tuesday. Then a trend toward cooler and drier weather later next week. The latest (January 8, 2020) longer-range weather outlooks issued by the NWS Climate Prediction Center suggest both temperatures and precipitation will be above normal for most of the MARFC region when averaged over the nine-day period January 14-22, 2020. Visit https://www.cpc.ncep.noaa.gov/ to view the outlooks.
ENSEMBLE RIVER FORECASTS - A LIMITED THREAT OF RIVER FLOODING DEVELOPING MAINLY IN NY DURING THE NEXT FEW DAYS
The most recent runs (January 8, 2019) of the short-term (one week) ensemble river forecasts, which take into account anticipated future weather conditions including precipitation and temperatures, show a limited threat of scattered river flooding developing as a result of the rain event this weekend. While current information suggests this will be a moderate rain event, there are some models that are indicating heavier rains for portions of NY and PA, which if realized could produce some river flooding. As such rainfall forecasts for the weekend event should be monitored during the next few days. Please visit https://www.weather.gov/erh/mmefs for short- term ensemble river forecasts.
The risk of river flooding during the next two weeks for streams and rivers within the MARFC service area is near average. Snow and river ice conditions are essentially insignificant currently in terms of contributing to river flood potential. However a moderate rain event is currently anticipated this weekend, with the heaviest rains expected across the northern half of the region. While no river flooding is currently expected to develop from this event, rainfall forecasts should be monitored since some models are suggesting heavier rain of 1-2.5 inches could fall this weekend.
WATER SUPPLY OUTLOOK
According to the latest (January 2, 2020) U.S. Drought monitor (https://droughtmonitor.unl.edu), a small area of abnormally dry conditions exists across a portion of the Delmarva Peninsula. Visit https://www.drought.gov, https://www.cpc.ncep.noaa.gov and https://www.weather.gov/marfc/wro_north for additional drought and water supply information. Assuming near-normal precipitation for the next few months, no water supply shortages are anticipated anywhere within the MARFC region through April, 2020.
Please visit the NWS MARFC homepage at https://www.weather.gov/marfc or find us on Facebook at https://www.facebook.com/nwsmarfc/?REF=aymt_homepage_panel and on Twitter@nwsmarfc.
The next outlook will be issued in two weeks, on or about January 22-23, 2020.