Outlook #1 released on January 9, 2019
Winter/Spring River Flood Potential Outlook
National Weather Service Middle Atlantic River Forecast Center (MARFC)
State College, PA
1:30 pm EST Wed, Jan 9, 2019
Outlook Number 19-01 – January 9, 2019 (outlook map).
This Winter/Spring River Flood Potential Outlook is valid for the two-week period January 9-23, 2019.
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 TO ABOVE AVERAGE
The river flood potential across the MARFC area of responsibility for the next two weeks is average to above average. Factors which contribute to this assessment of river flood potential are discussed in some detail below.
CURRENT FLOODING – NONE
There is no river flooding within the MARFC service area presently.
RECENT PRECIPITATION – ABOVE TO MUCH-ABOVE AVERAGE
The MARFC region experienced widespread near-record to record precipitation during calendar year 2018. The frequent doses of heavy precipitation led to a record number of flood events at the 175 official hydrologic forecast points within the MARFC service area. More recently, during the last 30 days (December 10, 2018 – January 8, 2019) the wet precipitation pattern has continued. With the exception of a portion of NY, precipitation during the last 30 days was above average to much-above average across the entire MARFC region. In a small portion of NY precipitation was near average. To view precipitation departure data please visit https://www.weather.gov/marfc/Precipitation_Departures.
SNOW CONDITIONS – BELOW AVERAGE TO AVERAGE
Presently the only snow on the ground within the MARFC service area is across portions of NY and northern PA. In these areas snow depths are 3 inches or less, with snow water equivalent values of less than a half inch. Snow conditions in NY, across much of PA and along the Appalachians are best described as being below average for early January. Across the southeastern half of the MARFC region, no snow exists which is about average for that region. Additional accumulations of lake-effect snow are expected during the next two days across northern PA and NY, where some locations could pick up several inches. Snow information can be found at https://www.weather.gov/marfc/Snow and https://www.nohrsc.noaa.gov.
RIVER ICE – BELOW AVERAGE TO AVERAGE
No river ice is currently being observed within the MARFC region which is below normal for about the northwestern third of the MARFC service area, and about normal elsewhere.
STREAMFLOW CONDITIONS – MOSTLY ABOVE MEDIAN
The latest data from the United States Geological Survey (USGS) indicate above normal to much-above normal streamflow conditions across most of the MARFC region. The exception is across southeastern VA and lower portions of the Delmarva Peninsula where streamflow conditions are closer to median for the date. Please visit https://waterdata.usgs.gov/nwis/rt for current streamflow data.
SOIL MOISTURE CONDITIONS - NORMAL/BELOW NORMAL
The long-term Palmer drought severity index is used to estimate deep soil moisture conditions. The January 5, 2019 chart (found at http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/regional_monitoring/palmer.gif) suggests deep soils across most of the MARFC service area contain moisture that is much-above normal for this time of year. This reflects just how extremely wet 2018 was across the MARFC region. Additional more detailed soil moisture information supports the idea that soils are extremely wet across all of the MARFC area. Go to http://www.cpc.ncep.noaa.gov/products/Soilmst_Monitoring and then click on U.S. Monitoring to view this soil moisture information.
GROUNDWATER – ABOVE NORMAL TO EXTREMELY HIGH
USGS groundwater monitoring wells are currently indicating above normal to extremely high groundwater levels across nearly all of the MARFC area. Please visit https://groundwaterwatch.usgs.gov.
RESERVOIR CONDITIONS – AVERAGE TO ABOVE AVERAGE
Most major reservoirs within the MARFC region are holding storages that are average to above average for this time of year.
FUTURE WEATHER CONDITIONS
Seasonably cool temperatures and generally light-moderate precipitation events are expected for about the next week across the MARFC region. Some significant lake-effect snow will accumulate across portions of NY and PA during the next two days. A storm system may impact portions of the MARFC region Saturday night-Sunday night, bringing what currently looks to be light-moderate amounts of snow and mixed precipitation to the region. A drier and somewhat milder pattern looks possible around midweek next week. Then a more significant storm system may impact the region toward the end of next week. Indeed, current longer-range weather outlooks suggest the second week of this two-week period may have wetter than normal weather conditions. Long-range outlooks can be viewed at http://www.cpc.ncep.noaa.gov/products/predictions/610day.
ENSEMBLE RIVER FORECASTS – NEGLIGIBLE THREAT OF RIVER FLOODING DEVELOPING THROUGH JANUARY 15, 2019
The most recent runs (January 9, 2019) of the ensemble river forecasts, which take into account anticipated future weather conditions including precipitation and temperatures, show little chance of river flooding developing within the MARFC region for about the next week through January 15, 2019. Please visit https://www.weather.gov/erh/mmefs for ensemble river forecasts.
For the next two weeks the river flood potential for rivers in the MARFC region is average to above average for this time of year. Although snow and river ice conditions are currently negligible, soils are wet and streamflow is high across the entire region. A single, widespread heavy rain event of 2-3 inches in 6-24 hours would likely result in some river flooding within the MARFC region. The good news is that there are currently no strong indications of any widespread heavy rain events for at least the first week of this outlook period, through next Wednesday, January 16, 2019. For the second week of this outlook period, the latest long-range weather outlook issued by the NWS Climate Prediction Center suggests precipitation could once again be above average across the MARFC region. Long-range outlooks are seen at http://www.cpc.ncep.noaa.gov/.
WATER SUPPLY OUTLOOK
According to the latest (January 1, 2019) U.S. Drought monitor (http://droughtmonitor.unl.edu), there are currently no drought conditions within the MARFC service area. 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.
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 Winter/Spring Flood Outlook will be issued by this office in two weeks, on January 23, 2019.