National Weather Service United States Department of Commerce

Winter/Spring River Flood Potential Outlook
NWS Middle Atlantic River Forecast Center (MARFC)
State College, PA
4:34 pm EST Wed, February 17, 2021

Outlook Number 21-04 - February 17, 2021


This Winter/Spring River Flood Potential Outlook is valid for the two-week period February 18 - March 4, 2021.

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 other factors. 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 - ABOVE AVERAGE TO AVERAGE

The river flood potential during the next two weeks (through March 4, 2021) is above average for late February across southern and eastern portions of the MARFC area of responsibility, and average elsewhere. The line separating the two categories runs roughly from southeast NY southwestward into west-central PA. Factors which contribute to this assessment of river flood potential are discussed in some detail below.

CURRENT RIVER FLOODING - NONE

As of this afternoon (Wednesday, February 17, 2021) minor flooding was occurring along a portion of the lower James River in VA. Flooding will end here this evening.

RECENT PRECIPITATION - WET SOUTH, NORMAL/BELOW NORMAL ELSEWHERE

During the last 30 days (January 18 - February 16, 2021) observed precipitation across the MARFC region has been above normal to much-above normal across far southern portions of the MARFC service area, including portions of central VA and the lower half of the Delmarva Peninsula. In this area amounts have been 1-2.5 inches above normal which is 25 to 75 percent above average. Otherwise, most of the rest of the service area has received below-normal to normal precipitation, 50-125 percent of average. Precipitation departure data is found at www.weather.gov/marfc/Precipitation_Departures.

SNOW CONDITIONS - NORMAL TO MUCH-ABOVE NORMAL

As of this afternoon (February 17, 2021), snow covers the ground across roughly 70 percent of the MARFC service area. The snow/no snow line runs roughly from near/along the WV/VA border, east through central MD and into central/southern NJ. The current snow cover extends somewhat further east than what is typical for mid February. In addition, moderate amounts of new snow are expected across much of the MARFC service area during the next two days. Within the MARFC service area, snow conditions are above normal to much-above normal for this time of year across much of NY, much of PA, northern NJ and portions of WV and MD. In this region snow depths this morning were generally in the 10-20 inch range, with scattered greater depths. Corresponding snow water equvialent values in this same region range generally from 1-4 inches, with isolated values of 4.5 inches. Snow depths in the remaining areas where snow exists are generally 1-8 inches, with 0.25-1.0 inches of snow water equivalent. These conditions are about normal for mid February. Little or no snow remains across most of VA, the Delmarva Peninsula and southern NJ, which is also about normal. But to repeat, moderate snowfall is expected across much of this region during the next two days. Snow information can be found at www.weather.gov/marfc/Snow and www.nohrsc.noaa.gov.

RIVER ICE - AVERAGE TO SOMEWHAT BELOW AVERAGE

Currently most streams and rivers in NY, much of PA, portions of NJ, western MD, eastern WV and northwestern VA have at least some ice in them. This is a fairly typical area for river ice to be observed in the second half of February. The most river ice is found in streams and rivers throughout the Susquehanna and Delaware River Basins, which is also typical for mid-late February. The river ice is not being reported as unusually thick or extensive for this time of year. Some additional river ice formation is possible for at least the first week of this outlook period. Then a gradually milder weather pattern appears likely to evolve later in this outlook period, preventing additional river ice formation.

STREAMFLOW CONDITIONS - HIGH SOUTH AND EAST, OTHERWISE NORMAL

The latest data from the United States Geological Survey (USGS) indicates current streamflow conditions within the MARFC region are much-above median across roughly the southeastern two-thirds of the region. Streamflow conditions then generally gradually decrease heading west and north from this area and are generally fairly close to median for mid February. For current streamflow conditions please visit waterdata.usgs.gov/nwis/rt.

SOIL MOISTURE CONDITIONS - WET SOUTHEAST, OTHERWISE NEAR NORMAL

Soils remain extremely moist across southeastern portions of the MARFC service area. The long-term Palmer drought severity index is useful to estimate deep soil moisture conditions. The February 13, 2021 map (seen at cpc.ncep.noaa.gov/products/analysis_monitoring/regional_monitoring/palmer.gif) suggests deep soils remain extremely moist across central/southeast VA and much of the Delmarva Peninsula. Outside of this very wet area, the map shows near-normal values. Additional soil moisture data confirms the very wet soils across southeastern portions of the area. Visit www.cpc.ncep.noaa.gov/products/Soilmst_Monitoring/ and then click on U.S. Monitoring.

GROUNDWATER - VARIABLE

Within the MARFC service area, real-time USGS groundwater monitoring wells indicate current groundwater levels generally range from below average in the far north, gradually increasing to above or even much-above normal in the south for this time of year. To see groundwater levels visit groundwaterwatch.usgs.gov/usgsgwnetworks.asp.

RESERVOIR CONDITIONS - AVERAGE

Most major reservoirs within the MARFC region are holding storages that are about average for this time of year. For example, reservoirs in the Delaware River Basin that supply NYC with water are showing near-average storages presently.

FUTURE WEATHER CONDITIONS - CHANGEABLE

A winter storm will produce widespread moderate amounts of snow, sleet and freezing rain over much of the region tonight through Friday. The system should be monitored for the possibility of producing just enough rain to cause some flooding again across lower portions of the James and Appomattox River Basins in VA. After the storm, seasonable weather conditions will likely prevail for the first week of this two-week period. However, a milder weather pattern appears likely to develop during the second week. After the storm moves out Friday, there currently are no strong indications of any widespread heavy rain events for the rest of the first week of this outlook period. The latest (February 17, 2021) weather outlooks issued by the NWS Climate Prediction Center suggest that both temperatures and precipitation will be normal or above normal when averaged over the entire nine-day period February 23-March 3, 2021. Please visit www.cpc.ncep.noaa.gov for the latest outlooks.

ENSEMBLE RIVER FORECASTS - SOME THREAT OF RIVER FLOODING

The most recent runs (February 17, 2021) of the short-term (6-10 day) ensemble river forecasts, which take into account anticipated future weather conditions including precipitation and temperatures, do show some threat of river flooding developing across southern portions of the service area. The threat is due to the possibility of locally heavy rain early in the outlook period, followed by snowmelt/additional rain later in the period. Please visit www.weather.gov/erh/mmefs. Current longer-term forecasts also suggest a somewhat increased chance for river flooding compared to normal during the next 30 days for some river basins within the MARFC service area, most notably the Potomac River Basin. This is primarily due to what is now above-average snow conditions in portions of that river basin. Any future river flooding will depend on shorter-term weather conditions, such as the widespread heavy rainfall and/or rapid snowmelt.

SUMMARY

A winter storm is expected across most of the MARFC service area beginning tonight (Wednesday, February 17) and lasting well into Friday. The storm will add to the already substantial snow conditions that exist across roughly the northwestern half of the region, and put down some new snow across much of the southern half of the region. The storm should be monitored for the possibility of producting just enough rain across portions of the James and Appomattox River Basins to produce some additional river flooding, though that possibility seems fairly low due to the cold temperatures. Meanwhile, in the longer range, while there are currently no strong indications of widespread heavy rainfall or widespread rapid snowmelt after this first storm departs late Friday, snow and to some degree river ice conditions have increased enough to be of some concern, especially over about the northwestern half of the MARFC region. A milder weather pattern is now expected to develop sometime during the second week of this outlook period, but it is too soon to tell if/where significant snowmelt will occur, and whether or not widespread heavy rainfall will occur. Needless to say, the river flood potential is becoming more elevated with time as we get closer to March, the month when river flooding due to snowmelt and/or heavy rainfall is fairly common. As such, conditions will need to be monitored closely for the rest of this winter into early spring, until such time that most of the snow has melted.

WATER SUPPLY OUTLOOK

According to the latest (February 9, 2021) U.S. Drought Monitor (droughtmonitor.unl.edu), abnormally dry conditions persist across a small portion of southern NY and northern PA. However, assuming near-normal precipitation over the next few months, no water supply shortages are anticipated within the MARFC region through May, 2021.

Please visit www.drought.gov, www.cpc.ncep.noaa.gov and www.weather.gov/marfc/WRO for additional drought and water supply information. Please visit the NWS MARFC homepage at www.weather.gov/marfc or find us on Facebook at www.facebook.com/nwsmarfc/?REF=aymt_ homepage_panel and on Twitter @nwsmarfc.

The next winter/spring river flood outlook product will be issued by this office March 3-4, 2021.

Winter/Spring River Flood Potential Outlook
NWS Middle Atlantic River Forecast Center (MARFC)
State College, PA
10:12 pm EST Wed, February 3, 2021


Outlook Number 21-03 - February 3, 2021


This Winter/Spring River Flood Potential Outlook is valid for the two-week period February 4 - February 18, 2021.

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 other factors. 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 - BELOW AVERAGE TO AVERAGE

The river flood potential during the next two weeks (through February 18, 2021) is about average for early February across southern and eastern portions of the MARFC area of responsibility, and somewhat below average elsewhere. This is very similar to the outlook issued two weeks ago. The line separating the two categories runs roughly from extreme northwest NJ southwestward into south-central PA. western MD, eastern WV and west-central VA. Factors which contribute to this assessment of river flood potential are discussed in some detail below.

CURRENT RIVER FLOODING - NONE

No river flooding is currently occurring within the MARFC service area.

RECENT PRECIPITATION - BELOW AVERAGE

During the last 30 days (January 4 - February 2, 2021) observed precipitation across most of the MARFC region has been below average to much-below average by generally 0.5 to 1.5 inches, or about 20 to 70 precent below average. Precipitation departure data can be seen at www.weather.gov/marfc/Precipitation_Departures.

SNOW CONDITIONS - NORMAL TO MUCH-ABOVE NORMAL

As of this evening (February 3, 2021), snow covers the ground across roughly 85 percent of the MARFC service area. The snow/no snow line runs roughly from Roanoke, VA northeast across the central Delmarva Peninsula and across extreme southeastern NJ. The snow cover currently extends somewhat further south and considerably further east than what is typical for early February, thanks to the recent snowstorm. Within the MARFC service area, snow conditions are above normal to much-above normal for this time of year across much of NY, much of PA and much of NJ. In this region snow depths this morning were generally in the 10-20 inch range, with scattered reports of 20-30 inches. Corresponding snow water equvialent values in this same region range generally from 1-3 inches, with isolated values of 3.5 inches. In portions of central and eastern MD, eastern WV and northern VA, 3-12 inches of snow exists which equates to about 1-1.5 inches of water. These conditions are somewhat above normal for early February. Then along and near the western border of our service area, from south-central NY southward through the Appalachian Mountains, snow conditions are normal/above normal with snow depths of 5-15 inches and water equivalent values mostly in the 1-2 inch range with locally higher amounts. Much of the light snow cover that existed across central VA and the southern half of the Delmarva Peninsula melted today, and more will melt during the next couple of days in northern VA, across the Delmarva Peninsula and across southeastern NJ. Snow information can be found at www.weather.gov/marfc/Snow and www.nohrsc.noaa.gov.

RIVER ICE - AVERAGE TO SOMEWHAT BELOW AVERAGE

Currently, most streams and rivers in NY, much of PA, northwestern NJ, western MD, eastern WV and northwestern VA have at least some ice in them. This is a fairly typical area for river ice to be observed in early February. The most river ice is found in streams and rivers throughout the Susquehanna and Delaware River Basins, which is also typical for early February. The river ice is not unusually thick or extensive for this time of year, but has increased a fair amount from just two weeks ago. In areas not specifically mentioned, little or no river ice exists, which is also normal for those areas. Additional river ice formation is expected during the next two weeks, as the coldest temperatures of this winter appear likely. Today`s NWS Climate Prediction Center`s 6-10 and 8-14 day (through February 17) temperature outlooks both strongly favor below-normal temperatures for our region.

STREAMFLOW CONDITIONS - VARIABLE

The latest data from the United States Geological Survey (USGS) indicates current streamflow conditions within the MARFC region range from above median across central and southeastern VA, the Delmarva Peninsula and southeastern NJ. Streamflow conditions then generally gradually decrease heading west and north from this area and are in the median to below-median range. For current streamflow conditions please visit waterdata.usgs.gov/nwis/rt.

SOIL MOISTURE CONDITIONS - WET SOUTHEAST, OTHERWISE NEAR NORMAL

Soils remain extremely moist across southeastern portions of the MARFC service area. The long-term Palmer drought severity index is useful to estimate deep soil moisture conditions. The January 30, 2021 map (seen at www.cpc.ncep.noaa.gov/products/ analysis_monitoring/regional_monitoring/palmer.gif) suggests deep soils are extremely moist across central/southeast VA and the lower Delmarva Peninsula. Outside of this very wet area, the map shows near-normal values. Additional soil moisture data confirms the very wet soils across southeastern portions of the region. Please visit www.cpc.ncep.noaa.gov/products/Soilmst_Monitoring/ and then click on U.S. Monitoring.

GROUNDWATER - VARIABLE

Within the MARFC service area, real-time USGS groundwater monitoring wells indicate current groundwater levels generally range from below average in the far north, gradually increasing to above or even much-above normal in the south for this time of year. To see groundwater levels visit groundwaterwatch.usgs.gov/usgsgwnetworks.asp.

RESERVOIR CONDITIONS - AVERAGE

Most major reservoirs within the MARFC region are holding storages that are about average for this time of year. For example, reservoirs in the Delaware River Basin that supply NYC with water are showing near-average storages presently.

FUTURE WEATHER CONDITIONS - UNFAVORABLE FOR HEAVY RAIN

At the present time, due to seasonable winter temperatures and only weak storm systems, there are no strong indications of any widespread heavy rain or substantial snowmelt events for the MARFC region for about the next 5-7 days. After a brief warmup, a cold front is expected to pass through the MARFC region Friday. Mixed light-moderate precipitation is expected. Sunshine on Thursday and milder temperatures ahead of the front will likely melt some snow across southeastern portions of our service area, but only minor rises in river levels are expected from the snowmelt. Afterwards, a generally colder and perhaps drier weather pattern looks likely in the longer range, The latest (February 3, 2021) weather outlooks issued by the NWS Climate Prediction Center strongly suggest that temperatures will be below normal when averaged over the entire nine-day period February 9-17, 2021. The outlooks also show a good chance that precipitation will end up being below average for that same nine-day period. Please visit www.cpc.ncep.noaa.gov/.

ENSEMBLE RIVER FORECASTS - VERY LIMITED THREAT OF RIVER FLOODING

The most recent runs (February 3, 2021) of the short-term (6-10 day) ensemble river forecasts, which take into account anticipated future weather conditions including precipitation and temperatures, show little threat of any river flooding developing during the next 6-10 days (through the morning of February 13, 2021) within the MARFC region. Widespread river flooding in February is uncommon within the MARFC region, but is still possible. Please visit www.weather.gov/erh/mmefs. Longer-term forecasts currently suggest no apparent increased chance for river flooding compared to normal into mid-February. However, with a fairly widespread and substantial snowpack now in place across much of the MARFC region, and river ice conditions increasing, it is likely that the river flood potential will increase for portions of the region after mid month. Any future river flooding will depend primarily on shorter-term weather conditions, such as the occurrence of rapid snowmelt and/or widespread heavy rainfall.

SUMMARY

The recent major east coast storm just brought moderate-heavy amounts of precipitation - mostly snow - region-wide. Now a substantial snowpack - above to much-above normal for early February - exists across a respectable portion of the region. Additionally, river ice has increased within the Susquehanna and Delaware River Basins from two weeks ago and is expected to increase and expand further during the next two weeks. Meanwhile, southeast portions of the region continue to have wet soils and above-median streamflows, though they have little/no snow or river ice. While these conditions suggest a normal or above-normal river flood potential for much of the region, the mitigating factor is that there are currently no strong indicators for heavy rainfall or significant snowmelt that could initiate river flooding during the next 5 to 7 days. On the contrary, the overall weather pattern for the next two weeks strongly suggests below-normal temperatures and a good chance of below-normal precipitation. Due to the predicted lack of warm, wet weather systems, the river flood potential for the next two weeks is being held at average to below average, similar to two weeks ago. But weather patterns can change quickly this time of year and should be monitored now that a significant snowpack exists across a portion of the region. Additionally, concern is increasing that a higher river flood potential may develop beyond this two-week period.

WATER SUPPLY OUTLOOK

According to the latest (January 26, 2021) U.S. Drought Monitor (droughtmonitor.unl.edu), two small areas of abnormally dry conditions and spotty restrictions on water use continue in PA and NY. Assuming near normal precipitation over the next few months, no water supply shortages are anticipated within the MARFC region through May, 2021. Please visit www.drought.gov, www.cpc.ncep.noaa.gov and www.weather.gov/marfc/WRO for additional drought and water supply information.

Please visit the NWS MARFC homepage at www.weather.gov/marfc or find us on Facebook at www.facebook.com/nwsmarfc/?REF=aymt_ homepage_panel and on Twitter @nwsmarfc.

The next winter/spring river flood outlook product will be issued by this office February 17-18, 2021.

SK/WJM

Winter/Spring River Flood Potential Outlook
NWS Middle Atlantic River Forecast Center (MARFC)
State College, PA
11:59 am EST Thu, January 21, 2021

Outlook Number 21-02 - January 21, 2021


This Winter/Spring River Flood Potential Outlook is valid for the two-week period January 21-February 4, 2021.

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 other factors. 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 BELOW AVERAGE

The river flood potential during the next two weeks (through February 4, 2021) is about average across southern and eastern portions of the MARFC area of responsibility, and below average for late January for the remainder of the region. Factors which contribute to this assessment of river flood potential are discussed in some detail below.

CURRENT RIVER FLOODING - NONE

No river flooding is currently occurring within the MARFC service area.

RECENT PRECIPITATION - NEAR AVERAGE

During the last 30 days (December 21, 2020 - January 19, 2021) observed precipitation across the entire MARFC region has been about average plus or minus up to an inch or so. Areas most likely to have been above average are southern New York and central Pennsylvania. Areas most likely to have been below average are the eastern panhandle of West Virginia and western Virginia. Precipitation departure data can be seen at www.weather.gov/marfc/Precipitation_Departures.

SNOW CONDITIONS - NORMAL TO BELOW NORMAL

As of this morning (January 21, 2021), snow is found on the ground across approximately the northern third of the MARFC region. The snow/no-snow line is roughly close to U.S. Route 220 in the Appalachians, then along Interstate 99, then near Interstate 80 in PA, and northeastward near Interstate 84 in NY. Typically for mid to late January, the snow/no snow line extends roughly 50 to 75 miles further south and east of the current line. Snow conditions are about normal for this time of year across some portions of northern PA and NY, where snow water equivalent values of 1-2 inches are common with isolated higher values. Snow depths in this region are mostly 1-8 inches with isolated deeper amounts. Elsewhere where snow exists, water equivalent values are less than an inch and depths are a few inches or less. Outside of northern PA and NY, snow conditions range from normal to below normal for mid to late January. Snow information can be found at www.weather.gov/marfc/Snow and www.nohrsc.noaa.gov.

RIVER ICE - NONE

Currently, no significant river ice exists on rivers within the MARFC service area. Some river ice formation is likely during the next two weeks given that this next two weeks is typically the coldest two weeks of the year, and the latest NWS Climate Prediction Center`s 6-10 and 8-14 day temperature outlooks both suggest colder than normal temperatures.

STREAMFLOW CONDITIONS - NEAR TO ABOVE MEDIAN

The latest data from the United States Geological Survey (USGS) indicates current streamflow conditions within the entire MARFC region are near to above median for the date. For current streamflow conditions please visit waterdata.usgs.gov/nwis/rt.

SOIL MOISTURE CONDITIONS - WET SOUTHEAST, OTHERWISE NEAR NORMAL

Soils remain extremely moist across southeastern portions of the MARFC service area. The long-term Palmer drought severity index is useful to estimate deep soil moisture conditions. The January 16, 2021 map (seen at www.cpc.ncep.noaa.gov/products/analysis_monitoring/regional_ monitoring/palmer.gif) suggests deep soils are unusually moist to extremely moist across central/southeast VA and the middle and lower Delmarva Peninsula. Outside of this very wet area, the map shows near-normal to unusually moist values. Additional soil moisture data confirms the very wet soils across southern and eastern portions of the region. Visit www.cpc.ncep.noaa.gov/products/Soilmst_Monitoring/ and then click on U.S. Monitoring.

GROUNDWATER - AVERAGE TO ABOVE AVERAGE

Within the MARFC service area, real-time USGS groundwater monitoring wells indicate current groundwater levels generally range from average to above average for this time of year. To see groundwater levels visit groundwaterwatch.usgs.gov/usgsgwnetworks.asp.

RESERVOIR CONDITIONS - AVERAGE TO ABOVE AVERAGE

Most major reservoirs within the MARFC region are holding storages that are average or somewhat above average for this time of year. For example, reservoirs in the Delaware River Basin that supply NYC with water are showing above-average storage for this time of year.

FUTURE WEATHER CONDITIONS -

At the present time there are no strong indications of any widespread heavy rain events for the MARFC region for about the next 5-7 days. A storm system across the Southeast next Monday-Tuesday should be monitored for the potential of heavy rain/snow should the storm track shift further north than currently predicted. A colder weather pattern looks likely in the longer range. The latest (January 20, 2021) weather outlooks issued by the NWS Climate Prediction Center suggest that both temperatures and precipitation may be below normal when averaged over the entire nine-day period January 25-February 3, 2021. Visit www.cpc.ncep.noaa.gov/ to view the outlooks.

ENSEMBLE RIVER FORECASTS - VERY LIMITED THREAT OF RIVER FLOODING

The most recent runs (January 21, 2021) of the short-term (6-10 day) ensemble river forecasts, which take into account anticipated future weather conditions including precipitation and temperatures, show little threat of any river flooding developing during the next 6-10 days (through the morning of January 30, 2021) within the MARFC region. Widespread river flooding in January and early February is uncommon within the MARFC region, but is still possible. Please visit www.weather.gov/erh/mmefs. Longer-term forecasts suggest no apparent increased chance for river flooding compared to normal for early February. Any future river flooding will depend primarily on shorter-term weather conditions, such as the occurrence of widespread heavy rainfall.

SUMMARY

Average or somewhat above average soil moisture and streamflow conditions region-wide indicate a slow drying of the MARFC region over the past two weeks. Though southeastern portions of the region are still the wettest, there are currently no strong indicators for heavy rainfall here that could result in river flooding during the next 5 to 7 days. That being said a weather system tracking across the Southeast Monday into Tuesday should be monitored in case the current predicted track of that system shifts northward with time. Rivers are free of river ice at this time, though some ice will likely form in the next two weeks. The only significant snow on the ground at this time within the MARFC region is across portions of northern PA and NY. There are no indications of any fast snowmelt events for this region at the present time, as temperatures are likely to be pretty close to normal or below normal for the next couple of weeks.

WATER SUPPLY OUTLOOK

According to the latest (January 14, 2021) U.S. Drought Monitor (droughtmonitor.unl.edu), scattered areas of abnormally dry conditions and spotty restrictions on water use are all that remain of a fairly significant summer/fall drought that existed over portions of PA and NY. Assuming near-normal precipitation over the next few months, no water supply shortages are anticipated within the MARFC region through May, 2021. Please visit www.drought.gov, www.cpc.ncep.noaa.gov and www.weather.gov/marfc/WRO for additional drought and water supply information.

Please visit the NWS MARFC homepage at www.weather.gov/marfc or find us on Facebook at www.facebook.com/nwsmarfc/?REF=aymt_homepage_panel and on Twitter @nwsmarfc.

The next winter/spring river flood outlook product will be issued by this office February 3-4, 2021, SK/WJM

 

Winter/Spring River Flood Potential Outlook
NWS Middle Atlantic River Forecast Center (MARFC)
State College, PA
1:25 pm EST Wed, January 6, 2021

Outlook Number 21-01 - January 6, 2021


This Winter/Spring River Flood Potential Outlook is valid for the two-week period January 7-21, 2021.

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 other factors. 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 - ABOVE AVERAGE SOUTH AND EAST

The river flood potential during the next two weeks (through January 21, 2021) is somewhat above average across southern and eastern portions of the MARFC service area, and about average for early January for the remainder of the region. Factors which contribute to this assessment of river flood potential are discussed in some detail below.

CURRENT RIVER FLOODING - NONE

No flooding is currently occurring within the MARFC service area.

RECENT PRECIPITATION - ABOVE TO MUCH-ABOVE AVERAGE

During the last 30 days (December 6, 2020 - January 4, 2021) observed precipitation across the entire MARFC region has been above to much-above average. Precipitation departure data can be seen at www.weather.gov/marfc/Precipitation_Departures.

SNOW CONDITIONS - ABOVE NORMAL FAR NORTH, OTHERWISE NEAR NORMAL

As of this morning (January 6, 2021), snow is found on the ground across roughly the northern third of the MARFC region. The snow/no-snow line is roughly close to U.S. Route 220 in the Appalachians, then along Interstate 99, then near Interstate 80 in PA, and northeastward near Interstate 84 in NY. This is a fairly typical location of the snow/no-snow line for early January. Snow conditions are somewhat above normal for this time of year across portions of northern PA and NY, where snow water equivalent values of 1-2 inches are common, with isolated higher values. Snow depths in this region are mostly 2-10 inches with isolated deeper amounts. Elsewhere where snow exists, water equivalent values are less than an inch and depths are a few inches or less. Outside of northern PA and NY, snow conditions are fairly close to normal for early January for most of the remainder of the MARFC region. Snow information can be found at www.weather.gov/marfc/Snow and www.nohrsc.noaa.gov.

RIVER ICE - NONE

Currently, no river ice exists on rivers within the MARFC service area and river ice formation during the next two weeks is currently expected to be limited due to the relative absence of arctic air. The lack of river ice at this time is somewhat below normal for rivers across roughly the northwestern third of the MARFC service area.

STREAMFLOW CONDITIONS - ABOVE TO MUCH-ABOVE MEDIAN

The latest data from the United States Geological Survey (USGS) indicates current streamflow conditions within the entire MARFC region are above to much-above median for the date. This is especially true for rivers in southern and eastern portions of the region. For current streamflow conditions please visit waterdata.usgs.gov/nwis/rt.

SOIL MOISTURE CONDITIONS - WET SOUTH AND EAST

Soils remain extremely moist across southern and eastern portions of the MARFC service area. The long-term Palmer drought severity index is useful to estimate deep soil moisture conditions. The January 2, 2021 map (seen at www.cpc.ncep.noaa.gov/products/analysis_monitoring/regional_ monitoring/palmer.gif) suggests deep soils are unusually moist to extremely moist across large portions of the region, especially in central/southeast VA, the Delmarva Peninsula, southeast PA and southern NJ. Outside of this very wet area, the map shows near-normal to unusually moist values. Additional soil moisture data confirms the very wet soils across southern and eastern portions of the region. Visit www.cpc.ncep.noaa.gov/products/Soilmst_Monitoring/ and then click on U.S. Monitoring.

GROUNDWATER - AVERAGE TO ABOVE AVERAGE

Within the MARFC service area, real-time USGS groundwater monitoring wells indicate current groundwater levels generally range from average to above average for this time of year. To see groundwater levels visit groundwaterwatch.usgs.gov/usgsgwnetworks.asp.

RESERVOIR CONDITIONS - AVERAGE TO ABOVE AVERAGE

Most major reservoirs within the MARFC region are holding storages that are average or somewhat above average for this time of year. For example, reservoirs in the Delaware River Basin that supply NYC with water are showing somewhat above-average storage for this time of year.

FUTURE WEATHER CONDITIONS 

At the present time there are no strong indications of any widespread heavy rain events for the MARFC region for about the next 5-7 days. Only light-to-moderate precipitation is currently anticipated, though southern storms will need to be monitored late this week and again before midweek next week. Either/both of these storms could clip southern/eastern portions of the MARFC region with significant rain and/or snow if the predictions of their tracks shift northwestward much. A somewhat colder weather pattern looks possible at least briefly toward the end of next week. In the longer range, the latest (January 5, 2021) weather outlooks issued by the NWS Climate Prediction Center suggest that both temperatures and precipitation may be near normal when averaged over the entire nine-day period January 11-19, 2021. Visit www.cpc.ncep.noaa.gov/ to view the outlooks.

ENSEMBLE RIVER FORECASTS - VERY LIMITED THREAT OF RIVER FLOODING

The most recent runs (January 6, 2021) of the short-term (6-10 day) ensemble river forecasts, which take into account anticipated future weather conditions including precipitation and temperatures, show little threat of river flooding developing during the next 6-10 days (through the morning of January 15, 2021) within the MARFC region. Widespread river flooding in January is uncommon, but still possible within the MARFC region. Please visit www.weather.gov/erh/mmefs. Longer-term forecasts suggest a somewhat elevated chance for river flooding compared to normal later this month, mainly due to currently high streamflows and wet soils in some regions. Any future river flooding will depend primarily on shorter-term weather conditions, such as the occurrence of widespread heavy rainfall.

SUMMARY

Wet soils and unusually high streamflow conditions across southern and eastern portions of the region result in a somewhat above-average chance of river flooding developing during the next two weeks in the MARFC region. However, at this time there are no strong indications of any widespread heavy rain events for at least the next five days. Rivers are free of river ice at this time, and the only significant snow on the ground within the MARFC region is across portions of northern PA and NY. There are no indications of any fast snowmelt events for this region at the present time, as temperatures are likely to be pretty close to normal for January for the next couple of weeks.

WATER SUPPLY OUTLOOK

According to the latest (December 31, 2020) U.S. Drought monitor (droughtmonitor.unl.edu), abnormally dry conditions are all that remain of a fairly significant summer/fall drought that existed over portions of PA and NY. Please visit www.drought.gov, www.cpc.ncep.noaa.gov and www.weather.gov/marfc/WRO for additional drought and water supply information.

Please visit the NWS MARFC homepage at www.weather.gov/marfc or find us on Facebook at www.facebook.com/nwsmarfc/?REF=aymt_homepage_panel and on Twitter @nwsmarfc.

The next winter/spring river flood outlook product will be issued by this office January 20-21, 2021.

SK

This year's Winter/Spring Flood Outlook schedule (all dates on or around):

  • March 4
  • March 11
  • March 18 (if necessary)
  • April 1 (if necessary)
  • April 15 (if necessary)
  • April 29 (if necessary)