National Weather Service United States Department of Commerce

Outlook #2 released on January 18, 2018.


WINTER/SPRING RIVER FLOOD POTENTIAL OUTLOOK
MIDDLE ATLANTIC RIVER FORECAST CENTER
NATIONAL WEATHER SERVICE STATE COLLEGE, PA
8:50 AM EST THU JAN 18 2018

OUTLOOK NUMBER 18-02 - JANUARY 18, 2018

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, nor the location or extent of localized flooding due to ice jams.

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

The river flood potential for MARFC rivers during the next two weeks (January 18-February 1, 2018) is near average across about the northern half of the MARFC region, and below average across the southern half.  Factors which contribute to this assessment of river flood potential are discussed in some detail below.

CURRENT FLOODING – NONE AT MARFC FORECAST POINTS

No MARFC forecast points are currently above flood stage within the MARFC region.  However, it is possible that some highly localized flooding due to ice jams is still occurring along stretches of streams and rivers in between official MARFC forecast points. 

RECENT PRECIPITATION – VARIABLE

During the last 30 days (December 18, 2017 – January 16, 2018) precipitation (liquid equivalent) was near normal to above normal across about the northern third of the region.  Further south, precipitation was generally below normal across about the central third of the region.  Finally across the southern third of the MARFC region precipitation has generally been much below average during the last 30 days.

SNOW CONDITIONS - BELOW AVERAGE TO AVERAGE

Snow currently covers the ground across about the northwestern half of MARFC region, which is fairly typical for mid-winter.  A few to several inches of snow is also found across portions of VA from yesterday’s snow event.  However the most hydrologically significant snow within the MARFC service area is found north of a line from about Johnstown to Allentown, PA, then northeastward to about Poughkeepsie, NY.  In this region snow depths generally range from 4-12 inches with corresponding water equivalent values of generally 0.5-1.5 inches.  Locally higher amounts are found within this area.  In this region snow conditions are currently considered perhaps a little below average for mid-winter.  To the south and east, snow conditions are fairly typical for this time of year, though the several inches of snow currently on the ground in VA is a bit uncommon.  Snow information can be found by visiting https://www.weather.gov/marfc/Snow and https://www.nohrsc.noaa.gov.

RIVER ICE - SOMEWHAT ABOVE AVERAGE TO AVERAGE

Unusually cold weather from late December through early January allowed considerable river ice to form across much of the MARFC region.  Then a milder, wetter weather pattern developed which broke up much of the river ice.  Numerous ice jams formed throughout the MARFC region as a result of the ice break-up, leading to isolated areas of flooding.  The rain and milder temperatures did not flush the ice from the rivers completely, and in fact much river ice remains, especially across the northwestern half of the MARFC region.  River ice conditions in this region remain average to somewhat above average for mid-winter.  With a milder and wetter weather pattern likely during the next week and perhaps longer, additional ice movement is anticipated.  As such, additional ice jams are possible which may result in localized flooding, especially along streams and rivers in the Susquehanna and Delaware River Basins.  Meanwhile, there is much less river ice remaining across southern and eastern portions of the region than there was even a week ago, so ice conditions there are now about average.

STREAMFLOW CONDITIONS - VARIABLE

While many stream gages remain affected by ice, the latest information from the United States Geological Survey (USGS) indicates below-average or much below-average stream flows continue across much of the southeastern half of the MARFC area.  However the mild, wet weather of last week elevated streamflow conditions across the northwestern half of the region back to the range of normal to much-above normal.  Please visit the USGS web pages at https://waterdata.usgs.gov/nwis/rt for current streamflow data.

SOIL MOISTURE CONDITIONS - NORMAL TO BELOW NORMAL

The long-term Palmer Drought Severity Index is used to infer deep soil moisture conditions.  The latest chart (http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/regional_monitoring/palmer.gif)  issued on January 13, 2018 suggests deep soils across much of the MARFC service area contain moisture that is fairly close to normal for this time of year, though some wetness has developed across portions of PA and NY due to the snowmelt and rainfall of late last week.  However, other detailed soil moisture information (go to http://www.cpc.ncep.noaa.gov/products/Soilmst_Monitoring and then click on U.S. Monitoring) indicates considerable soil moisture deficits remain across large portions of the MARFC region, especially eastern and southern regions.

GROUNDWATER – NORMAL TO BELOW NORMAL

Most USGS groundwater monitoring wells within the MARFC region are currently indicating groundwater levels that are in the normal to below normal range.  Noticeable improvement has been noted across about the northern half of the region due to the snowmelt/rainfall event in that region late last week.  Please visit https://groundwaterwatch.usgs.gov.

RESERVOIR CONDITIONS - AVERAGE TO BELOW AVERAGE

Most major reservoirs within the MARFC region are holding storages that are average/below average for this time of year.  For example, reservoir storage in the upper Delaware River basin is below the long-term median but still within the normal range.

FUTURE WEATHER CONDITIONS – MILDER AND WETTER

Moderating temperatures are expected this week, along with generally only light precipitation for the next several days.  A storm system and its associated cold front may produce moderate-heavy precipitation – much of which may be rain - around next Tuesday-Wednesday, January 23-24.  This storm should be closely monitored for its potential to cause snowmelt and heavy rainfall, especially across the northern half of the region where the most hydrologically significant snow is found.  Additionally, river ice movement is likely again in association with this weather system, and localized ice jam flooding is possible especially along streams and rivers within the Susquehanna and Delaware River Basins.  Longer range weather outlooks suggest a pretty good chance that both temperatures and precipitation may end up above average for the second week of this two-week outlook period as well.  Please visit http://www.cpc/ncep.noaa.gov for longer range weather outlooks.

ENSEMBLE RIVER FORECASTS – NOT AVAILABLE DUE TO MARFC SOFTWARE UPGRADES TODAY

Due to major software upgrades being performed at MARFC as this outlook was being prepared, Ensemble River Forecasts could not be run for this outlook.  We apologize for any inconvenience.  Ensemble river forecasts can normally be viewed at https://www.weather.gov/erh/mmefs.

AHPS RIVER FORECASTS – NOT AVAILABLE DUE TO MARFC SOFTWARE UPGRADES TODAY

Due to major software upgrades being performed at MARFC as this outlook was being prepared, AHPS River Forecasts could not be run for this outlook.  Again, we apologize for any inconvenience.

SUMMARY

For the next two weeks the river flood potential for rivers in the MARFC region is about average across about the northern half of the region, and below average across the southern half.  There is an indication that a fairly warm and wet weather system could cross the region around next Tuesday-Wednesday, January 23-24.  As such this storm could cause snowmelt, moderate/heavy rainfall, and river ice movement, especially across the northern half of the MARFC service area.  It is possible that some river flooding could result from the effects of this potential storm.  The evolution of this potential storm should be monitored during the next several days.

WATER SUPPLY OUTLOOK

According to the latest (January 9, 2018) U.S. Drought Monitor (http://droughtmonitor.unl.edu), large portions of the MARFC service area continue to show conditions that range from abnormally dry to moderate drought.  Driest regions are across the south and east.  Above-average precipitation in these areas this winter would be beneficial to prevent more serious water supply problems from developing this spring and summer. Visit https://www.drought.gov, http://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/ABOUT February 1, 2018.

MARFC/STK

Outlook #1 released on January 4, 2018.


WINTER/SPRING RIVER FLOOD POTENTIAL OUTLOOK
MIDDLE ATLANTIC RIVER FORECAST CENTER
NATIONAL WEATHER SERVICE STATE COLLEGE, PA
2:13 PM EST THU JAN 04 2018

OUTLOOK NUMBER 18-01 - JANUARY 4, 2018

 

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

The river flood potential for MARFC rivers during the next two weeks is below average. Factors which contribute to this assessment of river flood potential are discussed in some detail below.

 

CURRENT FLOODING

None.

 

RECENT PRECIPITATION - VARIABLE

During the last 30 days (December 5, 2017 – January 3, 2018) precipitation (liquid equivalent) was below normal to much-below normal across all of the MARFC service area.

 

SNOW CONDITIONS - BELOW AVERAGE TO AVERAGE

Snow covers the ground across most of the MARFC region as of this morning, due in part to the snowstorm currently affecting eastern portions of the service area. Across most of the area snow depths are less than 6 inches and snow water equivalents are less than a half inch. Of course isolated locations have somewhat higher values. Across eastern portions of the area, the current snowstorm is expected to deposit 6- 12+ inches of snow, with up to an inch of water equivalent. Most of this snow will accumulate east of MARFC`s river basins. However, river basins in NJ, southeast pa and northern de will see some significant snow from this storm. Snow conditions are currently considered below average to average for most of the region, and in fact are generally hydrologically insignificant. While the current snowstorm will create above-average snow conditions for extreme eastern portions of the area, the significant snow will be east of most of our river basins. Snow information can be found by visiting https://www.weather.gov/marfc/Snow AND https://www.nohrsc.noaa.gov.

 

RIVER ICE - SOMEWHAT ABOVE AVERAGE

The unusually cold weather recently has allowed river ice to form across much of the MARFC region. Both the extent and thickness of the river ice is considered somewhat above average at this time. After an extremely cold weekend, milder temperatures are anticipated next week which will begin to erode river ice across southern and eastern portions of the region.

 

STREAMFLOW CONDITIONS - BELOW TO MUCH-BELOW AVERAGE

While many stream gages are currently affected by ice, the latest data from the United States Geological Survey (USGS) indicate below-average or much below-average stream flows across the MARFC area. Please visit the USGS web pages at https://waterdata.usgs.gov/nwis/rt for current streamflow data.

 

SOIL MOISTURE CONDITIONS - NORMAL TO BELOW NORMAL

The long-term Palmer Drought Severity Index is used to infer deep soil moisture conditions. The December 30, 2017 chart (found at http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/regional_monitoring/palmer.gif) suggests deep soils across much of the MARFC service area contain moisture that is fairly close to normal for this time of year. However, other detailed soil moisture information (go to http://www.cpc.ncep.noaa.gov/products/Soilmst_Monitoring and then click on U.S. Monitoring) indicates considerable soil moisture deficits across large portions of the MARFC region, especially eastern and southern regions.

 

GROUNDWATER - MOSTLY BELOW NORMAL

Most USGS groundwater monitoring wells within the MARFC region are currently indicating groundwater levels that are below or much-below their long-term normals for this time of year. Please visit https://groundwaterwatch.usgs.gov.

 

RESERVOIR CONDITIONS - BELOW AVERAGE TO AVERAGE

Most major reservoirs within the MARFC region are holding storages that are below average/average for this time of year. Reservoir storage in the upper Delaware River basin is below the long-term median but still within the normal range.

 

FUTURE WEATHER CONDITIONS

Today`s coastal snowstorm will move away from the region tonight. Bitter cold but dry weather is expected this weekend, with some lake effect snow in the usual regions. Milder weather, compared to recently, is expected for much of next week. A storm system early next week will produce light-moderate precipitation, as will a late week storm system. At this time there are no strong indications of any widespread heavy rain events for at least the next week. Longer-range weather outlooks suggest temperatures will stay pretty close to normal for January, with normal or above normal precipitation.

 

ENSEMBLE RIVER FORECASTS

No threat of river flooding developing. The most recent runs (January 3, 2018) of the ensemble river forecasts, which take into account anticipated future weather conditions including precipitation and temperatures, show no river flooding developing within the MARFC region for at least the next week. No widespread heavy rain events are anticipated for at least the next week. Please visit https://www.weather.gov/erh/mmefs for ensemble river forecasts.

 

AHPS RIVER FORECASTS - NEAR TO BELOW NORMAL

The advanced hydrologic prediction service (AHPS) generates long-term (14 days or greater) probabilistic river forecasts based on current basin conditions (river levels, soil moisture, extent and condition of any snowpack) along with 50 years of historic temperature and precipitation data. However, it is important to note that AHPS river forecasts do not take into account actual future weather conditions whereas ensemble river forecasts (see previous section) do. For this outlook period (through January 18, 2018) current AHPS river forecasts indicate below-normal to normal chances of river flooding across the MARFC region.

 

SUMMARY

For the next two weeks the river flood potential for rivers in the MARFC region is below average. At this time no widespread significant rain events are indicated for at least the next week. Low stream flows, dry soils and limited snow conditions are also helping create the below average river flood threat.

 

WATER SUPPLY OUTLOOK

According to the latest (January 4, 2018) U.S. Drought Monitor (http://droughtmonitor.unl.edu), large portions of the MARFC service area continue to show conditions that range from abnormally dry to moderate drought. Driest regions are across the south and east. Above-average precipitation this winter would be beneficial across most of the MARFC region to prevent more serious water supply problems from developing this spring and summer. Visit https://www.drought.gov, http://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 18, 2018.