Extended Streamflow Guidance
Issued by NWS Middle Atlantic RFC

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000
FGUS61 KRHA 201912
ESGRHA
Spring River Flood Potential Outlook
National Weather Service Middle Atlantic River Forecast Center
(MARFC)
State College, PA
3:15 pm EDT Wed, Mar 20, 2019

Outlook Number 19-07 - March 20, 2019

This Spring River Flood Potential Outlook is valid for the two-week
period March 21-April 4, 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/ABOVE
AVERAGE

The river flood potential during the next two weeks (through April 4)
ranges from average to above average.  Factors which contribute to
this assessment of river flood potential are discussed below.

CURRENT FLOODING - NONE

There is currently no river flooding occurring within the MARFC service
area.

RECENT PRECIPITATION - DRY NORTH, WETTER SOUTH

During the last 30 days (February 18 - March 19, 2019) observed
precipitation has been below average across NY and much of PA.
Further south, near-normal precipitation fell across southeastern PA,
much of NJ, much of MD, and portions of WV and northern VA.
Finally, above-average precipitation was recorded across southern
portions of WV, central/southern VA and the Delmarva Peninsula.
Portions of west-central VA have been the wettest compared to
normal.  To view precipitation departure data please visit
https://www.weather.gov/marfc/Precipitation_Departures.

SNOW CONDITIONS - ABOUT AVERAGE

Snow has become very patchy within the MARFC region.  The most
significant snow remains across portions of NY, in the North Branch
Susquehanna, Chenango and Upper Delaware River Basins where
higher elevations are holding on to a few inches of snow depth.  These
small areas have 0.50-1.50 inches of snow water equivalent, again
mainly in higher, protected areas.  Elsewhere, only scattered patches
of hydrologically insignificant snow remain.  These snow conditions are
fairly close to average for the third week of March.  Snow information
can be found at https://www.weather.gov/marfc/Snow and
https://www.nohrsc.noaa.gov.

RIVER ICE - ABOUT AVERAGE

Nearly all of the ice is gone from the rivers within the MARFC service
area.  These river ice conditions are fairly close to average for the third
week of March.

STREAMFLOW CONDITIONS - NEAR AVERAGE

The latest data from the United States Geological Survey (USGS)
indicate approximately median streamflow conditions across most of
the MARFC region.  Streamflow conditions have decreased
considerably across the southern two-thirds of the region during the
last couple of weeks.  Meanwhile, across the southern two-thirds of the
region streamflow conditions are in the median to above-median
range.  Please visit https://waterdata.usgs.gov/nwis/rt.

SOIL MOISTURE CONDITIONS - GENERALLY MUCH-ABOVE
AVERAGE

The long-term Palmer drought severity index is useful to estimate deep
soil moisture conditions.  The March 16, 2019 chart (found at
https://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 continues to be much-above normal
for this time of year.  Additional more detailed soil moisture information
continues to support the idea that soils are still very wet across most of
the MARFC area despite recent relatively-dry weather.  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 - VARIABLE

Within the MARFC service area, real-time USGS groundwater
monitoring wells indicate groundwater levels generally increase from
below normal/normal across about the northern third of the region, to
above normal/much above normal elsewhere.  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 - MODERATE TO HEAVY RAIN

A significant rain event, with perhaps some snow in some northern and
northwestern areas, is likely tonight into Friday.  A swath of 1-2+
inches of rain seems likely.  The axis of heaviest rain at this time
appears to be across central and eastern portions of the MARFC
region.  Another rain event is possible in the Monday-Wednesday time
frame next week, March 25-27.  The latest (March 19) longer-range
weather outlook issued by the NWS Climate Prediction Center also
suggests a good chance of above-average precipitation for much of
the MARFC region for the nine-day period March 25-April 2, 2019.
Long-range outlooks can be viewed at
https://www.cpc.ncep.noaa.gov/.

ENSEMBLE RIVER FORECASTS - A LIMITED THREAT OF RIVER
FLOODING DEVELOPING DURING THE NEXT FEW DAYS

The most recent runs (March 20, 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 during the next few
days.  A significant rain event is anticipated tonight into Friday and it is
this event that could produce some river flooding within the MARFC
region during the next few days.  Please visit
https://www.weather.gov/erh/mmefs for short-term ensemble river
forecasts.

SUMMARY

The risk of river flooding during the next two weeks for streams and
rivers within the MARFC service area is near average across the north,
and above average elsewhere.  The only hydrologically significant
snow within the region lies across portions of NY in the Upper
Susquehanna and Upper Delaware Basins.  Significant rainfall would
still be required for river flooding to develop in NY even if all the
remaining snow melted where it exists.  There is a significant rain
event now predicted for central and eastern portions of the MARFC
region tonight into Friday, with some snow possible too in northern
areas.  This rain event will likely produce 1-2+ inches of rain in central
and eastern areas, which could produce scattered river flooding.  This
weather system should be monitored for its potential to produce
heavier rain than currently anticipated.  Please monitor your local NWS
forecasts during the next 48 hours for updated information regarding
this next weather event.

WATER SUPPLY OUTLOOK

According to the latest (March 12) U.S. Drought monitor
(https://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.  Assuming near-normal precipitation for the
next few months, no water supply shortages are anticipated anywhere
within the MARFC region through at least mid-June, 2019.

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, if needed, will be issued by this office in two weeks,
on or about April 3, 2019.

SK


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