Flood Potential Outlook
Issued by NWS Wakefield, VA

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WINTER/SPRING FLOOD POTENTIAL OUTLOOK
NATIONAL WEATHER SERVICE WAKEFIELD VA
538 PM EST Thu Jan 4 2018

...First Winter/Spring Flood Outlook for 2018...

...RIVER FLOOD POTENTIAL IS BELOW NORMAL THROUGH JANUARY 18TH...

Each winter and early spring, the National Weather Service office
in Wakefield, VA issues a series of flood potential outlooks.
These outlooks estimate the potential for river flooding across
the Wakefield Forecast Office`s Hydrologic Service Area (HSA).
The HSA includes Central and Eastern Virginia, the Lower Maryland
Eastern Shore, and portions of Northeast North Carolina. The
outlook is based on the current assessment of hydrometeorological
factors which contribute to river flooding. These factors include,
but are not limited too recent precipitation, soil moisture, snow
cover and snow water equivalent, stream flows, river ice and
expected future weather conditions.

In this part of the Mid-Atlantic Region, heavy rainfall is the
primary factor that leads to river flooding. Heavy rainfall can
rapidly cause river flooding at anytime of the year, even when
overall river flood potential is considered low.

The following is a summary of the current conditions as of
Thursday January 4 2018:

Current flooding - No rivers are currently in flood as of 2 PM
Thursday January 4 2018.

Recent precipitation - Over the last 30 days from December 5 2017
to January 4 2018, the precipitation has ranged from 1" - 4" with
the lower amounts across the Northwest Virginia Piedmont counties
and the most along the Albemarle Sound in Northeastern North
Carolina toward the coast. The deficits range up to 2"+ northwest
of the Richmond Metro area. The rain totals in Northeast North
Carolina are near normal for the 30 day period.

Looking back to the beginning of the water year through January
4th, the rain totals generally range from 5" - 12" with the
deficits as high as 6" across the VA Piedmont and also through the
Tri-Cities. Wallops Island VA reported 11.42 since the beginning
of the water year which is nearly 2" above normal and this is the
highest total across the HSA since Oct 1.


Snow conditions - A fresh snow pack has been laid over the last 24
hours with around 3" or less from Interstate 95 westward toward
the VA Piedmont. But east of the Interstate, the amounts increased
with totals of 5" - 12" across much of the easter half of the HSA.
Water equivalents in the western half of the HSA are about 0.25"
or less, while to the east the snow ratio were lower and the
liquid water contents were between 0.75" - 1.25".

River ice conditions - Due to the cold temperatures over the last
two weeks since Christmas and the low water levels in the streams
and creeks, there is thin patches of ice along many of the small
streams and creeks, especially along the edges of the river. It is
impacting some gage readings on the Rivanna river as well as on
the Appomattox River.

Stream Flow Conditions - The 14 day average stream flows, through
January 4TH, were below normal across the entire Wakefield HSA.
This is due to the lack of rain through much of the late summer
through the 2017 fall. While all gages were showing below normal
flows, most of river gages in Central and Eastern Virginia were
showing average flows that are either much below normal or the
lowest flow observed for this time period. Eight gages are
reporting those lowest observed flow for the 14 day time period
ending January 4.

When looking at the real time flows as of 2 PM January 4th, the
river levels are mainly in the below normal to daily low values
for this time of year. Here are some real time stream flows as of
2 PM January 4th:

LOCATION OBSERVED LEVEL/MEDIAN FLOW/PERCENTAGE OF MEDIAN
RIVANNA RIVER
PALMYRA VA   71 CFS/ 624 CFS/ 11.4
JAMES RIVER
CARTERSVILLE VA    1520 CFS/6360 CFS/ 23.9
RICHMOND VA    1070 CFS/6030 CFS/ 17.7
APPOMATTOX RIVER
    FARMVILLE VA    54 CFS/    225 CFS/    24.0
MATTOAX VA     153 CFS/ 568 CFS/ 26.9
    MATOACA VA     116 CFS/  983 CFS/ 11.8
NOTTOWAY RIVER
    RAWLINGS VA  36 CFS/    234 CFS/    15.4
    STONY CREEK VA      97 CFS/    515 CFS/    18.8
    SEBRELL VA     273 CFS/   1380 CFS/    19.8
MEHERRIN RIVER
    LAWRENCEVILLE VA       70 CFS/    373 CFS/    18.8
    EMPORIA VA   97 CFS/    517 CFS/    18.8
BLACKWATER RIVER
    FRANKLIN VA  58 CFS/    666 CFS/     8.7
MATTAPONI RIVER
    BOWLING GREEN VA      22 CFS/    230 CFS/     9.6
    BEULAHVILLE VA 116 CFS/    606 CFS/    19.1
POCOMOKE RIVER
    WILLARDS MD  28 CFS/     71 CFS/    39.4
POTECASI CREEK
    UNION NC      30 CFS/    240 CFS/    12.5

Soil Moisture Conditions - Below normal to much below normal.

Soil moisture indicators including the Palmer Drought Severity
Index, which is used to infer deep soil moisture and long term
drought, shows that as of December 30 2017, the Wakefield HSA, is
depicted as being near normal for deep soil moisture.

However, the CPC Soil Moisture Monitor, which looks more at top
soil moisture, shows that the entire region is below normal to
much below normal. The moisture deficits range from 20 mm below
normal along the coastal regions of the HSA, while the greatest
deficits of near 100 mm are located in the Central Virginia
Piedmont.

Ground Water - NORMAL TO BELOW NORMAL LEVELS.

Ground water levels across the HSA are in the normal range along
the coastal portions of Virginia and Maryland. However, further
inland across Virginia, including the Piedmont counties, the
ground water levels are running below normal to much below normal.
Across Northeastern North Carolina, the groundwater gage in
Elizabeth City is also showing below normal levels, but this is a
very shallow well and responds quickly to precipitation events.
With several inches of snow currently on the ground and water
equivalents of 0.50 - 1 inch this gage is expected to respond
quickly to return to more normal levels.

Reservoirs - Below normal pool levels

Area reservoir pool levels are in the below normal range for this
time of year due to the low rainfall totals over the last 6
months.

Future Precipitation...The region is recovering from a major
coastal low that produced heavy snow for much of the area and with
very cold arctic air expected to move over the region, no
precipitation is expected through Sunday Jan 7 and very little
melting of the snow is anticipated. The next chance for
precipitation comes on Monday night into Tuesday as an area of low
pressure ejects out of the Southern Plains and moves over the
region. Temperatures should have moderated for this system to be
all rain. High pressure returns for Wednesday the 10th - Friday
the 12th.

The latest CPC 8 to 14 day outlook for January 12 - 18 2018 is
indicating above normal temperatures and near normal to above
normal precipitation for the 7 day time period.

Lastly, for the 3 month outlook for February through April, the
precipitation forecast is for equal chance of being below normal,
near normal and above normal for the Central Virginia Piedmont to
below normal precipitation along the coast which is a typical
pattern with La Nina conditions. For temperatures the forecast is
for above normal conditions.

WWW.CPC.NCEP.NOAA.GOV

The river flood potential through January 18 2018 across the
Wakefield HSA is below normal for this time of year. Again,
remember that heavy rainfall is the most common cause of river
flooding in the Mid-Atlantic States. However river flooding can be
exacerbated when heavy rain is combined with snow melt.

The next outlook will be issued on January 18, 2018.

For additional weather or hydrologic information, please visit our
website at WWW.WEATHER.GOV/AKQ.

$$

Seymour



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