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Excessive Rainfall Discussion
 
(Latest Discussion - Issued 2339Z Nov 16, 2019)
 
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Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
638 PM EST Sat Nov 16 2019

Day 1
Valid 01Z Sun Nov 17 2019 - 12Z Sun Nov 17 2019

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS COASTAL
NORTH CAROLINA...

Coastal Carolinas...
While significant differences remain concerning where the heaviest
rains will occur across eastern North Carolina into far southeast
Virginia, there is a strong model signal for strengthening
easterly low level flow to the north of the strengthening deep
layer low off the Southeast/southern Mid-Atlantic coast.  The
850-700mb moisture flux anomalies from the ECMWF, NAM, and GFS all
show a west to east oriented moisture flux anomaly axis oriented
across eastern NC.  Moisture flux anomalies reach 2.5 to 4
standard deviations shortly within this axis and maintains this
strength through Sunday morning.  Heavy rains are possible in this
axis, with hi resolution model consensus and HREF mean showing
precip totals of 2 to 5"+ across the far eastern portions of NC
into far southeast VA, with potentially higher totals just
offshore where the best instability, 500-1000 j/kg mu-cape, is
forecast to be.  The global guidance remains drier than the
mesoscale guidance, though there have been recent radar trends
showing an advance of shower and thunderstorm activity towards
southeast NC.  If the heavier qpf solutions do occur across the
Outer Banks, flash flooding issues would be more urban rather than
due to soil saturation.   Very heavy rains may occur in bands
oriented southeast to northwest.  Hi res guidance is showing
hourly rates of 1.5-2.5" affecting the Outer Banks, overnight into
the morning hours.  These rains may produce localized runoff
issues, ponding of water across paved surfaces.  A marginal risk
area was drawn to encompass the model spread of where the heaviest
hourly rates are forecast by the hi res guidance.

Roth/Chenard/Oravec


Day 2
Valid 12Z Sun Nov 17 2019 - 12Z Mon Nov 18 2019

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Hayes


Day 3
Valid 12Z Mon Nov 18 2019 - 12Z Tue Nov 19 2019

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

...New England...
Deep moisture and increasing mid level frontogenetic forcing in
advance of short wave energy crossing New England on Day 3 is
still expected to produce bands of heavy rainfall, mainly over New
Hampshire and Maine. As the low level east northeast flow
increases to greater than 40 knots, there is the potential for
banded heavy rainfall that results in rainfall amounts in excess
of 1.50 inches over portions of Maine.

However, the is little to no instability expected anywhere in the
column which will keep rainfall rates from supporting a low end
flash flood threat. This continues to be more of a flood versus
flash flood threat. Therefore, no excessive area was assigned here
for Day 3.

Bann



Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt