AWUS01 KWNH 111327
FFGMPD
VAZ000-NCZ000-SCZ000-111800-

Mesoscale Precipitation Discussion 0606
NWS Weather Prediction Center College Park MD
926 AM EDT Thu Jul 11 2024

Areas affected...Coastal Plain of North Carolina, Northeast South
Carolina, Southeast Virginia

Concerning...Heavy rainfall...Flash flooding possible

Valid 111325Z - 111800Z

Summary...Nearly stationary showers and thunderstorms will persist
this morning along a slow moving cold front. Rainfall rates of
2-3"/hr are expected, which through this slow movement could
produce 2-4" of rain with locally higher amounts. Flash flooding
is possible.

Discussion...The regional radar mosaic this morning shows a line
of thunderstorms from the southern DelMarVa through the coastal
plain of North Carolina and into far northeast South Carolina near
the Grand Strand. This line is occurring along a cold front which
has stalled in response to impeding flow from the east, and this
front may waver back to the west through the afternoon. The
environment across the eastern Carolinas and into southern
Virginia is extremely supportive to heavy rain noted via the KMHX
12Z U/A sounding which featured 2.32" PWs, a daily record, and
freezing levels above 17,000 ft. This will support efficient
warm-rain processes, and radar-estimated rain rates have been as
high as 3"/hr, fueling some ongoing flash flood warnings and
mesonet reported rainfall as much as 2-4" already this morning.

As the day progresses, this cold front will waver and is progged
to retrograde slightly to the west in response to increasing
easterly flow merged with the sea breeze pushing west. The RAP
suggests PWs may go as high as 2.5", combined with SBCAPE reaching
2000-3000 J/kg to produce extreme thermodynamics through the day.
With both synoptic and mesoscale ascent plentiful through the day,
this will support rainfall rates which the REFS and HREF both
suggest have a higher than 40% chance of exceeding 2"/hr, and it
is likely short term rates will reach 3-4"/hr at times. With very
weak winds through 300mb in place, mean 850-300mb winds will
remain just 5-10 kts, which in the presence of minimal shear
suggests pulse type storms which will move very slowly, possibly
becoming stationary at times as noted by Corfidi vectors becoming
less than 5 kts with chaotic direction. This should result in
overturning of the instability along the front, but continued
resupply of the extreme thermodynamics into the front will drive
regeneration, and in some places this will result in 2-4" of rain,
with local amounts above 5" possible.

The coastal plain has been dry, noted by AHPS 7-day rainfall that
is generally less than 25% of normal and associated 0-40cm soil
moisture from NASA SPoRT that is below the 30th percentile in many
areas. This has raised FFG to 3-4"/3hrs, but HREF exceedance
probabilities reach above 40% in some areas, further reflecting
that the intensity of the rainfall today can overcome the
antecedent dryness. The greatest risk is expected across urban
areas, but anywhere these intense rates can linger could drive
rapid runoff to produce instances of flash flooding.


Weiss

ATTN...WFO...AKQ...ILM...MHX...RAH...

ATTN...RFC...MARFC...SERFC...NWC...

LAT...LON 37117670 36977614 36637587 36417569 36117557
35477592 34527671 33947774 33677830 33527877
33587904 33747905 34037897 34367886 34917845
35337822 36847717
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