Area Forecast Discussion
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FXUS62 KRAH 301459
Area Forecast Discussion
National Weather Service Raleigh NC
1050 AM EDT Mon May 30 2016
.SYNOPSIS...Tropical Depression Bonnie, located over the central
South Carolina coast, will drift slowly toward the northeast along
the North Carolina coast through mid week, before moving offshore.
A cold front will approach from the west late in the week.
.NEAR TERM /Today through Tonight/...
As of 1050 AM Monday...
Latest surface analysis shows the remnants of Bonnie centered near
Myrtle Beach with an inverted trough extending northeast of the
center across the NC Coastal Plain near interstate 95. To the east
of this boundary a southeasterly flow is transporting rich moisture
with dew points in the lower to mid 70s resulting in an increasingly
unstable air mass with mlcape values now exceeding 1000 J/Kg across
part of the central Coastal Plain. Regional radar shows isolated
showers increasing in coverage and intensity across the Sandhills
and Coastal Plain while a region of more widespread showers and
storms across northeast NC shifts northward into VA.
High resolution guidance pushes the surface trough across the
Coastal Plain westward into the eastern Piedmont today. A vorticity
maxima noted in WV imagery across southeast NC which is largely
driving the larger area of showers in northeast NC will lift north
this afternoon. Other than spurious vorticity maximums rotating
about the deep cyclonic circulation associated with Bonnie, most of
the convection today will be diurnally forced in a very wet, weak to
moderately unstable air mass. The greatest convective coverage will
be east of U.S. 1 with precipitation chances and amounts
significantly diminishing to the west across the western Piedmont
and Triad area where the air mass will be more stable and the low
level flow is more divergent. Convection today should be efficient
rain producers again which combined with slow storm motion will lead
to quick accumulations of rain and a localized flooding concern,
especially in locations which had significant rain yesterday.
While low level shear values are weak and storm organization will be
limited, convective cells approaching the surface boundary will need
to be monitored for enhanced, albeit short lived rotation. Highs
today will be largely a function of the position of the surface
boundary and periods of sunshine outside of precipitation. Look for
highs today to range in the upper 70s to lower 80s. The convection
tonight should diminish in coverage and intensity with the loss of
heating with just an isolated shower expected overnight, mainly
across the Coastal Plain. Lows will range in the mid to upper 60s
with areas of fog and stratus re-developing tonight. -blaes
.SHORT TERM /Tuesday through Tuesday night/...
As of 310 AM Monday...
The mid level shear axis will weaken further Tue and continue an
eastward drift into eastern NC/SE VA, as the center of TD Bonnie
drifts NE over the southeast coast of NC. With the shift of both the
mid level shear axis and the inverted surface trough eastward into
coastal sections, our rain chances Tue should be a bit lower than
today with the best coverage shifting into our far eastern sections
and at the coast. PW will remain anomalously high, above 1.5" mainly
east of Highway 1, so despite the waning dynamic forcing for ascent,
it won`t take much to generate scattered showers and perhaps a storm
or two especially over the eastern CWA. Will retain cloudy to mostly
cloudy skies east, although the western CWA could see some sunshine
if the weak mid level low center shifts into eastern NC/SE VA early
enough. Highs in the low-mid 80s, coolest east where clouds should
be thickest with greater shower coverage. Lows mostly in the mid 60s.
.LONG TERM /Wednesday through Sunday/...
As of 305 AM Monday...
Wednesday and Thursday: Tropical Depression Bonnie will continue to
churn off the North Carolina coast on Wednesday somewhere between
Wilmington and Cape Lookout. With no steering flow in place the
forecast remains status quo with the best chances for precipitation
in the east but models also hinting at precipitation forming as the
result of orographic uplift as northeasterly flow approaches the
Appalachians. Therefore will carry chance of showers and
thunderstorms everywhere. Hot and humid with highs in the upper to
middle 80s and dewpoints in the mid to upper 60s. Lows Wednesday
night in the mid 60s.
Thursday will see the depression move a bit further northeast and
thus central NC may see a bit of a lull in precipitation before the
next system approaches from the west. Will carry low chance pops in
the forecast but it is possible that precipitation isn`t realized
until later in the day as moisture transport ahead of the front
increases. By evening expect thunderstorms to become more numerous
in the Triad and points west. These will be driven mostly by diurnal
heating as any dynamics associated with the fronts parent low will
reside well to the north. Highs still in the mid 80s with lows in
the mid to upper 60s.
Friday through Sunday: Low pressure moving through the Northern
Great Lakes and into Ontario and Quebec will move a frontal zone
over the east coast and leave it there as it detaches and heads
northeast. Back to the southwest an upper level low developing over
Texas will help to initiate the development of a broad upper trough
that will drape itself over the eastern US for several days. At the
surface a couple of waves, most notably on Saturday afternoon, will
move along the front and supply extra forcing for showers and
thunderstorms over central NC. Expect best chances in the afternoon
each day. Temperatures will cool off some during this time starting
in the mid to upper 80s on Friday afternoon down to the lower 80s by
Sunday afternoon. Lows each night in the mid to upper 60s.
.AVIATION /12Z Monday through Friday/...
As of 645 AM Monday...
Periods of adverse aviation conditions are expected to dominate over
the next 24 hours at Central NC terminals, as very moist air remains
in place over the area. At INT/GSO, MVFR cigs are expected to
persist through the morning, before gradually lifting to VFR during
the early afternoon hours. Scattered showers this afternoon may
generate brief MVFR vsbys here, but otherwise VFR vsbys are expected
during the daylight hours today. At RDU/RWI/FAY, IFR/LIFR cigs will
persist early this morning, especially at RDU/FAY, where IFR vsbys
are also likely. Vsbys at these three sites should improve to VFR
later this morning, with cigs slower to improve, trending to MVFR
during the afternoon. Isolated showers with MVFR vsbys are likely to
pass near RDU/RWI/FAY through mid morning, then coverage will
increase by afternoon, with numerous showers and a few thunderstorms
this afternoon into evening producing brief MVFR to IFR conditions
mainly at RDU/RWI/FAY. Shower/storm coverage is expected to slowly
decrease this evening with a trend to MVFR to IFR conditions after
Looking beyond 12Z early Tue morning: MVFR to IFR conditions are
likely to hold through mid morning Tue, with improvement to MVFR
east and to VFR west during Tue afternoon. Nightfall will bring
another trend to sub-VFR conditions at all sites Tue night, as the
air mass remains moist and unsettled with the center of TD Bonnie
tracking slowly toward the NNE along the NC coast. Improvement to
VFR is expected Wed lasting into Thu especially at INT/GSO, as
Bonnie moves out over the sea, although sub-VFR vsbys in fog are
possible late Wed night into early Thu morning with light surface
winds. A cold front approaching from the west Thu night may bring
sub-VFR conditions in showers/storms on Fri. -GIH