Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 311037

Area Forecast Discussion
National Weather Service Raleigh NC
635 AM EDT Tue May 31 2016

.SYNOPSIS...Post Tropical Cyclone Bonnie over northeast South
Carolina will drift slowly to 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 /through Wednesday night/...
As of 240 AM Tuesday...

Today/tonight: With little change in the overall pattern today,
persistence will be the rule. The center of Post-Tropical Cyclone
Bonnie, located along the SC coast NE of CHS, will continue a slow
northeastward drift today along and just off the northern SC coast,
as a weak inverted trough lingers over coastal NC. Only isolated
patchy showers remain over northern NC, a function of weak low level
mass convergence and the continued presence of the weak mid level
shear axis that has been drifting ENE over the region over the last
few days. Plentiful low level moisture, decreasing clouds early this
morning, and very light surface winds will foster formation of fog
and stratus this morning, particularly over the piedmont. The column
remains quite moist over central/eastern NC with PW values holding
at 140-180% of normal, and models agree on low level moisture
transport ramping up starting this morning, so despite the lack of
strong mechanisms to force ascent, it won`t take much to kick off
showers especially along/east of Highway 1. Will maintain a trend to
chance pops west and likely pops east this afternoon. Cell motion
should again be fairly slow, facilitating locally higher rainfall
totals which could prompt localized street flooding again today, and
urban and small stream flood advisories may once again be needed.
Instability is projected to be marginal (peaking near 1000 J/kg in
the far east only) with very weak deep layer shear, so thunder
should remain isolated. Thicknesses are expected to be close to
normal but with considerable cloudiness, highs should hold in the
lower to mid 80s. Will trend shower coverage down to low chances
tonight with loss of heating, and more fog and stratus looks like a
good bet for later tonight with continued elevated low level
moisture transport over the region. Lows in the mid to upper 60s.

Wed/Wed night: More of the same, although the better rain chances
should shift slightly more eastward. The center of Bonnie is
expected to continue a northeastward drift off the southern coast of
NC, as the weak mid level shear axis maintains its very slow
eastward drift. PW is forecast to remain above normal, in the 1.5-
2.0" range over central and especially eastern NC, and models are
projecting perhaps a bit more instability (MUCAPE topping out at 750-
1500 J/kg), which should ensure at least scattered coverage. Will
again trend pops up to chance west and likely east Wed afternoon,
before trending them back down to isolated at most Wed night. With
similar thicknesses and similar cloud cover anticipated as compared
to today, will again have highs in the lower to mid 80s. Lows Wed
night in the mid-upper 60s with fair skies early and areas of
stratus once again forming overnight. -GIH


.SHORT TERM /Thursday through Friday night/...
As of 305 AM Tuesday...

Post-tropical storm Bonnie will continue to spin along the North
Carolina coast on Thursday with most of the precipitation occurring
east of I-95. Back to the west, a frontal system will move towards
the Appalachians and into western NC. For central NC this could mean
a lull in the soggy weather and perhaps a mostly dry day for much of
the area. Still expect partly to mostly cloudy skies however and
still a tropical air mass in place with highs in the mid 80s and
dewpoints in the upper 60s. Any showers and thunderstorms that do
occur could produce some locally heavy rain but otherwise not much
QPF expected. Lows Thursday night only dropping down into the upper

On Friday, the remnants of Bonnie will finally move offshore to our
northeast and attention will turn to the frontal system moving in
from the west. Any dynamics with this system will be well to the
north of our area. A few waves moving along the front from the south
to north will provide some vorticity in the mid to upper levels. The
main forecast problem surrounds how far south the front will be able
to push. At this time...the GFS solution has a big stronger of a
surface high over the Ohio Valley that helps to push the front
further south by Friday afternoon. This scenario suggest plenty of
showers and thunderstorms for the entire forecast area on Friday,
whereas the ECMWF solution has rain only in the north and western
portions of the CWA. With the lack of forcing the ECMWF solution
seems more likely at this time. This will also keep temperatures and
dewpoints up in the mid 80s and upper 60s respectively as there will
not be any air mass change on Friday. Lows Friday night in the upper
60s to near 70 degrees.


.LONG TERM /Saturday through Monday/...
As of 305 AM Tuesday...

The evolution of the front in both models is fairly similar for
Saturday as a tropical upper ridge helps to stall the front out over
the area making another wet weekend the most likely scenario for
central NC. Looking back to the west, a new and more organized low
pressure system moves into the western Great Lakes on Saturday with
a frontal system extending down the Mississippi Valley with an upper
trough to support it. This system will eventually take the stalled
front back to the north as a warm front as the cold front approaches
from the west later on Saturday and into Sunday. Pre-frontal
precipitation, supported by several strong waves from the southwest
will affect the area on Sunday. The current GFS scenario is very wet
on Sunday night into Monday and the ECMWF is much more subdued. This
leads to a very low confidence forecast for day 7 but will carry
pops through Monday. Continued low to mid 80s for highs with lows in
the mid to upper 60s.


.AVIATION /12Z Tuesday through Saturday/...
As of 635 AM Tuesday...

Persistence will be the rule today, with aviation weather likely to
follow a pattern similar to yesterday, meaning a high chance of
predominant adverse aviation conditions through much of this
morning, and again later tonight. Stratus and fog development this
morning has been focused at RDU/FAY/RWI with MVFR to IFR conditions,
while the slightly drier surface air (lower dewpoints) has limited
fog and stratus at INT/GSO so far. The MVFR/IFR fog/stratus should
slowly lift to MVFR at all sites by mid morning (by 13z-14z) and to
VFR by midday (by 15z-16z). Scattered showers with brief MVFR vsbys
and cigs are possible this afternoon and evening mainly at
RDU/RWI/FAY, and isolated storms are also possible, but overall the
afternoon should be VFR for most of the time. The showers should
gradually weaken and dissipate by late evening and through the
overnight hours. Winds will remain light, mainly under 10 kts, from
the NE today.

Looking beyond 12z Wed morning: Another round of MVFR/IFR fog and
stratus is expected late tonight into Wed morning, improving to VFR
by the noon hour. More scattered afternoon showers and isolated
storms will affect central NC TAF sites Wed with brief MVFR
conditions, although these should be focused near RWI/FAY with much
lower coverage at RDU/INT/GSO. More MVFR/IFR stratus/fog is then
expected late Wed night into Thu morning. The risk of showers/storms
appears to be less on Thu afternoon than in recent days, so VFR
conditions should dominate. An approaching cold front will bring a
return to mostly afternoon showers and storms Fri/Sat. -GIH





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