Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Raleigh NC
645 am EDT sun Aug 30 2015
Synopsis...weak surface high pressure will remain over the area
through early week. In the meantime...an upper level disturbance
will track north from the northern Gulf of Mexico and will cross the
western Carolinas late tonight and Monday.
Near term /through tonight/...
as of 330 am Sunday...
Middle-level circulation center currently near Mobile Bay will dampen
into an open wave and lift north-northeastward across western
Georgia today and then into the western Carolinas tonight through
daybreak Monday. Top-down moistening will commence late this
afternoon and through the overnight in advance of this feature with
associated 850-700mb southerly flow advecting plume of high ~2.0"
pwat(possible remnant tropical moisture plume from danny)into
eastern half of the Carolinas. Dry stable low-level airmass
associated with surface high pressure centered over the area will
act to deter rain chances until the arrival of the DPVA and moisture
surge from the south. Thus today will be mostly dry...with the
exception of a few sprinkles or diminishing isolated shower near the
SC/NC border...with rain chances increasing from south to north
Highs today at or just a category below normal...held in check by
opaque veil of middle and high clouds ahead of the ejecting upper wave.
Highs generally in the 80s. Lows tonight in the middle to upper 60s.
Short term /Monday and Monday night/...
as of 330 am Sunday...
Scattered showers should be ongoing across central NC Monday morning
and should continue into the afternoon and evening as dampened middle-
level wave shifts offshore by the afternoon. While upper forcing
looks to be waning/exiting the area by early afternoon...tempered
diurnal heating within the lingering moist ~2.0" precipitable water airmass in
place across eastern NC may result in an increase in coverage Monday
afternoon along with some thunder as weak to moderate buoyancy
develops(mucape of 700-1500 j/kg). Will keep probability of precipitation in the chance
ranges...highest in the east. Rain chances are expected to diminish
from west to east Monday evening as both upper forcing and moist
plume shift offshore.
Highs will ultimately depend on precipitation coverage...ranging from lower
80s in wetter model solutions to middle/upper 80s where showers are
scarce. Lows Monday night in the upper 60s to lower 70s.
Long term /Tuesday through Saturday/...
as of 400 am Sunday...
The models remain in relatively good agreement regarding the re-
development/discontinuous retrogression of a positively-tilted
trough from the lower Great Lakes to the Texas Gulf Coast...the
northern portion of which is forecast to cross the central
Appalachians Wednesday and Virginia/NC Wednesday night. The southern portion of the
trough --forecast to become a closed along the western Gulf Coast--
will drift slowly east and ultimately may get trapped beneath an
amplifying central Continental U.S. Ridge. It remains unclear...however...if
the closed low will indeed get trapped beneath in Rex block fashion
or instead become incorporated into a separate closed low forecast
to evolve off the middle Atlantic coast - a process started by the
aforementioned northern portion of the trough forecast to cross NC
Beforehand...a low-middle level shear/trough axis will be left behind
the shortwave trough forecast to approach and cross NC in SW flow
aloft during the near term; and this feature will bisect central NC
from NE to SW and serve as a focus for diurnal convection through
Wednesday...some of which will be augmented by the aforementioned
shortwave trough forecast to emerge east of the Appalachians late
While the remnants of Erika may regenerate over the far NE gom or Florida
Panhandle...not necessarily as a tropical entity owing to the
proximity of the gom upper low and associated synoptic/baroclinic
effects...any associated affects will still likely be suppressed
mostly south and/or west of central NC by the flow pattern outlined
As such...after around or slightly above climatology probabilities of
diurnal precipitation Tue-Wed...the remainder of the forecast period
will be characterized by at or below climatology pop...as relatively dry northwest flow
aloft sets up across the central Appalachians. Projected afternoon
low level thickness values around 1420 meters through the forecast
period should support highs generally in the upper 80s. Near climatology
lows mostly 65-70.
Aviation /12z Sunday through Thursday/...
as of 645 am Sunday...
Weak surface high pressure over the Carolinas will result in light
and variable winds and predominately VFR conditions through the
A weakening upper-level low...currently over the northern Gulf of
Mexico...will lift north-northeastward and over the western
Carolinas late tonight/early Monday. Top-down moistening is expected
in advance of this feature with rain/shower chances increasing from
the south between 06 to 12z Monday. Could see some MVFR conditions
within the heavier showers...otherwise.... expect mostly low end VFR
Scattered to numerous showers and thunderstorms will be
possible Monday afternoon and evening as the aforementioned upper
level disturbance moves through the area. Then through the remainder
of the week...scattered showers and thunderstorms with their
associated sub-VFR conditions will be possible each day...along with
the potential of late night and early morning areas of low clouds