Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Raleigh NC
300 PM EDT Monday Aug 31 2015
Synopsis...an upper level low will move northeastward away from the
area through the rest of today. Otherwise... a weak surface trough
will hold over eastern North Carolina... while high pressure
centered over Kentucky extends over western North Carolina.
Near term /through tonight/...
as of 300 PM Monday...
The shield of tropical rain has shifted east of the forecast area...
while the middle level low has moved well to our NE. While a few
shallow showers remain possible... the threat of additional
significant rainfall will hold just to our east for the remainder of
the day. Latest surface analysis shows low pressure just off the chs
coast... and this will track to the north-northeast along the surface trough
over eastern NC... accompanied by a middle level wave noted on water vapor
imagery just upshear. Extrapolation suggests that the rain shield is
likely to hold just to our east or perhaps brush along the far eastern
coastal plain as the low tracks over eastern NC... a scenario nearly in
line with the latest hrrr runs. Will retain a low chance pop over
the central/eastern forecast area into early evening... then expect dry
weather overnight as the drier air noted on water vapor imagery to
our SW continues to overspread all of central NC. It's a different
story near the ground however... as higher dewpoints and low level
moisture holding over the eastern half of NC along with a wet ground and
light or calm surface winds lead to favorable conditions for
fog/stratus development... particularly from the Triangle and Fay to
the east/northeast. Expect above-normal lows from 67-72. -Gih
Short term /Tuesday and Tuesday night/...
as of 300 PM Monday...
A weak surface pattern featuring a broad trough over eastern NC and Kentucky-
centered ridge extending into western NC will remain in place... while
aloft... heights rise over NC in the wake of the exiting wave... and
ahead of the low now over central Indiana. Forecast soundings depict
fairly dry and stable air through the middle and upper levels...
although a moderate amount of lingering low level moisture
especially in the east should result in scattered to broken stratocu
particularly from late morning through early evening. Once the
morning fog lifts and mixes over the northern and eastern County Warning Area... expect
generally partly cloudy skies. Will keep a slight chance of an
afternoon shower or storm in the far eastern County Warning Area... where low level
moisture will be better and where MUCAPE is forecast to approach or
exceed 1000 j/kg... but the lack of a focus for ascent and limited
moisture aloft should keep coverage low. Highs 88-92 with
thicknesses a bit above normal. Fair to partly cloudy Tuesday night with
lows 69-72. -Gih
Long term /Wednesday through Monday/...
as of 300 PM Monday...
A fairly low confidence forecast for the extent of the long term as
there is very little forcing in the upper levels with no real
discernible jets or strong shortwaves in the vicinity of central NC.
Therefore much of the long term forecast will be built around lower
Wednesday should be fairly uneventful with very weak high pressure
over the western Atlantic and a surface low moving through eastern
Canada. The surface front associated with this feature will be very
weak with not much of an airmass chance but maybe just enough
forcing for a slight uptick in convection on Thursday
afternoon/evening with showers lingering into the early morning
hours on Friday.
During the day on Friday high pressure will begin to strengthen over
New England and retrograde southwestward into the Middle Atlantic
States. This will help push a back door cold front through the area
later on Friday and giving US a cooler airmass for the weekend and
Temperatures will mainly run in the upper 80s/low 90s early in the
period and then drop into the low to middle 80s for the weekend and
into early next week. Lows generally in the middle to upper 60s. Precipitation
chances will mainly be slight chance through the work week with
chance probability of precipitation for the weekend. -Re
Aviation /18z Monday through Saturday/...
as of 125 PM Monday...
MVFR conditions are likely to dominate at int/gso/Fay into
tonight... while IFR/LIFR conditions are expected to dominate at
rdu/rwi. A stream of tropical moisture which brought this morning's
rain is being pushed slowly eastward into coastal NC... but lower
ceilings remain well back into central NC with weak surface winds and
plenty of lingering low level moisture. These two factors will keep
a high chance of sub-VFR ceilings through this evening at central NC
terminals... although int/gso/Fay may briefly break out to VFR this
afternoon. Ceilings should remain IFR at rdu/rwi... although these sites
too may briefly Jump Up a category to MVFR today. Clouds are
expected to become scattered at int/gso overnight... but with a threat of
MVFR to IFR visibilities in fog. At Fay and especially at rdu/rwi... ceilings
are expected to hold at IFR or even LIFR overnight into Tuesday
morning... with a risk of MVFR to IFR fog. Low clouds should slowly
lift and mix out to MVFR then VFR Tuesday morning in the 14-18z time
frame... with ceilings at rwi last to lift to VFR.
Looking beyond 18z Tue: VFR conditions are expected Tuesday afternoon
into Tuesday night... but MVFR to IFR fog is possible late Tuesday night
into Wednesday morning. VFR conditions should then prevail through Sat.
Scattered sub-VFR showers/storms are possible each afternoon/evening
Wednesday through Sat... although forecast confidence is quite low with
details of possible timing or coverage. -Gih