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000
FXUS62 KRAH 122335
AFDRAH

AREA FORECAST DISCUSSION
National Weather Service Raleigh NC
735 PM EDT Wed Aug 12 2020

.SYNOPSIS...
Weak low pressure will linger over the Carolinas through the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 345 PM Wednesday...

Convection thus far has held close to both expectations and the
morning CAM solutions, confined largely to areas E and NW of the
forecast area, with isolated showers/storms along and SE of the
inland-moving sea breeze and more numerous storms just NW of the
Triad, over the higher terrain of west-central and NW NC into VA and
SW WV. Steering flow remains weak, thus storm propagation will be
outflow-driven, making the attempts to forecast convection chances
in central NC over the next several hours quite challenging. Can`t
rule out a shower or storm anywhere through this evening, but the
best chances appear to be over the Triad, where some very weak mid-
upper level DPVA within very weak S/SW mid level flow will traverse,
in conjunction with weak but focused low level SE upglide. Will
retain the highest pops here until around midnight, with much lower
pops elsewhere, ending earlier as heating winds down in the absence
of any other mechanisms to force ascent. As has been advertised,
isolated pockets of flooding are possible given the high PW near 2"
and very slow storm motion favoring long-lasting heavy downpours and
inflated rainfall totals. Expect fair skies tonight to give way to
another round of fog and stratus, with model guidance and
persistence suggesting equal chances areawide. Expect lows to be
similar to last night, in the 70-74 range with some upper 60s in
rural locations. -GIH

&&

.SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
As of 355 PM Wednesday...

More of the same expected, but with a bit better coverage than we`ve
seen so far today. Steering flow from the SW will remain very weak,
although we may see it pick up slightly as the weak upper trough
over the Mid Miss Valley approaches. The weak low level low pressure
area over the central/E Carolinas today is expected to drift to the
NNE, leading to a band of more discernible confluence of low level
flow through central and E NC as inverted troughing becomes more
defined from NE NC SW through the CLT area. With the continued
slow/meandering storm motion and PW that is likely to be 2-2.5",
slow-moving heavy downpours remain possible, although the continued
lack of large scale forcing for ascent may curtail coverage once
again. But good chance to low-end likely pops still seem reasonable,
and have largely held onto these, with minor tweaks. Temps should
once again lean toward persistence, with highs in the upper 80s to
around 90 followed by lows near 70 to the lower 70s. -GIH

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
As of 230 PM Wednesday...

No major changes for the long term with the afternoon forecast
package. Upper-level low pressure will remain over the southern
Appalachians through the weekend, then slowly lifting east-northeast
early next week across the area. At the surface, an inverted trough
will remain over the Appalachians, extending from a low over
northern MS/AL through the end of the week, shifting into central NC
over the weekend as the low lifts through the Carolinas. This
pattern, along with precipitable water values around 2 inches, will
support scattered to numerous showers and thunderstorms across the
region through the weekend. Most shower activity will be in the
afternoons and evenings, with less coverage overnight.

The upper-level trough will push east sometime Sunday/Monday, with
slightly drier air behind the system. Showers and thunderstorms will
be more isolated Monday and Tuesday. Lower dewpoint temperatures
behind the system will make it feel less muggy early next week, with
heat indices only in the upper 80s to low 90s by Wednesday. Another
upper-level trough will develop just to our west by the middle of
next week, and with an increase in moisture over the region, helping
to increase shower and thunderstorm activity yet again across the
region. Highs through the extended will be just below seasonal
normals, with lows just above seasonal normals.

&&

.AVIATION /23Z WEDNESDAY THROUGH MONDAY/...
As of 730 PM Wednesday...

Several factors are in play for tonight`s aviation forecast.

First, in the near term it appears that a thunderstorm will clip
RWI, and have added a VCTS to that TAF. In addition, over the next
few hours, recent high-resolution models have shifted the timing of
precipitation around the Triad, showing that now is likely the
maximum for rainfall and that coverage will diminish through the
evening, instead of increasing around midnight. Added rain to the
INT TAF, but think that precipitation will stay west of GSO.

Inherited IFR forecasts for all TAFs around sunrise, although a
similar forecast last night only panned out at FAY/RWI, with
INT/GSO/RDU all remaining VFR through the night. Nearly all guidance
is once again indicating IFR conditions everywhere, and have decided
to go ahead with a modified persistence forecast. Kept the lower
visibilities at RWI/FAY, and actually decided to lower visibilities
based on conditions 12 hours ago and good model agreement. However,
a limiting factor to the development of fog/stratus overnight could
be the high overcast moving into North Carolina from northwest to
southeast. This could eventually temper low level impacts. Because
of this increasing cloud shield and no rainfall at GSO/RDU, have
decided to go with a VFR forecast overnight as the cloud shield
should limit radiational cooling potential. Finally, INT has picked
up over a quarter inch of rain in the last hour with a shower, and
think that the influence of this rain should allow for some
visibility reduction overnight, so kept the inherited MVFR
visibilities there.

Finally, for Thursday afternoon, inherited 50-60 percent chance of
thunderstorms in the public forecast, so have gone with VCSH at all
sites, as it seems too early to pick a particular site to mention
either TS or prevailing rain.

Looking beyond 00Z Fri, daily chances for showers and storms are
expected each afternoon into the evening through Sun, as a weak
upper low over the Mid Miss Valley drifts slowly eastward through
the Mid Atlantic region. Early-morning sub-VFR fog and stratus are
also expected across the area each morning through Sun. Some
improvement is possible Mon as drier air moves in.
-GIH

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$
SYNOPSIS...MWS
NEAR TERM...Hartfield
SHORT TERM...Hartfield
LONG TERM...JJT
AVIATION...Green/Hartfield