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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 150617
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
215 AM PM EDT Sun Apr 15 2018

.SYNOPSIS...
-- Changed Discussion --
A strong cold front will move east across the region late this
afternoon and this evening, proceeded by a few strong to severe
thunderstorms. Dry, cooler, and breezy conditions will follow for
Monday.
-- End Changed Discussion --

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 935 PM Saturday...

Bermuda high pressure continues to bring warm and moist air
advection from off the western Atlantic SC and SE NC. The dew
points were already in the mid to upper 60s along the SC coast, with
60+ dew points having reached the Southern Pines to Smithfield areas
as of mid-evening. A stratocumulus bank of cloudiness was seen on
satellite moving northward, onshore into eastern SC and NC. Expect
areas of low clouds to spread/develop into our region after
midnight, yielding a trend to mostly cloudy to cloudy skies by
daybreak. Isolated showers or sprinkles remain possible, more so
later tonight and mainly over the SE sections, closest to the
Atlantic-source inflow in a zone of low level mass convergence. But
coverage and amounts should be small, as the mid levels stay fairly
dry. Lows primarily in the lower to mid 60s.

&&

.SHORT TERM /SUNDAY AND SUNDAY NIGHT/...
As of 350 PM Saturday...

...Risk of severe storms and locally heavy downpours late Sun
through Sun evening...

Strongly forced convection, mostly linear but with a chance of
leading discrete cells, is still anticipated late Sun well into Sun
night, focused on the 21z-06z time frame. The powerful mid level low
will track from S IA across IL/IN to W OH through Sun night, with
the surface cold front progressing eastward (perhaps just north of
due east) through the Carolinas. The corresponding mid level trough
will take on a negative tilt as it swings ENE through the Carolinas,
resulting in a strengthening wind field, including 0-6 km bulk shear
of 50-60 kts and 35-50 kts of southerly flow at 925 mb. These
intense kinematics along with drastic 150-200 m height falls will
induce vigorous forcing for ascent, supporting a wide band of heavy
showers and strong storms within a prefrontal PW surge to around
1.5".

Moderate instability is anticipated ahead of the front Sun afternoon
into the evening, aided by incoming surface dewpoints near or over
60F, especially over the eastern two-thirds of the CWA. Most models
including the HREF mean indicate an SBCAPE of 1000-1500 J/kg from
late afternoon into the evening, highest E, and this with the deep
layer shear will support strong to severe storms with damaging winds
as a primary threat, given the intense dynamic forcing for ascent
and strong background wind field. It`s worth noting, though, that if
daybreak stratocu holds on longer, this could limit heating and
potential instability somewhat. QLCS mesocyclones and isolated
tornadoes are possible as well, with strong line-normal low level
winds, a long curved hodograph, and decent probs (aoa 50%) of an STP
over 3 according to the HREF mean.

While the heaviest precip is likely to fall well to our NW, over the
mountains (orographic enhancement of lift) and near the inflection
point of the tilting system, a period of heavy rainfall is also a
concern across all of central NC, with a deep warm layer (LCL-0C
depth near 4 km) facilitating warm rain processes, and the potential
for training echoes leading to locally higher amounts. Storm total
rainfall near 2 inches, give or take a quarter to half inch either
side, seems attainable areawide. Confidence in any one location
exceeding FFG is low, however, so will not consider a flash flood
watch at this time, but will certainly look at this again Sun
morning.

Precip chances will taper down behind the main band after midnight
from W to E, although trailing stratiform rain and a few lightning
strikes may linger for a few hours overnight. Will trend pops down
to lower chances W to E, but will need to keep shower chances going
through the night with waves of mid level DPVA traversing the base
of the negatively tilting trough as it crosses the region SW to NE.

Expect highs from the mid 70s to lower 80s Sun, with some eastern
sections likely to see partial heating (although, again, this will
depend on the extent of morning clouds). Lows Sun night from around
50 W to around 60 E. -GIH

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
As of 210 PM Saturday...

Fairly quiet long term forecast as the frontal system exits to the
east on Monday. There will still be a slight chance of some showers
in the northeast as the northern stream cold front pushes through
behind the initial surge from the main front and as the upper low
moves north of the CWA. Any showers that do occur would be confined
to the northern counties with the rest of the area remaining dry but
cloudy for much of the day. Temperatures will be much cooler than
previous days with a 15 degree drop in daytime highs which will top
out in the lower 60s Monday afternoon. A warming trend will then
begin through Wednesday as surface high pressure resides over the
Florida Peninsula and zonal flow aloft keep things warm and dry.

On Thursday a low pressure system will cross well to the north of
the area and drag a dry cold front over the area late in the day.
This will set up a fairly decent temperature gradient over the area
with the Triad topping out in the low 70s with southeastern
locations achieving 80 degrees. A few showers could be possible
across the VA border counties but otherwise no precipitation is
expected. Behind this front, continental high pressure over the Ohio
Valley will turn surface winds to northerly and thus cooler temps
for the end of the week with highs in the upper 60s to near 70
degrees both Friday and Saturday.

&&

.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
-- Changed Discussion --
As of 215 AM Sunday...

Aviation conditions will deteriorate through 12Z as low level
moisture will lead to the development of a low stratus deck,
resulting in IFR/LIFR ceilings across central NC. These ceilings
will slowly lift after 13Z, with low end VFR ceilings probable at
KRDU, KFAY, and KRWI by early afternoon. MVFR ceilings will likely
dominate in the Triad terminals through the afternoon.

Spotty light rain showers will be possible this morning across
central NC. The shower coverage will increase this afternoon as the
atmosphere destabilizes. Sfc winds ahead of a strong cold front will
be gusty with gusts in the 27-33kt range expected. The strong cold
front approaching from the west will increase the shower coverage by
late afternoon in the west with a few severe thunderstorms likely.
This band of heavy showers and severe storms will progress east
across central NC this evening. In vicinity of the stronger/severe
storms, expect wind gusts 40-55kts along with some hail and
torrential downpours.

The shower coverage will decrease from the west after 02Z, with
ceilings lifting after 06Z. The improving aviation conditions will
continue into Monday. VFR parameters anticipated Tuesday through
Thursday.
-- End Changed Discussion --

&&

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

&&

$$
SYNOPSIS...WSS/Badgett
NEAR TERM...Badgett/Hartfield
SHORT TERM...Hartfield
LONG TERM...Ellis
AVIATION...WSS