Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 220732

Area Forecast Discussion
National Weather Service Raleigh NC
330 AM EDT Tue May 22 2018

A moist and unsettled air mass will hold across central NC through
mid week. A cold front will drop into the area from the north late


As of 315 AM Tuesday...

The subtle backdoor boundary noted on the latest surface analysis
over NE NC is expected to wash out near or soon after daybreak,
leaving us in a light SW flow pattern with an initially weak but
sharpening lee trough. A few light showers persist over central NC
early this morning, a function of weak waves tracking NE around the
Bermuda ridge, although nocturnal stabilization and overturning have
greatly diminished activity since the past evening. The remaining
showers should track NE out of the forecast area later this morning
as a band of lower PW now extending NW-SE over SC pivots NE into NC.
Rising heights over the lower Miss Valley and adjacent Gulf States
region combined with a weak mid level shortwave trough crossing the
Great Lakes will turn the weak steering flow to a slightly drier
westerly direction, contributing to a brief relative lull in precip
for a good portion of the day over central NC. Passage of a weak
perturbation through central/E NC from mid morning through early
afternoon is expected to result in a short enhancement of shower
coverage over the NE CWA during that time, so have retained chance
pops in the NE from late morning through early afternoon, with
generally dry weather elsewhere until late this afternoon. The
aforementioned Great Lakes trough brushing by to our NW and N and
the preceding DPVA into W and N NC late today into tonight should
prompt scattered convection, moving into the W CWA after 5 pm as a
surface cold front accompanying the mid level trough approaches from
the NW. Soon after trending pops down and out from the NE CWA, pops
will then trend back upward late over the W and far NW CWA,
spreading over the rest of the W and N sections of the forecast area
overnight with the slow arrival of dynamic forcing for ascent,
supported by a strengthening mid level flow and resulting
improvement in deep layer shear. Expect highs today in the mid to
upper 80s, although longer-lasting stratus and showers in the far NE
CWA this morning/early afternoon may hold maxes there in the lower
80s. Following persistence with partly to mostly cloudy skies
tonight, expect highs from the mid 60s to around 70. -GIH


.SHORT TERM /Wednesday through Wednesday night/...
As of 330 AM Tuesday...

Expect scattered showers/storms across the W and N CWA Wed morning
in tandem with the sharpening surface lee trough and the DPVA
preceding the shortwave trough moving through the Northeast and
interior Mid Atlantic region. This initial shear axis will continue
moving ESE with strengthening and veering mid level flow, while the
surface cold front moves into the NE CWA late in the afternoon. In
addition to the strengthening deep layer shear from the WNW to 30-35
kts, models are indicating good destabilization during the mid to
late afternoon, primarily across the north half. Probably the
biggest question mark however is how quickly the morning convection
pushes E and S. If this activity departs by mid afternoon, there
could be enough recovery in the afternoon with residual low level
moisture and minor mid level drying/cooling, such that surface CAPE
values reach into moderate to strong instability categories. The NAM
Nest wind profile shows veering and strengthening with height
through 800 mb, with subtle backing 800-600 mb, and given the
expected CAPE, large hail along with damaging winds are possible,
mainly across the N Piedmont and N/C Coastal Plain. Again, though,
this is dependent upon there being sufficient recovery in the
afternoon. Will include a mention of possible severe storms across
the N and NE CWA Wed afternoon/early evening. The storms should
slowly decrease in intensity as they slide SE Wed night, with the
cold front dropping SSE through much of NC overnight. Expect highs
Wed in the mid 80s. Lows once again in the mid 60s to around 70,
with some cooler dewpoints starting to work into N NC late. -GIH


As of 330 AM Tuesday...

There may be a break in the wet weather to begin the long term on
Thursday as a front pushes through the southern portion of the
state, leaving the northern half of the forecast area under high
pressure and relatively dry. High pressure will remain northeast of
the area keeping perception chances confined to the southwestern
Piedmont through Friday before the high exits to the east and out to
sea. Highs during this time in the mid 80s with lows in the mid to
upper 60s.

The moisture transport from the south returns once again for the
weekend aided by the Bermuda high and a developing low pressure
system in the Gulf of Mexico. At this time, it is uncertain as to
how quickly the return of moisture will be able to produce
precipitation over the area, and so Saturday is up in the air as far
as rainfall is concerned. This is mainly because of the uncertainty
in the development and track of the Gulf low. Despite these
differences remaining on Sunday, it may not matter as a plume of
moisture from the south is expected to ramp up convection once again
over the Carolinas. This feature will remain in place through Monday
and thus the end of the long term forecast. While Saturday
temperatures will reach the upper 80s with some possible breaks in
the clouds, expected overcast on Sunday and Monday will help bring
temperatures back down into the low 80s.


As of 110 AM Tuesday...

Circumnavigable storms will continue near RDU before weakening by
08z. Otherwise, remaining showers over the region will dwindle
through 08z, leaving behind areas of sub-VFR conditions, primarily
IFR cigs/vsbys, over much of the area through daybreak Tue. The
greatest chance for prevailing IFR conditions is at RDU/RWI,
although INT/GSO may see a period of IFR conditions as well, with
the lowest risk at FAY.

IFR conditions around daybreak at INT/GSO/RDU/RWI are expected to
lift to VFR by 14z, with considerable mid and high clouds lingering
overhead through the day. Despite VFR conditions then dominating
after 14z areawide, scattered showers and storms with brief MVFR
conditions are possible near RDU/RWI in the 16z-20z time frame,
after which time this activity should be shifting to the NE
toward/into VA. After 20z, showers/storms are then possible near
INT/GSO as an upper trough approaches from the NW. This risk will
persist until 01z before any showers/storms in the Triad slowly
decrease in coverage and intensity through the end of the TAF valid
period. But VFR conditions should dominate through 06z Wed.

Looking beyond 06z Wed, VFR conditions should hold at all terminals
through daybreak Wed, but the aforementioned approaching mid level
trough and associated surface cold front will bring showers/storms
across the NW sections including INT/GSO by mid morning. This
convection will increase in coverage and strength by midday, with a
good chance of showers/storms at all sites 17z-22z Wed. Sub-VFR
conditions and gusty/erratic winds are possible within and near any
showers/storms. Convection will decrease slowly Wed night as the
cold front drops southward through the area. Thu through Sat are
likely to be mostly dry and VFR as high pressure builds in from the
north, although FAY may see a few afternoon showers. Also, sub-VFR
fog/stratus are possible early Sat morning with increasing low
level moisture over the region. -GIH





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