Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Highlight Changed Discussion --
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FXUS62 KRAH 210618
Area Forecast Discussion
National Weather Service Raleigh NC
217 AM EDT SUN AUG 21 2016
An upper level trough and attendant cold front approaching the
mountains from the west this morning will progress east through the
Mid-Atlantic and Carolinas this evening into tonight. In the wake of
the front, dry high pressure will build into the region from the
west through mid-week.
.NEAR TERM /TODAY AND TONIGHT/...
As of 145 AM Sunday...
Westerly flow aloft will strengthen over the region today as an
upper level low progresses ENE through the Upper Great Lakes into
southern Canada, additional shortwave energy digging southeast
through the central MS river valley amplifies an upper level trough
over the OH valley and Great Lakes, and an attendant cold front
approaches the mountains from the NW, progressing through central NC
this evening/tonight. Expect the best potential for convection north
of hwy 64 (closer to stronger DPVA progressing into the Mid-
Atlantic) during the late afternoon and evening hours (21-03Z) as
the surface cold front /low-level trough/ progresses into the region
around/shortly after peak heating in the presence of above normal
moisture and moderate destabilization. Deep moisture /cloud-cover/
and weak mid-level lapse rates may temper instability such that more
favorable deep layer shear attendant stronger flow aloft may not be
fully realized/capitalized upon by updrafts at this latitude, though
NAM forecast soundings from the Triangle NE into the Coastal Plain
show ~1500 J/kg MLCAPE and sufficient shear for SCP values of 1-2
around 23-00Z. Uncertainty remains high with regard to convective
evolution (timing/location/coverage/organization), though the latest
convection allowing models have trended toward decreased coverage
confined primarily along/north of hwy 64. Despite weak mid-level
lapse rates and weak DCAPE, brief supercellular organization
possible across the northern Piedmont and NE Coastal plain would
support an isolated potential for damaging winds (aided by precip
loading and downward momentum transport) and marginally severe hail.
Expect convection to end from west-east this evening/night (by
midnight) as the surface front /low-level trough/ progress toward
the Carolina coast. Expect highs in the upper 80s to lower 90s and
lows tonight driven by weak cold advection behind the front, ranging
from the lower/mid 60s W/NW to lower 70s far SE. -Vincent
.SHORT TERM /MONDAY AND MONDAY NIGHT/...
As of 145 AM Sunday...
Synoptic subsidence in the wake of the upper level trough
progressing offshore the Mid-Atlantic coast tonight will increase
surface pressure over the Ohio Valley and Appalachians during the
day Monday, aiding the advection of a drier airmass into the
Carolinas from the NW. Expect clear skies and a light NW breeze with
highs ranging from the lower/mid 80s NW to upper 80s SE. High
pressure will build east into the Mid-Atlantic Monday night, with a
sfc ridge axis extending SE into the Carolinas. With a much drier
airmass in place (dewpoints in 50s) and clear/calm conditions, lows
may fall below 60F into the upper 50s Monday morning, primarily
across the N/NW Piedmont, with lows in the lower/mid 60s elsewhere,
warmest in the SE coastal plain. -Vincent
.LONG TERM /TUESDAY THROUGH SATURDAY/...
-- Changed Discussion --As of 217 AM Sunday...
Ridging, both sfc and aloft, will promote a continuation of dry
weather across our area right through the work week. In addition,
look for little airmass change from Monday, so highs in the mid 80s,
lows in the mid 60s, and dewpoints in the low-mid 60s will continue
right through Thursday. By Friday we`ll begin to see the airmass
moderate to above-normal readings as the sfc ridge axis moves
offshore and southerly flow re-establishes over our area. On
Saturday, the next cold front will drift south toward then stall
across our area. While the front will bring a slight chance for
showers/tstms, given limited moisture, right now it appears that
most of the day Saturday should remain dry.
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.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
As of 155 AM Sunday...
24-hr TAF period: Expect VFR conditions to prevail this morning
through mid-afternoon...in advance of a cold front approaching the
mountains from the west. Sub-VFR conditions attendant convection
expected to develop along the front during the late afternoon and
evening hours (21-03Z) will be possible at all terminals, though
most likely at northern terminals, especially RDU/RWI. An isolated
severe thunderstorm with sfc wind gusts AOA 50 KT cannot be ruled
out. Expect WSW winds of 5-10 kt with gusts up to 15 kt this
afternoon to become NW at 5-10 kt in the wake of the front this
Looking Ahead: VFR conditions and light winds will prevail through
mid-week as dry high pressure builds eastward from the OH Valley
into the Mid-Atlantic. -Vincent