Severe Thunderstorm Warning 126, NWS Wakefield, VA

Area Forecast Discussion
National Weather Service Wakefield VA
407 PM EDT Fri Jun 16 2017

.SYNOPSIS...
A weak boundary lifts north of the area through tonight with
warm conditions expected through the weekend. Scattered
afternoon and evening showers and thunderstorms are expected
again Saturday with less coverage expected Sunday. A cold front
slowly approaches the region from the west on Monday, stalling
over the region through the middle of the week.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
Anomalously moist air mass remains over the local area as
satellite and RAP guidance indicates precipitable waters around
1.9 to 2.1 inches. Shortwave energy over the Southeast has
pushed the weak frontal boundary northward into northeast North
Carolina, stretching northwestward over the Piedmont. The front
has been the focus for widely scattered to scattered showers and
thunderstorms across southeast Virginia/northeast North
Carolina and the Piedmont. Earlier cloud cover limited overall
instability, but RAP analysis indicates mixed-layer CAPE of
1000-1500 j/kg (up to 2000 j/kg over the far southeast. A wave
is progged to lift northeast over the Piedmont later this
afternoon into this evening, leading to better organization and
coverage late today into this evening. Storms are expected to
grow upscale, lifting northeast. Best coverage expected across
the Piedmont and the southeast half of the forecast area,
remaining more scattered into central Virginia. Heavy rainfall
remains the main threat. Temperatures in the upper 70's to low
80's have limited downdraft potential (DCAPE) and deep layer
shear is less than 20 knots, but gusty winds are possible under
the strongest storms.

Added dynamics and elevated instability expected to keep showers
and thunderstorms ongoing through the evening hours west of the
Bay. Have retained likely POPs inland this evening. Convection
wanes late tonight, but will maintain a slight chance POP inland
due to the warm/moist air mass. Mild, with lows around 70.
Another night of low clouds and patchy fog expected.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/...
Warm/moist return flow persists over the region Saturday as
high pressure remains centered over the western Atlantic. Low
pressure centers over the Great Lakes as the attendant cold
front remains well west of the local area. Aloft, a baggy trough
stretches from the Ohio Valley into the Deep South as the
subtropical ridge locates offshore. While the air mass remains
quite warm and unstable, a lack of appreciable forcing and a
lack of surface convergence expected to result in only scattered
afternoon and evening showers/thunderstorms. Warming between
850-700mb also expected to prevent robust updrafts. Best chances
expected near the coast associated with sea-breeze boundaries
and remnant outflow boundaries. Highs in the mid to upper 80's.
Cooler near the coast. Mild Saturday night with lows generally
in the low 70's. Given the air mass, have kept slight chance to
chance POPs through late Saturday night.

Little change aloft Sunday as the baggy trough remains over the
Southeast. Stronger return flow expected Sunday ahead of an
approaching cold front. Precipitable waters fall off to 1.5 to
1.75 inches. Warming aloft and mid-level lapse rates less than 6
C/km will limit overall instability, with guidance indicating
mixed-layer CAPE values less than 1,000 j/kg. Perturbations in
the southwest flow will provide some subtle forcing for ascent,
so anticipate widely scattered to scattered showers and
thunderstorms Sunday afternoon and evening across the Piedmont
and near any sea-breeze boundaries. Warm, with highs in the
upper 80's to low 90's. Dry and mild Sunday night with lows in
the low to mid 70's.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Rather typical late-Spring/early-Summer conditions are
expected to continue into next week. A trough digging over the Great
Lakes will push a cold front toward the area Monday into Monday
night, resulting in an increasing chc of aftn/evening showers/tstms
Monday aftn/Monday night. Increasing flow aloft and a moderately
unstable airmass could trigger some locally strong storms with heavy
rain. The front lingers in vicinity of the coastal plain of SE VA
and the Carolinas Tuesday/Wednesday resulting in 20-30% PoPs Tuesday
and aob 20% by Wednesday. The latest data supports dry conditions by
Thursday as the boundary washes out. Another boundary/trough may
settle into the area by Friday but uncertainty is high at this time.
Highs Monday are generally in the upper 80s to around 90, then
dropping back to the mid/upper 80s by Tuesday/Wednesday as the front
gradually pushes through the area. By Thursday/Friday highs return
to the upper 80s to around 90. Lows will generally by in the upper
60s to low 70s through the period.

&&

.AVIATION /20Z FRIDAY THROUGH WEDNESDAY/...
Widespread MVFR conditions observed across the region as a
broken to overcast low deck persists. Some of the sites have
scattered out, but expected decks of 2500 to 3500ft AGL to
persist through the afternoon. Scattered to numerous showers and
thunderstorms expected to develop mid to late afternoon, with
the best coverage expected over the Piedmont and southeast
Virginia. Timing of convection will be challenging, so have
opted to only mention VCSH. Main threats will be gusty winds and
heavy rainfall. Winds are generally out of the south to
southeast at or below 10 knots. The boundary lifts northward
tonight into central Virginia, as flow becomes more southerly
over the region. The air mass remains quite warm and moist, so
expect another round of low ceilings and areas of fog again
tonight. Although stronger flow near the coast may inhibit fog
across the southeast.

Scattered to numerous showers expected again Saturday afternoon
and evening. Stronger southwest flow Sunday and Monday and less
moisture will limit precip chances. A cold front drops into the
area Monday night and Tuesday, with more unsettled conditions
through mid week.

&&

.MARINE...
A weak boundary will lift across the Mid-Atlantic coast as
a warm front this evening. Expect mainly a SE wind of 5-10kt, with
the potential for localized stronger wind gusts in any tstms. Seas
tonight into Saturday will generally be 2-3ft, with a dominant
period of 6-8sec, and embedded swell with a period of 18-20sec.
High pressure settles off the Southeast coast tonight through the
weekend. This will result in predominate southerly flow late tonight
into Saturday, with sea-breeze aided SSE flow of 10-15kt is expected
Saturday aftn/early evening. The wind will veer back to SSW Saturday
night remaining aob 15kt. The pressure gradient tightens Sunday into
Monday ahead of an approaching cold front bringing the potential for
pre-frontal SCA conditions. This could boost a SSW wind to 15-25kt
for the Bay/ocean, 15-20kt for the Sound/Lower James, and ~15kt
elsewhere. Seas build to 3-5ft N of Cape Charles, and potentially 4-
6ft out near 20nm, with 2-3ft waves in the Bay. This cold front
approaches from the northwest Monday and gradually drops into the
coastal plain of SE VA and the Carolinas Monday night into Tuesday,
and then dissipated Tuesday night into Wednesday.

&&

.AKQ WATCHES/WARNINGS/ADVISORIES...
MD...None.
NC...None.
VA...None.
MARINE...None.

&&

SYNOPSIS...SAM
NEAR TERM...SAM
SHORT TERM...SAM
LONG TERM...AJZ
AVIATION...SAM
MARINE...AJZ

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