Area Forecast Discussion
Issued by NWS Wakefield, VA-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KAKQ 010528
Area Forecast Discussion
National Weather Service Wakefield VA
128 AM EDT FRI JUL 1 2016
A cold front approaches from the northwest tonight as high
pressure remains over the western Atlantic. The front crosses the
region late Friday into Friday evening, before stalling across
North Carolina through early next week.
.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Forecast updated to bump up chance of rain over Eastern areas
where areas of shras/tstms are passing thru the region this eveng.
Threat of severe wx is ending, but still could see some small hail
and gusty winds. Pops decrease to 20% everywhere late ovrngt with
mainly dry conditions expected.
Latest radar trends depict isolated to widely scattered showers
developing along a dewpoint and instability gradient over central
Virginia. Sea breeze convection has remained south of the
Albemarle Sound thus far. Storm motion is slow in weak flow,
generally to the northeast. Expect a slight uptick in coverage as
a shortwave tracks across northern Virginia late this afternoon
into this evening. MLCAPE progged around 1,000 J/kg North Carolina
into central Virginia, with less instability noted toward the
coast. Will retain chance POPs for scattered showers and
thunderstorms inland. Less activity near the coast. SPC maintains
a marginal risk for severe weather as inverted V soundings
indicate the potential for gusty winds.
Convection expected to wane this evening with the loss of daytime
heating and instability. Upstream, scattered showers and
thunderstorms over the central Appalachians progged to track into
the Piedmont this evening. The shortwave tracking into the Piedmont
along with divergence aloft expected to maintain widely scattered to
scattered showers (and possibly a thunderstorm) from the Piedmont
across the northern forecast area to the Delmarva through late
tonight. Slight chance POPs maintained across the southeast as the
wavy front kinks northward behind the northern Virginia wave. Lows
in the upper 60`s to low 70`s under a partly cloudy sky.
.SHORT TERM /6 AM THIS MORNING THROUGH SUNDAY/...
Potent shortwave energy digs over the eastern Great Lakes Friday and
into the Saint Lawrence River Valley. Associated cold front reaches
the central Appalachians Friday morning. The front doesn`t drop into
the local area until late Friday, but pressure falls on the lee side
of the mountains will result in added low level convergence along a
thermal trough over the Piedmont. This trough, along with modest
height falls and increasing winds aloft will provide the focus for
scattered to possibly numerous showers and thunderstorms. Another
area of low level convergence will exist along the diffuse frontal
boundary in southeast Virginia and northeast North carolina. Low
level return flow and 850mb temps warming to around 18C (+1 standard
deviation) will push temperatures into the upper 80`s to around 90.
Dewpoints warming to around 70 and precipitable waters above 1.5
inches will result in an increasingly unstable air mass. MLCAPE
values climb to around 1,500 to 2,000 J/kg. However, marginal deep
layer shear, limited height falls, and modest mid level lapse rates
(refer to anomalous 850mb temps) will limit the overall convection
potential. SPC has expected a marginal risk of severe weather into
the Delmarva for gusty winds and hail, with only general thunder
back into the remaining forecast area. Coverage will be best over
the Delmarva, and have increased POPs to likely. Solid chance
elsewhere. Front reaches the coast Friday evening with lingering
scattered showers and thunderstorms expected from the Northern Neck
to the Delmarva. Drying after midnight as the best moisture pushes
offshore. The front stalls in the vicinity of northeast North
Carolina late Friday night. Lows range from the mid 60`s northwest
to mid 70`s southeast.
Short term guidance continues to stall the front over North Carolina
Saturday through Sunday. Deep moisture pushes south of the local
area Saturday, along with the best chances for measurable precip.
Will keep mention of scattered showers and thunderstorms Saturday
afternoon for far southern Virginia and northeast North Carolina as
moisture begins to return in low level southwest flow. Highs in the
mid to upper 80`s under a partly cloudy sky north to mostly cloudy
south. Front remains in the vicinity of northern North Carolina
Saturday night through Sunday as several waves in the westerly flow
ride along the front. Moisture also pools along the boundary with
precipitable water values around 2 inches. Good storm motion may
limit the overall potential for excessive rainfall Sunday, but
anomalous moisture and several upper waves will likely result in
periods of heavy rainfall. Highs Sunday only in the low 80`s under
a mostly cloudy sky.
.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
A frontal boundary shifts northward through the area Sunday night
into Independence Day as a trough drops into the Great Lakes and a
ridge builds over the East Coast. The general consensus is for the
trough to push through the region Tuesday into Tuesday night,
followed by a pattern that features a weak trough off the coast,
with a mid/upper ridge centered over the Southern Plains and Lower
Mississippi Valley Wednesday into Thursday. The 30/12z GFS remains
more amplified during the Tuesday-Thursday period than GEFS mean and
30/12z ECMWF. PoPs will generally be diurnally driven Monday and
Tuesday, averaging 30-40% across the area. PoPs drop to less than
15% by Wednesday as drier air builds in from the north. A shortwave
trough dropping in from the NW could trigger some afternoon/evening
showers/tstms by Thursday, but confidence with respect to details is
low at this range (a week in advance). Forecast high temperatures
are generally in the low/mid 80s Independence Day, and then trend
into the mid 80s to around 90 Tuesday through Thursday. Lows will
average in the mid 60s to low 70s.
.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
Challenging forecast even in the next six hrs wrt fog development
given temps not far away from crnt dp tmps and light winds. High
Res data suggests best shot for any significant fog should be
across the piedmont along with areas that did receive some rain
last night. Elected to go with some predominant MVFR BR at RIC
late and at PHF next few hours given the some BR development
there already. Went with a TEMPO group for BR elsewhere except
ORF. Feel patchy BR is possible most areas before 12Z.
Challenging forecast wrt pcpn chances at any one TAF site this
forecast period as the models suggest sporatic shwrs developing
across srn TAF sites by 12z with a rapid increase in mid level
moisture E of I95 after 16Z. Given a quiet radar sweep attm,
elected to keep pcpn out of forecast given timing uncertainities.
Expect a CU deck arnd 5K Ft to rapidly develop given daytime
heating acting on available mid level moisture. Best timing for
convection will be 18Z-02Z.
Outlook: Generally, VFR conds will prevail through much of the
period. However, look for potential brief windows of diminished
visibility and ceiling at all terminals in numerous showers/tstms
each day in the period, mainly during the aftn/evening hours.
A SE wind will average aob 10kt through tonight as high
pressure remains situated offshore with a trough inland. A cold
front approaches from the NW Friday, which will result in a wind
shift to SSW with speeds aob 15kt. The cold front drops into the
area Friday evening, and pushes through later Friday night, with
high pressure building into the area Saturday. A brief NNW surge is
expected in the wake of the front early Saturday morning. Generally
sub-SCA conditions are expected, but a brief period of wind gusts up
to 20kt is possible over the Bay. The wind becomes NE and gradually
diminishes Saturday. The front drops south of the area Saturday
night into Sunday, and then lifts through the area Sunday night into
Monday. A weak front approaches from the NW Tuesday. Seas average 2-
3ft through the period, with 1-2ft waves in the Bay. A brief period
of 2-3ft waves is possible in the Bay Saturday morning with the
RIC now up to 7.81" for the month of June through 3pm today. This
makes 2016 the 7th wettest June on record (2004 is wettest June
with 9.93"). Also, the May-June total at RIC now stands at 17.60"
and is the 2nd wettest (1972 is wettest with 17.69").