Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wakefield Virginia
822 PM EDT Friday may 29 2015
high pressure over the northeast states will gradually slide off
the coast tonight into Saturday. A slow moving cold front will
approach from the northwest late Sunday...and will settle over the
middle Atlantic Monday afternoon into Monday night.
Near term /until 6 am Saturday morning/...
a shortwave trough is slowly pulling off the New England coast
this afternoon...with a trailing weak cold front lagging back over
the middle Atlantic. This has provided enough low-level convergence
to support isolated-scattered convection over the Piedmont and isolated
convection from the Northern Neck to the Maryland/Delaware portion of the Eastern
Shore. Conditions farther southeast have stabilized evidenced by a more
spars cumulus field. MLCAPE values over the Piedmont are on the order
of 1000-1500 j/kg...with minimal deep layer shear. Hence storm
organization will be pulse in nature. A few stronger updrafts are
possible...but should be short-lived with minimal shear and
unlikely to produce large hail or strong wind gusts.
Showers/thunderstorms should dissipate quickly this evening followed by a
partly cloudy to mostly clear night. Lows should range from the
middle to upper 60s. Locations over the Piedmont that have received
rain this afternoon could potentially have some patchy fog
Short term /6 am Saturday morning through Monday/...
the primary trend amongst 12z/29 numerical models is an overall
slower progression with respect to the longwave pattern Saturday
through Monday. Middle/upper level ridging is expected to remain
strong along the middle Atlantic and southeast coasts through Sunday.
This will allow our period of Summer-like weather to continue.
Continuity will be maintained Saturday with probability of precipitation at or below 10% as there
is little forcing underneath the ridge. A shortwave trough lifts
across the upper Ohio Valley and eastern Great Lakes Sunday. This
could provide enough of a trigger for showers/thunderstorms to drift into
north/northwest portions later in the afternoon and into the evening. A
30-50% pop is forecast for the northwest half of the area.
Otherwise...expect a partly to mostly sunny sky Saturday and
Sunday...with mostly clear to partly cloudy nights. Highs Saturday
and Sunday should range from the upper 80s to around 90
inland...to the 70s to low 80s along the coast.
A better chance for showers/thunderstorms arrives for most of the area by
Monday afternoon. A northern stream trough drops into the Great
Lakes...which pushes a cold front toward the middle Atlantic region.
GFS/European model (ecmwf) each indicate a pre-frontal Lee-side trough...and the
GFS additionally depicting a weak surface low over the northern middle-
Atlantic. This should provide low-level convergence in what is
forecast to be a warm/humid unstable airmass. Forecast probability of precipitation range
from 20-30% over far southeast portions...to 40-50% over the northwest half of
the area. Sky condition should be partly to mostly cloudy...with
highs ranging from the middle 70s N/NW...to the low/middle 80s southeast...and
locally cooler along the immediate coast.
Long term /Monday night through Friday/...
low pressure settles over the region Monday night through Tuesday...then
becomes shunted south of the Virginia/NC border by Wednesday morning. Expect
unsettled conditions with periods of showers and thunderstorms
(although Monday appears to be the best day for widespread rainfall
across the entire fa). High pressure builds in from the northwest Wednesday
afternoon through Thursday and then slides off the Delaware-Maryland-Virginia coast by Thursday
night. With high pressure off the coast...any chance for
showers/storms should stay west of the middle Atlantic region. Long
range models are hinting at a coastal low developing anywhere from
the southeast coast to moving the Cape Hatteras coastline Friday into next
weekend. There are significant timing differences and have
preferred to lean the far extended portion of the long term
forecast more toward climatology across the far southwestern area of the forecast area.
High temperatures generally in the middle-upper 70s during the more rainy
periods Tuesday/Wednesday with a warm-up into the low 80s for the end of the
week (roughly 5 degrees cooler at the beaches). Lows Monday night
through Friday night generally in the low-middle 60s (roughly 5 degrees
warmer at the beaches overnight).
Aviation /01z Saturday through Wednesday/...
area of high pressure will slowly slide off the coast tonight and
outside of some lingering low level moisture...will see drier air
aloft move in. This will allow for VFR conditions to continue
tonight into the day on Saturday. The cumulus field should dissipate
tonight and will not be a prominent tomorrow with the drier air
The next chance for MVFR to IFR conditions would be beginning
Sunday night through early Tuesday as a cold front slowly moves
into the area and convection is expected to develop along and
ahead of the front.
a diurnal increase in onshore Ely winds has been observed this
afternoon with wind speeds around 10kt with gusts to around 15kt over
the waters...including the eastern Virginia rivers and Currituck Sound.
Winds are expected to diminish shortly after sunset as the wind
direction becomes more south-southeast. Waves 1-2 feet and seas 2-3 feet. As high
pressure remains over the western Atlantic through the weekend...
winds remain south-southeast with afternoon/early evening surges in speeds but will
they will stay within sub-Small Craft Advisory conditions (i.E. Generally at or below
15kt/seas 2-3ft/waves 1-2ft but up to 2-3ft during surges). Seas
will reach up to 4ft out near 20nm Sat night through early next
week. The overall flow weakens Monday into early next week as a
cold front settles into the region. Expect increasing NE flow by