Scientific Forecaster Discussion
fxus61 kakq 172026
Area forecast discussion
National Weather Service Wakefield Virginia
426 PM EDT Thu Aug 17 2017
a warm and humid air mass remains in place across the mid-
Atlantic states tonight and Friday as the flow continues out of
the south. The next cold front will arrive late on Friday night
and exit the region by Saturday afternoon. High pressure builds
in for Sunday through early next week.
Near term /until 6 am Friday morning/...
a warm and humid airmass is in place across the region this
afternoon. There is a weak convergence boundary across the south
central portion of Virginia into central NC from a lingering boundary
associated with low pressure near Bermuda. There is some
convection along this convergence boundary, but most of it is in
NC and will remain out of the region. The remainder of the area
is under the SW flow that is developing ahead of a cold front
that is making its way across the Ohio Valley. The models show a
swath of moisture streaming northward out of the NC mountains
with some associated convection that may impact the region this
evening into the overnight hours. The models, both the 12z GFS
and NAM take the energy associated with this convection and
gradually organize it into an area of showers over the lower Maryland
Eastern Shore by Friday morning. So have increased the pops in
that area toward morning getting pops to low likely range. The
remainder of the area will otherwise be mainly dry, warm and
humid overnight with lows in the low to mid 70s.
Short term /6 am Friday morning through Sunday/...
the next cold front approaches late in the day on Friday into
Friday night and moves the region by Saturday afternoon. This
will be the dominate feature for this period and should produce
some shower activity with the front with the best chance for
convection across northern portions of the cwa. Further to the
south, the lift is not as strong or as organized for not
expecting as much pcpn there. So on Friday, will see some
morning showers exiting the Delmarva and then a general wane in
precipitation. Expect to see some scattered convection due to
the heating of the day, but as the front arrives, activity
should increase. The front slowly pushes southeast overnight
reaching the southeast portion of the County Warning Area by Saturday morning. This is
a bit of a change from the 00z and 6z model runs which stalled
the front. But all the 12z guidance pushes the front to the
south of the area by 18z. So have sped up the clearance of the
pops by late Saturday afternoon.
A strong shortwave trough sweeps across the mid-Atlantic states
Saturday night, but it remains north of the area and with the
low level moisture gone, not anticipating much except some mid
level clouds. By Sunday, high pressure will be over the region
with dry and seasonable weather in place.
For temperatures, will continue to see near normal weather with
highs in the upper 80s to around 90 each day and lows in the low
to mid 70s each night except for Saturday night when the drier
air will allow temps to drop into the upper 60s to low 70s.
Long term /Sunday night through Thursday/...
sfc high pressure builds north of the area with stacked high
pressure residing off the southeast coast through Mon night.
A thermal trough develops in the Lee of the Appalachians for
Tue/Tue night, and then a cold front is expected to track
through the area on Wed...exiting the coast late Wed night.
Conditions will become increasingly more humid with each
passing day. Sfc features rather diffuse for Mon, however
seabreeze boundaries with the presence of ample moisture will
keep a slight chance for showers/storms in the forecast...
primarily for the aftn/early evening. Thunderstorm activity
expected to become widely scattered Tue as convection develops
invof Lee trough. The frontal passage Wed/Wed night will
provide a better focus for more organized thunderstorms to
occur. Highs Mon-Wed generally upper 80s to lower 90s;
low-mid 80s beaches. Lows sun-Tue nights generally 70-75f.
Lows Wed night mid-upper 60s northwest to 70-75f southeast.
Aviation /20z Thursday through Tuesday/...
latest radar shows some shower activity along the I-95 corridor,
mainly south of ric, moving east. The latest guidance suggests
that these showers will dissipate and dive southeast this
afternoon. As such, will keep any mention out of the terminals,
with the exception of ric where I will include vcsh 18-20z.
Otherwise, a weak boundary will move mainly north of the area
later tonight into Friday morning. This may allow for additional
shower activity at ric and sby, but confidence is not high
enough to include in the terminals. Main story will be IFR cigs
and possible visibility at ric late tonight into early Friday morning.
With the wind staying around 5 kt, am expecting more of a lower
stratus event vs. A low visibility event at ric. Elsewhere, it should
remain VFR or MVFR with low probability of IFR expected.
Outlook: a cold front approaches the region Friday into
Saturday bringing another chance for showers, thunderstorms, and
sub-VFR conditions. High pressure builds back into the region
a boundary remains stalled just south of the Mason-Dixon line
into Delaware this aftn. High pressure and fog/clouds earlier
this morning have hampered widespread thunderstorm development
today. However, isolated storms may still be possible over srn
waters late this aftn/early evening. Winds generally southeast around
10kt will increase to around 15kt and become more sly this
evening into Friday as a cold front approaches the region.
Seas/waves average 2-3ft. The cold front moves over the waters
late Fri night into Sat. South winds average of 15kt Bay and
15-20kt ocean with the frontal passage. Seas build to 3-4ft
north of Cape Charles Light Fri aftn and may even touch 5ft
for a few hours out near 20nm as the front crosses the waters.
Small Craft Advisory conditions still not anticipated with the increase in
winds/seas Fri except with thunderstorms associated with the
front. If any headlines are necessary, they can be handled with
short-fused mws or smw products.
Winds become more SW-west with speeds aob 10kt early Sat morning
into Sun morning as the front stalls near the mid Atlantic coast,
and then become more onshore sun aftn into Mon as the front sags
well south of the area. Seas subsiding from 2-3ft Sat morning to
2ft by Sat aftn through Mon night. Winds become S on Tue as a
thermal trough develops inland with seas building to 2-3ft. Winds
then become more SW aob 15kt Tue night/Wed as the next cold front
is expected to cross the region; seas build to 3-4ft.