Scientific Forecaster Discussion
fxus61 kakq 162300
Area forecast discussion
National Weather Service Wakefield Virginia
700 PM EDT Mon Sep 16 2019
a weak back door front will slide south across the lower mid
Atlantic region tonight and early Tuesday. Surface high
pressure gradually builds down into the region from the north
Tuesday night through Thursday. Meanwhile, tropical cyclone
Humberto is forecast to track well east of the southeast coast
Near term /until 6 am Tuesday morning/...
as of 315 PM EDT Monday...
Latest weather analysis reveals a weak cold front draped across
S NJ, extending west/northwest into northwest PA and the lower Ohio Valley. A
warm, pleasant late Summer afternoon across the local area. 19z
temperatures range from the upper 70s to mid 80s along the
immediate coast, with upper 80s to lower 90s over inland
sections under a sunny to mostly sunny Sky.
High pressure across upper Great Lakes/southeast Canada will build
across New England and the interior northeast tonight...slowly
forcing the front south in back door fashion across the
northern mid- Atlantic late tonight into Tuesday morning. A
mostly clear sky will therefore become partly to mostly cloudy
late tonight into Tue morning over northern sections. Remaining
dry for most of the area tonight, though a stray shower or two
cannot be ruled out over far northern zones, so a slight chance
pop will be maintained after midnight tonight. Early morning
lows will range from the mid 60s to around 70.
Short term /6 am Tuesday morning through Wednesday night/...
as of 315 PM EDT Monday...
The front will drop across the region on Tuesday. Not much in
the way of deep layer moisture, so will keep pops only about
20-40% for isolated to widely sct showers. A thunderstorm
cannot be ruled out over the SW tier of Piedmont counties, so
will include iso T wording from ric Metro/Tri-Cities area SW to
I-85 corridor. Would expect conditions to become mostly cloudy
from NE to SW during morning into the early aftn far SW. This
greater cloud cover and increasingly onshore flow will bring
cooler temperatures relative to those of today (especially over
the north). Forecast highs 75-80f north and 80-85 S (warmest for
interior NE NC and south central va).
Rain chances drop off with steadily falling precipitable water values Tue night.
However, lingering llvl moisture likely to result in slow
clearing from Tue night. Mixing and some lingering clouds will
keep it from getting as low as met guidance indicates, so will
err toward the warmer side of the guidance envelop. Thus, expect
lows in the low to mid 60s S, to 55-60f north.
High pressure continues to build S from the eastern Great
Lakes/New England on Wed. Soundings show some lingering low
level moisture with the onshore flow, so will keep it partly to
mostly sunny over the region. Should remain dry though, along
with comfortable temps (highs only 75-80f) and dewpoints falling
into the 50s for most areas. It will be fairly breezy along the
coast, due to the cooler airmass over the warm waters and a
strong pressure gradient between Humberto...by then well
offshore to the southeast and the high centered to the N/NE.
Long term /Thursday through Monday/...
as of 115 PM EDT Monday...
Cooler, drier conditions look to persist for the mid to latter
portion of the week. Ridge of sfc high pressure will extend
along the eastern Seaboard into the southeastern US Wed-Fri.
Aloft, the region will remain on the periphery of an upper level
ridge of high pressure, which will rebuild over the region from
the southwest during the upcoming weekend, bringing a gradual
warm-up late in the weekend into early next week.
Warm days and cool nights persist through much of the period.
High temperatures Thursday and Friday will be near to slightly
below seasonal averages with highs in the upper 70s to lower
80s. Overnight lows falling back into the low to mid 50s inland
(though a smattering of upper 40s possible in typical cool
spots Thu/Fri mornings)...with low to mid 60s at the coast. The
warming trend begins Saturday into early next week, with high
pressure at the surface and building heights aloft. Above
average temperatures likely prevail through this period with
highs in the mid/upper 80s to around 90 degrees.
Aviation /00z Tuesday through Saturday/...
as of 110 PM EDT Monday...
VFR conditions across area terminals this aftn with light winds
5-10 kt. NE winds/low level moisture will bring another chance
for MVFR ceilings and some iso-sct showers late tonight into Tue
aftn, along with somewhat breezy onshore (ne) flow near the
coast. Backdoor cold front drops south of the region Tue aftn
into Tue night, with some lingering showers/sub-VFR cigs into
early Wed morning.
Outlook: VFR conditions are expected behind the front Wed thru
Fri with clear to mostly clear and dry conditions.
as of 700 PM EDT Monday...
With Small Craft Advisory conditions expected to start within the second period,
went ahead and issued scas for all marine zones minus the upper
rivers Tuesday morning into Wednesday. Wind probs continue to
increase as we get closer to the event. Expect seas to begin to
increase to 5 feet by tomorrow morning, with NE winds ramping up
through the day. Winds increase to 15 to 25 knots by Tuesday
evening, with gusts to 30 knots possible especially Tuesday
night and Wednesday morning. Scas will likely need to be
extended past Wednesday morning.
Previous discussion: weak flow regime remains in place this
afternoon with high pressure over the Great Lakes and
increasingly impressive Hurricane Humberto located a few hundred
miles south of Cape Hatteras and east of the Florida/Georgia border.
Winds are generally 5-10 knots with waves ~1 ft and seas 3-4 ft.
High pressure will migrate eastward this evening setting the stage
for a backdoor cold front to cross the region from NE to SW on
Tuesday. The pressure gradient between the high to the north and
Humberto will lead to an extended period of NE flow beginning
Tuesday and lasting into Thursday afternoon. NE winds of 15-25kt are
expected during this time period with the highest values favored
across the southern ches Bay and coastal waters. Seas are expected
to build to 5-8ft north and 6-10ft S. Small Craft Advisory conditions are expected for
the ocean beginning Tuesday night, and potentially lasting into the
weekend as swell from Humberto continues to propagate into the area.
Small Craft Advisory conditions will begin in the Lower Bay/lower James/sound later
Tuesday and last into Thursday, and could also includes the Middle
Bay as well. The high is expected to settle into the region later
this week with the wind diminishing but seas (and waves near the
mouth of the bay) remaining elevated.
as of 410 am EDT Monday...
A strong NE wind will push tidal anomalies to 1.0-1.5ft above
normal by Wednesday and Thursday. This has the potential to
produce minor tidal flooding, particularly in the Lower Bay,
James River, and associated tributaries.
A moderate rip current risk is forecast today, with a return to a
high risk for the middle of the week, as swell from Humberto
propagates toward the coast.
kdox radar remains offline due to an equipment issue. Technicians
at the site hope to have needed parts tomorrow, with a return
to service by late tomorrow or tomorrow night. Further updates
will be passed along as they become available...and will also be
available through site free text message (ftmdox).
Marine...Small Craft Advisory from 1 PM Tuesday to 7 am EDT Wednesday
Small Craft Advisory from 10 am Tuesday to 7 am EDT Wednesday