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Area Forecast Discussion (AFD)

Issued by Wakefield, VA (AKQ)

FXUS61 KAKQ 170158

National Weather Service Wakefield VA
958 PM EDT Mon Sep 16 2019

A backdoor cold front will slide south across the lower Mid 
Atlantic region through 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 through 


As of 955 PM EDT Monday...

High pressure across upper Great Lakes/SE Canada will build 
across New England and the interior northeast overnight...slowly
forcing a cold front (along the Mason-Dixon line) south in 
backdoor fashion across the northern Mid-Atlantic through Tuesday
morning. The sky will become partly to mostly cloudy overnight 
into Tue morning. Remaining dry for most of the area overnight,
though a stray shower or two cannot be ruled out over far 
northern zones, so a slight chance POP will be maintained after 
midnight. Early morning lows will range from the mid 60s to 
around 70.


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 N and 80-85 S (warmest for 
interior NE NC and south central VA). 

Rain chances drop off with steadily falling PW 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 N. 

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 then well
offshore to the SE and the high centered to the N/NE.


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.


As of 955 PM EDT Monday...

NE winds/low level moisture will bring another chance for MVFR 
CIGS and some iso-sct showers overnight 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 SCA 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 FL/GA 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 N and 6-10ft S. SCA 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. 
SCA 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 955 PM 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 high rip current risk is forecast on Tuesday, then probably
continuing through midweek, 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 
     for ANZ630>632-634-638.
     Small Craft Advisory from 10 AM Tuesday to 7 AM EDT Wednesday 
     for ANZ633-650-652-654-656-658.