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Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
351 am EDT Sat Oct 19 2019

Synopsis...
high pressure will move offshore today while tropical storm Nestor
makes landfall over the Florida Panhandle. The remnants of
Nestor will move into Georgia tonight, across the Carolinas
Sunday, then offshore of the Outer Banks by Sunday evening. A
cold front will approach from the Ohio Valley Monday, then cross
the region Tuesday. High pressure will follow for Wednesday
through Friday before another cold front approaches by Saturday.

&&

Near term /through tonight/...
upper troughing is digging into the central Continental U.S. Early this
morning with ridging aloft over the eastern Seaboard. At the
surface, high pressure extends from near Toronto to Cape
Hatteras. Tropical storm Nestor is approaching the Florida
Panhandle. As the trough axis over the midsection of the country
deepens, high pressure will shift offshore and Nestor will
begin to accelerate northeastward.

There are already some thin cirrus well ahead of Nestor the
approaching upper trough. High clouds are expected to gradually
increase today from southwest to northeast, with a more
appreciable increase in cloud cover likely this evening as both
of the aforementioned features get closer to the mid-Atlantic.

The majority of the day should turn out mostly sunny with light
southerly or southeasterly winds as the surface high pressure
center shifts offshore. 925 hpa temperatures around 10 c should
result in surface high temperatures in the middle to upper 60s.

Overcast conditions are expected over the entire area by shortly
after midnight, with clouds lowering and thickening as the
remnants of Nestor move from Georgia into the Carolinas.
Increasing moisture and lift along a developing frontal zone
north of the low center should result in rain over much of the
area by daybreak Sunday, with the steadiest most likely east of
the Blue Ridge and south of US-50.

&&

Short term /Sunday through Monday night/...
the remnants of Nestor are forecast to move offshore of the
Outer Banks of North Carolina by Sunday evening. To its north,
an arc of rain is expected, forced by a strengthening low- to
mid-level frontal zone. Nestor will be Post-tropical by this
time, driven by temperature gradients and acquiring frontal
characteristics as it makes its closest approach.

Regardless of its structure, rain and a northeasterly breeze will
continue for much of the area Sunday. The NAM is the northern
most piece of guidance as of early this morning, and although a
steadier, heavier rain can't be completely ruled out as far west
as the eastern foothills of the Allegheny Highlands or as far
north as the Mason-Dixon line, it appears most likely that the
axis of heaviest rainfall will remain across southern and
eastern Virginia into southern and southeastern Maryland.

Rain should begin exiting the region pretty quickly by or
shortly after midday as the best lift/convergence rapidly moves
offshore. Residual low-level moisture may result in a few
lingering showers or spotty light rain, but overall the
steadiest rainfall should be focused during the first half of
the day. Drying northerly winds increase on the backside of the
low and could gust 20 to 30 miles per hour near the Chesapeake Bay.

With the rain and cloud cover around, high temperatures may
struggle to get much above 60 for most of the area (a few
degrees warmer outside the steadiest rain over portions of
eastern West Virginia and western maryland).

Surface high pressure will ridge briefly back over the area
Sunday night. If clouds clear quickly enough, fog may develop.
Southerly winds increase Monday ushering in warmer air with
highs nearing 70, but clouds will increase quickly Monday night
ahead of the next approaching cold front, with showers possible
by daybreak Tuesday.

&&

Long term /Tuesday through Friday/...
on Tuesday, a strong mid/upper trough will be sliding east out of
the northern/Central Plains into the Midwest/Great Lakes. The
associated surface low pressure system will be occluding over
southern Ontario. The cold front associated with this system
will push through the area Tuesday morning, with showers likely
across the entire forecast area. Doesn't look to be an
excessive rainfall event, but could see a quarter to half an
inch. High temperatures will be seasonable in the low to mid
60s. Overnight lows Tuesday night will be about 10 degrees
cooler than Monday night, with lows in the low to mid 40s.

Surface high pressure will build over the region out of the
southeast, resulting in dry weather with seasonable temperatures for
the remainder of the week. Highs each day will reach the low to mid
60s.

The next chance for some potentially heavier rainfall appears
to be next weekend, but too far out for exact details at this
point in time.

&&

Aviation /07z Saturday through Wednesday/...
VFR with light S or southeast flow expected through most of tonight,
before lower cigs and rain develop after 08-10z. Steadiest rain
and highest potential for IFR appears to be southeast of a line
from cho to dca Sunday morning. Winds increase out of the east
especially near and east of I-95 Sunday, then switch to
northerly Sunday afternoon with a few gusts of 20 kts possible.
VFR will likely return by late Sunday afternoon as cigs lift,
but fog may develop late Sunday night into early Monday morning.

Mainly VFR expected Monday into Monday night on a light S wind.

VFR conditions expected throughout the long term period for the most
part. A frontal passage Tuesday morning will likely lead to some
brief ceiling/visibility restrictions with some showers. After that,
though, high pressure builds into the area, keeping things dry
through the end of the week. Additionally, no high wind
concerns at this time.

&&

Marine...
high pressure will move offshore today as Nestor approaches from
the south. The Post-tropical remnants of Nestor will then pass
offshore of the Carolinas Sunday. Light southeasterly flow is
expected today into tonight, increasing out of the east and then
north on Sunday. Small Craft Advisory conditions are likely over much of the
waters by early Sunday afternoon, with a period of gale
conditions possible over the lower tidal Potomac River and
Chesapeake Bay south of North Beach Maryland on Sunday.

Winds will subside Sunday evening, then flip back to the south
ahead of an approaching cold front Monday into Monday night.

Small Craft Advisory conditions possible mainly Tuesday night into Wednesday
behind a cold front pushing through the area. Southerly winds
ahead of the front could come close to Small Craft Advisory criteria, especially
in the Bay, but low confidence at this time.

&&

Tides/coastal flooding...
light onshore flow is expected to develop today into tonight.
Snap-ex guidance has been insistent on near minor flooding at
Annapolis with this evening's high tide cycle, but that would
require tidal anomalies of about a foot which seems unlikely.
Sided with cbofs which is in between the more conservative
etss/estofs and more aggressive snap-ex through tonight, before
leaning on a blend of etss/estofs through the end of the weekend,
which are very similar holding higher water levels near the
mouth of the Chesapeake Bay in northeast flow. This should keep
the flood risk at a minimum for the tidal Potomac and western
shore of the Chesapeake Bay north of Smith Point Virginia.

Those higher water levels will likely linger in some form in the
Virginia side of the Chesapeake Bay, however, and then return
northward as winds go light and switch to the south late Sunday
night into Monday. There's a pretty substantial spread in the
guidance as it remains to be seen just how much water is left
piled up at the bottom of the Bay, but for now running with a
1-1.5 foot anomaly early next week which results in minor flooding.

&&

Lwx watches/warnings/advisories...
District of Columbia...none.
Maryland...freeze warning until 9 am EDT this morning for mdz003-501-502.
Frost advisory until 9 am EDT this morning for mdz004>006-
503>507.
Virginia...freeze warning until 9 am EDT this morning for vaz026>031-
038>040-050-051-501-502.
Frost advisory until 9 am EDT this morning for vaz025-036-037-
052-053-055-056-503>506.
WV...freeze warning until 9 am EDT this morning for wvz050>053-055-
501>506.
Marine...Small Craft Advisory from 10 am to 4 PM EDT Sunday for anz536.
Small Craft Advisory from 10 am to 6 PM EDT Sunday for anz531-
539-540.
Small Craft Advisory from 7 am to 6 PM EDT Sunday for anz532-
533-541-542.
Small Craft Advisory from 4 am to 6 PM EDT Sunday for anz534-
537-543.
Small Craft Advisory from 1 PM to 6 PM EDT Sunday for anz530-
538.

&&

$$
Synopsis...dhof
near term...dhof
short term...dhof

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