Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 281433

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1033 AM EDT Wed Oct 28 2020

A boundary will remain stalled over the area into Friday
morning. The remnants of Zeta and another low pressure will
track along this stalled front, impacting our area overnight
through Friday morning. High pressure will return later Friday
through Saturday before a cold front passes through Sunday.
Follow the National Hurricane Center for the latest information
on Zeta.


A weak boundary will remain in place this afternoon. A light
westerly flow should allow for breaks of sunshine leading to a
warmer afternoon with highs in the lower to middle 70s with
cooler temperatures in the western zones.

Zeta will track through the Gulf Coast States tonight while a
potent upper-level low associated with the southern stream of
the jet moves trough the southern Plains. Plenty of moisture
from the Gulf of Mexico will advect well north and east ahead of
these systems and the forcing along the boundary over our area
will begin to strengthen in response to a tightening theta-e
gradient (due to falling pressures to our south and weak high
pressure to our north). The increased forcing along with
moisture advection will cause clouds to increase this evening,
and rain will overspread the area later this evening and
overnight from southwest to northeast. A soaking rain is
expected for most areas overnight.


The remnants of Zeta will track along the boundary, passing
through our area late Thursday. The upper-level low will be
fast on its heels passing through our area Thursday night into
Friday morning. Coastal low pressure will likely develop along
the Mid- Atlantic coast as a result. The anomalous moisture
along with forcing from the remnants of Zeta, as well as the
upper-level low and developing coastal low appears that it will
cause widespread rain across the area during this time.

The heaviest rain is most likely Thursday, and this is when
PWATS will be highest as tropical moisture moves into the area
(NAEFS shows PWATS 3-4 SD above climo over portions of our area),
and the low-level forcing from the remnants of Zeta are passing

Most likely rainfall amounts for the event appear to be around
2 to 3 inches for most locations. However, locally higher
amounts around 4-5 inches cannot be ruled out. Scattered
instances of flooding are possible, but given the recent
relatively dry conditions along with the fact that rainfall
should be spread out, that does lower the confidence to some
degree. A Flood Watch may be needed for portions of the area,
and this will continue to be monitored later this morning and
today. Confidence is too low at this time for a watch.

The low will move away from the area Friday afternoon and drier
air will move in as high pressure approaches from the Great
Lakes. It will turn out blustery and chillier Friday with
northwest winds behind the departing low (Frequent gusts most
likely around 15-25 mph), but winds will diminish some for
Friday night. The lighter winds in response to Canadian high
pressure building overhead will provide a good setup for
radiational cooling Friday night. Min temps may drop below
freezing for mainly locations, especially west of Interstate


Canadian high pressure will briefly build over our region on
Saturday bringing cooler and drier weather. Morning temps on
Saturday morning will hover around freezing for areas west of the I-
95 corridor. Frost Advisory and freeze warnings are likely Saturday
morning. Skies will be clearer on Saturday with afternoon high temps
similar to Friday in the mid to upper 40s.

The high pressure over our region will exit to our northeast
Saturday evening and into Sunday. A weak cold front will pass
through our region late Sunday into Monday morning bringing a slight
chance of showers in our western elevations. Ahead of this front, a
weak southerly flow will form which will allow daytime temps to rise
up into the 50s with morning lows in the upper 30s to low 40s. I`m
not expecting much precipitation with this frontal passage as the
main upper level forcing remains to our north over northern PA and a
westerly 850mb flow will help sap the moisture in our region.

Behind the frontal passage on Monday, high pressure will build into
our region and remain in place through the middle parts of next
week. A much cooler air mass will remain in place our region for a
good portion of next week. The west to northwesterly flow that forms
on Monday may lead to a few light showers along the Allegany Front
as temperatures will likely drop down into the 20s with showers
possible due to the upper level trough dropping into our region.


MVFR ceilings will relinguish to VFR conditions during the
afternoon as sunshine breaks through the clouds.

The remnants of Zeta along with another low will approach
tonight before passing through the area Thursday and Thursday
night. Widespread rain is expected to develop overnight and
continue through Thursday night, possibly into Friday morning.
IFR conditions are likely for much of this time. Drier air along
with northwest winds (gusts most likely around 15-25kt) are
expected Friday, and high pressure will build overhead Friday

Light winds will form out of the north on Saturday. Fog will be a
threat for all terminals Saturday morning as light winds combined
with wet grounds from the previous days rain will make conditions
conducive for fog. VFR conditions expected for the rest of the
weekend with patchy fog possible Sunday morning once again. VFR
conditions expected Monday.


A boundary will stall out nearby later this afternoon and
tonight. South to southwest winds are expected ahead of the
boundary with a SCA through 11am. The gradient should weaken
some this afternoon into this evening with the boundary nearby.

The boundary will strengthen a bit overnight, and northeast
winds over the northern half of the waters and southerly winds
over the southern half of the waters may approach SCA criteria
toward morning.

The remnants of Zeta will pass through the area Thursday and
low pressure will develop Thursday night along the Mid-Atlantic
Coast before moving offshore Friday. A Small Craft Advisory
will be needed during this time and a Gale Warning may also be
needed for portions of the waters, especially Thursday
afternoon/early evening over our southern waters near Smith
Point, and again over the Bay and lower Tidal Potomac River late
Thursday night into Friday. Confidence in exact details remain
uncertain at this time, because any change in the track of Zeta
will have a significant influence on the winds, especially
Thursday afternoon/early evening. Refer to the National
Hurricane Center for the latest information on Zeta.

Winds should diminish Friday night as high pressure builds
toward the waters.

Behind an exiting cold front on Saturday, winds over our marine
areas will remain elevated which will likely require additional
Small Craft Advisories. Winds should taper off by Saturday afternoon
and SubSCA conditions expected through Sunday afternoon but SCA`s may
be needed once again Sunday evening.


Elevated water levels are expected Thursday as the remnants of
Zeta pass through. Minor flooding cannot be ruled out during
this time. Will continue to monitor the track of Zeta. A track
farther north across our waters will increase the chances for
minor flooding. Refer to the National Hurricane Center for the
latest on Zeta.


MARINE...Small Craft Advisory until 11 AM EDT this morning for


TIDES/COASTAL FLOODING...BJL is the U.S. government's official web portal to all federal, state and local government web resources and services.