Area Forecast Discussion
Issued by NWS Sterling, VA

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS61 KLWX 290751
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
351 AM EDT Thu Oct 29 2020

.SYNOPSIS...
A front will remain stalled over our region through Friday. The
remnants of Zeta along with a secondary low will move along the
front today through Friday. High pressure briefly builds into
our region on Saturday before a powerful cold front moves
through Sunday into early Monday. High pressure builds over our
region through the later parts of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
A frontal boundary remains stalled over our region this morning
with a light southerly flow advecting in moist air into our
region. Tropical Storm Zeta is currently located in northern
Alabama this morning and is moving NE at 31 mph. The current
track from the Hurricane Center has the center of Zeta moving
just south of the DC metro. This will place us on the favorable
wet side of the storm which will set up our region to receive a
decent amount of rain today into Friday. The outer bands of rain
are starting to move into our region with rain expected to
overspread all of our region over the next couple of hours.

Rain will start out as light this morning but an extended
period of moderate to heavy rain is expected later this morning
and into this afternoon. PW`s ahead of the Zeta are running in
the 1.6 to 1.7 range and are expected to continue to rise
through this afternoon. The high PW`s combined with the tropical
air mass from Zeta will lead to a swath of 1 to 3 inches of
rain throughout our region over the next 36 hours with locally
higher amounts near 4 inches possible. The possibility of 2 to 3
inches of rain in a 24 hour period will lead to the threat for
isolated to scattered flooding. The main areas of concern will
be our urban areas along with areas along the Blue Ridge
Mountains. I think overall the flood threat should be isolated
due to dry antecedent conditions with FFG running from 2.5 to 3
inches in an hour. The biggest concern will be clogged storm
drains along with small to moderate sized streams that could
receive 2 to 3 inches in multiple locations and translate the
water further down stream. A flood Watch is in effect through
10pm this evening.

The heaviest rain should start to shift eastward out of our
region later this evening with mainly light rain and showers
continuing through the overnight periods. A secondary low will
form along the frontal boundary and shift eastward through our
region bringing additional precipitation to our region during
the early morning periods of Friday.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
The remnants of Tropical Storm Zeta will have shifted off the
east coast by Friday morning. The front that has hovered in our
area will remain stalled over our region through Friday
afternoon. A surface low pressure system will form and move
along the frontal boundary bringing another round of rain to our
region during the early parts of Friday morning. The low should
track to our south over portions of central Virginia sparing
our area of the heaviest rain. As the low approaches the coast,
it will interact with an upper level trough along with an upper
level jet and strengthen considerably along the MD/VA eastern
seaboard. The main cyclogenesis should occur during the morning
periods of Friday as the low transitions off of the eastern
seaboard. A burst of moderate rain will be possible on the west
side of the low which could impact areas along and east of the
I-95 corridor. This additional rain on top of the moderate to
heavy rain we are expecting today could lead to isolated to
scattered instances of flooding especially in our urban areas
and along the Blue Ridge Mountains. The main threat from the
strengthening low will be the increasing winds that will be
focused over our marine waters.

The front and surface low should full move off the coast Friday
afternoon with a few lingering showers possible into the
evening periods. The pressure gradient should weakened as the
front pulls further away from the coast which will allow winds
to weakened but 18 to 20 knots winds will continue to be
possible for areas east of the I-95 corridor through early
Saturday. Showers will end by late Friday evening and dry
conditions are expected through Saturday. High pressure will
briefly build to our north over southern PA bringing cooler and
drier conditions to our region on Saturday. Saturday morning
temps will hover in the low to mid 30s along and west of the
I-95 corridor with upper 30s to low 40s along the Bay. A Freeze
Watch has been issued for our remaining counties along the MD/PA
border along with Jefferson County WV and western Loudoun.

The high pressure will shift off to our northeast by Saturday
evening leading to a weak return flow forming ahead of a weak
cold front. Daytime highs on Saturday will be mild in the upper
40s to low 50s.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
A powerful cold front will be approaching from the west on
Sunday, but will not arrive until Sunday night. Thus, we will
see a mild southwest flow which should allow temps to moderate
significantly compared to Saturday`s chilly temps, with a rise
of 10 or more degrees possible. This, however, would only bring
temps back to near normal.

The front will cross the region late Sunday into Sunday evening,
with some showers along or just behind the front possible. Will
have to watch for potential low-topped convection, as well as
for a burst of gusty winds behind such a powerful front.
Gradient winds will be strong behind the front, particularly on
Monday as low pressure strengthens to our northeast, providing a
windy and chilly start to the work week. Humidity will also be
low, and if it wasn`t for the rains we will get today, there
could be a fire weather concern. Winds could approach advisory
criteria on Monday, which might cause minor damage, mainly to
trees.

Temps Monday will be well below Sunday, and in fact stand a good
chance of being the coldest so far this season, with temps
potentially staying in the 30s and 40s all day long. This would
lead to another widespread freeze potential, with likely
the coldest night of the season thus far Monday night. Temps in
most suburbs could reach the 20s, especially if the wind
slackens late at night.

High pressure passing to our south should allow for a lighter,
more westerly wind on Tuesday, shifting southwesterly on
Wednesday, which will provide a dry mid-week with milder
temperatures.

&&

.AVIATION /08Z THURSDAY THROUGH MONDAY/...
Rain will overspread all of our terminals this morning with
moderate to heavy rain expected later this morning and into this
afternoon. Ceilings have dropped down into the MVFR to IFR
range for all of our terminals except for MRB. I expect ceilings
to drop into the IFR range for all terminals through this
evening with a period of LIFR ceilings as the moderate rain
moves through our region. Visibility will also drop down into
the IFR category with periods of LIFR and VLIFR during heavy
rain. The heaviest rain should move out of all our terminals
later this evening with light rain and showers continuing into
Friday morning. A second round of heavy rain will be possible
Friday morning as another low moves through our region. Strong
gust winds will be possible for terminals along and east of the
I-95 corridor with winds becoming northerly Friday afternoon.

Rain should completely stop by Friday afternoon with ceilings
increasing into the MVFR range and eventually VFR by Friday
evening. Clouds will start to break Friday evening with mostly
clear to partly cloudy skies by Saturday morning. VFR conditions
expected on Saturday.

Main aviation concern Sunday and Monday will be the strong cold
front and gusty winds along and after the front crosses the
region, along with a few showers. Sub-VFR conditions may briefly
occur with showers late Sunday, but VFR should prevail overall.
Winds could gust to 50 mph, however. Some low-topped convective
showers could also bring gusty winds with the front Sunday.

&&

.MARINE...
A stalled boundary will remain in place over the waters through
Friday. The remnants of Zeta along with a secondary low will
bring strong and gusty winds to our marine waters today through
early Saturday. A Gale Warning is in effect through early Friday
morning with a Small Craft Advisory continuing through Friday.
There is a potential for another round of Gale level winds late
Friday morning and into Friday afternoon but confidence remains
low at this time. Small Craft Advisories will likely need to be
extended into early Saturday morning but winds are expected to
taper off on Saturday afternoon and SubSCA conditions are
expected for the majority of Saturday.

Strong gusty winds are the main concern Sunday and Monday as a
powerful cold front blasts across the region. Gales look very
possible, possibly in two waves - one late Sunday with the
front, and one on Monday as low pressure strengthens to our
northeast.

&&

.TIDES/COASTAL FLOODING...
Elevated water levels are expected today as the remnants of
Zeta pass through. Minor flooding cannot be ruled out during
this time, but latest forecast track suggests that anomalies
will not build sufficiently to produce any flooding. Will
continue to monitor the track of Zeta and water level anomalies,
however, as 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.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Flood Watch through this evening for DCZ001.
MD...Flood Watch through this evening for MDZ004>006-011-013-014-
     016>018-503>508.
     Freeze Watch from late Friday night through Saturday morning
     for MDZ004>006-505-507-508.
VA...Flood Watch through this afternoon for VAZ025>027-029>031-
     036>040-503-504-507-508.
     Flood Watch through this evening for VAZ050>057-501-502-505-
     506.
     Freeze Watch from late Friday night through Saturday morning
     for VAZ505.
WV...Flood Watch through this afternoon for WVZ505-506.
     Freeze Watch from late Friday night through Saturday morning
     for WVZ053.
MARINE...Small Craft Advisory from 7 AM this morning to 1 PM EDT this
     afternoon for ANZ532>534-537-540>543.
     Small Craft Advisory from 10 PM this evening to 6 PM EDT
     Friday for ANZ532>534-537-540>543.
     Gale Warning from 1 PM this afternoon to 10 PM EDT this
     evening for ANZ532>534-537-540>543.
     Flood Watch through this evening for ANZ535.
     Small Craft Advisory from 7 AM this morning to 6 PM EDT Friday
     for ANZ530-531-535-536-538-539.

&&

$$
SYNOPSIS...JMG
NEAR TERM...JMG
SHORT TERM...JMG
LONG TERM...RCM
AVIATION...RCM/JMG
MARINE...RCM/BRO/JMG
TIDES/COASTAL FLOODING...



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.