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
000
FXUS61 KLWX 221427
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1027 AM EDT Fri Mar 22 2024

.SYNOPSIS...
An area of low pressure will lift north from the Gulf Coast and
southern Appalachians later this afternoon and into tonight bringing
a widespread soaking rainfall to the region. Meanwhile, a cold front
will push in from the Ohio River Valley Saturday before pushing low
pressure offshore Saturday night. Drier and breezy conditions are
expected Sunday and Monday as high pressure briefly builds over the
area. Another front and area of low pressure look to approach by
the middle and latter half of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Today starts out dry as clouds increase from the south this
morning and into the afternoon. High pressure over western New
England will remain wedged south along the eastern Appalachians
as an area of low pressure lifts north from the central Gulf
Coast region. Surface dewpoints will climb from the teens and
20s this morning into the 30s and 40s this evening as low
pressure pushes north toward southern Appalachians. Meanwhile, a
cold front will approach from the Ohio River Valley late
tonight into Saturday before exiting offshore Saturday night.
The combination of low pressure lifting north and the incumbent
cold front will result in widespread beneficial rain across the
entire forecast region. The steadiest/heaviest rainfall looks to
be along and east of the Blue Ridge where 1.50 to 2.50 inches
of rain can be expected. Locally higher amounts are possible
along and east of the I-95 corridor and along the eastern facing
slopes of the Blue Ridge where the upslope component will come
into play. Areas further west of the Blue Ridge will see
rainfall amounts on the order of 0.75 to 1.50 inch. Lower totals
may be found west of I-81 given where the potential deformation
axis sets up on the northern fringe of the coastal low passing
to our south.

The steadiest/heaviest rain (i.e strongest isentropic lift/upslope
flow) will occur between 06-13z (2am-9am) Saturday per the
latest 00z deterministic/ensemble guidance. Some rises on
streams and creeks will likely occur given the 6-8 hour window
of moderate to heavy rainfall especially within the urban I-95
corridor. As such, Flood Watches remain in effect for both the
Baltimore/Washington DC metro areas to encompass the heavy
rainfall threat. Within this area of the watch, scattered to
numerous instances of flooding can be expected.

With a cool air wedge in place and increasing southeasterly flow
Friday expect highs in the upper 40s and low to mid 50s. Slightly
warmer conditions can be expected along and west of the Allegheny
Front due to downsloping. Southeasterly winds will increase through
the day with gusts of 20-25 mph this afternoon and into the evening
hours. Lows Friday night will fall back into the low to mid 40s.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
Coastal low pressure will continue off the VA/NC coast Saturday
afternoon and evening with the upper trough/cold front set to push
offshore Saturday night into early Sunday morning. This will result
in decreasing rain chances from west to east across the area along
with cooling temperatures and increasing winds. Highs Saturday will
push into the low to mid 50s with north to northeasterly winds
gusting 25 to 35 mph. Lows Saturday night will fall into upper 20s
and low to mid 30s.

Dry high pressure returns Sunday with gusty north/northwesterly flow
continuing. Gusts of 15 to 25 mph with high temperatures in the mid
to upper 50s under mostly sunny skies. Lows SUnday night will fall
into the upper 20s and low to mid 30s as winds slowly diminish.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
1040 mb high pressure over eastern Canada will wedges it`s way
south along the Appalachian Mountains through the start of the
upcoming workweek. This will lead to decreasing winds, dry
conditions, and near normal temperatures for both Monday and
Tuesday. Highs will push into the mid to upper 50s and low 60s
with overnight lows in the 30s and 40s.

With the ridge of high pressure in place, 00z modeling has slowed
the progression of the upper level trough and resultant cold front
for the middle part of the workweek. The 00z GFS is a little quicker
with the low pressure cutting up through the Mid-MS and Ohio River
Valleys Tuesday night into Wednesday morning. The 00z ECWMF has low
pressure cutting up through the upper Midwest into the Great Lakes
region during the same time. Both models illustrate the associated
cold front crossing the area Wednesday into Wednesday night before
stalling offshore Thursday as an area of low pressure festers along
the southeast U.S coast. The 00z ECMWF tries to draw some of the
moisture with the coastal low pressure north Wednesday night into
Thursday while the 00z GFS holds the low pressure system off the
NC/SC coast before pushing it out to sea for the latter part of the
workweek. Resultant upper level ridging from Tuesday will delay the
progression of the rain as well as the overall amounts as the front
crosses midweek.

Rain chances will start to fade Thursday afternoon into Friday as
broad high pressure/upper level ridging build from the south. 00z
deterministic/ensemble guidance diverge a bit heading into this
period due in part to the evolution and placement of an area of
closed low pressure ejecting out of the upper Midwest region. The
00z ECMWF/ECNS is faster with this system arriving Saturday while
the GFS is drier with high pressure overhead. For now, will go with
a blend of these solutions favoring a dry start to the Easter
weekend with precipitation chances increasing toward the end of the
extended period. Temperatures will remain at or slightly above
average for the remainder of the extended period.

&&

.AVIATION /15Z FRIDAY THROUGH TUESDAY/...
IFR/LIFR conditions developing late tonight in moderate to
heavy rainfall and continuing through Saturday morning. Winds
will shift from SE today/tonight to a NNW/N direction Saturday
afternoon with sustained winds near 20kt and gusts to 30 kt.
Winds begin to diminish Sunday.

VFR conditions are expected Sunday through Tuesday as strong high
pressure wedges itself into the region. The departing front and low
pressure system offshore combined with the building high pressure
will lead to the continuation of gusty northerly winds through
Sunday evening. Gusts of 15 to 25 kts can be expected with the
highest gusts likely at terminals east of the Blue Ridge and in
particularly along the corridor Sunday afternoon. Winds will subside
and turn toward more of a westerly direction as upper level ridging
strengthens over the area Monday into Tuesday.

Next chance of sub-VFR conditions arrives with an area of low
pressure and its associated cold front Wednesday into Thursday.
Current 00z model projections show the potential for MVFR
conditions during this time with a brief period of IFR pending
the placement/intensity of the resultant surface low.

&&

.MARINE...
Winds will begin to strengthen today with SCA conditions
developing across the southern marine zones this afternoon and
continuing through Saturday. Elsewhere, winds pick up Saturday.

Gale conditions will likely continue through the first half of
Sunday due in part to the tightened gradient between the exiting
front/low pressure and incumbent high pressure system building in.
SCA level winds are expected Sunday night into early Monday morning.
Sub-SCA level winds out of the west and southwest return Monday into
Tuesday with wedging high pressure overhead. SCA level winds return
with a front and area of low pressure by the middle of next week.

&&

.FIRE WEATHER...
Still continuing to see fairly patchy to dense areas of smoke around
ongoing fires on VIIRS Day Night Band channel this morning
across the Shenandoah Valley and eastern WV. This has been
exacerbated due to in part to a nocturnal inversion this
morning. The inversion should break mid to late morning as
mixing takes place under increasing southeasterly flow.

With increasing southeasterly flow, expect moisture to
gradually return in the form of higher humidities as well as
increasing mid and high level cloud cover. RH values this
morning will start between 40-60 percent before dropping into
the 35 to 45 percent range this afternoon. Southeasterly
downslope zones along and west of the Alleghenies may see a
brief window for RH values between 30 to 35 percent.

Unfortunately, the wind will return with sustained
south/southeasterly speeds at 8-16 mph. Gusts of 10 to 15 mph
can be expected within the valleys with gusts up to 25 mph along
the higher/exposed ridges.

Widespread rain arrives from the south and west late tonight between
8-11pm. Heaviest rain looks to occur late tonight into Saturday
midday. Rainfall amounts of 1.5 to 2.5 inches can be expected east
of the Blue Ridge with 0.75 to 1.50 inches west.

Dry and breezy conditions return Sunday with decreasing winds Monday
and Tuesday next week.

&&

.HYDROLOGY...
Moderate to heavy rain will overspread the area later this evening
and into the first half of Saturday as a strong area of low pressure
approaches from the southern Appalachians/Gulf Coast region.
Heaviest rainfall looks to arrive overnight into Saturday morning
(between 6-13z/2-10am) within a 6 to 8 hour window. Rain will
quickly diminish in intensity and coverage as the cold front pushes
low pressure further offshore late Saturday afternoon into Saturday
evening.

PWATS will be on the order of a 1-1.25" per the 00z NAEFS/GEFS/HREF
with a focus along and east of the east of the Blue Ridge. Modeled
QPF values per the 12Z NAM/GFS/ECMWF/HREF sits between 1-2 inches
across a bulk of the region. 2.25-2.75 inch totals are likely along
and east of I-95 where a combination of enhanced isentropic lift and
onshore flow will be maximized.

6 hour FFG values sit between 1.75-3 inches across most of the
region outside the metros where runoff poses more of a concern. Any
flooding issues as a result appear to be localized/isolated
given the progressive nature of the system. Even with that said,
the amount of heavy rainfall with the shortened window could
lead to quick rises along small streams and creek especially
within the I-95 urban footprint which is noted per the latest
forecast per the NASA SPoRT and HEFS guidance (i.e Rock Creek
in northwest DC, Western Branch at Marlboro, Great Mills in St.
Mary`s County).

A Flood Watch remains in effect for both the Baltimore/Washington DC
metro areas along with northeast MD late tonight through Saturday
midday. For more info visit weather.gov/lwx.

&&

.TIDES/COASTAL FLOODING...
Increasing onshore flow ahead of approaching low pressure will cause
an increase in tide levels tonight into Saturday. Minor tidal
flooding is possible during this time, especially for typically
more vulnerable shoreline locales.

In the wake of low pressure, strengthening northerly flow will cause
a decline in water levels Saturday night through Sunday.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Flood Watch from late tonight through Saturday afternoon for
     DCZ001.
MD...Flood Watch from late tonight through Saturday afternoon for
     MDZ008-011-013-014-504-506-508.
VA...Flood Watch from late tonight through Saturday afternoon for
     VAZ053-054.
     Air Quality Alert until midnight EDT tonight for VAZ025>027-
     029-036>040-051-503-504-507-508.
WV...None.
MARINE...Small Craft Advisory from 10 AM to 6 PM EDT Saturday for
     ANZ530>533-535-536-538>542.
     Gale Watch from Saturday evening through Sunday morning for
     ANZ530>543.
     Small Craft Advisory from 2 PM this afternoon to 6 PM EDT this
     evening for ANZ532-533-540-541.
     Small Craft Advisory from 2 PM this afternoon to 6 PM EDT
     Saturday for ANZ534-537-543.

&&

$$

SYNOPSIS...EST
NEAR TERM...LFR/BRO
SHORT TERM...LFR/EST
LONG TERM...EST
AVIATION...LFR/EST
MARINE...LFR/EST
FIRE WEATHER...EST
HYDROLOGY...EST
TIDES/COASTAL FLOODING...DHOF


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