Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 221917
AFDLWX

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

.SYNOPSIS...
An area of low pressure will lift north from the southern
Appalachians late 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/...
A mixture of weather hazards are in place across the local area.
Given a slew of wildfires burning across the Blue Ridge back
into areas of the eastern West Virginia panhandle, Air Quality
Alerts are in effect across vast portions of that area. As
clouds overspread the region, the noted wildfires have become
more difficult to view on visible satellite imagery. There is
quite a bit of stability in the atmosphere with a slew of wave
clouds noted. From U.S. 15 westward, there has been a greater
deal of sunshine which has raised temperatures into the 50s.
Elsewhere, thicker cloud cover has been in place over much of
the day which has held temperatures in the mid 40s to low 50s.

For the evening hours, clouds will continue to increase in
coverage ahead of the next weather maker. The mild nature of the
air mass keeps all locations as rain throughout the event. The
associated shield of rain arrives this evening into the Potomac
Highlands, before overspreading the rest of the region
overnight. High-resolution models continue to waver with precise
details of the axis of moderate to heavy rainfall. The highest
confidence is along and east of I-95 where 1.50 to 2.50 inches
of rainfall are expected, locally approaching 3.00 inches.
Generally, 0.50 to 1.00 inch of rain is more likely for those
west of the Blue Ridge Mountains. For locations east of the Blue
Ridge, most are in a Flood Watch starting at 2 AM Saturday. The
brunt of the activity accompanies an 850-mb wave tracking
northeastward in the vicinity of the I-95 corridor. Within this
banding feature, hourly rates of 0.50 to 1.00 inch are possible.
Besides the rain, it will be a seasonably mild night with low
temperatures in the 40s.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
The mentioned Flood Watch continues through 2 PM Saturday. That
locally heavier band begins to exit the Baltimore metro area by
the early afternoon hours with any residual hydrology watches
likely being lifted thereafter. Immense cloud cover coupled with
a soaking rain will hold temperatures steady in the 50s with
mountain temperatures remaining in the 40s. As low pressure
departs the region, northerly winds pick up in earnest with
gusts up to 30 to 35 mph, locally approaching 40 mph across
mountain ridgetops. While most dry out, some residual rain
chances may loom near the Chesapeake Bay. In the wake of this
system, forecast temperatures will cool off on Saturday night
with lows in the mid 20s to low 30s. Some upper teens to mid 20s
are possible over the higher elevations.

On Sunday, high pressure approaching from the west will lead to
a dry conclusion to the weekend. Winds also decrease some as
gradients begin to weaken. Expect mainly northerly winds to
persist through the day with afternoon gusts up to 20 to 25 mph.
Forecast highs will be in the upper 40s to mid 50s. High
pressure should also provide plenty of sunshine after a cloud
filled start to the weekend.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
High pressure north of the area Monday slides offshore into the
Atlantic on Tuesday. Dry conditions expected Monday and for most of
Tuesday, with seasonal highs in the mid 50s to lower 60s, and
overnight lows in the 30s to 40s.

An unsettled weather pattern returns for the middle to late part of
next week as a mid-level and weak cold front cross the area
Wednesday. This could bring scattered to maybe more widespread
showers to the area. The forecast becomes very uncertain late in the
week. Models diverge on the placement, strength, and track of a
coastal low that moves up from the Carolinas, which will be
dependent on where/if a sharp mid-level trough cuts off over the
Southeast CONUS. That makes the current forecast of 30-40 PoPs for
mid to late next week very uncertain. Continue to monitor as the
days progress.

&&

.AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
While most terminals have seen VFR conditions today, KCHO has
been teetering between VFR and MVFR due to slightly lower
ceilings. Winds remain mainly out of the south to southeast
ahead of the next system. This particular low pressure center
and associated fronts will bring deteriorating conditions to the
area. For the overnight hours, most will sit between LIFR and
IFR, accompanied by increasing low-level wind shear.
Restrictions remain in place through the overnight and into
Saturday morning. Expect improvements from southwest to
northeast as rain departs the region the second half of
Saturday. As this system exits, north-northwesterly winds
strengthen to around 25 to 30 knots during the afternoon to
evening hours. Some gradual decrease in wind is likely heading
into the night.

For Sunday, approaching high pressure will allow for VFR
conditions along with a bit less wind. However, do anticipate
northerly winds gusting up to 15 to 20 knots, particularly
during the afternoon hours.

VFR conditions expected Monday and Tuesday as high pressure
maintains dry conditions across the area. Winds become east Monday,
then southeast on Tuesday, and generally remain around 5-10kt.

&&

.MARINE...
There will be a fairly steady period of marine headlines in
place through early Sunday. Small Craft Advisories are in
effect through early Saturday before Gale Warnings take shape
from Saturday afternoon through the overnight hours and into
Sunday morning. These stronger winds pick up in response to a
deep area of low pressure exiting the coast. Gusts up to 35 to
40 knots are expected while the Gale Warnings are in effect.
Thereafter, Small Craft Advisories may be required over much of
the waters through Sunday.

Favorable marine conditions likely for the start of next week as high
pressure north of the area Monday shifts offshore Tuesday. East
winds Monday shift to southeast Tuesday at around 10kt, with some
gusts to 15kt during the afternoons.

&&

.FIRE WEATHER...
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 drop 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 1.50 to 2.50 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 12Z
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.
The amount of heavy rainfall during the short 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).

Consequently, the Flood Watch was expanded across most locations
east of the Blue Ridge, which includes all counties east of
Frederick County, Maryland. This is in place on Saturday from 2
AM until 2 PM. 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, though the magnitude of flooding is
uncertain and will depend on the strength and duration of onshore
flow. Some guidance has stronger onshore flow for a few hours
longer, resulting in notably higher water levels.

In the wake of low pressure, strengthening northerly flow will cause
a decline in water levels Saturday night through Sunday. Low water
level issues may arise during the second half of the weekend,
especially over northern portions of the Chesapeake Bay.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Flood Watch from 2 AM EDT Saturday through Saturday afternoon
     for DCZ001.
MD...Flood Watch from 2 AM EDT Saturday through Saturday afternoon
     for MDZ004>006-008-011-013-014-016>018-503>508.
VA...Flood Watch from 2 AM EDT Saturday through Saturday afternoon
     for VAZ038>040-050-051-053>056-501-502-505-506-526-527.
     Air Quality Alert until midnight EDT tonight for VAZ025>027-
     029-036>040-051-503-504-507-508.
WV...Air Quality Alert until midnight EDT tonight for WVZ050>053-
     055-501>506.
MARINE...Small Craft Advisory from 6 PM this evening to 6 PM EDT
     Saturday for ANZ530-539.
     Gale Warning from 6 PM Saturday to noon EDT Sunday for
     ANZ530>532-539-540.
     Small Craft Advisory until 6 PM EDT Saturday for ANZ531-532-
     536-538-540.
     Small Craft Advisory until 10 AM EDT Saturday for ANZ533-534-
     537-541>543.
     Gale Warning from 10 AM Saturday to noon EDT Sunday for ANZ533-
     534-537-541>543.
     Small Craft Advisory from 10 AM to 6 PM EDT Saturday for
     ANZ535.
     Gale Warning from 6 PM Saturday to 6 AM EDT Sunday for ANZ535-
     536-538.

&&

$$

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


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