468
FXUS61 KLWX 171957
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
357 PM EDT Fri May 17 2024

.SYNOPSIS...
Low pressure will track to our south tonight, before progressing
offshore this weekend. High pressure will build into the area
early next week. A cold front will approach from the west during
the middle of the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 3 PM, visible satellite imagery shows cloudy skies across
the entire forecast area. Showers continue to spread eastward
from the Ohio Valley, and have reached western and central VA,
the WV Panhandle, and western MD. These showers are expected to
gradually weaken as they spread eastward through the remainder
of the afternoon, eventually dissipating before reaching I-95.
Additional showers and thunderstorms are expected to fire
further west across the WV Panhandle as weak DCVA driven large
scale ascent spreads eastward from the Ohio Valley. These
showers and storms will form in an environment that is nearly
saturated through the entire vertical profile. Model soundings
show around 500 J/kg and around 1.5 inches of precipitable
water. While the values of instability and moisture present
aren`t off the charts, they will be sufficient to produce heavy
rainfall. With the saturated vertical profiles in place and weak
flow (less than 20 knots) through the lower depth of the
troposphere), storms should be relatively slow moving (with weak
flow limiting advection driven movement, and saturated profiles
limiting propagation driven movement due to cold pool
generation), and some training of cells may be possible at
times.

In terms of convective evolution, CAMs generally show a cluster
of storms forming later this afternoon in the Potomac Highlands
of the WV Panhandle. These storms then slowly drift eastward
into the Shenandoah Valley later this evening. This activity is
then followed by additional, more strongly forced (in the left
exit region of a jet streak moving to our south) storms moving
in from the southwest later this evening. Multiple rounds of
storms may be possible across the Potomac Highlands, Shenandoah
Valley, and central Virginia late this afternoon through the
overnight hours. As a result, this raises concerns for instances
of flooding. Many of the 12z CAMs show widespread rainfall
totals in excess of an inch across this area, with isolated
pockets of 2-5 inches. As a result, Flood Watches have been
issued through 4 AM for the Potomac Highlands, Shenandoah Valley
and central Virginia.

Further east, showers will gradually move in later this evening
through the first half of the overnight. A steadier, soaking
rain will ensue through the second half of the night, but no
issues with flooding are anticipated. Low temperatures overnight
are expected to be in the upper 50s to near 60.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
Weak upper troughing will progress overhead tomorrow, causing
cloudy and showery conditions to linger through the day. With
the thick cloud cover in place and easterly winds off the ocean,
conditions will remain cool, with temperatures only reaching
into the low 60s.

Upper troughing will start to progress off to our south and east
on Sunday. This should lead to a reduction in shower activity,
with some breaks of sun developing by afternoon, especially to
the west of the Blue Ridge. Low cloud cover and periods of
drizzle may try to linger through the morning to the east of
the Blue Ridge within easterly low-level flow, but some breaks
in the clouds cover still appear likely there during the
afternoon. Highs on Sunday are expected to reach into the 70s
(warmer further west, cooler further east).

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
High pressure and dry conditions prevail for the start of the
extended. Winds will be generally light, starting off out of the
east early Monday, then becoming southerly return flow behind the
center of high pressure as it moves east. This, combined with ample
sunshine, will allow temperatures to rise into the upper 70s on
Monday, and possibly into the 80s by Tuesday.

A potent low pressure system moves from the Northern Plains into the
Great Lakes on Wednesday, swinging a strong cold front through our
area Wednesday into Thursday. The area will be well primed with
temperatures in the 80s and ensembles indicating upwards of 1500
J/kg of CAPE. Shear is less certain, the more favorable shear
arriving Wednesday night into Thursday. Much could stand to change
this far out, but we will continue to monitor the severe threat for
this system.
&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
Ceilings are currently high end MVFR to low end VFR this
afternoon, and should eventually reach low end VFR in most
locations before dropping back down to MVFR and then IFR later
tonight. Showers have overspread western VA, WV, and western
MD, but are gradually dissipating as they spread further east.
Additional showers and thunderstorms are expected to form this
afternoon into this evening, mainly to the west of the Blue
Ridge. Thunderstorms may be possible late this afternoon into
this evening at CHO and MRB. Further east, instability is
lacking. Showers will eventually spread further east to all
terminals this evening, but thunderstorms are expected to remain
confined to near CHO and MRB. Rain will be steadiest during the
second half of the night.

Showers and IFR ceilings will linger across much of the area
tomorrow into tomorrow night. Chances for showers will decrease
on Sunday, but IFR to MVFR ceilings will continue. Winds will
be out of the northeast today, southeast tonight, and then east
this weekend.

VFR conditions are expected Monday and Tuesday with high pressure
and dry conditions.

&&

.MARINE...
Sub-SCA northeasterly winds are expected through the remainder
of the day. Winds turn southeasterly tonight, and then easterly
this weekend. Winds may reach SCA levels in easterly flow
tomorrow.

Sub-SCA criteria winds are expected Monday and Tuesday with light
easterly winds to start on Monday turning out of the south. Winds
increasing out of the south on Tuesday could result in some
southerly channeling, but not currently expected.

&&

.TIDES/COASTAL FLOODING...
Persistent onshore flow will continue through early next week.
This will result in elevated tide levels. Minor flooding is
expected in more sensitive locations over the next several
tidal cycles.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Coastal Flood Advisory until 8 AM EDT Saturday for DCZ001.
MD...Coastal Flood Advisory until 7 AM EDT Saturday for MDZ014.
     Coastal Flood Advisory until 2 AM EDT Saturday for MDZ017-018.
VA...Flood Watch through late tonight for VAZ025>027-029-030-
     036>040-050-051-503-504-507-508.
WV...Flood Watch through late tonight for WVZ055-501-502-505-506.
MARINE...None.

&&

$$

SYNOPSIS...KJP
NEAR TERM...KJP
SHORT TERM...KJP
LONG TERM...CAS
AVIATION...KJP/CAS
MARINE...KJP/CAS
TIDES/COASTAL FLOODING...KJP