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000
FXUS61 KLWX 251856
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
256 PM EDT Thu Apr 25 2019

.SYNOPSIS...
A warm front will move north across Virginia today and into
Maryland tonight. Low pressure will track across the Ohio
Valley and eastern Great Lakes tonight into Friday, pulling a
cold front across the area Friday afternoon. High pressure will
build in behind this front for the early part of the weekend.
Another storm system could approach the region Sunday.

&&

.NEAR TERM /THROUGH TONIGHT/...
Frontal boundary is residing in southern Virginia this
afternoon and will move northward across the region this evening
and tonight. Isolated to scattered showers/sprinkles exist
across portions of the area this afternoon, but
coverage/intensity has been minimal so far. As the front lifts
north later today and this evening, the surface low tracks
northeastward through the Ohio Valley, and the upper trough
approaches, showers should increase in coverage. Some
instability may develop and an isolated thunderstorm or two is
also possible, mainly across eastern WV and VA.

Lows tonight will range from the mid 50s to low 60s.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
Surface low pressure will move northeastward through the eastern
Great Lakes during the day Friday with its attendant surface
cold front crossing the region during the afternoon and early
evening hours. Some showers and/or elevated isolated
thunderstorms may be ongoing early Friday morning, with activity
waning during the late morning hours. This will allow for
temperatures to rise and some instability to develop. Latest
model guidance including 12z NAM and 12z HREF members indicate
that between 500 and 1000 J/KG of SBCAPE is likely to develop
ahead of the frontal boundary. This combined with strong low to
mid level wind field and 40 knots or so of bulk shear will set
the stage for strong to locally severe thunderstorms, mainly
from the Blue Ridge Mountains eastward, with the highest
probability of severe across portions of central VA, eastward to
DC, and into southern Maryland where a Slight Risk of severe
thunderstorms was introduced.

Showers/thunderstorms will likely develop around noon or so
across eastern WV and central VA, and move eastward across the
region, exiting east of the Chesapeake Bay by 7 PM. The highest
threat window for severe thunderstorms will likely exist between
2 PM and 6 PM. Several discrete cells are possible ahead of what
may become a more organized developing squall line. The primary
threat will be isolated damaging wind gusts, but given
low level directional shear and relatively high helicity values,
an isolated tornado is also possible, with the highest
probabilities in southern MD.

Heavy rainfall will also occur with these showers/thunderstorms,
and while a widespread flood event is not likely, an isolated
incident of flooding is possible if any training thunderstorms
occur.

Highs on Friday will range from the upper 60s to low 70s.

The front will then push eastward Friday night with strong
west-northwest flow following behind. Gusty winds are expected
with 30-40 mph likely, although mixing may be limited at night.
It`s possible a Wind Advisory may be needed, especially across
the higher elevations, but uncertainty exists at this time. The
wind field begins to weaken Saturday but mixing will increase
during the daylight hours, so gusty winds may actually max out
Saturday morning. Highs Saturday in the 60s to around 70F.

A weak ridge of high pressure moves overhead Saturday evening
before shifting eastward and offshore by Sunday morning as a
weak area of low pressure approaches. Some showers become
possible Saturday night.Lows in the 40s to low 50s.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
A cold front will cross the area Sunday afternoon. Moisture and
instability will be limited with the best moisture and instability
focused to our region`s north. Rainfall amounts will be light.
Dry weather is expected Sunday night as strong high pressure builds
in from the northwest.

Moisture returns Monday night as high pressure shifts east. A
developing front over the Ohio Valley will be the focus for showers
and thunderstorms. Although disturbances will move along the front,
the front will remain nearly stationary with very little shower or
thunderstorm activity initially. Expect unsettled weather to
redevelop toward the middle and latter part of the week with a
chance for thunderstorms.

&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
Primarily VFR conditions expected through the period. Ceilings
will gradually lower and clouds will thicken this evening and
tonight. Showers and even a few isolated thunderstorms will
develop this evening and tonight. Brief reductions to MVFR are
possible, with the highest probabilities of more consistent MVFR
ceilings at MTN/MRB.

A strong cold front will then cross the terminals Friday.
Predominant VFR anticipated, but local IFR possible within
showers/storms. In addition, local gusty winds (40-50 kt)
possible in stronger storms. Placement of these cells
problematic this far out, but the general time frame for strong
winds/wind shift will be mid afternoon MRB/CHO and late
afternoon at the hubs (IAD/DCA/BWI).

Gusty northwest winds will continue behind the front Friday
night into Saturday before diminishing Saturday night. Gusty
NW winds anticipated once again Sunday afternoon through Sunday
evening behind another frontal passage.

A few showers are also possible Monday night. Conditions could
briefly become MVFR in these showers.

&&

.MARINE...
Generally light winds expected on the waters through tonight.
Flow which is predominantly northerly this afternoon will
become south this evening and tonight as a warm front slowly
crosses the waters.

By Friday, a sharp cold front will be approaching the waters.
While mixing won`t be ideal, there will be a healthy gradient
wind in advance of this front. A Small Craft Advisory is in
effect beginning at 12 Noon. The environment will also become
favorable for development of clustered showers/thunderstorms
Friday afternoon capable of producing gusty winds in excess of
34 knots and possibly up to 50 knots, and Special Marine
Warnings may become necessary.

In the wake of the cold front Friday night into Saturday the
gradient remains tight, with 30-35 kt (and depending upon model
solution, perhaps up to 40 kt) still available. Momentum
transfer will be more optimal. A SCA is in effect, but an
upgrade to Gale may be needed. The strong winds will continue
into Saturday morning before gradually relaxing during the
afternoon hours.

Small craft advisory conditions expected Sunday and Sunday night
with frequent gusts to around 25 knots. Winds diminish below
criteria later Sunday night through Monday night.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory from noon Friday to 6 AM EDT Saturday for
     ANZ530>543.

&&

$$
SYNOPSIS...MM
NEAR TERM...MM
SHORT TERM...MM
LONG TERM...KLW
AVIATION...MM/KLW
MARINE...MM/KLW