Severe Thunderstorm Warning 124, NWS Baltimore/Washington

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
246 PM EDT Tue Jul 4 2017

.SYNOPSIS...

A weak frontal boundary remains over north central Virginia
today and then meanders just south of the area into Thursday.
Low pressure crosses the area Thursday into Friday. A
cold front passes through the region Friday night. High
pressure will build into the Mid-Atlantic behind the front.

&&

.NEAR TERM /TONIGHT/...

Frontal boundary across this forecast area is extremely weak -
perhaps the besy way to see that there is a boundary out there
is by looking at the regional radar composite which shows a
scattered line of echoes from well east of the Delmarva...across
northern VA and into central WV.

Atmosphere is fairly moist. Wind field is extremely weak. Models
are showing skinny CAPE for the late afternoon/evening hours.
Showers and weak thunderstorms will continue to develop through
mid evening then should diminish in coverage, although there
will most likely be some storms on radar at 9 pm it is not
possible to pinpoint where those would be.

Heat indices are generally a degree or two above the air
temperature, which keeps things well below heat advisory
criteria. In the cities at 9 pm temperatures will be in the
lower 80s.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...

For the next few days and nights cloud cover is going to be
extensive as the forementioned boundary is caught over the Mid
Atlantic along with two short waves tracking into the region
from the west. This will help to keep daytime temperatures down
a few degrees. The western portion of our forecast area has
been placed in a marginal risk of excessive rainfall Wednesday.
SREF precip field is projecting as an area of moderate/heavy
rain in the southwestern part of the forecast area in the mid-
late afternoon. We currently have likely PoPs there, and I'll
hold with that for the time being.

Clouds and chances of rain will continue through Thursday night.
As we experienced a dry June the area could use the rain.
Perhaps the best chance for thunderstorms will be Thursday
afternoon/night as a short wave pushes into the forecast area.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...

Guidance continues to be inconsistent and in disagreement on
the long term forecast. In general guidance suggests a drier
Friday with diurnally driven showers and thunderstorms. A cold
front is expected late on Friday or Saturday... so showers and
thunderstorms could be seen on Saturday depending on timing of
the frontal passage. Dry conditions are expected over our area
behind this front. If it stalls close enough we could see
additional showers and thunderstorms between Sunday and Tuesday
but at this point is too uncertain.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...

VFR through the evening hours. Isolated showers/thunderstorms
could impact any airport through mid evening. CLouds are
expected to drop into the MVFR range after midnight. Extensive
cloud cover will occur through Thursday night with
showers/thunderstorms. Best chance for storng wind gusts would
be Thursday late afternoon/evening.

In general, VFR conditions expected Friday into Sunday. Some
periods of showers and/or thunderstorms could bring sub-VFR
conditions at times, expected mainly Friday afternoon into early
Saturday.

&&

.MARINE...

Winds are expected to remain below SCA values through Thursday.
Showers and thunderstorms are popping up but moving slowly. A
few SMW's may need to be issued.

Continued chances for thunderstorms the next few days, with the
best chance for organized storms being Thursday.

Mainly dry conditions expected Friday into Sunday. Some periods
of showers and/or thunderstorms at times, mainly Friday
afternoon into early Saturday. Wind gusts could reach SCA
criteria at times Friday afternoon into early Saturday.

&&

.TIDES/COASTAL FLOODING...

Light onshore flow develops today and persists into Thursday.
This will allow anomalies to increase...with water levels at
sensitive sites (Annapolis, Straits, DC) coming close to minor
flooding thresholds at times of high tide beginning as early as
Wednesday night and continuing through the end of the week.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...None.

&&

PRODUCTS...WOODY!/IMR

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