Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 171400
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1000 AM EDT Mon Jul 17 2017

.SYNOPSIS...
An upper level trough will affect the weather today and
Tuesday. After another period of tranquil weather during the
middle of the week, another cold front may approach the region
by the end of the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Morning analysis depicts upper level trough and surface front
located across the Ohio Valley northward through western
Pennsylvania and into western New York. While the surface
boundary will stall and wash out over the next couple of days,
the upper trough will move eastward and over the region through
today. Relatively steep mid level lapse rates exist with this
feature with the 12z IAD sounding and SPC mesoanalysis
depicting 700-500 mb lapse rates in excess of 7 C/km. While
these are projected to weaken some by the afternoon, these
combined with the warmth and humidity will lead to the
development of at least 1500-2000 J/KG of MLCAPE. It should also
be noted that a capping inversion also exists between 700-800mb
that should limit thunderstorm development for areas east of
the Blue Ridge, while a weaker cap and daytime terrain
circulations will lead to a greater risk for areas west. Some of
the showers/thunderstorms that do develop across the terrain
may tend to propagate eastward towards the metros while
weakening later in the day. While shear profiles are weak, there
is enough instability to warrant a marginal risk of severe
thunderstorms. Highs today upper 80s to near 90F.

Given lack of strong forcing, most convection should quickly
dissipate this evening, and the balance of tonight will be dry
with lingering clouds. Patchy valley fog is also possible,
especially where it rains today. Lows will be a bit milder, with
70s becoming more common.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
Upper trough slowly weakens and moves out of the area Tuesday
and Wednesday as high to the southeast continues to bring in
more warmth and humidity. Dew points will rise a bit more and so
will temps, but right now, expect heat indices to peak in the
mid-upper 90s Tuesday and upper 90s-low 100s Wednesday... just
below criteria for a heat advisory. Conditions will not be quite
as unstable overall on Tuesday as we are expecting today, but a
lee side trough combined with less of a cap means that the
chance of showers and t-storms along the I-95 corridor actually
looks higher on Tuesday than it does today. By Wednesday, pops
fall everywhere as what remains of the trough aloft is moving
away and there is less of a lee side trough. Highs will
generally be low-mid 90s with lows in the 70s.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
An upper trough present through the first half of the week over
the eastern states will shift east off the coast by Thursday. A
sprawling high centered over the southern Great Plains begins
to control area weather in the wake of this trough.

A shortwave trough crosses to the north on Thursday with a weak
cold front entering the LWX CWA later in the day. This front
looks to stall over the area and provide a focus for diurnally
driven convective storms Thursday through the weekend.

Heat will be a concern later in the week, particularly Thursday
ahead of the cold front and Sunday after the stalled front
moves out. As of now values around 100F seem reasonable for
Thursday in urban areas.

&&

.AVIATION /14Z MONDAY THROUGH FRIDAY/...
VFR overall through the TAF period and beyond. The main weather
concern today and Tuesday will be scattered showers/thunderstorms
during the afternoons, with best coverage west of I-95 today,
and near I-95 on Tuesday. Otherwise, patchy early morning fog is
possible, especially Tuesday and Wednesday mornings and
particularly where any rain falls the previous
afternoon/evening.

A weak cold front will then stall over the area later Thursday
into the weekend which may allow sub-vfr conds during
thunderstorms.

&&

.MARINE...
Generally sub-SCA today and Tuesday, though southerly channeling
could result in near SCA conditions Wednesday. Other than that,
main concern is for thunderstorms, which look more likely on the
waters on Tuesday, but are also possible both today and
Wednesday (just not as likely). Any storm could result in gusty
winds over the next couple of days.

Generally light NWly flow Thursday into the weekend behind a weak
cold front.

&&

.TIDES/COASTAL FLOODING...
South flow persists across the Chesapeake Bay region through
midweek. Water levels at the preferred high tide (late
afternoon/evening) will approach minor coastal flooding thresholds
at particularly sensitive sites like Straits Point (St. George
Island in St. Mars county), Annapolis and SW DC Waterfront today
through Wednesday.

&&

.CLIMATE...
Meteorological summer - June 1 to Aug 31, 92 days. Yesterday
was day 46 of that, so we`re at the midpoint. Here are a few
temperature stats on this summer so far.

Site   Average Temp  Rank  Record year (through yesterday)
DCA        79.1        6     2010
Balt       75.7        35    2010
IAD        74.9        10    1994

&&

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

&&

$$
SYNOPSIS...RCM
NEAR TERM...MM/RCM
SHORT TERM...RCM
LONG TERM...BAJ
AVIATION...BAJ/MM/RCM
MARINE...BAJ/MM/RCM
TIDES/COASTAL FLOODING...BAJ
CLIMATE...WFO LWX



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