Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 180109
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
909 PM EDT Sun Jun 17 2018

.SYNOPSIS...
High pressure will remain off of the Mid-Atlantic coast through
Monday. A cold front will approach the area from the north on
Tuesday and stall across the area during the middle of the
week.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
High level clouds and a fairly impressive inversion near the
freezing level (per 00Z LWX RAOB) pretty much kept convection in
check today. With sunset upon us, chances for additional
thunderstorms are nil at best.

The additional atmospheric moisture relative to the past few
days suggest that there will be a greater chance at overnight fog
development...contingent upon cloud cover. Going forecast has
favored the valleys/low spots, which would be where potential
would be the greatest.

Since dewpoints in the upper 60s/around 70, lows shouldn`t be
far from that...as already advertised.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH TUESDAY/...
Ridge builds in with higher temperatures Monday. Went with our
ensemble guidance that has been performing the best recently.
That gives highs 90-95, and heat index values around 100 with
dewpoints in the low 70s. Think any showers and tstms will be
isolated Mon afternoon.

Tue continues with the heat, but a cold front approaching the
area will increase our odds of thunderstorms, as well as bring a
bigger gradient of temps Tue PM in our forecast area. Heat index
values are currently expected to get into the lower 100s on our
southern tier, but only low 90s on our northern tier...high
temps in the upper 80s, and low to mid 90s respectively.

Westerly winds, weak lapse rates, and weak shear will likely
limit thunderstorm organization, but plenty of moisture and
instability will be pooled ahead of the front. With steering
flow parallel to the boundary, some training is possible for a
locally heavy rain threat. Frontal progression starting to trend
a pinch quicker. The boundary will begin to stall out Tuesday
night, though most models have winds turning northerly over at
least parts of the area. While some showers could persist
through the night, coverage should decrease with loss of
instability.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Model guidance is in good agreement that a frontal boundary will
stall out over, or just south of our area on Wednesday. Low-level
convergence in the vicinity of this frontal boundary will facilitate
the development of showers and thunderstorms across the area.

The main feature of interest locally for the remainder of the week
will be the positioning of the aforementioned frontal boundary. The
eventual location of this boundary will likely be modulated by the
positioning of a longwave trough tracking across eastern Canada and
New England. The 12z GFS is more progressive and amplified with this
trough compared to the 00z Euro. The GFS solution allows high
pressure to build in the wake of the trough across the Great Lakes
on Thursday, which acts to push the frontal boundary further south.
The Euro keeps high pressure centered over Ontario, which enables
the frontal boundary to remain stalled out just to our south.
Ensemble guidance shows a variety of solutions, but in general the
GEFS are more progressive with the boundary, while the EPS favors a
more stalled out boundary. If the boundary remains stalled out over
our area, chances for showers and storms will persist through
Friday. On the other hand, if the boundary is pushed further off to
our south, Thursday and Friday will be mostly dry.

By next weekend an upper-level low is progged to track from the
central US to the Great Lakes. Some showers and storms may be
possible as this system passes to our north.

&&

.AVIATION /01Z MONDAY THROUGH FRIDAY/...
VFR flight conditions will prevail through the evening with
light winds. Fog may develop overnight, but thats still
contingent on cloud cover. With that uncertainty still in play,
made no forecast adjustments...still a period of MVFR possible
predawn at CHO and especially MRB. Greater fog risk resides in
the valleys away from TAF sites.

VFR conditions are expected Monday. A cold front will drop
southward on Tuesday, increasing chances of showers and
thunderstorms with local IFR conditions during the afternoon
and evening.

A frontal boundary is expected to stall over our area on
Wednesday, bringing chances for showers and thunderstorms. This
could make sub-VFR conditions possible at times. The position of
this boundary is less certain Thursday and Friday, but if it
were to remain overhead showers and storms would be possible.

&&

.MARINE...
Winds will generally be 10 kt or less today. Monday, possible
channeling flow up the Bay will increase speeds from today, but
still expected to remain below Small Craft Advisory at this
time. Tue is more uncertain and will depend on the timing of the
cold front. But winds may approach Small Craft level Tue PM, also
with an increasing chance of thunderstorms.

Winds are expected to remain below the SCA threshold throughout
the long term period. Showers and thunderstorms may be possible
each afternoon with a frontal boundary nearby.

&&

.CLIMATE...
Well above normal temperatures are forecast Monday through
Tuesday. Below is a list of daily record warm temperatures.

Washington DC area (DCA)
Date      Record High      Record Warm Low
June 17   97 (2014)        76 (1952, 1939)
June 18   97 (1944)        77 (2014, 1957)
June 19   99 (1994)        75 (2011, 1994, 1981, 1978)
Temperature records for the Washington DC area have been kept
at Ronald Reagan Washington National Airport since 1945.
Additional temperature records observed downtown date back to
1872.

Baltimore MD area (BWI)
Date      Record High      Record Warm Low
June 17   96 (1939)        76 (1913)
June 18   97 (1957, 1944)  75 (1957)
June 19   99 (1994)        74 (1905)
Temperature records for the Baltimore MD area have been kept
at Baltimore-Washington International Thurgood Marshall
Airport since 1950. Additional temperature records observed
downtown date back to 1872.

Dulles VA area (IAD)
Date      Record High      Record Warm Low
June 17   92 (1994)        72 (1996)
June 18   94 (2007, 2006)  73 (2017)
June 19   98 (1994)        71 (2014)
Temperature records for the Dulles VA area have been kept at
Washington Dulles International Airport since 1960.

&&

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

&&

$$
SYNOPSIS...CS
NEAR TERM...HTS
SHORT TERM...CS/HTS
LONG TERM...CS/KJP
AVIATION...CS/HTS/KJP
MARINE...CS/KJP
CLIMATE...DH



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