Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 291404
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1004 AM EDT Mon May 29 2017

.SYNOPSIS...
Upper level low pressure will drift east across the north side
of the Great Lakes this week. In the meantime, weak high
pressure will prevail over the Mid Atlantic outside of weak
cold frontal passages Tuesday night and Wednesday night. Low
pressure approaches from the west this weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
Latest observations and satellite pictures indicate the edge of
low clouds on the doorstep of FDK-IAD-EZF, with a pretty sharp
improvement west of there. Therefore, am hopeful that we`ll be
able to see a period of sun today, before any diurnal cu
develop.

It remain possible that the frontal convergence zone crossing
the forecast area may spark a few showers and perhaps a
thunderstorm across the eastern quarter of the area. Have
preserved a period of isolated- scattered showers/thunderstorms
along and east of I-95. Atmosphere remains stable due to the
morning wedge, and doubt we`ll be able to recover from that.

The front/trough axis becomes more nebulous tonight, as it will
stall near the Bay. Onshore flow will be re-introduced, bring a
return of lower clouds, especially the northeastern quadrant of
the area. Fog and reduced visibility will be possible, whether
due to low clouds (east) or radiational cooling of the moist
airmass (west). Low pressure will develop along the frontal zone
to our south, which could bring a shower threat to the far
southeast, but otherwise dry. Lows will be in the upper 50s to
mid 60s.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
Upper level low pressure will continue to spin over Ontario
Tuesday and Wednesday with the jet stream located just to our
northwest. Surface features will continue to be less defined
though, as weak fronts (more pressure troughs than huge airmass
differences) waver across the region.

The first will push southeast on Tuesday afternoon. With low
stratus to start the day, it is uncertain how quickly and how
far east it will erode. West of the marine air, modest
instability will develop. Deep layer shear increases in
magnitude with northward extent. Thus there is some risk of
strong/gusty thunderstorms developing ahead of the front. SPC
has placed northern parts of the area in a Marginal Risk.

This front will lose its definition as it slips southward
Tuesday night, ending the chance for showers. A final and
slightly more well- defined front will push south Wednesday
afternoon and evening. While low level convergence isn`t great,
some scattered showers and storms will still develop along the
front. The front will align better with diurnal heating to our
west, so expect a decreasing trend for any storms that enter the
area. Once again though, deep layer shear will be strong, so
any organized storms could have a gusty wind threat. A Marginal
Risk is in place for the northwestern half of the area.

Highs both days will be in the 70s and 80s with lows in the 50s
and 60s.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
Canadian high pressure will dominate Thursday as a trough
passes aloft. Warm air will begin returning northward on Friday,
but by Saturday the next cold front is already dropping back
south across the region as another trough rotates around the
stalled upper low over southern Canada. That front looks to
stall south of the region by Sunday as the upper low starts
moving further east, with the front perhaps lifting back north
as a warm front early next week. We will have a chance of
showers and thunderstorms with the front dropping south across
the area late Friday into Saturday. By Sunday, with the
potential for the front to stall south of us, the weather is
uncertain, but if high pressure builds in strongly enough from
the north, it could be dry. Temperatures will mostly be cooler
than normal, with the warmest day likely Friday.

&&

.AVIATION /14Z MONDAY THROUGH FRIDAY/...
Low clouds have moved east of MRB/CHO already, and based on
current progress should see return of VFR to IAD/DCA shortly.
It`ll be a little bit longer for BWI/MTN as they`re more
entrenched in the wedged marine air, but current trends suggest
that VFR should return before noon.

A few showers may redevelop around Baltimore this afternoon,
but not enough coverage to put in the TAF.

Onshore flow will redevelop tonight. Low MVFR or IFR likely in
Baltimore area, and possible at the rest of the terminals except
CHO. It`s uncertain how quickly these clouds will erode on
Tuesday as well. Where they do, thunderstorms will be possible
during the afternoon and evening as the next boundary drops
southeast.

It`s possible the low cloud pattern repeats Tuesday night as
the front washes out. A more well-defined cold front will push
through late Wednesday with scattered showers and thunderstorms
possible.

Mainly VFR later this week with high pressure returning.
Thunderstorm chances are maximized late Friday into Saturday
with a passing front.

&&

.MARINE...
Overall light flow is expected on the waters through Wednesday.
Expect variable wind directions as weak boundaries waffle
across the area, though onshore flow may persist more often than
not until a more defined cold front passes through Wednesday
night. With the frontal passage after sunset, am not thinking
strong winds will be found in its wake. Also can`t completely
rule out a few thunderstorms each day, mainly focused in the
afternoon and evening, although it`s uncertain how many reach
the waters at this time.

Sub-SCA winds expected later this week. Thunderstorm chances
increase late Friday with an approaching front.

&&

.TIDES/COASTAL FLOODING...
Water levels remain high and should continue above normal for
the next few cycles due to the persistent onshore flow.
Advisories remain for Anne Arundel and Alexandria/DC for this
morning`s high tide cycle, and for St. Marys for this
afternoon/evening`s high tide cycle. It is also probable that
additional advisories will be needed for high tide cycles
through Tuesday for the sensitive locations, and possibly
elsewhere. After Tuesday, northerly flow may finally allow
anomalies to start falling.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Coastal Flood Advisory until 2 PM EDT this afternoon for
     DCZ001.
MD...Coastal Flood Advisory until 1 PM EDT this afternoon for
     MDZ014.
     Coastal Flood Advisory until 10 PM EDT this evening for MDZ017.
VA...Coastal Flood Advisory until 2 PM EDT this afternoon for
     VAZ054.
WV...None.
MARINE...None.

&&

$$
SYNOPSIS...RCM
NEAR TERM...HTS/ADS
SHORT TERM...ADS
LONG TERM...RCM
AVIATION...HTS/ADS/RCM
MARINE...ADS/RCM
TIDES/COASTAL FLOODING...RCM/MM


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