Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 240112
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
912 PM EDT Fri Jun 23 2017

.SYNOPSIS...
Tropical air will envelop the area today. A cold front will
cross the area late tonight into Saturday. High pressure will
return Sunday and persist through early next week.

&&

.NEAR TERM /THROUGH SATURDAY/...
Besides a few showers across the region late this afternoon and
early this evening...the LWX CWA has been quiet especially compared
to our neighbors to the west and north. This will change tonight
as remnants of TD Cindy and a cold front will move into the
Mid- Atlantic region. Showers will spread across the region
tonight with embedded heavy showers and gusty winds. The
atmosphere is moist with an observed PWAT from KLWX of 1.9 at
00z. Sfc dewpts in the 70s will give to moderate instability
across the region tonight. Shear is also moderate with near
50kts of 0-6km bulk shear. Thunderstorms are possible as the
cold front crosses the region overnight. Hi-res guidance depicts
some line segments that may produce stronger winds and severe
thunderstorm warnings can not be ruled out overnight. Seems like
the best chance will be across the northern half of the outlook
area. Rainfall amounts of 0.75- 1 in are expected across the
northern half and will taper off to around 0.25 in across the
Central Foothills/southern MD overnight with higher amounts in
heavier bands/thunderstorms.

Elsewhere...a strong LLJ will be on top of the region tonight
and widespread showers will likely bring down gusty winds.
Gusts 35-45 mph can not be ruled out across the region into
early Saturday morning. The cold front should cross the region
by 8AM Saturday morning and drying will occur behind it.

Prev discussion...
Latest GFS/NAM prog timing to be so quick that all precip will
be east of the forecast area by the start of the period. Am a
little bit caution of that solution, and have lingered some
precip into the Saturday morning hours. Then we`ll need to
assess how quickly front leaves area; there are some suggestions
in may get caught up across southern Maryland or the Virginia
tidewater.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/...
High pressure will be building across the area this weekend,
with no other weather hazards. Perhaps there will be a
reinforcing boundary Sunday, but moisture looks scant for even
clouds.

Accepted a MOS blend for temps. Sunday will be the cooler day,
with lower dewpoints also advecting in Saturday.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Surface high pressure sets to the west on Monday as a slow
moving upper level trough slides east into Tuesday with surface
westerly flow. Below normal temperatures, with showers and
thunderstorms possible during this period.

Conditions should become drier as surface high settles overhead
Tuesday night. The high will move offshore on Wednesday and continue
moving west into Thursday as flow becomes more southerly.
Temperatures will be on the rise as dry conditions continue into
Friday, when guidance suggest a boundary will bring showers and
thunderstorms over our area.

&&

.AVIATION /01Z SATURDAY THROUGH WEDNESDAY/...
A cold front, infused with tropical moisture, will cross the
terminals tonight, most likely after midnight but before dawn.
At this point, kept restrictions at MVFR. There is a decent
potential of local/brief IFR, probably due more to reduced vsbys
in heavy rain. There may also be localized wind gusts. Where
these gusts aren`t realized, there is a 50-70 kt wind max
several thousand feet off the deck, so low-level wind shear will
be a concern.

The front will be east of the terminals by Saturday morning. VFR
conditions will prevail for the weekend.

Mostly dry/VFR conditions expected Monday into Wednesday as
surface high pressure settles in. Some scattered showers and
thunderstorms possible Monday afternoon into Tuesday as upper
air disturbance moves through, which could cause periods of sub-
VFR conditions.

&&

.MARINE...
Update...A Gale Warning is in effect for all waters late
tonight into Saturday morning. Showers and thunderstorms will be
capable of producing gusty winds on the waters during this
time.

Southwest winds 10-15 kt with some gusts to 20 kt. Those winds
will be increasing ahead of a cold front tonight. Small Craft
Advisories remain in effect. There will be a 50+ kt low level
jet several thousand feet off the waters overnight. Do not
believe this will mix down in the gradient flow, but local
punches may near heavier showers. Marine Warnings may be
required tonight.

Northwest flow Saturday will contain better mixing. The
gradient will decease Saturday night. Have not extended the
Advisory further at this time.

Mostly dry conditions expected Monday into Wednesday as surface
high pressure settles in. Some scattered showers and
thunderstorms possible Monday afternoon into Tuesday as upper
air disturbance moves through. Winds gusts will be below the
small craft advisory criteria.

&&

.HYDROLOGY...
As mentioned above, precip waters will be exceeding 2 inches, so
heavy rain expected in storms tonight. However, only 0.1 to 0.3
inches fell this morning, so soils were not saturated. Further,
storms look to be progressive. So, while heavy rain expected,
believe that the soil will be able to handle it overall, based
on flash flood guidance. Thus, will not post any Watches at this
time. Local minor flooding is possible, especially in the
Potomac Highlands.

&&

.TIDES/COASTAL FLOODING...
A coastal flood advisory is in effect for Anne Arundel,
Baltimore and Harford counties late tonight into Saturday
morning. Anomalies around one foot are expected during this
time.

Beyond that, northwest winds should lead to levels returning
close to normal.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Coastal Flood Advisory from 2 AM to 2 PM EDT Saturday for
     MDZ011-014-508.
VA...None.
WV...None.
MARINE...Small Craft Advisory until midnight EDT tonight for ANZ530>543.
     Small Craft Advisory from 8 AM to 6 PM EDT Saturday for
     ANZ530>543.
     Gale Warning from midnight tonight to 8 AM EDT Saturday for
     ANZ530>543.

&&

$$
SYNOPSIS...RCM are expected during this
time.

Beyond that, northwest winds sho
NEAR TERM...HSK/HTS
SHORT TERM...ADS/HTS
LONG TERM...IMR
AVIATION...HSK/IMR/HTS
MARINE...HSK/IMR/HTS
HYDROLOGY...HSK
TIDES/COASTAL FLOODING...HSK


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