Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 201526

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1126 AM EDT Sat May 20 2017

A cold front is positioned across southern Virginia. The front
will return north into the area as a warm front late Sunday
before another cold front passes through from the west Monday.
High pressure will briefly return for Tuesday before another
cold front impacts the area Wednesday.



On satellite it is interesting to see the line of clouds being
pushed to the west across central Virginia on east winds. To the
west of that line temperatures have risen into the mid 80s in
Nelson County where skies have been clear. The heating there
should slow down as those clouds overspread the central
Shenandoah Valley.

Overall temperatures are warmer this morning west of the Blue
Ridge where more sunshine is being received. East of the
mountains the combination of clouds and easterly winds are
holding temperatures in the 60s.

The persistent onshore flow...with extensive a
saturated marine layer develops between 2-4 kft AGL. Presence of
cloud cover will greatly inhibit quality insolation. Cold front
will also shunt moisture to the south...with dewpoints dropping
into the low 50s by Sunday morning.

While most areas will remain dry...showers and a few thunderstorms
are possible closer to the cold front across the SW (e.g., mainly
Highland, Augusta, and Nelson counties) this afternoon. Any
thunderstorms that do develop across this area would weaken rapidly
as they move into a convectively-poor environment north of the


Easterly onshore flow continues through much of Sunday as CAD wedge
continues to dominate with surface high pressure centered off the
NY/NJ coast. Once cover will hinder insolation and
keep temperatures in the 60s.

Warm front will begin to lift back northward late Sunday...with
southerly return flow developing to its south. Rain chances return
into Monday as moisture quickly streams back into the area ahead of
frontal passage. Poor timing suggest limited instability ahead of
cold front. One exception could be across central VA...where some
destabilization could develop with a few thunderstorms possible.

We begin to dry out late Monday afternoon/evening as cold front
shifts away from the area.


A deep, large scale trough axis will be dropping into the Central
Plains Tuesday, and sharpening as it heads toward the East Coast
Wednesday and Thursday. The only differences are in the fine-scale
details, which will drive whether a secondary cutoff low can form in
Appalachia (GFS) or the parent low rotates south (ECMWF).
Regardless, they dynamic nature of this system should be able to
induce cyclogenesis. Therefore, the midweek is looking wet.

Tuesday will be the driest day of the stretch, as weakening high
pressure passes over the area. Guidance has been consistent that the
day would start out sunny, but clouds would be advancing through the
day. Latest guidance, however, is suggesting that showers will be on
the doorstep of central Virginia by the end of the day. Occasional
showers will be the rule through Thursday. Areal coverage (scattered
vs numerous) will be the biggest challenge...something that can`t be
sorted out at this time frame. For the most part, will be
emphasizing a precip type of showers. However, as the potential
upper low nears, there should be sufficient instability for some
thunder as well.

The deepening cyclone should migrate toward New England by the end
of the week, for considerable improvement by Friday.


Cold front will stall to our south through Sunday...with high
pressure sliding to our NE. This will allow for persistent easterly
onshore flow...which will keep the area entrenched with low clouds.
Long-lasting MVFR ceilings appear likely with cloud bases near 2-4
kft AGL. Warm front lifts northward into the area late Sunday and a
cold front will cross the area Monday. These features will allow
rain to develop with periods of sub-VFR with low ceilings.
Improvement is expected later Monday as cold front pushes east of
the area.

Tuesday should be VFR for most of the day. Showers will spread north
late Tuesday or Tuesday night, and will be scattered or numerous
through Wednesday. Flight restrictions quite likely, but details
uncertain this far out.


Small Craft Advisory remains in effect for the potential for
low-end SCA gusts near 20 knots through afternoon. Pressure
surge weakens by evening...with winds diminishing overnight.

Winds turn southerly late Sunday as warm front lifts back north
through the waters...wind gusts near SCA criteria are possible (the
low probability) as this occurs. Low-end SCA gusts remain possible
Monday as cold front slides across the area.

Transitory high pressure Tuesday will be replaced by showers
associated with an upper low Tuesday night into Wednesday. Gradient
flow not that strong, and mixing should be poor. Therefore, no
headlines anticipated at this time.


Easterly onshore flow develops this weekend as high pressure nudges
into the area from the northeast. Flow turns southerly by Sunday
night as warm front lifts into the area. Water levels will gradually
increase today through Monday, with anomalies supporting
elevated/minor coastal flooding at Annapolis, Straits Point, and DC
by Sunday night.


MARINE...Small Craft Advisory until 6 PM EDT this evening for


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