Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 271844

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
244 PM EDT Sat Aug 27 2016

.SYNOPSIS...High pressure surface and aloft will hold through
Monday then move offshore. A cold front will move through the
area Wednesday night. High pressure then builds for the second
half of next week.


.NEAR TERM /THROUGH SUNDAY/...Strong ridge of high pressure sfc
and aloft will hold through Sun morning before it begins to drift
east. This will continue to suppress convective development over
the area. Developing onshore flow tonight will probably result in
low cloud development east of the Blue Ridge as suggested by 00Z
NSSL WRF ARW and 12z NAM models. The 00Z ECMWF also suggested low
clouds rolling in, but the new 12Z has backed off now suggesting
low clouds staying over southeast VA. The latest GFS does not
indicate low cloud development and instead keeps skies clear
overnight. Given the onshore flow and high skill of the NSSL WRF
ARW have raised sky cover grids to show a 3-6 hr period of low
cigs overnight east of the Blue Ridge. Low clouds then mix out
during the mid-late morning. There will be a slightly better
chance of t-storms far west over the Appalachians Sun, but most of
the area will remain dry. Slightly cooler with temps in the low


pressure begins to weaken over the area Mon as it moves offshore
and a shortwave-trough digs across the northeastern states. Increasing
warmth and humidity will generate more instability with showers
and t-storms becoming more probable over the mtns. Activity will
drift east during the late afternoon and/or early evening before
dissipating, but is not likely to reach the metro areas. Hot and
humid with temps in the mid 90s and heat indices aoa 100F.



Warmer than normal temperatures should persist through the middle
part of the week. A few showers and thunderstorms are possible
Tuesday afternoon over the higher terrain in a warm and humid
airmass but with little forcing outside of terrain circulations. A
cold front dropping into the area may be able to bring a threat for
showers and thunderstorms closer to the metro areas Wednesday
afternoon and evening.

A shower or thunderstorm will remain possible Thursday across
southern portions of the area as some models/ensembles are slower
with the southward progress of the cold front.

An unseasonably strong area of high pressure will dive into the
region later in the week bringing cooler and drier weather which
looks to persist into the first part of next weekend.



Potential for low clouds to roll in overnight and affect metro
terminals as suggested by 00z ECMWF, NSSL WRF ARW and NAM models.
The new 12Z ECMWF has backed off on it suggesting low clouds
staying over southeast VA. Introduced a 3-hr period of IFR cigs at
BWI, MTN, and DCA and MVFR at IAD. Low clouds mix out quickly
tomorrow after 13Z.

Mainly VFR expected with southwesterly winds around 10 knots
Tuesday into Wednesday. A thunderstorm is possible Wednesday as a
cold front approaches.


.MARINE...Sub-SCA conditions through Mon. No t-storms expected.

The pressure gradient will remain relatively weak Tuesday
into Wednesday despite an approaching cold front, with winds likely
staying below Small Craft Advisory levels during this time.



Ranking of summer 2016 in terms of average temperature (JUN 1 - AUG 26)

Site          Rank                    Average Temperature

DC   3   80.5
Balt          19  77.2
IAD            3                            77.3




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