Area Forecast Discussion
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FXUS61 KLWX 190727
Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
327 AM EDT Tue Jul 19 2016
A cold front will stall out overhead before passing through the
entire area tonight. High pressure will build overhead for
Wednesday and Thursday. High pressure over the Atlantic will
control the weather pattern for Friday through Sunday. A cold
front may impact the area early next week.
.NEAR TERM /THROUGH TONIGHT/...
Light winds and breaks in the cloud cover combined with the fact
that a lot of areas saw rain on Monday has resulted in patchy
fog. Fog may be locally dense early this morning...especially
across central Virginia into the Shenandoah Valley. Do think that
there is enough high and mid-level clouds early this morning to
prevent widespread dense fog...but this will have to be monitored
over the next few hours. Also...a few showers/isolated
thunderstorms are expected along the cold front early this morning
near the Allegheny Highlands. Isolated showers may make it into
portions of the Shenandoah Valley...but instability is limited
east of the Appalachians so most activity should dissipate.
A weak cold front is currently located near the Mason-Dixon Line
early this morning. A dewpoint gradient is noticed along the
boundary with lower to middle 60s to the north and upper 60s and
lower 70s south of the boundary. The cold front will drop south
into the area today...but it is likely to get hung up across the
Potomac Highlands into northern Virginia and portions of the
Washington Metropolitan area. Little temperature difference will
be associated with the front...but a dewpoint gradient is expected
to develop. Therefore...areas across northern Maryland into
northern Virginia and eastern West Virginia will turn out less
humid today. However...higher dewpoints are expected to remain in
place across central Virginia into southern Maryland and even
close to Washington DC.
Max temps will top off in the upper 80s to lower 90s across most
locations and this will cause some instability to develop. The
most instability is expected to be along and south of the
boundary...with mixed layer CAPE around 2000 J/KG possible. The
highest amounts of instability will be across central Virginia
where dewpoints will remain in the upper 60s close to 70 degrees.
Farther north...instability will be more limited. A few showers
and thunderstorms are expected near and to the south of the
boundary this afternoon into this evening. Coverage will remain
isolated to scattered since the forcing mechanism will be
relatively weak. An upper-level trough over New England will dip
south into the Mid-Atlantic today and this will cause shear
profiles to increase a bit. Marginal shear profiles and moderate
to perhaps high instability will cause the potential for a couple
thunderstorms to become severe...with locally damaging winds and
large hail being the primary threats. The best chance for stronger
storms will be across central Virginia perhaps into extreme
southern Maryland where instability will be highest.
The cold front will stall out just to the south of the area
tonight and a northerly flow will allow for drier and more
comfortable conditions overnight.
.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
High pressure will remain over the region for Wednesday through
Wednesday night...bringing dry and seasonably warm conditions
along with lower humidity. The high will shift offshore Thursday
and a return flow will develop. Humidity will begin to increase
during this time. A popup shower or thunderstorm cannot be ruled
out over the Potomac Highlands into central Virginia during the
afternoon and evening hours...especially over the higher terrain.
Thursday night will turn out warm and humid as high pressure
settles off to the south and east.
.LONG TERM /FRIDAY THROUGH MONDAY/...
The return and amplification of heat and humidity will be the main
story for the end of the week and into the weekend.
Much of the time period will feature northwest flow aloft with
warming temperatures and a gradual return in humidity. Core of
large upper ridge will be centered over the central US with the
Northeastern US/Mid Atlantic on the periphery with largely
west/northwest flow. With this type of pattern would expect a risk
of some showers/thunderstorms with daytime instability and
potential MCS`s moving along the periphery of the ridge.
Expecting widespread 90s for high temperatures Friday through
Monday. Humidity should be initially tempered in the westerly flow,
but as northwest flow weakens Sunday and possibly turns southwest
ahead of an approaching front, will see humidity values rise. Thus
the combination of heat/humidity will likely lead to heat index
values in excess of 100F, and heat headlines may be necessary. The
most oppressive days currently appear to be Saturday and Sunday.
As frontal system approaches Monday, will see the chances for
synoptically driven showers/thunderstorms increase.
.AVIATION /07Z TUESDAY THROUGH SATURDAY/...
Patchy fog is expected early this morning. Vsbys should remain at
VFR levels and perhaps MVFR levels for most of the terminals...but
fog may be more dense across KCHO. MVFR to IFR vsbys are expected
early this morning. Any Fog will lift by 12-13z.
VFR condtions are expected most of the time today through
Wednesday night. A cold front will slowly drop south through the
area this afternoon into tonight. A few showers and thunderstorms
are possible this afternoon and evening. Coverage will be isolated
to widely scattered. The best chance for a thunderstorm will be
across KCHO...and any thunderstorms that do develop may contain
gusty winds or hail. High pressure will build overhead for
Wednesday through Wednesday night. The high will move off the
coast for Thursday and Thursday night...and a return southerly
flow will develop. However...VFR conditions will likely persist.
Generally VFR expected from Friday and through the weekend. A few
showers/thunderstorms are possible which may bring a brief period of
sub-IFR conditions. Patchy fog also possible during overnights, but
coverage not likely to be widespread.
A cold front will slowly drop through the waters today into
tonight. A few showers and thunderstorms will develop along and
ahead of the boundary. Coverage of convection will be isolated to
scattered...but thunderstorms will be capable of producing locally
gusty winds. A pressure surge will develop behind the cold front
late tonight into early Wednesday. Winds may approach SCA criteria
for a brief period during this time. However...the pressure surge
will be weak so confidence was too low for an SCA headline at this
High pressure will remain over the waters Wednesday through
Wednesday night before moving offshore Thursday. A return
southerly flow will develop for Thursday into Thursday night.
Mostly sub-SCA conditions expected for the end of the week and
weekend, however brief intervals of gusts up to around 20 knots