Area Forecast Discussion
Issued by NWS Sterling, VA
FXUS61 KLWX 200737
Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
337 AM EDT Wed Jul 20 2016
A cold front will stall out over central Virginia this morning and
high pressure will build overhead this afternoon through tonight.
The high will weaken and move offshore Thursday. High pressure
over the Atlantic will control the weather pattern for Friday
through Monday. A cold front may approach the area Tuesday.
.NEAR TERM /THROUGH TONIGHT/...
A weak cold front continues to drop south through the area early
this morning. The boundary will stall out near central Virginia
later this morning and high pressure will approach from the
north this afternoon. A northerly flow behind the boundary will
allow for less humid conditions compared to recent days and it
will remain seasonably warm...but cooler compared to recent days.
Max temps will top off in the mid to upper 80s across most
An isolated shower or thunderstorm cannot be ruled out across
central Virginia into extreme southern Maryland into this
evening...but even across these areas most of the time will be
High pressure will remain overhead for tonight...bringing dry and
.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
High pressure will weaken and move offshore Thursday into Thursday
night. A return flow will allow for slightly more humid
conditions...and max temps will be a few degrees hotter compared
to Wednesday with most areas topping off in the upper 80s to lower
90s. Min temps Thursday night will range from the 60s in the
Potomac Highlands and portions of the Shenandoah Valley to the
lower and middle 70s near Washington and Baltimore.
High pressure over the Atlantic will dominate the weather pattern
for Friday and Friday night. A subtropical ridge will also begin
to edge closer to the area...with the center of the ridge
remaining over the central Conus. The higher heights along with a
southwest flow will cause unseasonably hot conditions for Friday.
Max temps will be in the middle to upper 90s across most
locations...but cooler in the mountains. Do think that there may
be enough of a westerly component to the low-level flow for
dewpoints to mix down into the lower to middle 60s during peak
heating. If this occurs...then heat indices around 100 degrees are
expected. However...higher dewpoints may cause heat indices around
105 degrees and this cannot be ruled out at this time. Very warm
and humid conditions will persist for Friday night.
.LONG TERM /SATURDAY THROUGH TUESDAY/...
Heat will be the primary concern for the extended forecast. Area
will be influenced by westerly flow aloft, an artifact of the
broad ridge stretching across the Conus. Temperatures at 850 mb
will solidly reach 20C, and may even reach 22C. As a result, highs
will be well into the 90s if not approaching 100F.
Inherently there will be plenty of available instability given
the forecast heat. However, skill in forecasting placement and
timing of shortwaves in the extended forecast quite low. That will
be the key in determining which days have a thunderstorm threat.
If the ingredients were to assemble properly, an organized event
will be a possibility. Will refrain from those details at this
A cold front forecast to arrive by the end of the period. The
upper level pattern changes little though, so its effect may be
.AVIATION /07Z WEDNESDAY THROUGH SUNDAY/...
VFR conditions are expected most of the time through Friday night.
Patchy fog may briefly reduce vsbys during the early morning hours
VFR anticipated this weekend under high pressure. Its too early to
deterimine whether there will be a thunder threat.
A weak cold front will stall just to the south today and a
northerly flow is expected behind the boundary. A pressure surge
behind the boundary may cause winds to briefly approach SCA
criteria this morning...but confidence is too low for a headline
at this time. High pressure will build over the area later today
through tonight and winds will be light. An isolated shower or
thunderstorm cannot be ruled out near Smith Point into this
evening...but even across this area most of the time will be dry.
The high will move offshore Thursday and a return flow will
develop. A south to southwest flow will continue for Thursday
night through Friday night. Southerly winds may channel up the
middle portion of the Bay and Lower Tidal Potomac River...causing
winds to possibly reach SCA criteria during this time.
Summertime high pressure, with its heat and humidity, will be
affecting the waters this weekend. Such a pattern favors southerly
channeling late into the evening into the early morning hours.