Scientific Forecaster Discussion
fxus61 klwx 132047
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
447 PM EDT sun Oct 13 2019
a weak area of high pressure will hold through the first half
of the week. A strong cold front will cross the area Wednesday
afternoon followed by high pressure for the second half of the
Near term /until 6 am Monday morning/...
an upper level disturbance over the Carolinas this afternoon
will cross the Virginia Tidewater early this evening. A couple
of clusters of showers have been noted south and east of District of Columbia thus
far. Looking at regional radar across Virginia and North
Carolina believe coverage will increase, but won't necessarily
be widespread. Have likely pops at best across southern
maryland; chance pops across central Virginia and in Maryland
north to about US rte 50. Rainfall should be pulling out during
the evening hours, but a few drops may last past midnight along
Skies will clear in the wake of this system (the Potomac
Highlands already has considerable sunshine). Will little wind,
radiational cooling will transpire once again. Have shaded temps
down across The Highlands, Shenandoah Valley, and northern
Maryland once again tonight. Meanwhile, there may be south
lingering low-level moisture for patchy fog south/east of District of Columbia.
Short term /6 am Monday morning through Tuesday/...
high pressure will prevail Monday through Tuesday with light
winds and scant moisture. Expect mostly sunny each day and clear
at night. This may be an opportunity to raise daytime temps
above guidance based on recent model trends.
Long term /Tuesday night through Sunday/...
a strong upper level trough will shift into the mid-Atlantic and the
northeast US on Wednesday. This trough will bring along a strong
surface low and its corresponding cold front through our region on
Wednesday. The surface low will stay to our north in Canada and New
York. Another surface low is expected to form over the southeastern
US and make its way northward early on Wednesday. There is decent
agreement on the surface low remaining to our south and moving
through northern North Carolina and southern Virginia. If this
coastal low moves further north, our region could experience
increased precipitation on top of what is expected as the cold front
moves through our region. Timing at this time looks to be mid
morning through late Wednesday afternoon for precipitation. There is
expected to be a lot of shear associated with this frontal passage
with model guidance indicating near 50 knots of shear possible. I
have included an isolated chance for thunderstorms during the
afternoon periods on Wednesday as this when the upper level
disturbance is expected to move through our region providing some
lift which could allow some thunderstorms to kick off. Since shear
values will be elevated you can't rule out a severe threat but it
should remain limited. First guess from models have around inch of
precipitation during this period but locally higher amounts will be
possible especially if the coastal system shifts further northward.
We will need to monitor the trend of both low pressure systems but
the main threats seems to be rain with isolated thunderstorms.
The cold front is forecast to be through our region by late
Wednesday afternoon. The pressure gradient associated with this
system will likely lead to increase threat for strong gusty winds
especially over our coastal waters in the tidal Potomac and the
Chesapeake Bay. There will be the potential for gale force winds
Wednesday afternoon and into Thursday. Behind the frontal passage,
high pressure will build back into our region from the west and
linger through the weekend. Temperatures will be much cooler behind
the frontal passage with highs in the 60s Wednesday and Thursday.
Overnight lows Wednesday into Thursday look to be cool in the 40s
but the coolest evening looks to be Thursday night as lows could
drop down into the mid to upper 30s to low 40s. Near 32 temps could
be possible over our higher elevations. A slight warming trend is
forecast for the weekend with highs in the low to mid 70s and
overnight lows in mid to upper 40s to 50s.
Aviation /21z Sunday through Friday/...
as an upper level disturbance slides southeast of the terminals,
guidance suggested that VFR will prevail. However, have noted
numerous metar sites dropping into MVFR since noon. Latest tafs
may need an amend shortly if these trends continue. Think that any
showers should avoid the terminals, but residual low level
moisture would provide (another) opportunity for flight
restrictions. Aside from a touch of 5sm br predawn, kept this
threat southeast of the terminals as well...something else to
VFR should prevail Monday-Tuesday under high pressure.
A cold front moving through our region on Wednesday will likely lead
to some subvfr restrictions due to widespread rain. Some gust winds
out of the west to northwest will be possible behind the cold
frontal passage Wednesday into Thursday. Skies are expected to clear
Wednesday evening into Thursday. VFR conditions expected for
Thursday at this time.
winds presently less than 10 kt. The pressure gradient will remain
light though Tuesday.
A strong cold front will traverse the coastal waters Wednesday
afternoon. The pressure gradient will likely require the need for at
least small craft advisories but gale warnings can't be ruled out as
gusts will like be near or just above the 30 knot threshold.
Advisories and gale warnings may need to be extended into Thursday
behind the frontal passage.
tidal departures have been decreasing substantially today. Tides
will continue to decrease tonight into tomorrow. No more coastal
flood warnings are in effect (saint mary's County converted to
District of Columbia...coastal flood advisory until 2 am EDT Monday for dcz001.
Maryland...coastal flood advisory until 1 am EDT Monday for mdz011.
Coastal flood advisory until 8 am EDT Monday for mdz014.
Coastal flood advisory until 6 am EDT Monday for mdz017.
Virginia...coastal flood advisory until 2 am EDT Monday for vaz054.