Scientific Forecaster Discussion
fxus61 klwx 240129
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
929 PM EDT Tue Jul 23 2019
a cold front will continue to push south of our region as high
pressure builds into our area Wednesday through this weekend.
Near term /until 6 am Wednesday morning/...
shear vorticity and the right rear quadrant of a jet streak
associated with the deep upper level trough have brought some
showers and isolated thunderstorms to the Potomac Highlands to
central Shenandoah Valley. The intensity of these showers has
been decreasing, but Storm Prediction Center mesoanalysis and 00z iad sounding show
up to 500 j/kg of MUCAPE, so wouldn't be surprised to see a few
showers continue to pop up as the trough axis progresses to the
east. Hrrr solutions have been showing activity to end around
Main rain shield associated with frontal zone/low near southeast Virginia has
now exited south-central Maryland. However, likely some local
convergence and the warm waters of the Bay have been producing
showers offshore of Anne Arundel County. We even received a
report/photo of a needle waterspout earlier this evening.
However, since the convergence is located over the Bay and
steering winds are light, most of these showers should not
affect land. Some models have this shower activity lasting
through the night, but would think increasing northerly winds
due to offshore low pressure will lessen local convergence
effects by late tonight.
Otherwise, clouds should gradually erode from the northwest
tonight. Models are hinting there could be some patchy fog where
it clears out. Lows ranging from the mid 50s west to mid 60s
east look on track.
Short term /6 am Wednesday morning through Thursday night/...
high pressure will build into our region from the west. An
upper trough axis will slowly move across our region from the
west. North to northwesterly flow will continue to transport
into drier and cooler air into region which will lead to cooler
than normal temperatures in the upper 70s to mid 80s. Some
isolated showers can't be ruled out over the higher elevations
due to the trough axis being overhead of our region but a
northerly flow should limit the area coverage. I have kept pops
in the 20s and should be limited to the afternoon periods and
the western part of our forecast area. A coastal low will form
off the frontal boundary to our south and move just off our
coast Wednesday afternoon. The tight pressure gradient from the
passing low may cause some stronger winds over our coastal areas
and eastern Maryland and northern Virginia.
On Thursday, the upper level trough axis will lift eastward out of
region and high pressure will remain over our region. Winds will be
light and variable mainly out of the north. Temperatures will remain
mild in the upper 70s to mid 80s with overnight temperatures
dropping into the upper 50s to mid 60s.
Long term /Friday through Tuesday/...
the long term period will feature an extended period of dry
conditions, along with ample sunshine, low humidity, light winds,
and near normal temperatures.
Heights aloft will rise as high pressure builds overhead on Friday.
In the absence of any disturbances at mid-upper levels, this area of
high pressure will stay in place through the weekend, before
shifting just offshore on Monday. With high pressure in control,
quiet weather conditions are in the forecast. Temperatures will be
near normal, with highs predominantly in the 80s to near 90, and
lows mainly in the 60s.
Aviation /01z Wednesday through Sunday/...
there are some showers associated with a mid level trough axis
that are slowly closing in on mrb and cho this evening but are
weakening. Will amend tafs if needed. VFR ceilings may last a
good part of the night but should be scattering out by Wednesday
with light north winds increasing to 5-10 kt during the day.
All MOS guidance has some sort of visibility restriction in br
at cho late tonight as skies clear, so have inserted MVFR in the
VFR conditions will dominate through Thursday as high pressure
remains over our region.
VFR conditions will persist through the long term period with high
pressure in control.
wind convergence and warm Bay waters are leading to showers
along the Main Channel, especially near Anne Arundel County. We
have received one report of a waterspout, so with conditions
remaining similar, additional waterspouts will remain possible
this evening. As low pressure moves northeast along an offshore
front, north winds will increase late tonight (which would
likely end the waterspout threat), and an Small Craft Advisory GOES into effect
at 3 am, lasting through 2 PM Wednesday.
Sub-Small Craft Advisory conditions expected through the rest of the week as high
pressure builds in.
A prolonged stretch of precipitation free conditions and sub-Small Craft Advisory
level winds is expected this weekend into early next week.
District of Columbia...none.
Marine...Small Craft Advisory from 4 am to 2 PM EDT Wednesday for