Scientific Forecaster Discussion
fxus61 klwx 240757
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
357 am EDT Sat Aug 24 2019
a cold front will move into the southern mid-Atlantic today.
Strong high pressure will build north of the region through
early next week. A tropical cyclone could form over the weekend
and move near the southeast coast and out to sea.
Near term /through tonight/...
isolated light rain showers are moving west to east across Nelson
and parts of Albemarle counties in Virginia. Rain amounts will be
only a few hundredths of an inch at best. Aside from the showers,
patches of dense fog have formed in valleys in the Potomac Highlands
and Shenandoah Valley. These are areas where wind has grown calm and
dewpoint temperatures are near 60. Visibility has fluctuated in most
of these areas from around 2 miles to one-quarter mile then back up
to 1 mile. Low confidence in a prolonged period of dense fog but
will closely monitor the situation over the next hour or so to
decide if an advisory will be needed or not.
As for today, high pressure will continue to build to our north and
usher in drier and cooler air than during the early to middle of
last week. Obviously, the cloud cover and light to moderate rain
showers with the passing front on Friday had kept our temperatures
in the 60s throughout the day for the most part. However, we are
anticipating a little more sunshine today that will inevitably lift
our temperatures from the lower 60s to the lower to middle 70s over
most of the region. A few showers can't be ruled out near the
Chesapeake Bay area with a northeast to onshore flow during the
Dry conditions will continue tonight as temperatures drop to the
middle to upper 50s on a light northerly wind and partially clearing
Short term /Sunday through Monday night/...
with high pressure in control to our north and soon to be to our
northeast Sunday into Sunday night, another dry and cool day in
store for US during the period. High temperatures Sunday will be
about the same as today, if not about 3 degrees warmer. The cooler
scenario would rely on whether we have a northerly component to our
wind or an easterly component to our wind Sunday into Sunday night.
Again, a stray shower or two can't be ruled out along the Chesapeake
Bay during the afternoon.
As for Monday into Monday night, the high pressure center makes a
move toward the northeast to allow for an easterly wind and then a
gradual southeast wind. These change in direction will allow for
warmth and moisture to return to the region Monday into Monday
night, primarily the moisture.
Temperatures will still only reach the middle to upper 70s Monday
afternoon. There is a chance that rain showers will develop not just
along the Chesapeake Bay, but in other places as well. Rain amounts
will be light, if they occur.
Long term /Tuesday through Friday/...
coastal low pressure will be sliding offshore Tuesday, increasing
the threat of showers. Onshore flow may provide a bit of a cooler
wedge, but its too soon to rule embedded thunderstorms out-- a small
deviation in the details would allow for sufficient heating. Ample
moisture will be in play, and heights will be dropping by the end of
That trough axis, with a surface cold front, will be crossing the
area Wednesday...making this period the most likely time frame for
precipitation. Given the humidity of the air mass ahead of the
front, thunderstorms also possible, but its uncertain whether there
will be enough upper level support for strong storms.
Continental high pressure will gradually build Thursday-Friday, with
the 500 mb trough axis gradually dampening. Given the low heights,
wouldn't completely rule out a diurnally driven shower on Thursday,
but the trend will deviate toward seasonable/dry conditions by the
end of the week.
Aviation /08z Saturday through Wednesday/...
patchy dense fog has been causing visibility to fluctuate in the
Shenandoah Valley and toward the Mason-Dixon line. Although we are
anticipating IFR conditions near mrb, there is a chance that LIFR
could occur at some point near daybreak. All in all for the
remainder of the terminals, and for mrb from mid-morning on, VFR
conditions are expected with building high pressure. Winds will be
northwest at first becoming northerly then northeasterly over the
course of today, tonight and Sunday.
VFR conditions expected again Monday into Monday night. Any isolated
showers could bring lower ceilings to the taf sites Monday
afternoon. Winds northeast becoming southeast Monday into Monday
Onshore winds Tuesday may bring a marine layer inland. While
confidence in details low, flight restrictions due to ceilings
possible. If low ceilings do form, they would be likely to lift
wednesday; however, as a cold front advances, the threat for showers
and thunderstorms increase. Restrictions on Wednesday likely to
be more brief/spotty in nature.
a Small Craft Advisory is in effect through noon today for all
zones, then for the tidal Potomac and central Chesapeake Bay
this evening and overnight. Additional small craft advisories
may be imminent for the marine zones Sunday afternoon and then
again for Monday. One factor could be the pressure gradient
between the high pressure to the north and northeast and the
developing coastal sub- tropical or tropical low pressure system
over the southeast U.S.
East/northeast winds Tue will become west Wed. At this point, the
strongest winds appear as though they may be associated with
showers/thunderstorms due to a cold front Wednesday.
District of Columbia...none.
Marine...Small Craft Advisory until noon EDT today for anz531>534-537-
Small Craft Advisory from 6 PM this evening to 6 am EDT Sunday