Scientific Forecaster Discussion
fxus61 klwx 170907
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
407 am EST sun Nov 17 2019
a strong area of low pressure will linger off the Carolina
coast today, slowly inching to the northeast. Meanwhile, a
strong area of high pressure shifts east into the Canadian
Maritimes, keeping chilly air over the region. A milder Pacific
high pressure will then build into the region from the west
in the middle portion of the week before another cold front
approaches towards the end of the week.
Near term /through Monday/...
latest surface analysis shows low pressure barely moving over
the Gulf Stream southeast of the Carolina coast. Meanwhile,
chilly high pressure is sitting over northern New England.
A cold front is crossing the northern and Central Plains, with
another high pressure centered over the intermountain west.
Today the main player will be the coastal low, with some
influence from the high to the north. Dry air dominates thanks
to the high, so no precipitation is expected, but warm advection
around the low has allowed clouds to overspread the region, and
we expect these to persist through the day. Thus, cloudy and
cool weather should predominate, with highs stuck in the 40s.
The breeze should be a little weaker overall today, but still
noticeable, as the gradient relaxes thanks to The Wedge of high
pressure building southward across the inland regions.
Tonight the low will continue slowly pushing northeast and
should be abeam of Virginia Beach by early Monday morning. The
risk of a few showers creeping into our eastern zones will
increase, but again, odds favor dry weather. The high will
continue sliding east to our north, leaving a cut-off air mass
over our region with a lingering wedge. Between the detached
nature of this air mass, clouds, and increasing ocean
influence, lows tonight should be a bit milder than Saturday
night's, with much of the region staying above freezing.
The cold front over the plains currently will reach our region
on Monday as the coastal low pushes northward towards the
Canadian Maritimes. The high pressure wedge will break down over
our region, and a shortwave aloft may help generate a few
showers, but the odds of precip remains well below 50 percent.
With the high pressure ridge locally breaking down thanks to the
front pushing in from the west, highs should moderate somewhat
despite the clouds, with temps approaching 50.
Short term /Monday night through Tuesday night/...
the coastal storm will be long gone by Tuesday, and clouds
should generally be decreasing in its wake Monday night. Any
lingering showers early, which are not likely, should also
quickly move away from the region. Some sun should be present
as a weak high pressure of more Pacific origin moves into the
region, and this should allow temps to rebound into the 50s.
Another weak cold front will then cross the region Tuesday
night, but there is very little forcing and moisture with it.
Thus, while a few upslope rain/snow showers are possible, most
of the region should see little if any effect from this front.
Lows both Monday night and Tuesday night will be in the 30s
across most of the area.
Long term /Wednesday through Saturday/...
high pressure will build into the region and sponsor dry
conditions Wednesday through Thursday morning.
As high pressure moves to the East Coast Thursday, a cold front
will plunge southeastward late Thursday and Thursday night.
This front will bring a chance for rain Thursday night and
The cold front should pass to our east and across the Delmarva
Peninsula Friday afternoon. Cooler and drier air will filter in
during the day. There could be some upslope rain or snow showers
Friday and perhaps Saturday in the Potomac Highlands and
perhaps the Blue Ridge mountains.
Aviation /09z Sunday through Thursday/...
clouds rotating into the region from the southeast thanks to the
coastal storm are producing some high-end MVFR cigs at times,
intermingled with low-end VFR cigs. This likely continues much
of the day given that the pattern won't change much. Cigs may
then lower tonight as the low passes to the east and more
moisture advection occurs, but since no rain is expected, cigs
should stay MVFR at lowest and vsby restrictions are not
expected. Cigs likely start to improve later Monday as the
system starts pulling away, with VFR likely Monday night thru
VFR conditions Wednesday through Wednesday night. Winds
northwest around 10 knots, then light and variable at night.
Winds becoming southerly 5 to 10 knots.
winds have mostly diminished below gale force and while a few
stray gusts to 35 knots are possible over the Middle Bay, it
should be primarily Small Craft Advisory levels. Thus, after coordination with
neighbors, decided to cancel the gale and go with high-end Small Craft Advisory
thru Monday. More sheltered/inland portions of the waters will
start to see the Small Craft Advisory drop off before then as the low gradually
pulls northeast and the gradient diminishes, with all waters
likely below Small Craft Advisory Monday night through Tuesday night.
No marine hazards expected Wednesday through Thursday night.
Winds northwest around 10 knots Wednesday night. Winds light and
variable Wednesday night becoming southerly around 10 knots
Thursday into Thursday evening.
onshore flow near the mouth of the Bay has helped build very
large anomalies near Norfolk, and despite the northerly flow
over our portion of the Bay, these anomalies are spreading up
from the south. Thus, while the current cycle likely stays below
minor flood thresholds, the next few cycles will have
significant risk of minor flooding. Anomalies may continue to
increase tonight and Monday as the winds diminish, so while am
not confident enough to raise a coastal Flood Watch yet, would
not be shocked if we need to. However, current forecast keeps
all sites at minor flood levels, if rather high into minor in
some places. Tide levels likely start to drop by Tuesday.
District of Columbia...none.
Marine...Small Craft Advisory until noon EST Monday for anz532-533-
Small Craft Advisory until midnight EST tonight for anz530-538.
Small Craft Advisory until 6 PM EST Monday for anz534-537-543.
Small Craft Advisory until 6 am EST Monday for anz531.
Small Craft Advisory until noon EST today for anz535.
Small Craft Advisory until 6 PM EST this evening for anz536.