Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus61 klwx 170136 

Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
836 PM EST Sat Nov 16 2019

a strong area of low pressure will linger off the Carolina coast
through Sunday, slowly inching to the northeast. Meanwhile, a
strong area of high pressure shifts east into the Canadian
Maritimes, pushing cooler air into the region. High pressure
will then build into the region from the west into the middle
portion of the week before another cold front approaches towards
the end of next week.


Near term /until 6 am Sunday morning/...
coastal low pressure will strengthen off the southeast coast
tonight while high pressure remains over New England. The high
will wedge south into the mid-Atlantic during this time.

An easterly flow at the low-levels will allow for some moisture
from the Atlantic to overrun the surface northerly flow in
place. This will allow for an increasing stratus deck across
most areas. Min temps will range from the 20s across most
locations to the lower 30s near and east of I-95. Did lean
toward the warmer side of guidance across eastern areas thinking
that cloud cover and a gradient wind should keep temps up.
Therefore, the coldest temperatures are expected in the valleys
west of the Blue Ridge mountains where cloud cover will hold off
the longest.


Short term /6 am Sunday morning through Monday night/...
a steady northerly breeze expected on Sunday, but will be less
intense than Saturday, as low pressure slides by well offshore.
However, this will be the closest pass of this coastal low, so
could see some rain along the Chesapeake Bay, but best chances
are still off to the east. Can't rule out a passing shower
though. Temperatures likely a couple degrees cooler on Sunday,
with more clouds around.

Flow turns a little more northwesterly Sunday night, with more
clouds around as well, so temperatures may moderate a bit, with
lows in the low to mid 30s. Low-end rain chances continue along
the Chesapeake Bay, but find it hard to believe anything makes
it any farther west than that, as the coastal low remains well

By Monday morning, any chances for precipitation should be
shifting off to the northeast. Some rain is possible over
northeastern MD, as a piece of shortwave energy swings through,
which is also what is pushing the coastal low farther away from
the area. However, in the wake of this shortwave, some upslope
showers are possible in the normal areas along/west of the
Allegheny Front. These could mix with some snow during the
morning hours, but should primarily be rain, given temperatures
mostly above freezing a few hours after sunset. Slight chance
for that at this point though, and best chance for any snow will
be for the highest elevations.

Precipitation should be over with across the entire forecast
area by Monday evening. Though, am carrying slight chance pops
in the far northwest portions of the cwa, as there is some
uncertainty as to just how quick the coastal low moves away.
Clouds likely linger into Monday night, with lows in the low to
mid 30s.


Long term /Tuesday through Saturday/...
the base of a mid to upper level trough will pivot through the
region Tuesday and Tuesday night, delivering a fair amount of cloud
coverage but not much in the way of precipitation with a weak and
diffuse frontal boundary nearby. Temperatures will remain near
normal for the middle of November.

By Wednesday, high pressure over the southeast will build northward
across the mid-Atlantic through the first half of Thursday before
shifting offshore. This will lead to continued dry conditions and
near or slightly above normal temperatures. An area of low pressure
originating near The Four Corners region Wednesday looks poised to
track into the Great Lakes on Thursday. This will push a cold front
into the Ohio Valley Thursday night into Friday, bringing our next
chance of appreciable precipitation. Given it's day 7, there is some
model discrepancy in the timing of the front and the arrival of
colder air in its wake. For now, will advertise precip of the liquid
variety as temperatures remain slightly above normal.


Aviation /02z Sunday through Thursday/...
VFR conditions will continue through late this evening, but a
stratus deck around 5kft will increase. The stratus deck will
continue to increase overnight from east to west, and MVFR cigs
are expected toward morning. The MVFR cigs may continue for much
of Sunday, but cigs will likely be closer to 3kft.

Winds gusting 15-20 knots from the north to north-northeast possible into
Sunday at dca, BWI and mtn, before finally beginning to taper
off into Sunday night. Some rain possible overnight Sunday into
Monday, as coastal low pressure makes its closest pass to the
region, though chances are very low. Also during this time, any
lower cigs will start to push northeast of the area into Monday
morning. So, VFR conditions will then be expected on Monday.

VFR conditions expected Tuesday and Wednesday as high pressure
builds over the terminals. Light westerly winds on Tuesday will
shift west-northwest Wednesday and increase to around 10 knots with gusts up to
20 knots Wednesday afternoon.


gusty northerly winds continue over the waters, especially for
the middle Chesapeake Bay and lower tidal Potomac River. A Gale
Warning remains in effect through Sunday south of Drum Point
along the Bay and south of Cobb Island along the Potomac River.
An Small Craft Advisory remains in effect for the rest of the waters during this
time, but it will be marginal for tonight over the upper tidal

Small craft advisories will likely need to be extended into
Monday morning on the Chesapeake Bay. Winds begin to taper off
Monday afternoon.

Sub Small Craft Advisory conditions expected Tuesday and Tuesday night as winds
remain at 15 knots or less. Gradient increases on Wednesday as we
reside between exiting low pressure well to our northeast and
building high pressure to the south. Thus Small Craft Advisory conditions will be
possible over the waters Wednesday and Wednesday evening.


Tides/coastal flooding...
complex tidal forecast over the next few days with coastal low
moving slowly off the coast, as north/northeast winds try to push
water southward while the tidal surge with the low pushes excess
water into the Bay. This is already on display this evening,
with water closer to near normal on the Northern Bay, and two
feet above normal at Norfolk. At the moment, the opportunity for
flooding looks minimal until at least the third high tide
cycle, so no advisories at this time. On Monday, there may be a
"snap- back" as winds lighten and excess water on the southern
Bay is allowed to surge northward. Don't have the confidence for
moderate thresholds to be reached to issue any coastal flood
watches yet.


Lwx watches/warnings/advisories...
District of Columbia...none.
Marine...Small Craft Advisory until 6 PM EST Sunday for anz530>533-535-
Gale Warning until 6 PM EST Sunday for anz534-537-543.


near term...bjl/cjl
short term...cjl

National Weather Service Glossary of Abbreviations