Scientific Forecaster Discussion
fxus61 klwx 181509
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
1009 am EST Mon Nov 18 2019
low pressure off the coast will slowly move northeastward into
the western Atlantic through Tuesday. High pressure will then
build to our south during the middle of the week. A cold front
will cross the region by week's end.
Near term /through tonight/...
coastal low pressure will continue to move to the east today
while an upper level trough axis approaches from the west. Low
clouds and visibilities are hanging tough, but winds are slowly
taking a more westerly component, which should lead to improving
conditions through the midday hours. However, it's still
unlikely we see much sun through the day. Have thus lowered high
temperatures by a couple degrees or so across the board...in the
The upper disturbance will then work its way across the region
late this afternoon and this evening, and guidance has become
much more consistent with developing showers with it, so have
went likely with pops. This system then moves out overnight, so
expect it to dry out towards morning, though we will need to
watch for patchy fog or even black ice late tonight. There could
also be some light wintry precipitation in the upslope areas,
but probabilities are low...will take a closer look at new
guidance. Lows tonight will be dropping a bit more towards or
below freezing tonight thanks to potential for the clouds to
Short term /Tuesday through Wednesday night/...
a more Pacific-type air mass will dominate Tuesday through
Wednesday night, with highs returning to the 50s. Lows will
remain in the chilly 30s, but by this time of year this is
getting to be less abnormal. A weak cold front will cross the
region Tuesday night into early Wednesday, and a few upslope
snow showers could occur with it along the Allegheny Front, but
overall, midweek will feature improvement in the weather
compared to the last several days.
Long term /Thursday through Sunday/...
high pressure over the region Thursday will move offshore the
East Coast Thursday night. A warm front will move northward
across the region Thursday night and could bring a brief rain
shower or two to the northern Potomac Highlands or Mason-Dixon
region. Otherwise, most areas will remain dry.
Through the day Friday, a cold front will push through the
region and then move off to the southeast Friday night. An
increased chance of rain showers is expected in the western and
northern zones during the day Friday. The chance for rain
showers will evolve in the southern and eastern zones late in
the day into Friday evening as the cold front plunges
Cooler and drier air will follow the front Saturday through
Sunday as high pressure builds in from the west. There could be
some upslope rain or snow showers in the Potomac Highlands on
Saturday, but for the most part, areas will be dry with a chilly
Aviation /15z Monday through Friday/...
low level moisture continues to present this morning. Have
actually seen lowering cigs (and vsbys in some cases) this
morning, contrary to what guidance is suggesting. Winds should
be taking on a more westerly component through the day, so am
still expecting at least the IFR conditions to improve shortly.
Guidance suggests that drier air should work southward later
today, allowing cigs to rise further. However, another
disturbance will bring some showers into the region late this
afternoon and this evening, which may present sub-VFR vsby and
perhaps a brief return of sub-VFR cigs. If winds go light and
skies clear late tonight, fog may also become a concern. VFR
should then return Tuesday and persist through Wednesday night.
VFR conditions at the terminals Thursday and Thursday evening.
Brief MVFR conditions possible Thursday night at mrb and iad,
depending on the coverage of any rain showers or patchy fog. VFR
conditions again Friday with exception to any showers near mrb
and iad in the afternoon or dca and BWI in the evening. Winds
south to southwest 5 to 10 knots Thursday and Thursday night.
Winds southwest becoming northwest late Friday at 10 knots with
have already cancelled a large portion of the Small Craft
Advisory this morning, and will likely be able to do likewise
for the remainder soon. Winds have been diminishing quickly as
the coastal low pressure pulls farther away. As pressure
gradient should remain fairly light tonight through Tuesday
night, expect sub- Small Craft Advisory winds, though some showers may affect
the waters tonight. Winds may increase again on Wednesday behind
a weak cold front, so sca's may be required.
No marine hazards expected Thursday through Friday. Small
craft advisories possible Friday night. Winds south around 10
knots Thursday and Thursday night. Winds becoming southwest 10
to 15 knots Friday, then shifting northwest 10 to 20 knots
anomalies remain steady since last evening, and flooding looks
unlikely with this tide cycle. However, as northerly flow
diminishes, the high anomalies of over 2 feet are likely to
spread northward up the Bay as the water levels attempt to
equalize. Thus, maintained the watches for Straits Point and
Annapolis for this afternoon/evening. Assuming the anomalies do
spread northward, additional advisories are likely, though am
uncertain about the need for warnings. By early Tuesday,
anomalies should start to drop again as the excess water at the
bay's mouth finally diminishes, so flood threat should wane.
District of Columbia...none.
Maryland...coastal Flood Watch from 6 PM EST this evening through late
tonight for mdz014.
Coastal Flood Watch from 3 PM EST this afternoon through this
evening for mdz017.
Marine...Small Craft Advisory until 6 PM EST this evening for anz534-