Scientific Forecaster Discussion
fxus61 klwx 161853
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
253 PM EDT sun Jun 16 2019
a cold front will stall out near the area tonight and remain in
the mid-Atlantic region through much of the upcoming week. This
will lead to a prolonged period of unsettled weather.
Near term /through Monday/...
for the afternoon and evening, we continue to watch a shortwave
moving into and through the County Warning Area. Cloud cover has recently
developed in the I-81 corridor but (as of 1800 utc) there was
still fairly little on radar. Although guidance has not been
much help, I do think we will see rain showers/thunderstorms and rain development
increase, especially by and after 4 PM. As mentioned in the
previous discussion, we have 30-40kt bulk shear and some modest
MLCAPE that is projected to reach around 1000 j/kg.
The question for the rest of the afternoon is can something get
going and organized during peak heating. If it does, damaging
wind gusts will be the primary threat in robust storms between
now and 8 PM. The Storm Prediction Center Maryland issued for this region says everything
else i'd type here, so i'll save the space.
This afternoon's shortwave is the first in a series that will
ultimately affect the region for several days. Looking west on
radar, there's more activity upstream. So while the severe risk
will wane, the chance for showers and perhaps a thunderstorm
continues throughout the night. Even with that, model output
varies wildly on when breaks in the rain will occur, making it a
challenging forecast for timing any breaks.
Monday morning is uncertain for the same reasons as above, but
there's actually reasonable consensus in a shortwave coinciding
with peak heating tomorrow afternoon, sparking showers and
thunderstorms. The difference is that the "lineup train" will be
in place by that point as the surface front sags toward (or
into) the area, and moisture will have further increased. Thus
not only is severe weather possible but the risk for flooding or
flash flooding is increased as well. Did not yet issue a Flash
Flood Watch because i'd like to see where that front gets to and
where the upstream rain is going to point, to aid in confidence
in where to issue the watch -- rather than just blanketing the
entire area 24 hours out.
Short term /Monday night through Tuesday night/...
we remain largely in the same setup as Monday, through Tuesday
night, with the surface front in the vicinity, and westerlies
spreading energy into and through the area. As we get repeated
rounds of activity, the flood/flash flood threat will persist
(and preceding rain might increase its likelihood by Tuesday
afternoon). The severe storm threat is non-zero but decreasing
as shear decreases and heating may be suppressed depending on
timing of mcss/decay cloud cover.
Long term /Wednesday through Sunday/...
active convective pattern will continue through Thursday, as a
stubborn stalled frontal boundary lingers near/north of the area.
Meanwhile, high pressure over the Atlantic continues to funnel warm
and moist air into the region. This will feed shower and
thunderstorm development each afternoon.
Some relief is possible by Friday however, as a stronger low
pressure system is expected to bring a cold front through and sweep
out this unsettled pattern. A little bit of uncertainty amongst the
guidance as to exactly when that occurs, so will carry pops into
early Friday afternoon, but after that, seems likely that the area
dries out. If not Friday, then definitely drying out for Saturday.
Canadian high pressure will build into the region behind the
aforementioned cold front, leading to dry conditions and decreased
temperatures and humidity. Rain chances return by Sunday.
Aviation /18z Sunday through Friday/...
still a fair amount of uncertainty in the aviation forecast for
the early part of the taf period. Could see development of
rain showers/thunderstorms and rain this afternoon, especially at BWI/mountain and perhaps
dca/iad/cho. The convective window might already be closing at
mrb for the afternoon unless a secondary line develops.
Certainty isn't high enough to include much in the tafs yet, but
storms that do develop will have potential for gusty winds and
particularly vsby restrictions, if they pass near/over a
Potential for rain showers overnight, but not high enough probability to
mention in the taf. Could see clouds break in between systems
long enough to promote patchy fog development, mainly at cho and
mrb, given light/calm winds. Monday, rain showers/thunderstorms and rain develop by early
afternoon. Ultimately, vsby restrictions and gusty winds and
heavy rain seem likely at some point during the afternoon or
evening, though only for part of the time. Same situation on
Generally expecting VFR conditions to prevail throughout the
Wednesday/Thursday timeframe. However, thunderstorms will be a
concern in the afternoon/evening hours both days, which could also
bring cig/vsby reductions, and perhaps even gusty winds.
still seeing gusty winds above Small Craft Advisory criteria south of the Bay
Bridge and south of the nice bridge, with isolated gusts above
Small Craft Advisory north of those points. There are some land-based gusts to
the west at 20 kts, so i'm leaving the Small Craft Advisory up for all waters
through 9 PM, and then tapering to the lower Potomac and Bay
after that. The waters -- especially the northern waters -- have
perhaps the best chance of showers and storms this afternoon and
there could be special marine warnings issued for gusty winds.
Winds decrease on Monday. A couple gusts to Small Craft Advisory criteria can't
be ruled out on the open waters of the lower Maryland Bay, but
confidence is too low to raise a headline. Showers and storms
are expected Monday afternoon and evening with special marine
warnings possible once again.
Winds will generally remain below Small Craft Advisory criteria on Wednesday and
Thursday. However, with thunderstorms expected each afternoon, gusty
winds can be expected as these cross the waters, so special marine
warnings will probably be needed.
concern is increasing about flood/flash flood potential; not so
much today, but moreso Monday and Tuesday. Moisture is not as
significant or deep as we might typically like, but having a
stalled front in the area does mean there's an increased
likelihood of training thunderstorms and thus perhaps some
For now, we are watching what's happening upstream, and waiting
to see where the surface front ends up tonight. Since the
activity is convective in nature and these weak impulses don't
lend themselves to high confidence well in advance -- plus we
currently have relatively high flash flood guidance -- I have
elected to wait and see how today plays out. From a flood
perspective, Tuesday might actually have a higher potential than
Monday (with monday's rains serving as the primer).
District of Columbia...none.
Marine...Small Craft Advisory until 9 PM EDT this evening for
Small Craft Advisory until 8 am EDT Monday for anz534-543.
Small Craft Advisory until 1 am EDT Monday for anz537.