Area Forecast Discussion
Issued by NWS Sterling, VA
FXUS61 KLWX 181839
Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
239 PM EDT Sun Sep 18 2016
A weakening cold front will approach from the northwest through
the remainder of today before stalling and dissipating over the
region tonight through Monday night. High pressure will build into
the region for mid to late week.
.NEAR TERM /THROUGH MONDAY/...
Weakening frontal system continues its gradual push southeastward
towards the region as Tropical Depression Julia spins off of the
North Carolina coastline. Out ahead of the front, widespread
showers and possibly a thunderstorm will make their way into
western portions of the region over the next couple of hours. Some
scattered activity make it towards the I-95 corridor, but most
locations in that region likely to remain dry through the
remainder of the daylight hours. Precipitable water values out
there this afternoon are around 1.75 inches, so locally heavy
rainfall is possible.
Front will make slow progress eastward through the region tonight,
before washing out over the area on Monday. As it moves eastward,
will see a moisture surge from Julia get picked up along the
front, with precipitable water values surging to over 2 inches
from the metros eastward late tonight and on Monday. Best signal
in terms of moisture convergence, deformation, and omega fields,
for widespread showers and embedded thunderstorms shifts from
western areas this afternoon/evening to the metro areas tonight to
metros and east on Monday. Jet dynamics also become more favorable
on Monday as region is projected to lie in the right entrance
region of the upper jet.
All of this means that showers/embedded thunder move eastward
through the region tonight, and remain/intensify late tonight and
Monday from the I-95 corridor eastward. There may be a lull in the
activity during the late evening and first half of the night. Thus
expecting two main foci for heaviest rainfall amounts, first in
western areas this afternoon and evening, and a second late
tonight and tomorrow from DC/Baltimore south and east. Total
rainfall area- wide generally 0.5-1.5 inches, locally higher in
any areas that see repeated convective activity. Greatest threat
for that will be in the 2 areas mentioned above. Because of dry
antecedent conditions, flash flood guidance values are quite high,
from about 2-3" in 1 hour to 3-5" in 6 hours, so flash flood
threat remains low, however can`t rule out something isolated.
Shower activity tapers off a bit by Monday afternoon, especially
western areas. Lows tonight in the mid 60s to low 70s, with highs
Monday in the 70s to near 80F.
.SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/...
With frontal boundary washing out and dissipating near the region
and the remnants of Julia still meandering off of the Carolinas,
will see at least a chance for some rain showers continue into
Monday night and Tuesday across our southern and eastern regions.
High pressure should finally start to push southward into the area
by Tuesday night. Lows in the 60s and highs in the 80s for
.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
Surface high pressure keeps dry conditions over our region
Wednesday into parts of Saturday. Cold front pushes south Saturday
into Sunday, which could bring precipitation into our area. High
temperatures will be above normal... in the upper 70s and low 80s.
.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
VFR at all TAF sites this afternoon. MVFR and possibly some
localized IFR conditions then likely again later tonight and into
Monday with showers and a few thunderstorms moving into the
region. Conditions should improve gradually by Monday night with
VFR returning Tuesday.
VFR conditions expected Wednesday into Friday with high pressure
dominating conditions over our area.
Southerly winds from 5-15 knots expected through the rest of the
afternoon. Later this evening and tonight, expect an increase in
southerly flow, with SCA conditions likely. Thus have issued a
Small Craft Advisory for portions of the lower tidal Potomac and
Chesapeake Bay from 6PM-6AM. Showers/t-storms also expected later
tonight and into Monday. Winds taper back off for Monday through
High pressure keeps light winds and dry conditions over our area.
Therefore, small craft advisory conditions not expected Wednesday
into Friday as winds will be below 15 kts.
South flow across the waters has maintained positive water levels
of 0.75 to 1.0 ft above astronomical prediction (normal). Minor
coastal flooding is expected to continue at the sensitive sites in
Anne Arundel and St. Mary`s County for at least one more high tide
cycle. Coastal flood advisories continue at this time for Anne
Arundel and St. Marys counties, and may need to be extended
further. DC/Alexandria sites will need to be monitored for
possible minor flooding as well.
MD...Coastal Flood Advisory until 11 PM EDT this evening for MDZ014.
Coastal Flood Advisory until 8 PM EDT this evening for MDZ017.
MARINE...Small Craft Advisory from 6 PM this evening to 6 AM EDT Monday