Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 220057
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
857 PM EDT Fri Apr 21 2017

.SYNOPSIS...
A cold front push southeast across the region tonight. The
front will stall to the south Saturday and low pressure will
develop along the boundary...impacting our area for the weekend
through early next week.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
The cold front appears to be near the Blue Ridge at this hour.
The last of the severe weather consolidating over the Northern
Neck and Virginia portion of the Chesapeake Bay. The remainder
of the evening and the first part of the overnight should be
dry. Frontal passage will be marked mainly by a wind shift.
However, upon widening the focus, additional showers and
thunderstorms can be found across eastern Kentucky and western
Virginia. These showers/storms will be riding along the frontal
boundary. Although instability will be gone, the precipitation
likely will arrive late in the overnight/pre-dawn. Am
maintaining chance PoPs (for showers) to account for this
activity...especially southwest of the Potomac River.

Temperatures will be mild this evening, but will be dropping
into the 50s overnight. Will be touching up low temperature
forecast shortly.


&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/...
The front stalls in the Carolinas Saturday as a slow moving wave
of low pressure moves eastward along it. High pressure nosing in
from the north may produce a dry period Saturday especially in
Maryland, but chance of rain extends through the day, with
greater risk as one heads further south and west. By Saturday
night, rain looks likely as the low approaches and some decent
FGEN develops over our region. This FGEN and the low itself may
shift southward on Sunday as a shortwave passes to our north,
displacing it, but the low is then expected to start pushing
back north Sunday night, ending any gap in the rain by the end
of the night. Given continuing uncertainty among guidance as far
as timing and amounts of rainfall, have not added any flood
mention to HWO yet, but certainly if some areas get the rain
modeled, we could have one. The question is whether several
inches of rain can indeed fall over any one area over the next
few days.

With cool Canadian high pressure wedging southward on the east
side of the mountains and the air mass becoming saturated with
the nearby front and approaching low, the weekend will be quite
cloudy and cool, with temperatures below normal. Sunday looks
like the coolest day, with highs likely to get stuck in the
50s. Temperatures Saturday will be rainfall-dependent, but may
also be stuck in the 50s. Lows at night will probably nudge into
the 40s.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Low pressure along the southeast coast will remain cutoff from
the jet stream and slowly drift northeastward early next week,
keeping the area in a cool and dreary pattern. The wind and
subsequently the temperatures do an about-face around midweek
with significantly warmer temperatures (possibly near 90) by
next weekend. One interruption in the warming trend will be a
front boundary that may clip the region Thursday. Other than
that, temperatures will start the week at levels more typical
for early March, and end the week at levels more typical for
late June.

&&

.AVIATION /01Z SATURDAY THROUGH WEDNESDAY/...
All thunderstorms have pushed south/east of the terminals. We
are in a VFR period at this time, and it should last into
Saturday morning.

Rain will spread back into the area as we head through the day
with lowering cigs and vis returning. Tempered the restriction
forecast for Saturday. Focused on the higher confidence MVFR.
IFR still possible, with increasing likelihood as we progress
through the weekend. In fact, its looking like a significant
period of IFR will be possible Saturday night into Sunday night
with northeast winds.

Sub-VFR likely early next week with low clouds/northeasterly
onshore flow around 10 knots.

&&

.MARINE...
Thunderstorm risk continues across the lower Tidal Potomac and
mid Chesapeake Bay, but this threat will be waning as the storms
continue to travel east ahead of a cold front. The front should
cross the waters late evening for the upper waters, and just
after midnight for the mid Bay/lower Potomac.

Rain will spread back across the waters Saturday. Believe this
will provide a stabilizing layer, and thus am forecasting
winds under the Small Craft Advisory threshold for Saturday and
Saturday evening. Better risk of SCA Sunday as low pressure to
the southwest starts to intensify, increasing the gradient.

Northeasterly flow between high pressure to the north and low
pressure to the south may result in Small Craft Advisory level
gusts across the waters early next week.

&&

.TIDES/COASTAL FLOODING...
A persistent onshore flow will develop behind a cold front
Saturday through early next week. Elevated water levels are
expected during this time...and minor flooding cannot be ruled
out near times of high tide...especially Sunday into Tuesday.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...None.

&&

$$
SYNOPSIS...RCM
NEAR TERM...HTS
SHORT TERM...RCM
LONG TERM...DFH
AVIATION...HTS/RCM/DFH
MARINE...HTS/RCM/DFH
TIDES/COASTAL FLOODING...BJL



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