Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 130806
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
406 AM EDT Fri Apr 13 2018

.SYNOPSIS...
High pressure will build across the western Atlantic through
Saturday. A large area of low pressure over the Central Plains
will move northeastward into the eastern Great Lakes by Sunday,
dragging a powerful cold front across the Mid-Atlantic Sunday
night and early Monday. High pressure will return for the middle
portion of next week.

&&

.NEAR TERM /THROUGH SATURDAY/...
Surface high will remain to our east through Saturday. A weak
disturbance is passing by to the north early today, and some
clouds or even a stray shower isn`t impossible, but most of the
region should be dry. By midday this disturbance will have
passed well to our northeast and it should turn out mostly
sunny. Temperatures aloft are continuing to warm, however the
pressure gradient has relaxed, so while today will be warmer, it
will be a bit less windy, with gusts mainly in the 20-30 mph
range as opposed to yesterday`s 30-40 mph gusts. With 850s
continuing to climb and plenty of insolation especially by
afternoon, highs should soar into the 80s across most of the
region. Have generally gone low 80s, but if max mixing is
realized, we could end up a little warmer than currently
forecast.

Tonight and Saturday, the high will remain to the east and
southwest flow will continue to dominate, but increasing
moisture advection will start to result in more cloudiness. This
won`t be noticed much tonight, but as we head through Saturday,
the trend will be increasing high and potentially mid clouds.
This may result in reduced insolation and thus keep temps a
little lower than today`s. With the gradient just a little
weaker once again, expect winds to be a little lighter once
again, but still breezy in the afternoon.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/...
Systems will be converging on the region during the short term.
The first of these will be a backdoor cold front sliding
southwest from the Northeast. This will start ending the region
late Sunday night, and really push across much of the region by
later Sunday, which when combined with increasing clouds and
developing showers ahead of the other storm, will result in a
cooler day, especially for the northeastern portions of the CWA
in Maryland. Highs in the far south may still approach 80, but
in parts of MD it will likely end up stuck in the 60s.

Speaking of the other storm, that system will be approaching
from the west on Sunday. As the backdoor front drops south, the
surface cold front to the west will approach, and a triple point
low looks to form where they meet. This will likely cross our
CWA, potentially enhancing rainfall. Besides this, the system
aloft will be going negative tilt, and there is quite a flow of
moisture that it will be pulling in from the south. Suffice it
to say, the potential for widespread heavy rain is significant.
That having been said, it has been rather dry of late, with most
of the CWA having had less than an inch of rain in the last two
weeks. Given the potential for maximum rainfall near the spine
of the Appalachians, one of the few areas which has seen
significant precip recently, will mention potential flooding in
the HWO for these areas, but have inserted mention of heavy
rainfall everywhere. With limited instability north of the
backdoor front, do not expect widespread significant t-storms,
but elevated CAPE and forcing with the front could certainly
result in isolated thunder as it crosses the region Sunday
night. Lows will remain relatively mild Sunday night as the
system comes through, with 50s most areas, but near the
Allegheny Front temps will drop back into the 30s late, behind
the front.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
A cold front will be pushing away from our CWA early on Monday
and precipitation associated to it should be tapering off
through the day. A rumble of thunder cannot be ruled out, mainly
in areas east of the Blue Ridge. Behind the front, dry
conditions are expected for most of our CWA, with precipitation
continuing west of the Allegheny Front, even maybe some snow
showers if precip lasts into Monday night. Gusty northwesterly
winds are expected as well with below normal temperatures.

Surface high pressure builds from the southwest Monday night
into Tuesday as a more zonal pattern settles aloft. Dry
conditions expected into Wednesday before a quick moving low
pressure system and its associated cold front move across late
Wednesday into early Thursday. QPF amounts are not looking too
impressive at the moment with this fropa. High pressure returns
behind this system on Thursday.

&&

.AVIATION /08Z FRIDAY THROUGH TUESDAY/...
VFR thru Saturday evening as high pressure dominates. Main
concern is the gusty southwest wind which will continue. Some
spotty low-level wind shear may also occur where surface winds
relax a bit late at night/early in the morning.

Sub-VFR increasingly likely as we head from Saturday night
through Sunday night as a backdoor front potentially brings low
cigs to the northeastern terminals, then a storm from the
midwest brings widespread rain, potentially heavy at times, and
perhaps a thunderstorm or two later Sunday and Sunday night.
Worst conditions probably Sunday night with the main system, but
IFR cigs could develop at BWI earlier thanks to the backdoor
front.

Sub-VFR conditions expected early on Monday as a front moves
away early in the day with rain and maybe thunder. VFR
conditions should return later on Monday behind the front and
remain into Tuesday and Wednesday before another front
approaches. Gusty winds, up to 20 knots possible Monday into
Tuesday.

&&

.MARINE...
Gusty winds continue today and SCA conditions expected for all
waters by afternoon. That said, winds look just a bit lighter
than yesterday. Tomorrow winds look a smidge lighter still, but
likely still enough for SCA all waters by afternoon. Backdoor
front may cut back risk of SCA to southern waters by Sunday.

Small craft advisory possible Monday into Tuesday as winds are
expected to remain above the threshold behind a cold front.
Winds should gradually decrease Tuesday night and remain below
criteria into Wednesday.

&&

.FIRE WEATHER...
RH`s remain low and winds remain gusty. However, given guidance
indicates winds should be a bit lighter today, and RH just a
little higher, will opt for an SPS for the time being. An
upgrade to Red Flag may end up being necessary, but confidence
at this time is low. Conditions should relax Saturday as RH
continues to increase. Widespread rainfall is expected to
greatly reduce fire danger Sunday night.

&&

.HYDROLOGY...
A strong upper trough and attendant surface front will barrel
through the area Sunday night. PWATs ahead of the front are
progged to be around 1.5 inches, near record highs for the month
of April. Unidirectional flow and the parent upper low cutting
off suggests training of heavy rain is possible, though the
flooding threat may be mitigated by fast rain/storm motions and
antecedent dry conditions. WPC is placing the western portions
of the CWA in a slight risk for excessive rainfall, with
marginal risk further east.

&&

.TIDES/COASTAL FLOODING...
Gusty southwest winds have caused elevated water levels. Minor
flooding is not expected tonight into Friday since winds are
expected to be west of south, but it may be close for sensitive
areas. There is a better chance for tidal flooding Sunday into
Sunday night as south to southeast winds increase ahead of a
cold front. Winds may also turn toward the east and northeast
for time depending on how far south a backdoor boundary can make
it into the area Sunday. Either way, stronger winds with an
easterly component will enhance the threat for tidal flooding.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 6 PM EDT Saturday for ANZ530>534-
     537-539>543.
     Small Craft Advisory until 5 AM EDT early this morning for
     ANZ535-536-538.
     Small Craft Advisory from noon today to midnight EDT tonight
     for ANZ535-536-538.
     Small Craft Advisory from noon to 6 PM EDT Saturday for ANZ535-
     536-538.

&&

$$
SYNOPSIS...RCM
NEAR TERM...RCM
SHORT TERM...RCM
LONG TERM...IMR
AVIATION...IMR/RCM
MARINE...IMR/RCM
FIRE WEATHER...RCM
HYDROLOGY...BJL/RCM
TIDES/COASTAL FLOODING...BJL/RCM/IMR



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