Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 131413
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1013 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 passing by to the north has resulted in a scattered
sprinkles and even a stray shower. Added chance PoPs to the
northern tier, but that threat has mainly passed.

The rest of the day 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 entering the
region late Saturday 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 /14Z 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; coordination with state
Forestry officials confirms this. 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 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/HTS
SHORT TERM...RCM
LONG TERM...IMR
AVIATION...IMR/RCM
MARINE...IMR/RCM
FIRE WEATHER...RCM/HTS
HYDROLOGY...BJL/RCM
TIDES/COASTAL FLOODING...BJL/RCM/IMR



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