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FXUS61 KLWX 151452
Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1052 AM EDT Tue May 15 2018
A cold front will slowly approach the region from Pennsylvania
this afternoon, then stall across the area tonight, remaining
stationary through late Friday.
.NEAR TERM /THROUGH TONIGHT/...
At 1430Z, regional radar shows line of convection approaching
western PA, otherwise quiet. Satellite shows skies generally
sunny to mostly sunny, except in extreme southern from southern
MD towards Charlottesville.
The clear skies will allow for temperatures to reach near 90
across much of the region this afternoon. A slow moving cold
front is slowly sagging south from PA. This front will set up
parallel to this afternoon`s predicted storm motion, which will
allow for convective training, particulary in the northeast
portion of our CWA where the front is anticipated to stall. The
area most prone to flooding and severe weather late this
afternoon and evening will be in a region defined north of US
50 in MD and I-66 in northern Virginia, and east of I-81.
CAM model blends show our region being on the southern tail-
end of a linear convective system that is already apparant
entering western PA as previously described. Expecting this
organized convection to continue to develop and move eastward
across PA this afternoon, with the tail end finally entering
our CWA by late afternoon. The CWA will also be in the right
rear quad of a H7 jet targeting the NYC region. There will
likely be scattered convection before the organized linear
system arrives mid-afternoon. RAP has MLCAPE nearing 2500 j/kg,
with effective shear in the 25-30KT range in the highest
likelihood region outlined above, with less shear further south.
These storms will start to taper off after 10 PM, with shower
and tstm probabilities decreasing even more after midnight.
.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
We should become cooler overall Wednesday as the front settles
to our south, but another wave of low pressure will ride
eastward along the front late in the day and at night, so while
we will be more stable, another round of showers and t-storms
looks likely as we head through Wednesday into Wednesday night.
The severe risk should be reduced, however. Highs will be
cooler, and our current forecast may in fact be notably too
warm, with some guidance suggesting highs will get stick in the
A low pressure system should become positioned in the northern
Gulf of Mexico early Thursday. An approaching upper level short
wave trough ejecting out of the lower MS valley, along with a
strong subtropical ridge over the western Atlantic will funnel
moisture from this system into our direction Thursday. With the
stationary front still parked over the region, this will only
enhance rainfall even more. Thursday night looks to be the
timeframe where the heaviest rain will fall. Ensemble guidance
suggests that 1 to 2 inches of rain could fall in many areas.
This additional rainfall, combined with what will already have
fallen in the past several days leads to concerns over flooding,
especially along the I-95 corridor. Temperatures during this
period will remain around average, as clouds and precipitation
will keep things from getting too warm.
.LONG TERM /FRIDAY THROUGH MONDAY/...
Continued unsettled weather expected to round out the work week as
the strong subtropical ridge over the western Atlantic continues to
bring a plethora of moisture to the region. Upper level troughing
will reside aloft with shortwave energy passing overhead, bringing a
continued threat of heavy rainfall. Couple these features with the
pesky stationary boundary remaining nearby, this will result in the
potential for another one to three inches of rainfall for much of
the area heading into the weekend. The stationary boundary will lift
northward on Saturday and remain stretched across Pennsylvania into
Sunday. Continued unsettled conditions expected with daily rain
chances, altho Sunday looks the drier of the two days as the mid
level trough starts to dampen out a bit and a cold front nears late
Sunday into Monday. Temperatures throughout this period will remain
near normal for the middle of May.
.AVIATION /15Z TUESDAY THROUGH SATURDAY/...
Areas of low clouds and fog are possible overnight into early
today due to low-level moisture being trapped underneath the
nocturnal inversion. IFR conditions cannot be ruled out.
Any low clouds and fog should break early this morning with VFR
overall today. Showers and storms are again expected later today
and this evening, however. Showers and storms will remain
possible on Wednesday as well, but low cigs are also possible
much of the day as the front drops back south across the region.
With a stationary front lingering around the region Thursday
and Friday, it is likely that we will see clouds throughout that
entire period. Sub-VFR conditions could be possible at times
during the period. Scattered afternoon thunderstorms are also
possible during this period.
Episodes of sub VFR conditions will be likely through the end of
the work week and into the weekend as plentiful moisture in the form
of showers and thunderstorms look to plague the terminals each and
every day. Winds will remain light at less than 10 knots for much of
A Small Craft Advisory remains in effect for the Potomac River
and Chesapeake Bay through later this evening.
More likely to have gusty winds across the waters much of
today as low pressure passes to our north. Storms again may
result in special marine warnings later today and this evening.
Winds probably relax a bit Wednesday, but showers and storms
will remain possible.
Despite all of the unsettled weather in the area on Thursday
and Friday, thanks to a stubborn stationary front and deep
southerly flow, winds look to remain below SCA criteria.
However, any thunderstorms that may form could create windy
conditions on the waters.
Unsettled weather will continue through weeks end as a pesky
stationary boundary remains nearby. This will bringing light winds
and sub SCA conditions, however passing showers and thunderstorms
could result in the requirement for Special Marine Warnings.
A Coastal Flood Advisory remains in effect through early this
morning for Straits Point. Additional minor coastal flooding will
be possible at Annapolis and Straits Point during the late
evening/early morning high tide cycle next few days. New minor
coastal flood thresholds are expected to be implemented later today
for Annapolis and Straits Point assuming there is no flooding
ongoing which may temper the coastal flood threat somewhat.
DC...Flash Flood Watch from 3 PM EDT this afternoon through late
tonight for DCZ001.
MD...Flash Flood Watch from 3 PM EDT this afternoon through late
tonight for MDZ003>006-011-013-014-501>508.
VA...Flash Flood Watch from 3 PM EDT this afternoon through late
tonight for VAZ028-031-053-054-505-506.
WV...Flash Flood Watch from 3 PM EDT this afternoon through late
tonight for WVZ050>053-055-501>504.
MARINE...Small Craft Advisory until midnight EDT tonight for ANZ530>543.