Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 171911

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
311 PM EDT Wed May 17 2017

High pressure will remain near Bermuda through Friday. A cold
front will pass through the area late Friday into Friday night
before stalling well to our south on Saturday. The boundary will
return north as a warm front Sunday before a stronger cold front
from the west passes through Monday into Monday night. High
pressure may briefly return for Tuesday.


Satellite observation at 19z shows a cumulus field developing
on and west of the Blue Ridge. The surface dewpoint depression
is very high, in some places nearly 30 degrees. So a lack of
moisture will be a limiting factor in convective development
this afternoon. 16Z RAP at KIAD has CAPE about 1500 j/kg, but
with weak shear and still some CINS. Contrary to this, both the
HRRR and NCAR Ensemble convective allowing models forecast an
area of showers and thunderstorms across north central Virginia
into central Maryland between 3 PM and 8 PM. So have a slight
chance of thunderstorms between these times for the remainder of
the afternoon.

A warm night tonight, with overnight min temps about 10 degrees
above normal. Models develop a nocturnal 35-40kt jet at 950 mb
in response to the contrast between the cold Atlantic and the
warm air mass in place. However, inversion should quickly setup
and not allow much of this wind to translate to the surface.


Thursday will start out much like today, but with surface
dewpoints increasing 5-10 degrees above today, expecting more of an
afternoon cumulus field. MAV guidance has decreased max temps
by a couple of degrees for tomorrow, but still expecting 90F+ in
most areas. Have used BCONSALL for guidance for both Thursday
and Friday. Once again, without a forcing field, not expecting
too much in the way of convection except perhaps terrain based
circulations causing localized storms.

Friday looks to have a good chance of showers and thunderstorms
as a cold front drops through the region right about peak
heating. Models CAPES are around 1000-1500 j/kg but only 20 kts
of 0-6km shear, so expecting mainly non-severe day and evening.


Ridging aloft will persist over the area as high pressure wedges in
from the northeast at the surface Saturday. The cold front that is
forecast to cross the area from north to south at the end of the
week will stall near the VA/NC border during this time, then return
slowly north as a warm front by late Sunday. A broken overcast is
likely over the weekend with easterly flow off the ocean. This will
result in cooler temperatures closer to normal for this time of year
(highs in the 70s, lows in the 50s). Despite the clouds,
precipitation chances should be minimal over the weekend.

Models continue to oscillate with regards to the timing of frontal
passage on Monday. This front will bring the next chance of showers
and possibly thunderstorms, but convective potential will rely
heavily 1) on the exact timing of frontal passage, and 2) the amount
of cloud cover/cloud debris from prior day`s convection over the
Midwest. Moisture and shear both increase along/ahead of the cold
front/shortwave driving it so storms that do develop will have the
potential for organization if there is enough instability present.

Behind the front, a slightly cooler/noticeably drier airmass will
move in for later Tuesday into Wednesday of next week.



Sub-VFR psbl at times over the weekend w/ lower CIGS in
moist ELY flow 10-15 kts.



Small Craft Advisory conditions may continue for portions of
the waters over the weekend in easterly flow between high pressure
to the north and a stalled front to the south.



Unusually hot conditions are expected today and Thursday.
Record heat is possible during this time. Below are the record
highs and high low temps for today through Thursday night...
May 17th and 18th.

Today`s (5/17) Record Highs:
DCA: 92 in 1974, 1896 and 1877
BWI: 93 in 1896
IAD: 89 in 1986

Thursday (05/18) Record Warm Lows:
DCA: 72 in 2015
BWI: 68 in 1900 and 1896
IAD: 68 in 2015

Thursday (05/18) Record Highs:
DCA: 96 in 1877
BWI: 97 in 1962
IAD: 91 in 1987

MARINE...Small Craft Advisory from 6 PM this evening to 10 AM EDT
     Thursday for ANZ531>534-537-539>541-543.
     Small Craft Advisory until 7 PM EDT this evening for ANZ535-


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