Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 161413

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1013 AM EDT Tue May 16 2017

High pressure will drift east from the Carolina coast today
before stalling over Bermuda through Saturday. A cold front
will cross from the north Friday night. The cold front will
stall over the southern Mid-Atlantic Saturday, before returning
north as a warm front Sunday. A stronger cold front looks to
move east through the area Monday night.


As of 10am, 1020mb surface high pressure is centered east of
Cape Hatteras. This high will drift east to Bermuda through
tonight and persist there at least through Saturday. A return
southerly flow is developing over the area, but the pressure
gradient will remain light through midday. High thin clouds are
moving south of the area with abundant sunshine rest of today.

Agreed with previous shift about leaning toward the higher
guidance with max temps and even a couple degrees higher in some
cases based on the fact that most guidance was too cool with
temps yesterday. Max temps will be in the lower to middle 80s
across most locations, particularly as the south wind 5-10mph
develops this afternoon.

High pressure will set up near Bermuda tonight...and continued
southerly flow will allow for milder conditions compared to
recent nights. Min temps will range from the lower to middle 50s
in the colder valleys and rural areas to the lower and middle
60s in downtown Washington and Baltimore.


High pressure will remain near Bermuda through Thursday night.
An upper-level ridge will also build overhead during this time.
The subsidence with this combined with a south to southwest flow
will usher in unusually hot conditions for this time of year.
Max temps both days will be in the 90s for most locations.
Humidity will also increase with dewpoints in the 60s for many
locations. The heat and humidity may lead to an isolated
thunderstorm during the afternoon and evening hours each day.
However...with the ridge overhead any convection would be
isolated in coverage and most areas should remain dry. Latest
forecast keeps a slight chance for a shower/thunderstorm across
northern Maryland and for locations near/west of the Blue Ridge
mountains where terrain circulation and a weak pressure trough
may act as lifting mechanisms.

Min temps Wednesday and Thursday night will range from the 60s
for most locations to the lower and middle 70s in downtown
Washington and Baltimore.


Both the 00Z ECMWF and GFS are in generally good agreement with the
H5 pattern through Sunday, with zonal flow through Friday night,
then slight ridging through Saturday night. The ridge slides off
Delmarva on Sunday, bringing with it H5 height falls associated with
the trough rooted in the closed low over central Quebec.  This setup
of the ridge between two closed lows...the Quebec low and the low
over the north Atlantic, will produce a sluggish flow in the Sunday
through Monday timeframe with unsettled weather.

Both models have the surface cold front slowly passing through the
area on Friday, before hanging up over the VA/NC border Saturday
night.  Then surface high pressure builds over New England Friday
night and Saturday, and the mid-Atlantic will get an easterly ocean
flow/cold air damming pattern as a back door cold front moves
through the area Friday night into early Saturday. This looks to
keep Saturday chances of rain low along with temperatures, but on
Sunday the New England high pressure moves out to sea as a cold
front approaches. There is still timing differences between the 00Z
GFS and ECMWF, but there should be a considerable period
rainfall between Sunday and Monday, as precipitable water
exceeds 1.5" Sunday night and Monday.

Friday appears to be a high CAPE, low shear environment, with 00Z
GFS surface CAPES approaching 1500 j/kg and 0-3km helicity only
around 50. This will bring a threat of isolated severe to our
region on Friday.

Friday max temperatures will still be well above normal nearing 90
once again, but then a cooling trend will begin on Friday night as
the back door front drops Saturday daytime highs into the low to mid
70s. Sunday the clouds from the front to our west will spill into
the area, keeping temps near normal.


VFR conditions prevail through Thursday. A south to southwest
flow will develop this afternoon with max gusts around 10 to 15
knots possible. Light south flow continues tonight. Patchy fog
may reduce vsbys late tonight in fog prone areas such as
sheltered valleys. MVFR conditions are most likely but brief
IFR conditions cannot be ruled out.

A south to southwest flow is expected Wednesday through Thursday
with gusts around 15 knots. VFR conditions are likely during
this time. An isolated thunderstorm cannot be ruled
out...especially across the western terminals during the
afternoon and evening hours each day. Even across these
areas...most places will end up dry.

A cold front will approach Friday before passing through Friday
night. A better chance for thunderstorms is expected during this


High pressure will drift from the Carolina coast today and it
will set up near Bermuda tonight and persist through Saturday.
A south to southwest flow will slowly increase through the
midweek. Southerly channeling may cause winds to gust past SCA
criteria Wednesday night into Thursday and again Thursday night
into Friday.

A cold front will approach the waters Friday before passing
through Friday night. Thunderstorms are possible during this


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

Wednesday Record Highs:
DCA: 92 in 1974.
IAD: 89 in 1986.
BWI: 93 in 1896.

Thursday Record High Minimums:
DCA: 72 in 2015.
IAD: 68 in 2015.
BWI: 68 in 1900.

Thursday Record Highs:
DCA: 96 in 1877.
IAD: 91 in 1987.
BWI: 97 in 1962.




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