Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
929 PM EDT Wednesday may 27 2015
high pressure will remain offshore through Friday. A southerly
flow will bring warm humid conditions to the middle-Atlantic through
Saturday. Showers and thunderstorms will be possible each
afternoon and evening. A weak cold front will approach the region
Thursday but weaken and stall over the region. A stronger cold
front will arrive Sunday. The active pattern continues into next
Near term /until 6 am Thursday morning/...
it was a marginal severe case today with 1000 to 1500 j/kg MLCAPE
and bulk shear around 30 knots. Outflow from early activity overswept
the area and limited the severe threat...hence the Severe
Thunderstorm Watch was cancelled early.
Moisture continues to advect into the region with dewpoints back
up to middle 60s to around 70f. This level of moisture...along with
boundaries from earlier activity should enable isolated showers
and possible thunderstorms through the rest of the evening. A
boundary is evident across the Delaware-Maryland-Virginia south to southeastern Virginia...so the
greatest chance for more rain is over southern Maryland waters. With decent
clearing and some places decoupling...expect patchy radiational
fog to develop...particularly in valleys and in the Piedmont.
Min temperatures high tonight...low to middle 70s.
Short term /6 am Thursday morning through Friday night/...
shortwave trough will be moving into New England on Thursday as a
surface cold front approaches from the northwest. However...the front will not
make a lot of southern progress through the region. While these
features will once again allow scattered showers and thunderstorms
to once again form...bulk shear is on the weak side...so severe weather
threat is minimal. Humidity will still be high though so locally
heavy downpours possible. Highs temperatures well into the 80s. Front
begins to lose definition overnight as precipitation chances diminish. Some
slightly drier air may work into the northern part of the County Warning Area. Lows
will drop into the 60s...except 50s in higher elevations and around
70 urban centers.
By Friday...the middle and upper level ridges build back to the
north...as what/S left of the surface front lifts back to the north.
Without a defined forcing mechanism...convective development will be
be more diurnally and terrain driven. Thus coverage should be lower
than Wed/Thu...especially east of the Blue Ridge. Daytime highs a
touch lower on Friday...but the overall look and feel of the
forecast remains the same...warm and muggy.
Long term /Saturday through Wednesday/...
a cold front will approach the region Saturday...bringing a chance
of showers and thunderstorms to the region into Saturday night.
Temperatures Saturday will reach the middle to upper 80s with lows
Saturday night getting into the middle 60s.
The cold front should slowly push through the region Sunday. The
European model still remains the slower model over the GFS.
Showers and thunderstorms will form ahead of and along the front.
Temperatures will be above normal Sunday.
A wedge of high pressure will build southward along the East
Coast Sunday night and Monday...helping to cool conditions down a
little. However...overrunning moisture and middle-level
disturbances approaching from the west will bring yet another
threat for rain showers and perhaps a thunderstorm. Temperatures
may be a few degrees above normal each period but cooler than recent
As the ridge of high pressure breaks down Tuesday...upper level
disturbances are expected to move across the Ohio Valley into the
lower Great Lakes. These disturbances could pose a shower threat
Tuesday with high temperatures only in the lower 80s.
A shower or thunderstorm is possible Wednesday...but the strength
of the high pressure along the eastern Seaboard may reduce that
threat even further. It will be a few degrees warmer Wednesday.
Aviation /01z Thursday through Monday/...
humid conditions persist tonight and IFR visibilities/fog may impact the
terminals into early Thursday. Sub-VFR conditions possible. High
pressure builds north of the area...should enable low chances for
thunderstorms generally east from the Blue Ridge again.
Scattered thunderstorms possible Friday afternoon...with slightly
higher chances near/west of Blue Ridge. Overall lower coverage than
previous days. There is a chance of sub-VFR visibilities in br early Friday
and Saturday mornings...mainly in the typical locations...but
overall confidence is not great.
Localized sub-VFR conditions possible Saturday through Sunday
with showers and thunderstorms in parts of the area.
southerly channeling with gusts to 20 knots still occurring south of Sandy
Point. This will continue to ease through the overnight with lower
southern Maryland waters gusting longest. Small Craft Advisory reflects this. Light and
variable flow Thursday with a Bay breeze expected. Up to scattered
gusty showers and thunderstorms Thursday afternoon.
Light/vrb winds Thursday night will become southerly again Friday as
high pressure re-establishes offshore. Gusts may come close to Small Craft Advisory
criteria by late Friday afternoon over the Bay due to
channeling...but confidence is too low to issue at this time.
While thunderstorms will be possible Friday afternoon...overall
coverage appears fairly isolated.
Widespread marine hazards are unlikely Saturday through
Sunday...although scattered afternoon/evening thunderstorms will
pose localized threats.
District of Columbia...none.
Marine...Small Craft Advisory until midnight EDT tonight for anz532-533-
Small Craft Advisory until 6 am EDT Thursday for anz534-543.