Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
926 PM EDT Friday may 29 2015
high pressure will persist offshore through Saturday with
continued warm and humid conditions to the mid-Atlantic. A cold
front will enter the region late Sunday and stall over the region
into Tuesday. High pressure is expected to slide into the region
for the middle part of next week.
Near term /through tonight/... convective activity waning with
sunset. It was yet another afternoon/evening of popup
shower/thunderstorm activity with a warm and moist atmosphere from
high pressure off the middle-Atlantic coast.
Another warm night on tap for the area. Lows tonight gnrly in
m60s..l70s in the cities.
Short term /Saturday/...
area remains in the same air mass Sat - cold fnt remains to our northwest but is
working its way in this direction. Best chance of thunderstorms will be in the
afternoon in the western part of the County Warning Area. Highs will again be in the mu80s.
Long term /Saturday night through Friday/...
on Saturday night...the upper level ridge offshore will begin to be
suppressed by a shortwave trough pushing through Canada. A cold
front will be approaching from the northwest...extending down the St
Lawrence Valley into the souther Great Lakes. After any diurnal
convection subsides...a chance of showers will remain near the PA
border for any activity that races ahead of the front. Otherwise
just another muggy night with increasing clouds and lows in the
60s...lower 70s urban areas.
Confidence in the Sunday to Sunday night period is not particularly
high as the cold front advances into the area. There is still some
model spread in how quickly the front will push southward...but the
overall trend has been slower. This makes sense because the front
will become parallel to the upper flow as it pushes into the strong
ridge. A wave of low pressure will also move along the front
sometime in this time period. Thunderstorms seem like a good
bet...but will not be going higher than likely yet due to the timing
uncertainty. This also means high temperatures Sunday will likely be a bit
higher...and could once again approach 90 over the southeast County Warning Area which will
have fairly low precipitation chances during much of the day.
It looks like any severe potential Sunday will be limited and tied
to building instability as shear will not be particularly strong. A
bigger threat may be due to heavy rain and flooding due to the
stalling front...developing low level jet Sunday night...and favorable upper
divergence in a high precipitable water environment. However...a little difficult
to say which time period and which part of the middle-Atlantic would
have the biggest threat at this time.
A big shift in the pattern will occur behind a cold front early next
week. As the front drops slowly south...rain chances will slowly
diminish Monday into Tuesday. Meanwhile...high pressure will build
over New England setting up a cool air damming wedge across the
region. Temperatures will shift from heat and humidity more typical
of middle-July to temperatures more typical of mid-April.
As the high gradually shifts to the east and weakens...temperatures
will gradually rebound to near normal levels by the end of the week.
Aviation /01z Saturday through Wednesday/...
isolated showers rest of the evening in the District of Columbia metros. Fog possible
late tonight at cho/iad/mrb. There will be chances for thunderstorms again Sat
afternoon...best chance at mrb.
Timing of cold front Sunday-Sunday night a bit slower...but
thunderstorms will still be likely at some point during the time
period. Heavy rain possible...so IFR flight conditions more likely
than they have been with recent scattered storms.
Northeasterly flow 10 knots or so Mon-Tue. Sub-VFR possible in low cigs/-ra.
southerly flow 10 to 15 knots continues tonight up the main portion of the
Bay with high pressure off the coast. Flow increases Sat ahead of a
cold fnt. Small Craft Advisory for all but middle and upper tidal Potomac Saturday
afternoon into the overnight.
Winds will decrease some Saturday night and will keep Small Craft Advisory in place
as originally issued...which will be in effect for the Main Channel
of the Bay through the night. Southerly flow on Sunday may approach
Small Craft Advisory conditions but will be marginal. Cold front passage appears it
will be a bit slower...but thunderstorms will still eventually
become likely Sunday afternoon/night and pose a localized wind
threat. Gradient wind field uncertain by Sunday night and will
depend on frontal position.
High pressure building in behind a cold front will likely push
northeasterly winds to Small Craft Advisory levels Monday into
District of Columbia...none.
Marine...Small Craft Advisory from noon Saturday to 2 am EDT Sunday for
Small Craft Advisory from 10 am Saturday to 8 am EDT Sunday