Scientific Forecaster Discussion
Area forecast discussion...corrected
National Weather Service Baltimore Maryland/Washington District of Columbia
359 am EDT Friday Sep 4 2015
Synopsis...a backdoor cold front will sink south across the
waters today. High pressure builds in the wake for the weekend.
Near term /through tonight/...an upper level low over the Great Lakes will
weaken today while high pressure over New England builds southward.
Clouds are dissipating from earlier convection across the region
this morning making for mostly clear skies. Patchy fog has
developed this morning due to the calm winds and recent moisture
from showers and thunderstorms. Patches of dense fog are possible
in low lying areas. Fog will dissapate shortly after sunrise.
High pressure across New England will build south today pushing a
backdoor cold front into the region. The front will slowly sag
southward today moving across the Maryland/PA border this morning and
reaching Nova/DC/S Maryland by this afternoon. Winds become easterly as
the front sags southward which will advect in marine conditions
today. Due to the high dewpoints and the slow movement of the
front...showers and thunderstorms will form mainly west of the Blue
Ridge and south of District of Columbia today as this area will be unstable through
the afternoon. A few storms may become strong with gusty winds and
heavy rain. Activity will diminish after sunset tonight. Temperatures will
likely be cooler than previous days this week with temperatures rising into the
upper 70s to low to middle 80s. The front will move south and likely
stall across central Virginia overnight. This will lead to the chance for
showers overnight in vicinity of the front. Easterly flow will cause
low clouds to form late tonight and last through Saturday morning.
Stratus will be slow to dissapate across central Virginia and against the
eastern slopes of the Blue Ridge.
Short term /Saturday/...high pressure continues to move southward Saturday
and cooler drier air will make its way into the region. Clearing
will increase from north- S as well with the exception of the SW where
the front may still be located. Temperatures in the 70s to low 80s are
Long term /Saturday night through Thursday/...surface high pressure over
the northeast will keep a dry east-northeast flow and comfortable temperatures
through Monday. Surface high weakens more rapidly Monday through the end of
next week while middle-upper level heights rise over the middle Atlantic
resulting in a warming trend. Is not really until Wednesday when surface
high weakens enough to allow moisture return into the area. Will
keep forecast dry through Tuesday night then bring chances of showers
and T-storms Wednesday afternoon west of the Blue Ridge into Thursday for the
entire area. Global models show a slow moving cold front crossing the
area Thursday or Thursday night but show sig differences with respect to
timing and whether front clears the entire area or not.
Aviation /08z Friday through Tuesday/...sub-VFR conditions possible this
morning as patchy fog develops at mrb-cho-iad. IFR conditions
likely at mrb/cho this morning. Fog dissapates after sunrise and
dry conditions are expected for the rest of the morning. A cold
front will move S today. North winds become NE-east from north to S today and
tonight. Rain showers/thunderstorms in the vicinity expected across the area with the best chance
at mrb-cho-iad. Some storms may produce heavy rain and gusty
winds. Activity diminishes tonight. Easterly flow will likely
cause sub-MVFR ceilings tonight across the region. Low ceilings will
likely take the longest to improve at cho Saturday morning.
Otherwise...clear occurs from north to S Saturday.
No aviation concerns beyond Sat night.
Marine...north winds become NE-east today as a cold front slowly moves
across the waters from N-S. Winds will increase this evening and
Small Craft Advisory conditions are expected tonight and into Saturday. The
pressure gradient will be favorable for gusty winds on the Bay
through Saturday. Confidence is lower across the upper tidal
Potomac as it is closer to the center of the high.
Small Craft Advisory may linger over the middle and Lower Bay into the firs part of sun.
Tides/coastal flooding...anomalies have increased to about a
half foot as light north-northwest flow occurs on the waters. The flow will
turn to the east today but it should be light enough to keep water
levels below flooding thresholds.
The easterly flow will strengthen tonight into Saturday. Minor tidal
flooding is possible near time of high tide.
Climate...well above normal temperatures are forecast to persist
across the area through Friday. As a result...some sites may
approach record daily high minimum temperatures during the next 24
Below is a table of record daily high minimum temperatures for
Site.....Record maximum min for Sep 4................
dca...76 (set in 2012 and 1953)..................
BWI...75 (set in 2012/1953/1944/1937 and 1932)...
iad...71 (set in 2012)...........................
District of Columbia...none.
Marine...Small Craft Advisory from 6 PM this evening to 2 PM EDT
Saturday for anz530>534-537>543.
Small Craft Advisory from 6 PM this evening to midnight EDT
tonight for anz535-536.