Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
358 am EDT Sat Sep 5 2015
Synopsis...high pressure will build through tonight then weaken
and move offshore with a return to hot humid conditions by middle
next week. A cold front expected to cross the area at the end of next
Near term /through tonight/...low clouds will continue to
advect/develop westward early this morning due to onshore flow and
mix out late morning. Otherwise...high pressure will build through
tonight and support fair and pleasant weather.
Short term /Sunday/...high pressure still in control although it will
start weakening. Air mass expected to remain too dry for any
showers. Models suggest high clouds will affect central Virginia tonight.
Long term /Sunday night through Friday/...surface ridging will be centered off
the New England coast. Aloft...a closed low will become trapped over
the southeastern states as heights build over the northeastern
Continental U.S.. there will still be an easterly low level component...so
cloud forecast uncertain Sunday night...and NAM hints there could be
moisture east of Blue Ridge. Lows dependent on this...but 60s should
be found for most. Trimmed back probability of precipitation for showers for the high
terrain southwestern County Warning Area Monday as the atmosphere looks fairly dry
and stable. Highs may approach 90 but will stay just short for many.
Dry weather and seasonably mild temperatures continue Monday night.
During the middle of the week...mid/upper level ridging pushes east
off shore and what is left of the closed low drifts toward the Gulf
of Mexico. This will allow southerly flow to be
established...resulting in rising temperatures and humidity. Highs
in the 90s will be possible Tuesday and Wednesday for most areas.
Convection should remain isolated and over the mountains on
Tuesday...but may increase in coverage Wednesday and have a better
chance of pushing east of the mountains.
Models diverge toward the end of the week and the approach of the
next significant trough and cold front. European model (ecmwf) faster than GFS...but
right now passage appears to be near the end or after the forecast
period. The end result will be increasing chances of thunderstorms
for Thursday and Friday. Temperatures may be somewhat limited by the
increased cloud cover and precipitation but still likely near or
Aviation /07z Saturday through Wednesday/...MVFR ceilings will
continue to develop early this morning and may come down to IFR at
kmrb...kcho and kiad. Visibilities expected to stay in the 3-5sm range.
Low clouds expected to mix out later today with ceilings becoming VFR.
Low clouds and/or fog will be possible Sunday night into Monday
morning. Except for possible morning fog in prone locations...VFR
should prevail the remainder of the period. Isolated thunderstorms
are possible Wednesday afternoon.
Marine...winds expected to strengthen today and peak this
afternoon but Small Craft Advisory conditions may linger into the evening on the
lower portion of the Bay.
High pressure offshore will be the main influence over the waters
through the middle of next week. Winds should remain below Small Craft Advisory
levels. Southerly channeling will become possible during the middle
of the week...but have kept the forecast at 15 knots or less for now.
Tides/coastal flooding...water anomalies expected to stay up next
couple of days due to onshore flow. Latest estofs and etss
guidance bring water levels above minor coastal flooding threshold
tonight at all forecast points on the Chesapeake Bay except at Havre
Delaware Grace. On the Potomac River...water levels expected to remain
just shy of minor coastal flooding at SW Waterfront.
District of Columbia...none.
Marine...Small Craft Advisory until 11 PM EDT this evening for
Small Craft Advisory until 2 PM EDT this afternoon for anz530.
Small Craft Advisory from 8 am this morning to 8 PM EDT this
evening for anz536.