Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
349 am EDT sun Sep 21 2014
low pressure will track north along the southeast and middle Atlantic
coasts today. A cold front will cross the region late this afternoon
into this evening...followed by a return of high pressure Monday
Near term /through tonight/...
developing low pressure will move along the Carolina coast this
morning before heading out to sea this afternoon. Rainbands
associated with this system are expected to remain to the south and
east of the forecast area. Some patchy fog is still possible early
this morning but westerly winds will help mix out the boundary layer
after sunrise with remaining fog burning off. Behind the departing
low...westerly winds will aid in downslope warming across the
region. Afternoon high temperatures are expected to reach the 80s in
most locations...especially east of the Blue Ridge. Daytime heating
combined with an approaching cold front will help touch off
scattered afternoon and evening showers and thunderstorms first over
the Potomac Highlands and I-81 corridor then spreading east across
the metropolitan areas late this afternoon and into the evening. Some of
the storms could produce damaging winds although an isolated threat.
Convective threat will end by middle evening. A few showers may remain
over the Potomac Highlands. Cooler and drier air will filter into
the region overnight with temperatures cooling back to the 40s to
50s west and upper 50s to middle 60s east.
Short term /Monday through Monday night/...
high pressure will build into the middle Atlantic on Monday bringing
plenty of sunshine and pleasant temperatures. Afternoon highs
mainly in the 60s to lower 70s can be expected along with lows in
the upper 30s to low 40s west to the middle 40s to 50s east of the Blue
Long term /Tuesday through Saturday/...
surface hipres will be across most of the eastern Continental U.S. Through the end of the
weak. 500 mb ridge will be building too. At first glance...that would seem like a
cut-N-dry forecast. However...there is a catch.
European model (ecmwf) guidance suggesting a cutoff low in the midst of the 500 mb ridge...or
in other words...a weakness in the height pttn. There/S rather poor
agreement on a feature so subtle several days out. However...surface flow will
be northerly Tuesday but veer Ely Wed-Thu...as the center of the surface high will
be atop New England/New York state by then. At the very least...cannot rule out
an increase in moisture and maybe a sprinkle or two /or a patch of dz?/.
so at this juncture...will keep Tuesday sunny...bring clouds inland Wednesday...
and offer up some low end probability of precipitation /20-30 percent/ Wednesday ngt-Thu. Choosing a
stratiform pcp character.
Am thinking as the upper ridge builds to the west of the area...that may be
enough to allow surface ridging to retrograde. If that does hppn...then we/ll
lose the onshore flow...and the marine air mass will lose its grip on the
region. Dont have the hiest of confidence in this outlook...but dont want
to carry a prolonged period of low probability of precipitation under hipres west/o a clearer
Can say this...higher heights will lead to warmer temperatures. Maxt Tuesday-Thursday not
far off from Bay water temperatures...which is about 5 or 6 degf cooler than
climatology. We/ll be back near normal again Fri-sun.
Aviation /08z Sunday through Thursday/...
patchy early morning fog will give way to VFR conditions by middle
morning. Scattered showers and thunderstorms will develop this
afternoon and evening ahead of a cold front. Some impact to the
terminals may be possible...especially 18-00z. Patchy fog could
redevelop late tonight into early Monday.
Mon-Tue...VFR under hipres.
Wed-Thu...onshore flow may bring a stratus deck inland. Flgt
restrictions possible...but confidence low.
winds will remain below Small Craft Advisory levels today except where showers and
thunderstorms develop late this afternoon into this evening. Small Craft Advisory
conditions are expected behind a cold front overnight through
Northerly fow Tuesday will veer Ely for Wed-Thu. Guidance suggesting Ely flow may be
stiff...potentially supporting Small Craft Advisory conds over a portion of the
waters /mid Bay/.
tidal departures...which rose dramatically yesterday...have since lessened
as high tide rolls in. As a result...tides maxing out right near
minor criteria at Solomons/Piney Point/Annapolis. The tide is in aa
County right now. Thus will be able to canx advisory for Calvert and Saint
Marys. Further...since departures lower...do not believe thresholds
will be met at Baltimore. Will cancel that one as well. Do not have
a good feel for the upper Potomac right now...so will allow those
advisories to continue.
The PM tide will be a bit more of a challenge to forecast. It will
be the lower astronomical tide. Southwesterly winds will become westerly...so
perhaps we will get a pinch of relief from that. And...baseline
departures going in appear to be below +1. All said...will follow the
premise that reaching caution stage probable but minor threshold
District of Columbia...coastal Flood Advisory until 9 am EDT this morning for dcz001.
Maryland...coastal Flood Advisory until 8 am EDT this morning for mdz014.
Virginia...coastal Flood Advisory until 9 am EDT this morning for vaz054.
Marine...Small Craft Advisory from 4 am to 6 PM EDT Monday for