Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
927 PM EDT Wednesday Aug 20 2014
high pressure will linger over the deep south through this weekend
and low pressure will continue to dissipate over the Great Lakes
through Thursday. High pressure will build over New England Friday
and spread southwest through the weekend then persist over the
middle-Atlantic into the middle of next week.
Near term /through Thursday/...
heavy showers and thunderstorms will continue to move south from
Charlottesville through the late evening.
An upper ridge will continue to develop over the eastern Continental U.S. With the
axis stalling over the MS river Thursday. A northwesterly jet from this
axis will shift across the northern mid-Atlantic...putting the
central middle-Atlantic in the preferred right exit region. This will
aid lift and bulk shear tomorrow. Remnant boundaries from the
activity tonight could factor into where thunderstorms
initiate/favor. Further more...organized convective storms from
the Midwest will shift southeast toward the area. MLCAPE looks
limited to around 1000 j/kg due to weak lapse rates...but that is
similar to today...so it should be sufficient for activity. Expect
more isolated severe thunderstorms...mainly damaging wind. Precipitable waters
are expected to rise near 2 inches Thursday producing a threat for
localized flash flooding. Maximum temperatures middle to upper 80s again with
dewpoints in the upper 60s for heat index near 90f.
Short term /Thursday night through Friday/...
the chance of showers and thunderstorms will continue Thursday night
and into Friday as a 250mb jet sits near the region and
disturbances approach from the Great Lakes. Subsidence behind the
departing disturbances may lead to clearing Friday and therefore
instability will likely increase. At this time...confidence is low
on the timing of showers and thunderstorms. Forecast maximum temperatures will
reach the low 80s on Friday.
Long term /Friday night through Wednesday/...
a weak wave of low pressure focused in the middle and upper levels
will cross the area overnight Friday...providing one final period of
enhanced rainfall as a backdoor cold front moves through at the
surface. A subtropical ridge will build over the eastern US for
weekend as surface high pressure centered over the northeastern US
ridges down the eastern Seaboard. This ridging combined with
easterly flow around the north side of a coastal low off of Cape
Hatteras will bring onshore flow for the middle-Atlantic midday
Saturday through the beginning of next workweek. The marine layer
that will fill in will bring seasonably cool and moist air...leading
to a low cloud deck that will hang around through the weekend and
likely into Monday evening...particularly east of the Blue Ridge.
Chance probability of precipitation will remain in the forecast along and west of the Blue
Ridge where there will be an upslope component to the moist easterly
The surface high will migrate off of the middle-Atlantic coast Monday
night and southerly flow will begin to fill in locally. This will
signal an increase in temperatures as highs will go from the middle to
upper 70s Saturday through Monday to near 80 Tuesday and middle 80s
Wednesday. No significant precipitation features are expected
through the first half of next week.
Aviation /01z Thursday through Monday/...
rain showers and thunderstorms and rain will continue to move south from Charlottesville
this evening. Light southerly flow will keep moisture in the
region overnight and patchy IFR visibilities are possible at mrb and cho.
MVFR visibilities are possible at iad. MVFR/IFR ceilings are possible near
BWI-mountain but confidence is low at this time.
Rain showers and thunderstorms and rain possible Thursday afternoon and into Friday and may
cause MVFR/IFR restrictions.
Periods of low ceilings are possible as a middle and upper level
disturbance crosses the area Friday night and then again over the
weekend and into early next week as a marine airmass settles into
southerly flow will continue on the waters through Friday. Winds
gusted to around 20 knots on main portions of the waters this
afternoon as thunderstorm activity moved through the area. Another
round of thunderstorms are expected Thursday afternoon.
A Small Craft Advisory may be necessary Saturday night through
Sunday night in breezy easterly flow around the north side of a
coastal low off of the North Carolina flow.
coastal Flood Advisory for Anne Arundel County. Southerly flow has
increased this evening...which should keep water levels at least
three quarters of a foot at Annapolis and cause minor coastal
flooding at that sensitive site. The gauge stopped reporting this
afternoon...and it is not known when data will be restored. High
tide is at 3:21am at the naval Academy. Water levels will be
elevated elsewhere. Will need to monitor the upper tidal Potomac
for potentially meeting the minor threshold at the southwest
District of Columbia...none.
Maryland...coastal Flood Advisory from 1 am to 6 am EDT Thursday for