Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
911 PM EDT Tuesday Jul 22 2014
high pressure will near the eastern Seaboard tonight. A cold front
will approach from the west Wednesday...and move through the
region Wednesday night into early Thursday. High pressure is
expected to return to the region to end the work week.
Near term /through Wednesday/...
high pressure continues in the western Atlantic off the middle Atlantic/Carolina
coast. Rain showers have been limited...relegated mainly to the aplcn rdgs.
With the loss of daytime heating...there shudnt be much more to
their lifespan. For that matter...clouds have been less xtnsv than
last night. Since there/S less influence from the southeastern Continental U.S.
Disturbance /dry air ahead of the next cold front has been shunted southeastward
over cwfa/...think there will be less cldcvr. That poses more fog
concerns instead. Gnly going a more optimistic rte...as patchy fog
has been added to the mountain/foothill valleys...but am keeping the I-95
crrdr fog-free. Winds hvnt dcpld yet...and the light southerly flow/upper
60s-lower 70s dewpoints not great for radl cooling. May have to nudge
min-T grid upwd due to those dewpoints.
Wednesday starts with high pressure extending from the offshore
waters and into the Carolinas...with a cold front extending across
the lower Great Lakes and Ohio Valley. The cold front will
approach during the day...while a 500mb trough strengthens over
the the same region. Combination of instability...lift and
moisture is expected to support showers and thunderstorms...with
activity more likely over northern and western portions of the
forecast area that will be closer to the approaching front.
Isolated severe storms will also be possible across western Maryland and
the eastern WV Panhandle...which should be in the right entrance
region of the jet stream by late in the day. Damaging winds is
likely to be the main threat.
Wednesday will be the warmest day of the week...with highs in the
low 90s at most locations.
Short term /Wednesday night through Thursday night/...
the cold front is expected to move through most of the forecast
area Wednesday night...and should be east of the I-95 corridor by
Thursday morning. Shower/thunderstorm activity should shift eastward
accordingly. Severe threat is uncertain...as better dynamics will
be offset by lower nighttime instability. Lows range from the middle
60s over eastern WV...behind the front...to the middle 70s along and
east of I-95.
Cold front moves east of the region on Thursday...while an upper
trough approaches from the west. Shower/thunderstorm chances continue with
cooler air aloft...but with a north-northwest flow chance of severe weather is
unlikely at this time. Temperatures will be cooler with highs ranging
from the upper 70s over higher elevations to the middle 80s elsewhere.
Upper trough moves through Thursday night...with dry conditions
expected except possibly over southern Maryland and portions of the Piedmont.
Lows drop into the 50s and 60s.
Long term /Friday through Tuesday/...
a ridge of high pressure will build in from the northwest Friday and
Friday night to allow cooler and drier air to push into the region
With the high moving to the coast and offshore during the day
Saturday...southeast to southerly winds will evolve...thus perhaps
spawning a shower in the Potomac Highlands with the upslope
Disturbances in the upper levels will rotate in from the Ohio Valley
and lower Great Lakes Saturday night and Sunday...thus...bringing
the chance for showers and thunderstorms.
As for Sunday night through Tuesday...a potent upper level storm
system will linger across the Great Lakes region. Several waves of
energy will rotate around it and across the middle Atlantic region. The
chance of showers and thunderstorms...once again...will become a
nuisance to the region.
Aviation /01z Wednesday through Sunday/...
VFR most of the night...but MVFR visibilities with fog is possible late
tonight into the early morning hours with moist air over the
region. Have confined the visibility restictions to cho-mrb...away from The
Hubs. Its not beyond the realm of possiblity that MVFR visibilities could occur at
iad too...or that mrb-cho may briefly drop to IFR.
Scattered showers and thunderstorms possible Wednesday afternoon into early Thursday. An
offshore high will push up the heat/humidity before thunderstorms
arrive/develop...while a cold front approaches from the northwest. The
front will likely move across the area late Wednesday into early
Thursday...sweeping this activity off the coast by late Thursday afternoon.
VFR conditions with light and variable winds expected Friday
through Saturday at all terminals.
southerly channeling has come up the chesepeake Bay...placing tplm2 at the
doorstep of Small Craft Advisory. WRF-arw4 has been stronger than the rest...and
latest runs have been stronger still...but even it suggesting that the
peak occurring at this time...W/ winds below any crit level by 02-03z.
Therefore...opted for marine weather stmt vs a targeted Small Craft Advisory.
Southerly winds around 10 knots for the overnight hours.
Light S-SW flow will continue Wednesday and maximize just before the
passage of a cold front early Thursday. Showers and thunderstorms possible Wednesday
evening into the overnight.
No marine hazards expected Friday through Saturday.
tidal anomalies dropped to around a half-foot earlier today...and
remain there at this time. Those departures...if steady...would pose no
concern during high tide tonight...even at sensitive locations.
However...am not certain whether departures wont be increasing
again with the incoming tide considering the 15 knots southerly flow that
has developed on the Bay this evening. Based on low confidence and low
impact /it would be a threshold eevnt at Annapolis/...have opted
to not issue an advisory at this time.
District of Columbia...none.