Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion...updated 
National Weather Service Baltimore Maryland/Washington District of Columbia
902 PM EDT Wednesday Jul 9 2014

Synopsis...
a cold front will slowly move into the area tonight. The boundary
will stall out and dissipate over the region for Thursday and
Friday. High pressure over the Atlantic will bring hot and humid
conditions for the weekend into early next week.

&&

Near term /tonight/...
a second-straight active day across much of the area...though a
shorter-duration event and more confined to areas east of the Blue
Ridge. We are still under the zone of higher moisture and heating
potential west/ the large-scale upper trough axis still back to our
west. Until this feature clears the East Coast...the potential
will continue to diurnal showers/thunderstorms across the area. Isolated
showers will be possible into the late night hours tonight...but a
only a few locales and at this time - in the middle-part of the northern Virginia Blue
Ridge S of Front Royal. Loss of the sun will likely dissipate this
activity shortly.

Evidence that we're still under the same airmass...dewpoints east of
I-81 are still in the u60-l70s and some locales have seen an
increase since earlier this evening. The surface winds have dropped off
from a steady S-SW breeze to nearly calm. The combination of these
elements have a warm overnight period in store for the
area...though the Appalachians have seen a decent drop in dewpoints so
they will see some lows in the u50s-l60s.

&&

Short term /Thursday/...
an upper-level trough will build overhead Thursday through tmrw
night. The cold front over the region will gradually dissipate...and
a light return flow will develop during this time. This means that
little dry air will make it into the area. With higher dewpoints
and the upper-level trough building overhead...more showers and
thunderstorms are possible mainly in the afternoon and evening.
Still feel convection coverage will be scattered since the shear
will be weak and any lifting mechanism from the boundary or
terrain circulation will also be weak. He cold front will stall
out over the region and dissipate. Maximum temperatures will range from the
70s in the mountains to the middle and upper 80s across most other
locations.

Convection coverage should dissipate overnight Thursday...but with
the upper-level trough overhead an isolated shower or thunderstorm
cannot be ruled out...especially across the southeastern County Warning Area where
moisture will be deepest.

&&

Long term /Friday through Wednesday/...
ill-defined surface boundary will retreat northward as warm front
for Friday. Subsidence aloft should hinder convective development
for Friday along this front across the majority of the
area...although stronger moisture gradient and vorticity maximum aloft may
trigger development toward southern Maryland...along with terrain
circulation convective development across the Potomac Highlands.
Moisture advects across the region for Saturday as high pressure
pushes off the northeast coast. While instability increases with
this moisture return...short wave ridging aloft should limit
convective development. However...cannot rule out terrain and
surface heating induced afternoon convection at this time and have
left probability of precipitation in the forecast. As closed Canadian low dives south over
the Great Lakes...westerly flow aloft increases Sunday and Monday.
Short waves in this flow will bring better chances for organized
convection to push through Sunday and Monday ahead of synoptic cold
front. A more comfortable airmass looks to advect into the region
for middle week.

&&

Aviation /00z Thursday through Monday/...
a cold front will move into the area tonight and it will stall
out and weaken Thursday through Thursday night. A light northerly
flow is expected behind the front late tonight into Thursday
morning...but winds will turn toward the southeast later Thursday
and speeds will remain light. Scattered showers and thunderstorms
are expected Thursday afternoon and evening.

Patchy fog is possible late tonight into early Thursday. MVFR
visibilities are expected during this time...but IFR conditions cannot be
ruled out especially across kmrb and kcho. More fog is possible
Thursday night into Friday morning.

A stalled front and surface trough will bring chances of
afternoon storms to the region Friday and Saturday. An approaching
cold front will bring a better chance of more widespread storms
Sunday and Monday.

&&

Marine...
winds will shift to the north late tonight into Thursday before
gradually turning toward the southeast Thursday afternoon. Speeds
should remain below Small Craft Advisory criteria. Showers and thunderstorms are
possible...especially this afternoon and evening...and again
Thursday afternoon and evening. Thunderstorms may contain gusty
winds and hail.

A stalled front and surface trough will bring chances of
afternoon storms to the region Friday and Saturday. An approaching
cold front will bring a better chance of more widespread storms
Sunday and Monday.

&&

Lwx watches/warnings/advisories...
District of Columbia...none.
Maryland...none.
Virginia...none.
WV...none.
Marine...none.

&&

$$
Update...gms
previous discussion...bjl/aeb

National Weather Service Glossary of Abbreviations