Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
301 PM EDT Monday Aug 31 2015
high pressure will remain offshore through Tuesday. An upper-
level disturbance along with its associated surface trough will
pass through the region Wednesday. Weak high pressure will build
overhead Thursday before a backdoor cold front moves into the area
late Friday into the weekend.
Near term /through Tuesday/...
several competing factors in regards to convection this afternoon.
Vorticity maximum is lifting NE across the area...with rapid clearing in the
subsidence behind it. However...cumulus have filled in over the
higher terrain. This feature has only provided a few light showers
as most moisture is in the middle levels. Meanwhile low level
convergent boundary is sinking south and this is where scattered
convection has formed in southern PA/western Maryland. All told...think
this will lead to most of the convection remaining mainly north and west of
District of Columbia...where better instability is also located. Can/T rule out isolated
development elsewhere though.
Precipitation chances will sink south with deeper moisture this
evening...eventually dissipating. Skies will likely become mostly
clear across the majority of the area...although some clouds could
linger in the short wave. With winds calm and elevated dew points...some
patchy fog could develop dependent on cloud cover. Favored areas
would be short wave of metros. Lows in the 60s with lower 70s along and
east of I-95.
Broad surface ridging remains in place on Tuesday. Middle and upper level
ridging will also build...and a closed low over the Ohio Valley will
remain to the west. Atmosphere will likely be capped over most of
the area...so have left the small chance of diurnal convection
limited to the western terrain. With mostly sunny skies east of the
mountains...highs should be able to near or exceed 90 in many
locations. Heat indices should remain below 100 though.
Short term /Tuesday night through Thursday/...
any mountain convection will wane during the evening. Otherwise
continued muggy conditions are expected as weather pattern changes
very little. Lows could even be a degree or two higher...with more
locations in the upper 60s to lower 70s.
An upper-level disturbance and its associated surface trough will
pass through the region later Wednesday into Wednesday evening.
More unusually warm and humid conditions will continue...but there
will be an increased chance for a shower or thunderstorm. The best
chance for convection will be across the Potomac Highlands into
central Virginia...closer to track of the upper-level
Most convection should dissipate Wednesday evening as the upper-
level disturbance and surface trough move off to our south and
east. A northwest flow is expected behind the trough...but with no
temperature or dewpoint gradient more warm and humid conditions
Weak high pressure will build toward the area Thursday. A
northwest flow will continue...but again more hot and humid
conditions are expected due to sunshine and a downsloping flow. An
isolated shower or thunderstorm may pop up across the higher
terrain...but most of the time will be dry.
Long term /Thursday night through Monday/...
warm and humid conditions will continue Thursday night...but most
areas will turn out dry. A backdoor cold front will approach the
region Friday before moving into the area Saturday. The boundary
may trigger a few showers and thunderstorms. Cooler and less humid
conditions are possible behind the boundary later this weekend.
There is still some uncertainty though as to how far south and
west the boundary will make it. High press builds in sun through
Monday bringing drier conditions.
Aviation /19z Monday through Saturday/...
as of mid-afternoon...trends suggest most showers and storms will
remain northwest of the metropolitan areas through this afternoon. However cannot
rule out an isolated shower affecting a terminal by late afternoon.
Impacts would be brief if this were to occur. Chance will diminish
with sunset. Assuming skies clear tonight...br will likely develop
at mrb/cho. Confidence to low to include at iad for now. For
Tuesday...storms should remain west of the terminals. Winds remain
under 10 knots through the taf period.
VFR conditions are expected most of the time Wednesday and
Thursday. A popup thunderstorm is possible Wednesday afternoon and
evening. Patchy br may briefly reduce visibilities early Wednesday
morning and again early Thursday morning. VFR conditions expected
Thursday night. Sub VFR conditions possible due to showers and thunderstorms on
southwest flow will continue across the waters through tonight.
Speed could increase this evening...but have capped at 15 knots given
the SW component. An isolate shower or storm is possible near the
District of Columbia/Baltimore area through evening...but these should be weak if they
occur. High pressure becomes reestablished Tuesday and flow will be
variable and under 10 knots.
Winds should remain below Small Craft Advisory criteria Wednesday and Thursday. A
backdoor cold front will pass through the waters late Friday into
Saturday. A Small Craft Advisory may be needed for portions of the
waters during this time. High pressure will return for early next
District of Columbia...none.