Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
1014 am EDT Tuesday Sep 2 2014
Bermuda high will persist today ahead of a weak cold front that
will cross the area tonight. High pressure will then build from
the Midwest through Wednesday then persist offshore Thursday into
the weekend. A cold front will enter the region in the Saturday
night time frame.
Near term /through tonight/...
very warm and moist air mass remains over the County Warning Area today. This will
likely help fuel thunderstorms from middle or late afternoon into the
evening. Before then...County Warning Area should be dry save for a passing/stray
shower clipping the Allegheny Highlands.
Sunshine this morning will eventually be replaced by increasing
clouds this afternoon. Sunshine...toasty 850 mb temperatures and a west/SW
flow will help boost surface temperatures at or above 90 degree f for most
areas this afternoon. Combine the humidity and it may feel more
like middle to upper 90s east of the Blue Ridge.
Pre-frontal convection over the Ohio Valley has been weakening
with time. Whatever is left of it will likely make it to the
Potomac Highlands by mid-afternoon...and then undergo a
re-intensification further downstream in what may be a moderately
unstable /modified 12z kiad sounding reveals 3000 j/kg cape/ and
moist air mass. In addition...presence of a surface trough /sort
of parallelling I-95/ would also support convection.
Given the expected buoyancy...a few thunderstorms may be able to
produce strong to damaging wind gusts as they move eastward across
the County Warning Area through this evening. A high precipitable water
environment also supports heavy rainfall however storm motion may
be sufficient enough to preclude flash flooding /unless training
Pop/weather grids have been updated to reflect a little more detail in
timing of convection...severe weather potential statement mentions damaging wind gusts.
Eventually...cold front catches up to the trough later this
evening and then pushes offshore. This will effectively end the
chance for showers and thunderstorms overnight.
Short term /Wednesday through Wednesday night/...
dry and stable on Wednesday. No probability of precipitation in the forecast. Another warm and
relatively humid day...as highs will again approach the 90f degree
mark across much of the area. Dewpoints will still be in the
l-m60s...creating heat indices right around the ambient temperature
Wednesday night...high pressure center over the area shifts
offshore with a return flow developing in the overnight hours.
Dewpoints quickly raise back to near 70f...might as well get areas
of fog wording in the grids. With the high persisting
offshore...an unstable Gulf airmass brings the middle-Atlantic right
back into an active pattern by Thursday. Chances for diurnal
driven scattered thunderstorms. Should low level flow be more southeasterly
than southerly...terrain enhancement would also be a factor in
thunderstorm development. Similar pattern for Friday with the next
Maximum temperatures Thursday and Friday around 90f though cloud cover will
be a factor.
Long term /Thursday through Monday/...
another weak cold front approaches Friday night. Likely probability of precipitation for
thunderstorms west from the Blue Ridge Saturday as there is good
consensus between the 00z GFS and 00z European model (ecmwf). Question is how
quickly the front pushes through the area. The European model (ecmwf) lingers the
cold front over southeastern zones through Sunday.
Aviation /13z Tuesday through Saturday/...
main issue will be rain showers/thunderstorms and rain affecting the terminals this
afternoon/evening. At The Hubs...latest runs of the hrrr/WRF-arw
highlight 21z-01z as the primary window of concern. Cold front
accelerates to a trough and then moves offshore by late evening.
Prevailing/synoptic wind shift likely occurs 02z-05z. NAM/GFS both
suggest some fog tonight. Low level moisture does linger into the
overnight...but with wind shift to northwest will lean toward a more
optimistic approach at this time.
High pressure overhead Wednesday and Wednesday night. With
light/calm winds may have some fog Wednesday night. Light southerly return
flow Thursday and Friday with mainly afternoon chances for
thunderstorms. Cold front enters the area late Saturday with
thunderstorms ahead of it.
SW flow continues today ahead of a cold front. Wind shift to northwest
occurs late this evening behind the front but northwest push/gradient
appear weak enough for winds to remain below Small Craft Advisory. Main concern
will be thunderstorms late this afternoon and evening which could
produce strong winds that would prompt smw/S.
Wednesday will see high pressure build into the region and drop wind speeds
down even further. Light and variable flow Wednesday evening
gives way to southerly flow as high pressure moves offshore. Will have
to watch for channeling again (probably Thursday evening) but as
of now there are no Small Craft Advisory headlines expected. Cold front approaches
the waters Saturday with good chances for thunderstorms.
District of Columbia...none.