Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
315 PM EDT Tuesday Sep 2 2014
Bermuda high will persist this afternoon 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 /until 6 am Wednesday morning/...
very warm and moist air mass persisted over the middle-Atlantic this
afternoon. Temperatures were rising into the lower 90s in many areas
and the combination of heat and humidity was making it feel more
like the middle to upper 90s east of the Blue Ridge.
Heat and humidity will help to fuel thunderstorms this afternoon
into this evening. We have seen cumulus development
already...although cumulus have had limited vertical growth thus far due
to some capping. This is expected to change later this afternoon
into the evening.
We will have to watch convection that may develop near a surface
trough this afternoon. There/S also upstream convection in central
WV /convection which re-fired/intensified from early morning Ohio
Valley convection/ which will move east with time...and there could
also be additional upstream convection later on more directly
along/ahead of the cold front. Thus there may be several clusters of
convection to keep an eye on through this evening. However...details
regarding the exact evolution and coverage of any one remain
Based on radar trends...will have likely probability of precipitation across the northwest
portion of the County Warning Area. Further downstream...will keep probability of precipitation in the
chance/scattered category but these may need to be bumped up if any
one cluster congeals as it moves east either later this afternoon or
Modified 12z kiad radiosonde observation indicated around 3000 j/kg of cape.
Precipitable water value was around 1.8 inches...this may be closer
to 2 inches by 00z. Instability and moisture will be
decent...however better shear likely resides just northwest of the
County Warning Area. This may limit a widespread severe risk...however buoyancy
alone could Foster a few thunderstorms producing damaging wind
gusts through this evening.
Given high moisture content...heavy rainfall will also occur in the
strongest storms. But given forecast storm motion...storms should
move enough to preclude a flash flooding risk unless training were
Cold front eventually catches up to the trough later this
evening...moving offshore tonight. Chance of thunderstorms will end
behind the cold front.
Short term /6 am Wednesday morning through Friday/...
County Warning Area will be Post-frontal on Wednesday. Northwest winds will bring
some drying through the County Warning Area...leading to plenty of sunshine and
lower humidity. Front looks like it gets hung up in southern
Virginia as weak high pressure builds in from the north.
High moves offshore on Thursday. May see isolated showers and
thunderstorms develop up/near the Blue Ridge by afternoon. Activity
would likely be diurnal in nature. Trough develops on Friday...with
the potential for more diurnal convection.
Long term /Friday night through Tuesday/...
another cold front approaches Friday night. Question is how
quickly the front pushes through the area. It may move through by
Saturday night...but its possible it doesn/T clear the southeast
part of the County Warning Area until Sunday. High pressure and dry airmass will
build into the area Monday.
Aviation /19z Tuesday through Sunday/...
main issue revolves around afternoon and evening convection. Focused
on late afternoon into the evening for The Hubs mainly based on
upstream convection over WV and ahead of the cold front...although
isolated thunderstorms and rain ahead of these can not be ruled out earlier. Cold
front moves through late in the evening with a wind shift to the
northwest. Low level moisture lingers tonight. If winds become
calm...fog may form. This appears most likely at cho. Expectation is
for enough wind to occur at other sites to inhibit fog formation.
VFR expected Wednesday Post-frontal and with high pressure in
control. High moves offshore to end the week. Next cold front will
affect the area over the weekend.
primary concern late this afternoon and evening will be strong gusty
winds and lightning in scattered showers and thunderstorms. Smw/S
may become necessary. Chance of thunderstorms will continue until a
cold front passes tonight. High pressure builds in for Wednesday
then moves offshore to end the week. Cold front moves through over
District of Columbia...none.