Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
931 PM EDT Thursday Oct 8 2015
a warm front will cross the region from southwest to northeast
tonight. A cold front will then cross the region from northwest to
southeast on Friday evening. High pressure will build in on
Saturday and persist through Monday. Another cold front will cross
the region Tuesday.
Near term /through Friday night/...
hints of hipres still hanging on along the middle Atlantic coast.
However...waa-induced high clouds spreading across the County warning forecast area this evening.
Believe these clouds will be thickening through the night...especially during
the overnight hours. GFS /18z cycle/ still trying to bring light precipitation into
County warning forecast area...almost to I-95...by dawn. Its alone in this solution. Latest radiosonde observation
indicates theres plenty of dry air to overcome...so this solution is
not preferred. Instead...sticking with what lwx-WRF-arw4 and the
hrrr suggests-- maybe some rain showers arriving along the Appalachians by 12z.
Grids recvd a light freshening...otherwise going forecast on track.
For Friday and Friday night...still watching a cold front currently
over the middle west to approach and move through the region. The pre-
frontal trough becomes more defined and aligns along the I-95
corridor by the afternoon...with the progression of the front bringing
it into western areas in the morning...and clearing to the east
and south by Sat morning. Zonal flow weakens as heights aloft fall
during the day Friday...with the main shortwave energy associated
with the trough aloft not reaching the area till later Friday...a
slower progression than noted on previous model runs. Have slowed
the precipitation slightly due to the timing of the 12z mesoscale and global
models. Western areas could see showers and isolated thunderstorms by
midday...with precipitation becoming more likely east of the Blue Ridge later
in the afternoon and through the evening...with the precipitation then pushing
Most of the County Warning Area remains under a marginal risk for severe weather
potential on Friday with the main threat being strong/gusty winds.
0-6 km shear showing between 30-35 kts...with ensemble SBCAPE
values hovering between 800-1200 j/kg...especially over northern Virginia and
to the north and east. The low level jet looks to be stronger well to the
north while forcing aloft also looks to almost split the area.
Thinking is that a line develops right ahead of the front over the
northern half of the County Warning Area during the day/evening...with showers
becoming more widespread...and not severe...during the evening and
overnight associated with the second area of forcing aloft.
Short term /Saturday through Sunday/...
shortwave trough pushes on past US Saturday morning behind the
surface cold front. Cut-off low now looks like it will stay
sufficiently south such that any rain or even most cloud cover
will stay to our south...allowing for a sunnier day. Still
expecting a breezy and cooler day with cold advection as high
pressure builds. Saturday night will also be chilly and with
clearing skies plus high pressure overhead...could even be a
little patchy frost in the valleys near and west of the I-81
corridor. Sunday should see lighter winds than Saturday along with
slightly warmer temperatures.
Long term /Sunday night through Thursday/...
cut off upper level low centered over Carolinas will weaken and mv as strong
shortwave during early half of weak. Zonal flow continues through latter
half of weak. Cold fnt will crs the County Warning Area Tuesday. Best chance for precipitation will occur
Tuesday morning. Hi prs centered over Gulf sts will briefly crs Maryland atl reg
Tuesday night through Wednesday morning. Low prs trofg asscd with low prs center near
Great Lakes will affect Maryland atl reg Wednesday afternoon and evening. Any precipitation asscd with
this feature will stay north of County Warning Area.
Aviation /01z Friday through Tuesday/...
VFR conds through Ely morning. Theres some suggestion of fog from guidance.
Dewpt depressions should be low enough...and winds should dcpl overnight.
But would rather there not be as much high cloud around. Inserted some
sunrise MVFR br...but with rather low confidence.
VFR conditions initially Friday morning...with sub-VFR conditions
becoming more likely with the heavier precipitation in the afternoon. Have left this
out of taf at this time due to timing uncertainties. Southerly wind increase ahead of
the fnt /g15-20 kt/...with the wind shift coming Friday night as the
front swings through. Expect northwest 10-15 kts in the wake of the front.
Possible sub-VFR conditions lasting through Friday night until he front
clears the area.
Gusty northwest wind Saturday should give way to lighter winds
through the rest of the weekend. VFR conditions should prevail
Saturday through early next week aside from patchy inland fog.
southerly winds at or below 10 knots at this time...should be increasing overnight. Expect to be
reaching Small Craft Advisory criteria at some point during the morning across most of
the waters...expanding to all waters in brief gusts during the
afternoon. Have retooled Small Craft Advisory headline to fit this thinking.
We should see a big enough lull Friday night to allow the Small Craft Advisory to
drop before Small Craft Advisory conditions start up again close to daybreak Sat
morning. In addition...some of the storms Friday afternoon/evening could
produce gusty winds...resulting in smw criteria.
Gusty northwest wind behind the cold front should result in Small Craft Advisory
conditions Saturday...but these should subside by Saturday night
as high pressure builds overhead and remains for Sunday. Continued
sub-Small Craft Advisory into early next week.
anomalies increase tonight as southerly flow increases on the main
channels to 10-15kt. Challenge remains by how much and how
quickly. Guidance once again suggesting a threshold advisory event
overnight at Annapolis. Certain it will be -real- close to
criteria /an inch?/. however...quite uncertain which side of the
line it/ll be. Based on trends since noon...have opted to go on the
low side. Will not be issuing any advisories for the overnight hours
at this time.
However...as tidal departures increase during the morning on Friday...
minor inundation becomes more likely during the daytime tide cycle
Friday. Water levels will remain high until late Friday night when
a cold front moves through and 20 knots northwesterly/northerly flow overspreads the
waters into Saturday.
District of Columbia...none.
Marine...Small Craft Advisory from 2 PM to 6 PM EDT Friday for anz530-
Small Craft Advisory from 10 am to 6 PM EDT Friday for
Small Craft Advisory from 5 am to 10 PM EDT Friday for anz534-
Small Craft Advisory from 10 am to 10 PM EDT Friday for anz537.