Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
1033 am EDT Tuesday Jun 30 2015
low pressure will slide eastward over the eastern Great Lakes
today. A cold front will slide southeast into the middle Atlantic on
Wednesday...and then stall across the region on Thursday. The
stalled front will linger in the area through the weekend before
lifting northward again on Monday.
Near term /through tonight/...
surface analy depcits subtle fetures today. Tough to pin down
specifically where the warm front is...but clerly theres convergence in vicinity of
the balt/District of Columbia crrdr based on southeasterly flow across northestern Maryland vs S/southwesterly flow
elsewhere within the County warning forecast area. That has resulted in a patch of clouds in the
metros. A cluster of rain showers have been able to develop under cloud deck...
with a hint of a line beginning stretching down to cho.
Lwx 12z radiosonde observation depicts warm layers h10-8 and again h6-5. However...the
current radar suggests that may not be a deterrent. The mountains/shen
valley seem to be getting enough heating...so would expect instability to
intensify. A modified sndg...based on lamp and a temperature/dewpt forecast
of 85/65f...suggests 1500-2000 j/kg SBCAPE available. Shear measured
at 30 knots...which model forecasts retain through the day.
In terms of evolution...obviously the convergence will dominate for the
morning. Lwx WRF-arw4 capturing it. However...believe that terrain
circualtion should develop in the blurdg or in the crrdr of heating in
the shen valley. Have probability of precipitation in the former location for the morning...
then expand chance probability of precipitation elsewhere by Ely afternoon.
Some strong to severe storms could develop based on modified radiosonde observation
and the more aggressive model guidance. The primary threat would be
localized damaging wind gusts. However the shear suggests a cpl
supercells not out of ther question.
While there should be an overall eastward progression and diurnal
weakening of activity this evening...models maintain elevated instability
overnight...and middle/upper level trough will be approaching toward
daybreak. Therefore some showers and storms may linger well into the
overnight period. Min temperatures in the Lower/Middle 60s west and upper
60s/lower 70s east.
Short term /Wednesday through Thursday night/...
middle level trough axis will be lifting north during the morning
hours. Surface cold front will be approaching from the northwest but
likely won't enter the area during the daytime hours. Timing and
coverage of precipitation quite uncertain without strong forcing
mechanisms. If forecast soundings are correct in decreasing instability
behind the trough passage in the afternoon...convection may be
rather limited. Have maintained low chance probability of precipitation throughout day.
On Wednesday night...the cold front will stall out over the middle
Atlantic just to our south. Support aloft will wane as the trough
passes so expect convection to quickly dissipate or move away.
With the front stalled in the area...guidance is beginning to hone
in on a wave of low pressure moving east along the front from the
middle Mississippi Valley Thursday or Thursday night.
However...timing is still much in question...so generally keep
chance probability of precipitation around with likelys to the south closer to the stalled
front. With the front to the south and increased cloud
cover...temperatures should be cooler on Thursday.
Long term /Friday through Monday/...
through the long term the pattern will remain fairly static with a
broad trough over Canada...and a strong ridge out west. This will
keep funnelling disturbances southeast and east across our area as
a frontal boundary remains stalled out over the region. Showers
and thunderstorms will be possible each day with the front nearby
but timing disturbances will be increasingly difficult as we go
further out. Right now one system may affect US Saturday...and
another Monday...but confidence on timing is not high.
So...generally have kept temperatures a bit below normal...with a chance
of showers and thunderstorms in the forecast each day. As we get
closer...we should have better clarity as far as days which will
turn out mostly rain-free...and those which will be pretty wet.
Aviation /14z Tuesday through Saturday/...
southerly winds will increase during the midday with occasional gusts
to 20 knots. Thunderstorm coverage and timing still lower confidence
today. Convergence developing some storms in vicinity of dca/iad/BWI this morning.
Think the activity should jump to the blurdg during the afternoon.
However...cannot rule anything out in terms of timing and placement.
Restrictions would be brief...but MVFR/IFR potl exists. Strong wind
gusts could accompany any storm.
Disturbance crosses area late tonight/Wednesday morning...so a shower or
storm will remain possible...but lower potential for ceiling/visibility
reductions. Questionable how much of this activity
lingers/redevelops Wednesday afternoon...low chance of impacts.
Main concern through extended is potential for scattered
thunderstorms each day. Winds will be uncertain given the front
will continue to meander in the area after arriving Wednesday.
Wave of low pressure may provide a more concentrated period of
rain and IFR ceilings/visible at some point Thursday...Friday or Saturday
but low confidence right now on when this is...or if it even
S/southeast channeling occuring over the waters. Small Craft Advisory in effect.
Thunderstorms will develop with the potential for strong wind
gusts-- some smw/S are possible. Gradient winds will diminsh
overnight. SW flow through Wednesday around 10 knots...although may be
slightly stronger toward Tangier Sound. Lower chance of storms
Winds expected to remain below Small Craft Advisory criteria through the
extended...though will need to monitor as front will be near area
each day. Showers and thunderstorms are also possible each day...which
could impact marine concerns.
water levels will be increasing through middle week. The water levels topped
out on the edge of advisory criteria this morning at wasd2 and axtv2.
Better chance tmrw during the same time cycle...midngt through noon.
District of Columbia...none.
Marine...Small Craft Advisory until 4 am EDT Wednesday for anz531>534-
Small Craft Advisory until 8 PM EDT this evening for anz530-