Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
929 PM EDT Monday Jun 29 2015
high pressure moves east this evening. Low pressure over the Great
Lakes will ride a nearly stationary front to the north...with the
associated cold front swinging into the region on Wednesday. This
front will stall over the middle Atlantic through Saturday.
Near term /through Tuesday night/...
upper level trough positioned over middle west this evening...with
trough axis oriented across Ohio River valley. 00z surface analysis
indicating frontal boundary extending western WV into central PA.
On going convection at this time in the vicinity of this surface boundary with
support aloft coming from embedded shortwave rounding the base of
the trough. Precipitation has been weakening/dissipating as it nears the
western fringes of the County Warning Area with the area having been capped during
the day. Some elevated instability already in place could aid in
continuing the convection forming to the west into areas west of
the Blue Ridge as the shortwave swings eastward. Minimal shear and
instability overall though would suggest a weakening trend...with
only isolated-scattered showers expected. Will hold off on thunderstorm mention until
Tuesday morning. Most of the area will remain dry for tonight.
Surface low over the Ohio River valley will ride the nearly stationary
front on Tuesday...reaching the eastern Great Lakes by Tuesday evening.
Models develop surface trough along eastern edge of the Blue Ridge by
the afternoon...which will aid in triggering afternoon convection when the
best support from aloft rounds the base of the upper level trough.
Strong surge of both warm air advection and moisture advection...especially east of the
Blue Ridge...will lead to increasing instability...with SBCAPE
values between 500-1000 j/kg. Deep layer shear is forecasted
25-35 kts...which combined with the increased instability could
lead to isolated strong to severe storms.
Tuesday night...trough lingers over the area...activity should
shift east to the Bay through the night. The upper trough enters the
central Appalachians late in the night...with scattered showers
possible. Min temperatures low to middle 60s west of the Blue Ridge...upper
60s to low 70s east...middle 70s near shore.
Short term /Wednesday through Wednesday night/...
trough axis move slightly east on Wednesday while cold front creeps southeastward toward area.
Overall forcing mechanisms do not look that great. However...if Euro
depiction of shortwave crossing Maryland during the day pans out...then there
will be a better chance at thunderstorms and rain. Shear exits Ely...but still have favorable
instability parameters. Have taken probability of precipitation down a bit...forecast gnly around 30-40
percent...but placed a bit more emphasis in the Lee trough lt in the day.
Diminished precipitation after loss of daytime heating. Kept temperatures near
Long term /Thursday through Monday/...
at 12z Thursday meandering front is currently prognosticated to be along our
northern border with most...if not all...of our area in the warm
sector. Some question remains with regards to timing of frontal
passage...with some guidance suggesting front passes through
early...while others suggest a later passage. Regardless...surface lp
tracks along the front and...with baroclinicity...some upper level
support...and deep moisture...could setup a rather wet period. Upper
level flow not overly impressive (aob 30 kts at 5h) as subtle short
wave approaches the area...so not expecting extremely organized
storms...though could be enough instability for stronger pulse-type
Front oscillates around the area through the remainder of the
period...which keeps forecast muddled. Chance probability of precipitation remain in the
forecast each day for mainly diurnal thunderstorm activity. With the
typically favored higher terrain locations having the highest probability of precipitation.
Temperatures expected to remain near normal through the extended
period...with a slight increase through the weekend. Dewpoints not
overly oppressive...generally at or below 70f...which should keep it from
getting too uncomfortable.
Aviation /01z Tuesday through Saturday/...
mainly VFR conditions through the taf period expected. Light southerly flow
tonight...incrsg 12-14z Tuesday. Occasional gusts to 20 kts possible midday.
Generally dry weather tonight...kmrb could see a stray shower. Increasing
chance of shower/thunderstorm on Tuesday...especially District of Columbia/Baltimore taf sites. Hard to
pinpoint timing at this time...so will maintain thunderstorms in the vicinity through the afternoon
hours. Any thunderstorm could reduce conditions MVFR or lower...as well as
bring a brief period of gusty-strong winds and heavy rain.
Low confidence in flgt restrictions Wednesday. Potl certainly there...but
timing/placement a real struggle. VFR should prevail most of the
Most periods Thursday through Sat will be VFR...though expect sub-VFR
conds in any thunderstorm activity. Variable winds expected through the
sub-Small Craft Advisory conditions tonight. Southerly flow increases to 15 to 20 knots
with gusts up to 25 knots on Tuesday. Small Craft Advisory for all waters begins at 10am
Tuesday and continues until 8pm...will continue the Small Craft Advisory into the
overnight for all waters minus northern zones of the Chesapeake.
Scattered gusty thunderstorms develop late Tuesday afternoon and
continue through Tuesday night.
Winds at or below 10 knots Wednesday-Wednesday night...mainly from the SW.
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. Afternoon thunderstorms are also possible each day...which could impact
water levels will be increasing tonight through middle week. The
water levels may approach minor thresholds around SW District of Columbia high tide
Tuesday morning...and then again Wednesday along the western Chesapeake during
the higher high tide...which is the am cycle /midngt through noon/.
District of Columbia...none.
Marine...Small Craft Advisory from 10 am Tuesday to 4 am EDT Wednesday
Small Craft Advisory from 10 am to 8 PM EDT Tuesday for anz530-