Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
305 PM EDT sun Aug 2 2015
high pressure will dominate through tonight. A cold front will
approach from the northwest on Monday and enter the area Monday
night. The front will stall in the area Tuesday...slide southeast
Wednesday...then wiggle back north Thursday. A wave of low
pressure will then ride east along the front Friday. After this
low passes the front will slip south of the area over the weekend.
Near term /through Monday/...
at present...high pressure is centered over the central
Appalachians...with the next frontal boundary still located well
to the northwest in the northern plains. For tonight...the high
will remain in place...and with dry air over the area with many
areas seeing dew points down into the 50s at present...radiational
cooling should start quickly after sunset. As winds begin to turn
southerly overnight with the approach of the front to the
northwest...dew points will begin to rise...and should reach the
lower 60s by morning. This will limit just how cool it can
get...but also may help some patchy fog to form away from the
coastal and metropolitan areas. Otherwise...very benign weather with
Front approaches from the northwest on Monday...but with forcing
remaining well northwest during the day and limited moisture /most
guidance keeps precipitable waters below 1.5 inches/...generally we expect dry
weather through afternoon. The pressure gradient will tighten up
so we do expect winds to become a bit gusty...and the
southwesterly flow will drag warmer air north so highs will rise
several degrees compared to today. However...with a relative lack
of moisture /dew points expected to remain in the low 60s/...heat
indices should stay well below heat advisory criteria and in fact
probably won't even crack 100 at our reliable reporting stations.
Highs will be in the low 90s in most areas with middle 90s in the
Short term /Monday night through Wednesday/...
front moves in Monday night. Shear does
increase...however...moisture will still be relatively limited
and this will in turn limit cape...so this should result in
thunderstorm activity having to advect into the area rather than
develop locally. Best forcing aloft will stay north. Thus...it
appears that storms which develop to our northwest will enter the
County Warning Area during the evening...but appear likely to diminish to showers
overnight...possibly even before reaching the metropolitan area. The
increased cloud cover should hold lows up a bit warmer than
tonight's readings. Places that recieve any rain could also see
patchy fog overnight if some breaks in the clouds develop.
Low pressure in southern Quebec will be moving northward while a
Bermuda high persists in the Atlantic Tuesday. A cold front will
be stalled across the middle-Atlantic in the vicinity of the I-95
corridor Tuesday. Due to the time of year...the temperature
gradient is weak but drier air will be moving into the Potomac
Highlands. In vicniity of the front and in the warm/moist sector
..iso-scattered showers and thunderstorms are possible. Forecast soundings
at dca-nhk show 1-2k j/kg of SBCAPE with unidirectional shear. A
stable layer will likely be overcome by late afternoon and some
storms may produce gusty winds especially across S Maryland and
The cold front moves off the coast Tuesday night as high pressure
builds into the region from the SW. Dry conditions expected
Wednesday. Warm air advection will begin Wednesday afternoon as
the next system approaches.
Long term /Wednesday night through Saturday/...
medium range guidance is gradually coming into better agreement
with the timing of a wave of low pressure moving along a stalled
boundary across the County Warning Area Wednesday night into Thursday. While finer
scale details remain to be seen...felt confident enough to go with
high chance probability of precipitation as the wave passes. Convection potential will
depend on exact timing/placement of the wave.
Guidance diverges after Thursday...with some solutions suggesting
the front sags far enough south to leave the area dry...while
other solutions keep the front stalled over the area with a second
wave of low pressure Friday into Saturday. Climatology would
suggest a slower southward progression of the front...and as such
have kept chance probability of precipitation in the forecast through the end of the week.
High pressure should attempt to make a return next weekend.
Aviation /19z Sunday through Friday/...
generally VFR ceilings and visible through Monday night. Chance of sub-
VFR ceilings/visible at mrb/cho tonight with patchy fog...with best chance
at cho...then chance of sub VFR ceilings/visible Monday night with
thunderstorms in the evening and showers/patchy fog overnight.
Other concern will be winds from the southwest gusting to around
20 knots as the cold front approaches Monday afternoon.
A stalled cold front will be near the I-95 terminals Tuesday and
rain showers/thunderstorms and rain possible through Tuesday evening.
Sub-VFR possible in lower ceilings/visibilities associated west/ showers/thunderstorms Wednesday
night- Thursday. Wind direction forecast uncertain and depends on
placement of stalled front...but speeds should be light at or below 10 knots.
winds will strengthen from the south on Monday as the pressure
gradient tightens ahead of an approaching cold front. This will
help winds to reach Small Craft Advisory levels...and have kept Small Craft Advisory going through
Monday evening all waters...with the Small Craft Advisory for the Bay and adjacent
waters continuing through Monday night.
A stalled cold front will be near the waters Tuesday and showers
and thunderstorms are possible in the afternoon and early evening.
Some storms may produce gusty winds that may warrent a smw.
Depending on the location of the gradient...a Small Craft Advisory may be needed
Tuesday afternoon for portions of the waters.
Winds should remain below Small Craft Advisory levels Wednesday and Wednesday
night. Showers and scattered thunderstorms are possible mainly on
Thursday as a wave of low pressure approaches the waters along the
front. Should this wave of low pressure be stronger than what the
current consensus suggest then there is a chance of Small Craft Advisory gusts
Thursday...but confidence in any one solution is low at this time
given model spread.
astronomical tides are lowering with the full moon now behind
US...and anomalies are low enough that tidal flooding will not be
a threat through tonight. Southerly flow ahead of the next front
will elevate tidal anomalies on Monday...but at this point we are
not expecting minor flooding. This possibility will require
District of Columbia...none.
Marine...Small Craft Advisory from noon Monday to 6 am EDT Tuesday for
Small Craft Advisory from 3 PM Monday to midnight EDT Monday
night for anz535-536.