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Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia
927 PM EDT Sat Aug 1 2015

high pressure will dominate the area through Sunday night. A warm
front will move across the area Monday. A cold front will move into
the area and stall Tuesday. A wave of low pressure will develop
nearby along the front Wednesday and Thursday before moving away


Near term /through Sunday/...
surface trough stretches across southern Maryland this evening...more or
less coincident where thicker cloud cover still resides. As of
01z...the isolated showers which developed have crossed the Bay.
Given these were likely aided by diurnal instability...may be able to
remove the probability of precipitation for the remainder of the night despite it taking
some time for the trough to push east. Drier air (dew points in
middle 50s) has had a difficult time pushing east of the Blue Ridge.
That could play a role in how much fog develops in the central Virginia
Piedmont later tonight. Outside of this uncertainty...fog should
be patchy and relegated to the typical rural low lying spots.
Otherwise mostly clear and calm conditions are expected with lows
mainly in the 60s...except lower 70s in urban centers and 50s in
the mountains.

Surface high pressure persists through Sunday as heights rise
aloft and the flow aloft becomes more west to southwest. This
should promote mostly sunny skies and a lack of precipitation.
Highs will be near normal again but dew points will drop back into
the upper 50s so overall...Sunday should be slightly more
comfortable than today.


Short term /Sunday night through Tuesday/...
high pressure will maintain control Sunday night with mostly clear
skies...though dew points will begin to creep back up. Patchy fog
will again be a concern in the sheltered inland locales away from
the metropolitan where radiational cooling should allow temperatures to reach
the dew point. With the rising dew points...lows should end up a
bit milder than tonight.

Monday looks to be quite hot with gradually increasing humidity
and 850 mb temperatures increasing to 19- 22 c. It will be the first day
with appreciable southerly return flow so expect dew points to
remain in the 60s...leading to apparent temperatures in the middle
to upper 90s during the afternoon.

A cold front will approach from the west late in the day...along
with an upper jet maximum around 250 mb. Thinking this will fire
showers and thunderstorms during the afternoon to the northwest of
the County Warning Area...propagating into the Potomac Highlands during the
evening. Most guidance is in agreement with moderate cape and
shortwave well as modest shear over these areas. As
such...Storm Prediction Center has the northwestern corner of the area in a marginal
risk for severe thunderstorms on day 3/Monday. Cannot rule out a
strong storm or two accompanied by gusty winds. Went with likely
probability of precipitation/chance thunder over The Highlands in the evening...gradually
tapering off as activity moves east and diminishes overnight with
the loss of heating. A pop up thunderstorm is also possible in a
zone of enhanced convergence ahead of Lee side pressure trough
over central Maryland/Baltimore metropolitan area Monday have
isolated probability of precipitation for these areas as well.

Tuesday will be another very warm day as the front stalls
near/just south of the area. Deep-layer westerly flow
/downsloping/ takes over on Tuesday and with no real forcing
mechanism expect rain chances to be pretty minimal...but that
could change if the front stalls further north /keeping low-level
winds more southerly and moist/.


Long term /Tuesday night through Saturday/...
mean troughing aloft will linger over the northeastern Continental U.S.
During the second half of the week. At the surface...a front will
remain stalled near the area. Unsettled conditions are likely at
times...but pinpointing the exact timing at this time range is
difficult at best. Gefs/ec mean seems to want to highlight
Wednesday night into Thursday with higher probability of precipitation as a wave of low
pressure moves along the front...but timing/placement/strength of
said wave are all in question.

The pattern persists but with even lesser certainty in details
through the end of the week.


Aviation /01z Sunday through Thursday/...
surface trough has pushed east of the terminals this evening. High
pressure will then dominate through Sunday night. VFR conditions
will be the rule with few if any clouds (diurnal cumulus base of 5-6
kft) and sustained winds less than 10 knots. Have maintained a
mention of MVFR br at kcho late tonight...but confidence is not
high and could depend on how much dry air can filter in. There is
a chance of fog at the inland terminals again Sunday
night...although guidance does not look overly favorable.

Generally remaining VFR Mon-Wed...but sub-VFR possible especially
for mrb/cho Monday evening...initially in rain showers/scattered thunderstorms and rain...then lower visibilities
possible overnight in patchy fog as winds lighten west/ front overhead.
Southerly winds 10-15 knots Monday become westerly Monday night-Tuesday at or below 10 knots. Wind
forecast becomes uncertain by Wednesday and depends on positioning of
front/approaching wave of low pressure.


have seen a little uptick in winds this evening as a pressure trough
approaches the Bay...however gusts have been less than 18 knots. If
there were a stray gust higher than would likely occur
before midnight. Given the low probability and short time frame...will
not issue a Small Craft Advisory. As high pressure builds in later tonight...winds
will remain light through Sunday night.

Small Craft Advisory gusts look likely Monday afternoon into Monday night in
southerly channeling ahead of an approaching cold front/Lee side
pressure trough. Gradient weakens as front moves overhead and
winds turn westerly Tuesday into Wednesday.


Tides/coastal flooding...
astronomical tides are higher due to the nearly-full moon...but
anomalies are low enough that tidal flooding will not be a threat
through Sunday. Southerly flow ahead of the next front will elevate
tides on Monday...but at this point not expecting minor flooding.
This possibility will require monitoring however.


Lwx watches/warnings/advisories...
District of Columbia...none.


short term...rcm/dfh
long term...dfh

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