Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 300056

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
856 PM EDT Fri Jul 29 2016

High pressure over the region tonight. A frontal boundary across
the Carolinas will return north Saturday. An area of low pressure
will track along the front on Sunday. The front will move
southward again on Monday, with high pressure building in early
next week.



How hot has this summer been so far? In terms of average temperature
(Jun 1-Jul 28) at the three major airports it is interesting to
note how many of the warmest years have been since 2010.

 DC (since 1871)   Balt (since 1870)     Dulles (since 1962)
Rank Year  Avg
  1  2010  81.9    1  2010  80.3         1 2010 78.2
  2  2011  81.2    5  2011  78.3         3 2011 77.5
  4  2012  80.1    11 2012  77.5         6 2012 76.2
  6  2015  79.6    26 2013  76.6         7 2016 76.1
  9  2016  79.3    39 2016  76.2         8 2013 76.0
  13 2013  79.0

With high pressure over the region this evening the weather is
quiet with typical late July temperatures. The frontal boundary
across northern NC extending across WV will be working its way
into the Mid Atlantic after midnight bringing the region a chance
of showers. The bettter opportunity will be Saturday afternoon/


A trough axis will cross the area Saturday-Saturday night.
Anticipate moisture transport ahead of the trough, with the
southwest flow dragging the weak quasi-stationary boundary back
north again. So, we once again will be dealing with a marginally
unstable, sheared environment with weak surface and PVA forcing.
Therefore, expect conditional instability, the extent of which
will be predicated by how much daytime heating we will receive. In
the end, there is sufficient evidence to increase PoPs to
categorical, with locally moderate to heavy rain possible. SPC
outlook for Saturday carries a MRGL risk area to account for the
potential of wet microbursts. In addition, believe there once
again will be a local flood threat.

Believe the will be a break Saturday night, due in part to loss of
daytime heating. However, shortwave passage will also play a role,
so the timing may need to be adjusted. But, the lower heights
aloft likely to induce low pressure once again for Sunday. Again,
have focused highest PoPs with the diurnal cycle. That may need to
be adjusted.

High temperatures will be limited by lack of insolation and
anticipated rain Saturday, and slight cool thermal advection
Sunday. Minimal change anticipated for lows through the period.


The front that has been meandering over our area for the past
week or two looks like it will finally push offshore by Monday
night as a 1020+ mb surface high moves in from the north. Before
then, a few showers and thunderstorms will again be possible
Monday. But after that conditions look much more seasonably mild
and less humid through the middle part of next week.

The high will move offshore by the end of the week likely leading to
increasing heat and humidity once again.


VFR conditions expected overnight..

Probability for flight restrictions will improve Saturday as
shortwaves will act upon an increasingly warm, moist, and unstable
atmosphere. Still a bit too far out for specific timing. Have
focused on midday and afternoon hours in the TAFs, limited
restrictions to MVFR at worst. However, local downpours possible,
which could briefly create IFR or below. In addition, there also
will be a gusty wind threat.

Those storms likely to exit at some point in the evening on
Saturday. However, additional storms possible on Sunday...again
with possible flight restrictions.

Generally VFR expected Monday and Tuesday with northwesterly flow
around 10 knots.


Winds have diminished to 10 knots or less. Anticipate similar
speeds for the next several days.

Showers and thunderstorms return Saturday, some of which may
contain heavy rains and gusty winds. Additional thunderstorms
possible Sunday. Any hazards will come from these winds.

A cold front will finally push offshore early next week. A
brief period of Small Craft Advisory winds cannot be ruled out
immediately behind the front in northwest flow.


Water levels running about a half-foot above astronomical normals
at this time. There may be a slight decrease tonight, but that
will increase once again on Saturday as storms will return--
drawing moisture north. Sensitive locations may threaten minor
thresholds both Saturday and Sunday. The overnight tide cycle
will be the higher astronomically; that`s where the better risk




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