Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
901 PM EDT Wednesday may 6 2015
a weak front over Pennsylvania will dissipate overnight. High
pressure will build over the northern middle-Atlantic Thursday. Low
pressure off the Carolina coast Friday will gradually erode this
weekend. A cold front looks to move into the region Tuesday.
Near term /until 6 am Thursday morning/...
two clusters of showers and thunderstorms...one over the eastern
West Virginia Panhandle and near the city of Winchester and the
other over the Virginia Piedmont...are weakening as they drop
southward the remainder of this evening. Earlier...this activity
was producing frequent lightning...heavy downpours and even some
large hail. Now...this activity holds not much more than a quick
downpour or a wind gust over 35 miles per hour. One thing to note is to be
cautious about driving this evening in case you come across some
ponding of water on roadways due to the downpours or if you are
outdoors to be Leary of an occasional lightning strike with the
Any other residual showers should dissipate within the hour and
are few and far between each other. No big issues expected
overnight. Regarding recent rainfall from earlier activity...some
places may encounter patchy fog that could reduce visibility
quickly but briefly. Lows mainly in the 55-60 range
overnight..sltly warmer in the cities and cooler in The Highlands.
Short term /6 am Thursday morning through 6 PM Thursday/...
fnt is expeceted to dissipate over the middle Atlantic Thursday then weak induced
high pressure over the area. Perhaps southern part of the forecast area will see
some high clouds as a result of the low pressure area off the Georgia/SC
CST. Highs gnrly around 80.
Long term /Thursday night through Wednesday/...
the period from Thursday night through Friday night may be among the
most tranquil of the period...yet still feeling a little more like
Summer than Spring. Middle/upper level ridge axis will be centered
overhead with surface high pressure offshore. Coastal low pressure will
be trapped under the ridge just off the Carolina coast. Its effects
on the local area should be minimal through this time
period...although a surge of higher precipitable waters begins to move north late
Friday. There won't be much forcing to tap into it though...and it
appears any precipitation will stay south of the County Warning Area. Otherwise expect only
isolated diurnal convection tied to the terrain...as locations east
of the alleghenies will likely be capped.
As we saw this morning...moist low levels (dew points around 60f)
and light winds may lead to fog formation around dawn. While this
potential will exist both Thursday and Friday mornings...forecast
soundings and sref probs indicate more favorable conditions Saturday
morning...especially if skies clear under the ridge. Something to
keep in mind for the time being as fog will be conditional on subtle
influences. With very minimal change to the airmass...lows will be
in the upper 50s to lower 60s both mornings. Highs in upper 70s to
lower 80s Friday.
Heat and daily isolated afternoon T-storm chances continue to be the
main weather story for the long term...as we remain under the influence
of ridging and a decent moisture fetch from gom and low off Carolina
coast. Most days will see temperatures in the 80s...with Monday the warmest
(high temperatures M/u 80s)...before a cold front moves through sometime
Tuesday. Dewpoints will also be increasing during the period...which
will keep nighttime lows in M/u 60s...and make it feel muggy for
may. Could start approaching record hi mins temperatures at a some
locations sun/Monday night.
Aviation /01z Thursday through Monday/...
moderate showers and occasional lightning near mrb terminal until
about 0130z...then activity moves south. Thunderstorms near cho
terminal will collapse over the next 30 minutes to 1
hour...resulting in reduced visibility less than 3 sm and ceilings
between 3k and 4k feet. Conditions gradually improve through 02z
and 03z. Brief rain showers near iad between 01z and 02z may lead
to brief MVFR conditions. Elsewhere...terminals will be VFR
conditions for the most part through the overnight.
There is a chance of patchy fog near some terminals where showers
and thunderstorms have occurred Wednesday afternoon and
evening...mainly mrb...cho...iad and dca. Don't anticipate visibility
and ceilings to lower too much...perhaps briefly to IFR for a few
hours or mainly MVFR. The best chance to encounter IFR would be
between 8z and 12z. VFR conditions all terminals for Thursday.
Subvfr visibility possible in fog during the early morning hours of
both Friday and Saturday...favoring the more typical fog prone
areas. Current indications that better fog potential will be
Saturday morning. Otherwise expect little to no weather impacts Friday.
S/southeast winds under 10 knots.
VFR conditions expected through the weekend...except near afternoon
T-storms...where brief sub-VFR conds are possible.
winds will remain below Small Craft Advisory the rest of tonight
Little to no weather impacts on the waters Thursday night through Friday
night under the influence of high pressure. Expect southeast winds less
than 15 knots...and likely less than 10 knots most of the time.
Winds will remain weak through the weekend...so not expecting Small Craft Advisory
District of Columbia...none.