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NWS Baltimore, MD/Washington, DC/Sterling, VA Weather Forecast Office

NWS Weather Forecast Discussion
County Warning Area [CWA]: LWX
Regional NWS Weather Office: Baltimore, MD/Washington, DC/Sterling, VA

FXUS61 KLWX 230045

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
845 PM EDT Sat Jul 22 2017

High pressure remains off the southeast coast. Multiple upper
level disturbances will be possible through Sunday. An upper
level trough of low pressure will move over the northeastern US
early in the week.


What the first round didnt stabilize this afternoon, the second
round did. A cluster of thunderstorms currently moving southeast
of Point Lookout at this time. There is a gap from there back to
round 3, which is entering the Potomac Highlands. However, a few
cells have been popping up in the void between convective

Mesoscale analysis suggests that a few hundred joules of MLCAPE
present across much of the area. On the other hand, around or in
excess of 1000 J/kg present across the Highlands southeast
towards Charlottesville...which has not been worked over yet.
Effective shear around 30 kt. So, we`re not out of the woods
with respect to vigorous convection yet, but with the loss of
daytime heating, its becoming less about winds and more about
repeated rainfall.

A composite of guidance sources suggest that the third round
should be in the metros (I-95, Baltimore-Washington corridor)
around 10 pm to midnight. This rapid propagation will be key, as
precipitable water still in excess of 2 inches. If there has
been one adjustment to make wrt timing, precip has been arriving
quicker than progged. Due to that, accumulated rainfall thus
far, and current radar presentation...have no plans for a Flood
Watch at this time.

Will be adjusting temperatures, too. Ultimately, the low temp
will be whatever we have after round 3.

Conditions should be quieter overnight. But in this air mass,
cannot rule out a pop-up shower of thunderstorm at any time.


Warm and humid weather Sunday as we continue to reside in the
warm sector and high temperatures remain in the 90s with
dewpoints in the 70s. Heat dome recedes just a bit to the SE as
heights fall...which will keep the hottest temperatures across
central VA...where a heat advisory appears more likely.
Along/East of I-95...temperatures may be a degree or two cooler
than today...though, prolonged nature of event, coupled with
heat indices near 100 to perhaps 105F, suggest that a Heat
Advisory may again be needed...especially considering the
accumulated effect of the heat and humidity.

Convective evolution tomorrow rather muddled and will likely
depend on the spatiotemporal evolution of convection later
tonight (which will allow finer scale details to become more
clear). While CAPE/Shear parameters may become more favorable
than they are today (which would enhance storm organization), timing
and evolution will likely determine degree of coverage of the
strongest storm. Gusty winds and a few instances of large hail
are the primary hazards.

A cold front will approach the region Monday before pushing across
the region Monday night. Showers and thunderstorms will develop
along and ahead of this front...some of which could be strong.
Highs will reach the 90s again.


A cold front should stall across the Virginia and North Carolina
border Tuesday, allowing for a few showers to linger across our
southern areas.

High pressure will build in from the west and northwest Tuesday
night and Wednesday. Temperatures will be nearly 10 degrees cooler
than previous days with a comfortable relative humidity.

The next cold front will arrive and push across the region Thursday
into Friday. Another active pattern of showers and thunderstorms
during the period and could linger into the weekend if the front
stalls across portions of the region.

A second area of high pressure will build in for the weekend,
bringing drier and cooler conditions.


Thoughts have not changed from this afternoon. VFR conditions
will prevail through Monday...outside of thunderstorm activity.
Multiple rounds of thunderstorms are possible during this time
(with the best chance during the afternoons and evenings) with
gusty winds and reduced visibility in the strongest storms. A
third round of thunderstorms approaching this evening, and
should be affecting the terminals for 2-3 hrs between 9pm and
1am. More storms likely tomorrow.

Vfr conditions expected Tuesday through Wednesday night. Winds north
10 knots Tuesday, becoming northeast 5 to 10 knots Tuesday night.
Winds light and variable Wednesday and Wednesday night.


No changes to thoughts from this afternoon. Winds will remain
below SCA values through Monday. However, strong thunderstorms
capable of producing gusty winds above Special Marine Warning
criteria are possible tonight and again Sunday/Monday.

No marine hazards expected Tuesday through Wednesday night.
Winds becoming northwest 10 knots Tuesday, then northeast 5 to 10
knots Tuesday night. Winds light and variable Wednesday and
Wednesday night.





Weather Forecast Discussion from: NOAA-NWS
Script developed by: El Dorado Weather & modified by: SE Lincoln Weather