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626
FXUS61 KLWX 230134
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
934 PM EDT Mon Jul 22 2019

.SYNOPSIS...
A cold front will slowly move southeastward across the Mid-
Atlantic through Tuesday morning. High pressure will build north
of the region through the remainder of the week.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
Severe weather threat is winding down as two separate clusters
of storms have effectively overturned the airmass for most of
the area. Some of the storms in southeast Virginia could be on
the strong side if they make a run at southern Maryland in a few
hours, where it is still hot and humid. However, the remaining
Watch (only along the Bay now) should be able to expire at 10
PM.

Cold front is slowly sagging into northwestern parts of the CWA
this evening. There has been an uptick in convection as the
forcing reaches some elevated instability where the airmass
wasn`t turned over. With low level stability, the main threat
here will be heavy rain and potential for flooding.

Overall the flash flood threat is reduced a bit overnight as
regional radar shows convection upstream isn`t particularly
intense and the heaviest elements have been progressive.
However, the front will be encountering some elevated
instability and precipitable water values are approaching two
inches. So as the front slows, it`s still possible there could
be training moderate to heavy rain.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH WEDNESDAY NIGHT/...
The cold front will push southeastward on Tuesday. Showers will
likely linger into the morning for much of the region, but
clearing is expected to commence in the northwest by afternoon
and low- level dry air spills into the region. Did increase PoPs
based on latest guidance, as it may turn out to be rainy at
times much of the day southeast of DC. In addition, as clouds
break in the northwest and the mid level trough axis crosses,
instability showers and perhaps a thunderstorm could develop.
High temperatures will likely struggle to each 80 degrees,
nearly 25 degrees cooler than Sunday, due to cloud cover and
expected precipitation.

Near to slightly below normal temperatures and noticeably lower
humidity are expected through the middle of the week as high
pressure builds to the north.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
The long term period of the forecast will feature an extended period
of pleasant weather, with dry conditions, ample sunshine, low
humidity levels, and below to near normal temperatures for late July.

As the mid-upper level trough responsible for today`s active weather
departs off to the east on Thursday, heights will rise aloft, and
surface high pressure will start to build in from the west. The area
of high pressure will move overhead Friday and Saturday, before
sliding offshore Sunday. Other than a few passing fair weather
clouds, each day should feature near wall to wall sunshine.
Temperatures will gradually moderate from below normal, to near
normal, with highs in the low to mid 80s on Thursday and highs in
the upper 80s to near 90 by Sunday. Low temperatures will start off
in the 50s and 60s on Thursday Morning, and moderate to the 60s to
near 70 by Sunday Morning. Humidity levels will remain relatively
low, with dewpoints starting in the upper 50s to near 60 on
Thursday, then gradually climbing into the mid 60s by Sunday.

&&

.AVIATION /01Z TUESDAY THROUGH SATURDAY/...
Prevailing MVFR in ceilings will likely develop around or after
06Z (already occurring at MRB) as a cold front and areas of rain
move into the area. There could be some embedded thunderstorms,
but chances will decrease overnight. Some periods of IFR aren`t
out of the question, but not likely to be extended.  VFR
expected to return from NW to SE as Tuesday progresses.
Scattered instability showers may develop in the afternoon. VFR
continues through Wednesday in NW flow.

VFR conditions will persist through the long term period, as high
pressure dominates our weather.

&&

.MARINE...
Occasional SCA gusts likely ahead of a cold front in WSW flow
through this evening, with much higher gusts still possible in
and near any thunderstorms. SCA in NW flow again for parts of
the waters (especially on the Bay, but could in theory occur
anywhere) behind the front late tonight through Tuesday
morning, then sub-SCA and dry through mid to late week.

A prolonged stretch of precipitation free conditions and sub-SCA
level winds is expected through the middle to latter portions of the
upcoming week.

&&

.HYDROLOGY...
High PWATs of 2 inches are expected tonight ahead of a slowly
approaching cold front. Steering flow will be parallel to the
boundary, and with mid-level height falls moving overtop of
persistent and excessively humid low- levels, re-generative
thunderstorms capable of very heavy rain seem likely. The exact
placement is still somewhat uncertain, but it seems most likely
that these factors will all come together across
northern/central MD, the eastern WV panhandle and portions of
northern Virginia into the Shenandoah Valley and Potomac
Highlands where synoptic lift from the surface front/trough
approaching from the north will overlay higher instability
airmass to the south.

Areal average rainfall of 1-1.5 inches is expected for much of
the Mid-Atlantic, but isolated totals in excess of 3 or 4
inches are possible. The higher end solutions are beginning to
appear less likely though. Due to the convective nature of this
system, much of this rain may fall in a short amount of time,
resulting in the risk for flash flooding.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Flash Flood Watch until 6 AM EDT Tuesday for DCZ001.
MD...Flash Flood Watch until 2 AM EDT Tuesday for MDZ501-502.
     Flash Flood Watch until 6 AM EDT Tuesday for MDZ003>006-011-
     013-014-503>508.
VA...Flash Flood Watch until 2 AM EDT Tuesday for VAZ025>027-029-
     030-038>040-051-501>504-507-508.
     Flash Flood Watch until 6 AM EDT Tuesday for VAZ028-031-
     052>054-505-506.
WV...Flash Flood Watch until 2 AM EDT Tuesday for WVZ050-055-
     501>506.
     Flash Flood Watch until 6 AM EDT Tuesday for WVZ051>053.
MARINE...Small Craft Advisory until noon EDT Tuesday for ANZ531>534-537-
     539>543.
     Small Craft Advisory until 10 PM EDT this evening for ANZ530-
     535-536-538.

&&

$$
SYNOPSIS...DHOF
NEAR TERM...ADS/DHOF
SHORT TERM...ADS/DHOF
LONG TERM...KJP
AVIATION...ADS/DHOF/KJP
MARINE...ADS/DHOF/KJP
HYDROLOGY...ADS/DHOF