691
FXUS61 KLWX 301406
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1006 AM EDT Sun Jun 30 2024

.SYNOPSIS...
Low pressure will move across the Great Lakes region early this
morning. A cold front will then push through this afternoon and
evening. A strong area of high pressure settles over the area
Monday and Tuesday before drifting offshore the second half of
the week. A warm front nears the region by mid-week yielding a
warming trend.

&&

.NEAR TERM /THROUGH TONIGHT/...
Scattered showers continue across the area this morning, with
elevated instability evident on the 12Z IAD sounding.
Occasional deeper convection has percolated across central West
Virginia. It`s possible this ripple ultimately initiates the
first round of deep convection toward early-mid afternoon as it
intersects the terrain and greater instability along/east of a
lee trough. Additional convection may ensue later along the
actual cold front (currently across NW Pennsylvania into the
Ohio Valley) or to- be-determined mesoscale boundaries, although
its coverage/intensity may be dependent on the coverage of
initial storms and how much the atmosphere is turned over.
Otherwise not much to update at this juncture from the threat
analysis discussed below. Given ample mid and high level
cloudiness across the region, still am thinking it will be
difficult to achieve Heat Advisory criteria, but will be
monitoring.

Previous discussion:

The latest radar trends and hourly update high-resolution
models support showers during portions of the morning. This
would introduce a hefty amount of cloud cover which will
influence how afternoon convection unfolds. The 00Z HREF mean
shows plenty of clouds through the lunch hour before some breaks
become evident west of the Blue Ridge. If this is the way
things play out, the forcing from a formidable mid-level trough
should help ignite some convection by the early afternoon.
500-mb wind fields are fairly healthy this afternoon, generally
running around 40 to 45 knots. The forecast surface-based CAPE
values along and east of U.S. 15 run between 1,500-2,500 J/kg.
Thus, expect convection to further intensify when pushing from
U.S. 15 and points eastward. Thunderstorms are expected to
coagulate into an eastward surging squall line. A Slight Risk
continues across from I-81 eastward with damaging winds and
large hail being the primary threats. However, cannot rule out a
brief tornado from I-95 eastward given some interactions with
local bay/river breezes. All of this activity exits into the
lower Chesapeake Bay by the mid/late evening hours as a cold
front ushers in drier air in the wake.

Regarding the threat of daytime heat and humidity, there is a
lot of question marks in whether heat indices are able to push
to advisory thresholds (105 east of the Blue Ridge and 100 to
the west). There has been a subtle cooling trend in the guidance
which caps high temperatures to around 93 to 95 degrees. This
is in response to the extensive cloud cover which may hinder
some of the afternoon heating. Based on the air mass in place,
dew points in the low/mid 70s should stick around much of the
day. Some vertical mixing could lower dew points by a couple
degrees. The net combination of heat and humidity carries heat
indices into the 100 to 104 degree range. Despite falling short
of a Heat Advisory, the public should ensure to stay hydrated,
find shade or the indoors to escape the heat, and wear light
clothing.

For the night, expect cooler temperatures than the past several
nights. Lows will be in the mid 50s to low 60s, locally falling
into the mid/upper 40s along the Alleghenies. This comes with
northerly winds that gusts up to 10 to 20 mph at times.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
A seasonably strong area of high pressure will advance from the
Upper Midwest toward the northeastern U.S. on Monday and
Tuesday. This ushers in an air mass characterized by below
average temperatures and lower humidity levels. Ample sunshine
is likely on Monday, accompanied by high temperatures in the
upper 70s to low 80s. 60s to low 70s will be more commonplace
for those in mountain locations. Along the eastern extent of the
ridge of high pressure, a steady northerly wind is expected
through the day with afternoon gusts up to 20 to 25 mph. By
Monday night, the ridge settles over interior New England down
into the Mid-Atlantic region. This helps lower overnight
temperatures into the 50s to low 60s. A few mid 60s are possible
along and east of the I-95 corridor.

As the ridge slowly nears the New England coast, the surface
winds will respond to become more east-southeasterly in nature.
Tuesday`s high temperatures will be a tad warmer as they rise
into the low/mid 80s. This comes with a few more clouds, but sky
conditions should still be mostly sunny across the area.
Humidity levels remain on the low side for early July standards.
Wind fields become southerly overnight yielding a milder night
than the previous two. Forecast lows will be in the low/mid 60s,
with mid/upper 50s across mountain locales.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
Return flow from surface high pressure offshore will usher in warm
and moist air on Wednesday. High temperatures will be in the upper
80s to low 90s for most with overnight low temperatures staying in
the upper 60s to low 70s. With high pressure in charge, dry weather
is expected throughout the day. As an area of low pressure north of
the Great Lakes tracks eastward, the associated cold front will
approach the area. This will bring a slight chance to a chance of
showers and thunderstorms to the area beginning Wednesday night.
Shower and thunderstorm chances will remain confined to along and
west of the Blue Ridge overnight Wednesday into Thursday, before
becoming areawide Thursday afternoon. With upper level ridging over
the east coast on Independence day, temperatures will warm to the
mid to upper 90s for those east of the Blue Ridge. With high
relative humidities, heat indices are expected to rise into the low
100s in the afternoon.

Similar pattern continues Friday and Saturday as the cold front
looks to stall to our northwest. This will allow for daily chances
of showers and thunderstorms, with highest chances in the
northwestern portions of the forecast area. High temperatures each
day will rise into the upper 80s to mid 90s with higher elevations
staying in the upper 70s to low 80s.

&&

.AVIATION /14Z SUNDAY THROUGH THURSDAY/...
Scattered showers exist across the area as of mid morning, but
should cause minimal impact to any of the TAF sites through
midday. Still some uncertainty on timing of convective
initiation and whether or not there will be multiple rounds at
any of the terminals. May only make minor tweaks at 15Z and
amend if any trends become evident. Otherwise mid/high ceilings
and light south/southwest winds until convection develops.

Strong to severe thunderstorms may erupt this afternoon and
evening in response to an approaching cold front. While much of
the day will feature VFR conditions, a 2 to 4 hour window of
restrictions are likely sometime in the early afternoon to early
evening timeframe. Gusty and erratic winds, frequent lightning,
and reduced visibility/ceilings are possible in such
thunderstorms. Any threat wanes by the mid-evening as the cold
front pushes off to the east. Winds shift to northwesterly with
gusts up to 15 to 20 knots tonight.

VFR conditions are expected on Monday and Tuesday as high
pressure takes control of the weather. Northerly winds may gust
up to 20 knots during the afternoon to early evening. As the
ridge of high pressure pushes off toward the New England coast,
winds shift to east-southeasterly on Tuesday, before becoming
southerly at night.

Prevailing VFR conditions are expected Wednesday and Thursday
at all terminals. Shower and thunderstorm chances increase
Thursday morning, mainly for western terminals, with
precipitation possible at all terminals in the afternoon.

&&

.MARINE...
Southerly winds persist through the day which could near Small
Craft Advisory thresholds. However, these should fall short and
be handled by Marine Weather Statements. Eventually, hazardous
weather could impact the waterways late this afternoon into the
evening. Strong to severe thunderstorms are possible as a cold
front migrates east toward the waters. Thus, Special Marine
Warnings may be needed at times, mainly between 3-10 PM
(southern waters would be on the later side of this range).

In the wake, a gusty northwesterly wind eventually shifts to
northerly on Monday. Small Craft Advisories have been issued late
tonight through Monday during period of cold advection. Winds
turn more east-southeasterly on Tuesday, largely staying below
advisory thresholds.

Southerly winds on Wednesday shift to westerly on Thursday. Small
Craft Advisories are likely across the Chesapeake Bay on Wednesday
with winds gusting 15-20 knots. Winds decrease to below SCA criteria
for Thursday.

&&

.TIDES/COASTAL FLOODING...
Tidal anomalies begin decreasing this morning as winds become
more southwesterly. No tidal sites are expected to reach minor
flood stage, but DC Waterfront, Straits Point, and Annapolis may
reach action stage in the next couple high tide cycles. As
winds shift to northwesterly tonight, tidal anomalies continue
to fall with all tidal sites expected to stay below action
stage.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory from 10 PM this evening to 2 PM EDT
     Monday for ANZ530-531-535-536-538-539.
     Small Craft Advisory from midnight tonight to 6 PM EDT Monday
     for ANZ532>534-537-540>543.

&&

$$

SYNOPSIS...BRO
NEAR TERM...ADS/BRO
SHORT TERM...BRO
LONG TERM...AVS
AVIATION...ADS/AVS/BRO
MARINE...ADS/AVS/BRO
TIDES/COASTAL FLOODING...LWX