-- Discussion containing changed information from previous version are highlighted. --
903
FXUS61 KLWX 121412
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1012 AM EDT Wed Jun 12 2024

.SYNOPSIS...
A weak area of low pressure passes off to the southeast while
high pressure returns through Thursday leading to mainly dry
conditions. A cold front tracks through the area on Friday
leading to renewed shower and thunderstorm chances. High
pressure settles over the area this weekend with lower humidity.
Next week looks to become hot as a strong upper ridge builds
towards the region.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
MORNING UPDATE: Still seeing some mid-level clouds traverse the
region from west to east in response to the upper trough that is
gradually moving offshore. Another area of low pressure is
currently located over the southeastern CONUS, with the northern
periphery of its cloud shield starting to move into southwestern
portions of the forecast area. For the most part there is more
sun than clouds out there this morning outside of those areas.

PREVIOUS DISCUSSION: For the remainder of the day, the
aforementioned upper low is forecast to continue to pull away
from the New England coast. A weak shortwave ridge pushes
through this morning before eroding toward the Delmarva
Peninsula. Some diffuse lift from additional perturbations in
the flow aloft may spark isolated afternoon rain showers across
the Potomac Highlands eastward toward central Virginia. However,
updrafts are not expected to drive tall enough convection to
produce any lightning activity. Any instances of showers should
decay by dark given the loss of heating. Otherwise, the rest of
the region stays dry underneath a mix of fair weather cumulus
and high cirrus. Forecast highs rise a bit from previous days
owing to a wind shift to southwesterly. Today`s high
temperatures likely range from the upper 70s to low 80s, locally
in the low 70s across mountain locales.

Residual surface high pressure holds on into the overnight
hours. This will make for another cool night for mid-June
standards. Upper 50s to low 60s are expected across most areas,
accompanied by some mid 60s in the usual warmer pockets. Some
patchy fog may materialize overnight for locations west of I-95.
However, its development could be hindered by any cloud cover
that lingers into the night.
-- End Changed Discussion --

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
-- Changed Discussion --
Thursday will mark the start of a brief period of above average
temperatures as highs begin to near the 90 degree mark. The flow
aloft turns quasi-zonal in nature with 24-hour height rises on
the order of 4 to 6 dm. At the same time, the prevailing surface
high exits off the coast on Thursday. In response, the
lower/middle atmosphere will further warm with 850-mb
temperatures rising into the 14-16C range. Typical deep
afternoon mixing should allow for dry adiabatic profiles down
to the surface. This would yield spotty 90 degree temperatures
across the area. The persistence of low-level warm advection
also aids in moistening the boundary layer. This favors an
increase of dew points into the mid 60s. Some spotty showers are
possible during the peak in diurnal heating. Any such activity
should be more pulse/instability driven and decay pretty quickly
after genesis. Expect dry weather through the later evening and
overnight hours. Conditions turn milder at night with lows
around 4 to 8 degrees above preceding nights.

By Friday morning, a cold front tracking across the Lower Great
Lakes and Ohio Valley will set the stages for a possible round
of showers and thunderstorms. Before this occurs, Friday will
mark the hottest day of the week and perhaps the first crack at
a 95 degree day in 2024. Relative to preceding model runs,
forecast highs have dropped down from the upper 90s back to the
low/mid 90s. Heat indices should be in the mid/upper 90s based
on the latest dew point forecast. While falling short of typical
heat headlines, it is the first real bout of summertime heat
this season.

Model guidance have begun to show an increasing signal for
showers and thunderstorms Friday afternoon into the evening.
This is all in response to a cold front set to slide through the
region during the near peak in the diurnal heating cycle. While
just outside the realm of the convective-allowing model world,
coarser-scale models do show an envelope of ample buoyancy in
the pre-frontal environment. Forecast vertical shear values
between 35-45 knots would be more than enough to support
organized convection. Damaging winds would be the primary threat
for any more potent storm or along an eastward propagating
squall line. This activity should all exit into the Eastern
Shore by late Friday night. In the wake, prevailing
northwesterly flow will gradually usher in some drier air from
central Canada. However, temperatures do stay slightly above
average with widespread 60s expected (50s over the mountains).
-- End Changed Discussion --

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
-- Changed Discussion --
In the wake of the cold frontal passage, a ridge of high
pressure settle over the Great Lakes to northeastern U.S. this
weekend. This allows for a dry forecast along with less humidity
than previous days. Each day should bring mostly sunny skies
with high temperatures that increase through the weekend. Sunday
will certainly be the warmer day of the two as surface winds
shift back to southerly. This eventually sets the stages for a
hot work week ahead.

A building subtropical ridge aloft gradually parks over the
eastern U.S. during the early to middle portions of the week.
Depending on the global ensemble, some show mid-level heights
around 2 standard deviations above average. This sprawling
594-dm ridge will really begin to crank up the heat with
widespread mid to upper 90s expected. Some of the more upper
echelon solutions carry temperatures to just over 100 degrees.
Given dew points ranging from the mid 60s to low 70s, heat
indices should easily reach and exceed the century mark most
afternoons. If this all holds, heat-related products will
likely be necessary ahead of this expected heat wave.

While not explicitly shown in the forecast package, there
should be some instability forced convection. However, this will
be largely dependent on the position of the upper ridge as well
as any capping that becomes evident in thermodynamic profiles.

This hot and steamy air mass could persist through the entire
work week if the ensemble means are taken at face value. The
Climate Prediction Center agrees with this notion with a
moderate risk for excessive heat in the June 19-21 period.
-- End Changed Discussion --

&&

.AVIATION /14Z WEDNESDAY THROUGH SUNDAY/...
VFR conditions are expected today with dry weather likely. Also
a few spotty showers are possible near KCHO, there is not enough
confidence to introduce this into the TAF. Some patchy fog may
develop tonight which would lead to sub-VFR conditions at times
at KCHO and KMRB. Otherwise, winds remain on the light side with
a shift from mainly northerlies to south/southwesterlies.

Prevailing southerlies are expected on Thursday as high pressure
retreats off the coast. Although isolated showers are possible,
it is difficult to say whether this would impact any of the
local terminals. The period heading into Friday afternoon into
the evening will likely lead to some restrictions given the
threat for showers and thunderstorms. Some of these could become
severe given the degree of warmth and instability in the
atmosphere. Winds quickly shift over to west-northwesterly in
the wake.

VFR conditions are likely for the weekend under the influence of
high pressure. North-northwesterlies given way to a warm
advection pattern to finish out the weekend.

&&

.MARINE...
-- Changed Discussion --
Winds should stay below advisory threshold through Thursday
morning given the influence of surface high pressure over the
waters. Some model soundings do have around 15-20 knots of wind
up just above the mixed layer this afternoon over the lower
Chesapeake Bay zones, so will have to watch those areas for some
sporadic higher wind gusts this afternoon.

As this ridge slides offshore, southerly channeling effects may
require Small Craft Advisories across wider portions of the
Chesapeake Bay. The period of interest mainly covers Thursday
afternoon through the overnight hours before the heftier flow
diminishes.

A cold front tracking across the area Friday afternoon/evening
will lead to the threat of strong to severe convection. This
could require some Special Marine Warnings for the area
waterways. As the convection and frontal zone exit off to the
east, expect an uptick in the post-frontal northwesterlies.
Small Craft Advisories may be needed late Friday into the first
half of Saturday. Otherwise, winds decrease in strength for the
rest of the weekend under the influence of high pressure.
-- End Changed Discussion --

&&

.TIDES/COASTAL FLOODING...
As winds turn southerly late tonight into Thursday, tidal
anomalies will rise as a result. This could result in some minor
tidal flooding towards the end of the week. No flooding is
forecast at this time, but the current forecast does gradually
rise some of the more sensitive sites well into action stage, so
it will certainly be close.

&&

.CLIMATE...
High temperatures could approach records on Friday afternoon,
and again early next week. Below is a list of record high
temperatures for June 14, 17th, and 18th, the year the record
was set, and the current forecast high temperatures for those
days. Daily temperature records are currently only maintained at
DCA, IAD, BWI, and MRB. Others are shown for reference.

                                     Friday Jun 14th
Climate Site                  Record High     Forecast High
Washington-National (DCA)     98F (1994)          93F
Washington-Dulles (IAD)       98F (1994)          92F
Baltimore (BWI)               98F (1994)          92F
Martinsburg (MRB)            101F (1943)          89F
Charlottesville (CHO)         96F (1954+)         93F
Annapolis (NAK)               95F (1994+)         88F
Hagerstown (HGR)              95F (1994+)         89F

                                     Monday Jun 17th
Climate Site                  Record High     Forecast High
Washington-National (DCA)     99F (2022)          94F
Washington-Dulles (IAD)       96F (2022)          94F
Baltimore (BWI)               96F (2022+)         93F
Martinsburg (MRB)             98F (1939+)         92F
Charlottesville (CHO)         97F (2022)          94F
Annapolis (NAK)               96F (1939)          88F
Hagerstown (HGR)              96F (1952)          94F

                                     Tuesday Jun 18th
Climate Site                  Record High     Forecast High
Washington-National (DCA)     97F (1944)          96F
Washington-Dulles (IAD)       94F (2018+)         96F
Baltimore (BWI)               97F (1957+)         94F
Martinsburg (MRB)             99F (1943)          94F
Charlottesville (CHO)         96F (2014+)         95F
Annapolis (NAK)               96F (1957)          90F
Hagerstown (HGR)              95F (1957)          96F


+ indicates that value has been reached on multiple years, with
the year displayed being the most recent.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...None.

&&

$$

SYNOPSIS...BRO
NEAR TERM...BRO/CJL
SHORT TERM...BRO
LONG TERM...BRO
AVIATION...BRO
MARINE...BRO/CJL
TIDES/COASTAL FLOODING...BRO
CLIMATE...BRO