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FXUS61 KLWX 231411
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1011 AM EDT Sun Jun 23 2024

.SYNOPSIS...
A cold front will approach from the northwest today and move
through by Monday morning. High pressure briefly returns
Tuesday before another cold front crosses the area Wednesday and
Thursday.

&&

.NEAR TERM /THROUGH TONIGHT/...
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MORNING UPDATE: A very warm start to the day already with
temperatures already well into the 80s for most. Dew points in
the upper 60s to low 70s already have heat indices in the 90s as
well. This is the mark of a truly hot air mass, with very little
overnight relief. Current analysis from the 12z IAD RAOB and
ACARS data depict steep lapse rates off the deck just above the
eroding inversion, with very dry air up at around 700mb.
Satellite continues to show some upper-level clouds streaming in
from the west. This may play a pivotal role in the forecast
later on today.

Heat: The thickness and duration of cloud cover today could
greatly affect temperatures, although most guidance suggests
highs in the mid to upper 90s remain likely. A surface trough
near the Blue Ridge will should higher dew points to pool to
the east, which will lead to heat index values around 102-107.
A few counties along the Shenandoah River were added to the
Heat Advisory earlier this morning since even a somewhat
conservative forecast would result in peak heat index near 100
(the lower criteria west of the Blue Ridge). Dew points should
mix down pretty efficiently today however, and that paired with
clouds potentially limiting temperatures could bring these
numbers down a few degrees. But that is a low certainty
occurrence at this time, so holding firm on the previous
forecast for now.

Generally speaking, not enough data is in to change much in
regards to the severe/flood sections below. Early indications
from hi-res guidance show very sparse coverage this afternoon
due to a strong capping inversion that remains present
throughout the day. This could really reduce the severe weather
threat, which is alluded to in the sections below.

PREVIOUS DISCUSSION: Thunderstorms/severe weather: Several
different scenarios could play out with thunderstorms today,
with little model convergence on any one solution, and some
potential for multiple rounds. The next ripple in the flow could
result in some isolated showers west of the Blue Ridge through
the morning. As it intersects the surface trough and greater
moisture this afternoon, scattered storms could intensify toward
the I-95 corridor. However, forecast soundings show a stout cap
around 10kft with a very dry layer of air just above it. So
it`s completely possible this round never develops or produces
only anemic updrafts. Meanwhile, storms will develop closer to
the actual cold front in the Ohio Valley. Some of these storms
could survive across the Appalachians this evening. Or, new
convection could develop as greater forcing moves into the area
and the previous cap erodes somewhat, with the atmosphere still
being rather unstable despite the time of day. Guidance does
indicate the potential for at least some scattered showers and
storms to be moving across the area for a good part of the
night, although there are solutions where most convection
dissipates during the evening, meaning many locations could miss
out on seeing rain altogether. Regardless of what scenario
materializes, increased flow aloft will result in around 30 kt
of deep shear, which could lead to storm organization.
Instability will be largely driven by the hot and humid airmass
with poor mid level lapse rates indicated. The main hazard will
be damaging wind gusts.

Flash flood threat: There is little guidance support for
excessive rain totals, which combined with the current dry
conditions, suggests the threat for flash flooding is low.
However, we`ll have to be cognizant of the airmass east of the
Blue Ridge with precipitable water values near 2 inches and a
nearly unidirectional low level wind field that could promote
back building. Any threat would likely be confined to sensitive
urban areas.
-- End Changed Discussion --

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
By Monday morning, the surface cold front will be nearly through
the area, with any lingering showers and storms quickly exiting
southern Maryland. While temperatures will still be a little
above normal in the mid 80s to near 90, dew points falling into
the 50s and a gusty northwest wind will likely feel refreshing
compared to the weekend. A few showers may linger through midday
along the Allegheny Front as the primary upper trough axis
passes. As the wind abates Monday night, lows will range from
the mid 50s in the mountains to 60s in most other places.

The surface high will translate through on Tuesday and move to
the southeast Tuesday night. Comfortable dew points in the mid
to upper 50s remain through the day, although temperatures will
rebound a little to the upper 80s and lower 90s. A light
southerly flow and potential clouds will result in a slightly
warmer night. There is a slight chance weakened convection from
the Ohio Valley makes a run at the Appalachians toward
Wednesday morning.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
The synoptic pattern becomes more amplified over the CONUS heading
into Wednesday as an upper shortwave moves into the Great Lakes and
Mid-Atlantic. S/SW flow ahead of this feature will bring warm, humid
air from the south into the region, with high temperatures reaching
into the upper 90s with dewpoints in the 60s to low 70s. As the cold
front associated with the shortwave moves through, showers and t-
storms are likely, though depending on the timing of the front. As
of now, timing appears to be Wednesday afternoon and evening, with
some shower activity possibly lingering into Thursday. Temperatures
lower behind the cold front Thursday into the 80s to low 90s, but
dewpoints look to remain in the mid 60s.

A quick-moving area of high pressure passes to our north on Friday.
Mostly dry conditions are expected, but a few showers are possible
as the center of high pressure swiftly moves offshore by the evening
and minor perturbations pass by aloft. Temperatures will be in the
80s to low 90s.

Saturday is less certain, depending on another area of low pressure
moving into the Great Lakes. Some shower activity is possible if the
associated warm front works into our area, but PoPs are currently
around 20-30% leaning towards our western zones.

&&

.AVIATION /14Z SUNDAY THROUGH THURSDAY/...
South to southwest winds increase today with gusts around 20 kt
beginning mid morning. Intermittent mid level ceilings are
likely through the day. Convection forecast is highly
uncertain. One round is possible this afternoon, mainly across
the metro terminals, as a weak disturbance intersects a surface
trough and hot/humid airmass. However, a stable layer may result
in these storms struggling or not developing at all. Additional
storms may arrive from the Ohio Valley this evening and
overnight...or form in situ as the surface cold front
approaches. However, there is uncertainty with coverage and how
far east this activity makes it. For now, the TAFs indicate two
rounds (except the Baltimore area, where the only storms may
morph out of the earlier forcing), if only for the sake of not
wanting to indicate thunderstorms for 8 to 12 hours. Expect
these details to be modified as the forecast becomes clearer.
Any of the stronger storms will be capable of producing strong
winds, frequent lightning, and heavy rain rates. Some showers
could linger well into the night as the cold front crosses.

The wind shift to the W/NW with the cold front will occur toward
sunrise Monday morning. Gusts up to 25 kt will be possible
through the day with a developing cu field. High pressure will
result in lighter winds Monday night into Tuesday.

Prevailing VFR conditions are expected Wednesday and Thursday.
Showers and thunderstorms could bring brief restrictions to the
terminals during both afternoon/evenings, with the greater
likelihood on Wednesday. SW flow on Wednesday becomes NW behind a
cold front on Thursday.

&&

.MARINE...
Southerly channeling effects continue to result in marginal
advisory conditions on the bay early this morning. Expect a
gradual shift to southwesterly flow with winds strengthening by
mid morning. The Small Craft Advisory expands to all waters from
11 AM through midnight tonight with gusts of 20-25 kt at times.
There is also a potential for multiple rounds of thunderstorms
this afternoon into tonight. Strong to severe wind gusts are
possible, so be alert for Special Marine Warnings.

The cold front will pass through Monday morning with a wind
shift to the northwest. The wind forecast has trended upward for
Monday, with advisories likely needed for all waters. Gusts of
20-25 kt are likely, with a few gusts to 30 kt not out of the
question. Winds gradually subside Monday night, but advisories
will likely continue.

High pressure builds across the area Tuesday, with light west
winds becoming southerly by Tuesday night. An SCA may be needed
for the bay Tuesday night due to southerly channeling.

SCAs may be needed by Wednesday afternoon and into the evening as
winds strengthen out of the southwest ahead of an approaching cold
front. Winds over the waters diminish with NW flow behind the front
on Thursday.

&&

.TIDES/COASTAL FLOODING...
With S/SW flow today, a few sensitive tidal sites will reach Action
stage, and Annapolis may approach Minor flood stage. Tidal anomalies
decrease Monday onwards as winds turn NW behind a cold front.

&&

.CLIMATE...
Very hot temperatures are expected today, and again on
Wednesday next week. Several records could be in jeopardy, as
seen below. Below is a list of record high temperatures for Jun
23rd, and 26th, the year the record was set, and the current
forecast high temperatures for those days. A plus sign after the
date signifies the record was set multiple times, with the most
recent year indicated below. RERs are only issued for DCA, IAD,
BWI, and MRB, but other sites are shown for reference.


                                    Sunday Jun 23nd
Climate Site                  Record High     Forecast High
Washington-National (DCA)     98F (1988)          98F
Washington-Dulles (IAD)       96F (1988)          98F
Baltimore (BWI)               97F (2010)          99F
Martinsburg (MRB)            100F (1934)          94F
Charlottesville (CHO)        100F (1894)          97F
Annapolis (NAK)               98F (1988)          96F
Hagerstown (HGR)              98F (1988)          94F

                                    Wednesday Jun 26th
Climate Site                  Record High     Forecast High
Washington-National (DCA)    101F (1952)          98F
Washington-Dulles (IAD)       95F (1998)          98F
Baltimore (BWI)               99F (1954+)         98F
Martinsburg (MRB)            102F (1943)          92F
Charlottesville (CHO)         99F (1998)          98F
Annapolis (NAK)               98F (1952)          94F
Hagerstown (HGR)          98F (1954+)         95F

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
DC...Heat Advisory until 7 PM EDT this evening for DCZ001.
MD...Heat Advisory until 7 PM EDT this evening for MDZ003>006-008-
     011-013-014-016>018-503>508.
VA...Heat Advisory until 7 PM EDT this evening for VAZ029>031-
     037>040-050-051-053>057-501-502-505-506-526-527.
WV...Heat Advisory until 7 PM EDT this evening for WVZ052-053.
MARINE...Small Craft Advisory until 6 AM EDT Monday for ANZ530>534-
     537>543.
     Small Craft Advisory until midnight EDT tonight for ANZ535-536.
-- End Changed Discussion --

&&

$$

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