638
FXUS61 KLWX 291821
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
221 PM EDT Mon Apr 29 2024

.SYNOPSIS...
Strong high pressure off the southeast U.S coast will result in near
record warmth and mainly dry conditions today. Unseasonably warm
temperatures continue Tuesday despite renewed chances for showers
and thunderstorms as cold front crosses the region. Additional
showers and thunderstorms are possible Wednesday for portions of the
area as the front is slow to sink south and east. High pressure
briefly returns Thursday into Friday before another cold front this
weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
The new NWS Experimental HeatRisk has most of the area under a
Moderate Risk for heat-related impacts this afternoon. Temperatures
today are running 15 to 25 degrees warmer for highs and 10 to 15
degrees above normal for lows for this time of year. This level of
heat early in the warm season could cause impacts to heat-sensitive
populations, including those outdoors and without adequate
cooling/hydration. Additional information about HeatRisk can be
found at wpc.ncep.noaa.gov/heatrisk.

It`s a hot start to the workweek and final few days of April thanks
to strong upper level ridging and surface high pressure off the
southeast U.S coast. This will yield a continuation of dry
conditions and perhaps a few broken temperature records (see climate
section below) across the region. Afternoon highs will reach into
the mid to upper 80s for most with lower 90s along the I-95 corridor
south into the central VA Piedmont. Mountain locations will be a
touch cooler in the upper 70s and low 80s. Humidity values will
remain in check with dewpoints in the mid to upper 50s and low 60s.
Heat index values as a result will remain below 95 degrees. An
isolated late afternoon and evening thunderstorm cannot be ruled out
over the mountains with chances less than 15 percent given weak
upslope/orographic lift and instability build up during the course
of peak heating. Scattered to widespread convection will be stunted
due largely in part to the upper level ridge and a mid-level capping
inversion overhead. Skies will remain mostly sunny otherwise with
scattered to broken mid-high level strato-cumulus clouds building up
especially around the terrain/near the waters this afternoon.

Any shower and thunderstorm activity will quickly diminish after
sunset although cloud cover will gradually increase from the west
as a cold front pushes toward the region. As a result, little relief
is expected overnight with lows in the low to mid 60s.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
Subtle relief from the early warm season heat arrives late Tuesday
into Wednesday as an upper level trough and associated cold front
cross the region. The front will bring renewed chances for showers
and thunderstorms to the region on both Tuesday and Wednesday
afternoons. 12z model guidance continues to show a slower
front/upper level trough arriving late Tuesday afternoon before
finally pushing south and east of the area Wednesday into Wednesday
night.

This will lead to several rounds of scattered to widespread shower
and thunderstorm activity mainly during the diurnal periods.
Activity will wane during the overnight hours before re-firing
in the afternoon especially along and east of the boundary as it
passes through.

As for the threat of severe weather it remains low, but not zero.
Instability will remain fairly low on the order of 500-1000 j/kg
with 0-6km bulk effective shear values running 20-30 kts. Both SPC,
CSU Machine Learning, and CIPS analogue products continue to back
off on the threat for a widespread severe weather event. Even with
that said, one or two storms could become strong given the
antecedent conditions. Biggest threats with any storms Tuesday or
Wednesday look to be wind gusts 40-50 mph, frequent lightning, and
locally heavy rainfall (PWATS running 0.75-1.25 inches). High
temperatures Tuesday will push back into the mid to upper 80s with
70s over the mountains/near the bay. Lows Tuesday night will fall
back into the upper 50s and low 60s with areas of patchy fog that
due see the rain.

The main upper trough/front is forecast to be east of the area
Wednesday. An additional shortwave trough and weak front will
quickly follow in it`s wake Wednesday afternoon touching off
additional showers and thunderstorms. The highest probabilities for
precipitation will be along and east of the I-81 corridor. Drier
conditions return as high pressure builds south from New England
Wednesday evening and night. Highs Wednesday will push into the mid
to upper 70s and low 80s with overnight lows in the mid to upper
50s.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
A ridge of high pressure will remain firm and in control Thursday
through midday Friday. This ridge will keep the region very warm and
dry throughout the period. Highs Thursday will be low to mid 80 s.
Highs Friday, due to some increasing clouds, will not be as warm
with temperatures in the upper 70s. These numbers are still above
average for early May.

Increasing clouds and showers arriving from west to east late Friday
into Friday evening will be in response to the ridge of high
pressure gradually breaking down and mid-level disturbance riding up
and over the ridge. Showers aren`t expected to be widespread but
could be accompanied by a few thunderstorms, especially over the
mountains and our far northwestern zones.

The unsettled conditions of showers and additional thunderstorms
could continue Friday night through Sunday, as multiple weak to
modest mid-level disturbances continue their assault on the large
ridge of high pressure in the east. With the expected cloud cover
and precipitation throughout the weekend, temperatures will be more
average or slightly below average. Any cooler temperatures will be
compromised by any modest southerly flow around the backside of the
ridge of high pressure. Highs Saturday and Sunday should be lower
70s for most, but cooler in the mountains.


&&

.AVIATION /18Z MONDAY THROUGH SATURDAY/...
VFR conditions are expected to continue through tonight with strong
high pressure centered off the southeast U.S coast. Dry conditions
will prevail at most of the terminals with passing stratocumulus
hovering between 4-7kft. An isolated shower or thunderstorm is
possible back toward K2G4, KCBE, and perhaps KMRB/KOKV. Coverage is
too low to include in the MRB TAF at this time.

The next chance for sub-VFR conditions arrives with a cold front
Tuesday afternoon and evening. This front will bring renewed chances
for scattered showers and thunderstorms. The strongest storms will
be capable of producing wind gusts over 35 knots, frequent
lightning, and brief vsby reductions from locally heavy rainfall.
Any shower or thunderstorm activity moves east of the area late
Tuesday evening with a few spotty showers lingering Tuesday night
into Wednesday morning.

A few showers and thunderstorms remain possible Wednesday as an
additional upper level trough and weak cold front push through. This
will lead to a few scattered showers and perhaps a couple of
thunderstorms at terminals mainly east of I-81. This activity
quickly moves east of the area by Wednesday evening. Outside of
shower/storm activity, VFR conditions are expected Tuesday and
Wednesday.

VFR conditions Thursday through Friday night. Any showers Friday
afternoon or evening may bring a brief reduction in conditions to
MVFR, but not everywhere will get showers. Winds southeast 5 to 10
knots Thursday and Thursday night. Winds southeast 10 to 15 knots
Friday and Friday night.

&&

.MARINE...
Favorable marine conditions are expected through Tuesday morning as
high pressure brings warm and dry conditions to the waters. Winds
will remain out of the southwest today at 5-10 knots before increase
to 10 to 15kts Tuesday with gusts up to 20 kts at times especially
over the open waters Tuesday afternoon.

A cold front is set to cross the local waters Tuesday afternoon and
evening bringing scattered showers and thunderstorms. These storms
will be capable of producing wind gusts of 35+ knots, frequent
lightning, and locally heavy rainfall. Special Marine Warnings may
be needed as these storms cross the waters Tuesday afternoon.
Showers and thunderstorms push east of the waters Tuesday evening
into Tuesday night. Winds will turn back toward the northwest at
this point, but should remain below SCA levels during this time.

Northwest winds may come close to SCA criteria Wednesday as a cold
front pushes to the south. A thunderstorm is also possible. Winds
will become southerly again Thursday and Friday. Marginal SCA
conditions could occur in channeling on the bay in the
evening/overnight each day.

No marine hazards expected Thursday through Friday night. Winds
southeast around 10 knots Thursday and Thursday night. Winds
southeast 10 to 15 knots Friday and Friday night.


&&

.CLIMATE...
Near-record to record warmth is likely this afternoon. Below is
a list of record high temperatures for April 29th, and the year
the record was set.

                                       Apr 29th
Climate Site                  Record High     Forecast High
Washington-National (DCA)     91F (2017+)     92F
Washington-Dulles (IAD)       89F (2017)      91F
Baltimore (BWI)               91F (1951)      90F
Martinsburg (MRB)             93F (1974)      88F
Charlottesville (CHO)*        92F (1974)      90F
Hagerstown (HGR)*             90F (1974)      88F
Annapolis (NAK)*              92F (1974)      85F

+ denotes that multiple years reached this value, but the depicted
  year is the most recent
* denotes sites where Record Event Reports (RERs) are not issued

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory from noon Tuesday to midnight EDT Tuesday
     night for ANZ530>543.

&&

$$

SYNOPSIS...EST
NEAR TERM...KRR/EST
SHORT TERM...EST
LONG TERM...KLW
AVIATION...KLW/EST
MARINE...KLW/EST
CLIMATE...LWX