-- Discussion containing changed information from previous version are highlighted. --
105
FXUS61 KLWX 290724
AFDLWX

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

.SYNOPSIS...
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Very warm temperatures for late April are expected through
the middle of the week as high pressure sits off the Mid-
Atlantic Coast. A cold front crosses the region Tuesday into
Wednesday, bringing shower and thunderstorm chances. High
pressure briefly returns Thursday. Another cold front arrives
over the weekend.
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&&

.NEAR TERM /THROUGH TONIGHT/...
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Deep ridging across the Carolinas, Mid-Atlantic and western Atlantic
Ocean will produce the hottest temps of the week this afternoon.
Expect highs to reach the upper 80s to lower 90s, with upper 70s to
low 80s in the mountains. Dew points in the upper 50s to low 60s
keep the heat index below 95. Isolated showers and thunderstorms are
possible late afternoon and evening in the Potomac Highlands and
Shenandoah Valley. This is due to upslope winds taking advantage of
just enough instability, in addition to deep mixing expected today.
A shower/storm or two could develop east of the Blue Ridge, but
coverage and confidence is too low to include more than a 10pct
chance of rain. Shower/storm activity quickly diminish after sunset,
with all activity dissipating by late evening.

The new NWS Experimental HeatRisk has most of the area under a
Moderate Risk for heat-related impacts today. This is due to back
days of well above normal warmth, and less relief at night due to
mild temperatures, as compared to what is normal for late April
(low/mid 70s for highs, and upper 40s to low 50s for lows). This
level of heat this early in the 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.

Expect warm temps in the 70s to low 80s this evening, and mild
overnight lows in the 60s for most.
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&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
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The ridge aloft moves east Tuesday as an upper trough and associated
cold front approach from the west. The latest models indicate a
slower moving trough that reaches the area Tuesday afternoon, and
finally moving east of the area Wednesday night.

This is going to generate a couple rounds of showers and storms
across the area, beginning Tuesday afternoon as a cold front crosses
the area. Scattered to widespread showers and scattered
thunderstorms develop Tuesday early afternoon west of the Blue
Ridge, pushing east of the Blue Ridge late afternoon into the
evening. Most shower/storm activity dissipates by late evening,
though isolated showers will be possible through the overnight.

Come Wednesday morning, the main upper trough is forecast to be east
of the Blue Ridge and the cold front east of the area. A reinforcing
upper trough quickly crosses the area Wednesday, helping to produce
scattered showers, mostly along/east of I-81. Some instability
present east of the Blue Ridge should allow some thunderstorm
activity in the afternoon. The entire system moves east of the area
by Wednesday evening as dry conditions return.

The prospects for severe storms on Tuesday continue to be low given
low instability and very weak shear. If any strong storms do
develop, they are most likely to occur west of the Blue Ridge
Tuesday afternoon. Any strong storm will be capable of producing
wind gusts of 40-50mph, in addition to frequent lightning strikes.

Well above normal temperatures continue through mid week as highs
reach the mid to upper 80s Tuesday, and low to mid 80s Wednesday.
Very mild Tuesday night lows in the low to mid 60s, cooling slightly
to the mid to upper 50s Wednesday night behind the front.
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&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
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After a weak frontal passage Wednesday, strong ridging builds over
the East Thursday and holds through the end of the week. The ridge
pattern begins to break down Sunday as a weakening southern stream
disturbance approaches from the west. A slow moving and decaying
frontal zone will attempt to cross the area early next week bringing
the threat of showers and thunderstorms Sunday. Moisture looks
plentiful, but both forcing and instability look weak to support any
significant threat of either severe wx or flooding.

By Monday, the front appears to push far enough south to limit PoPs,
but treating this like a summer front, when models are too fast in
pushing fronts through the area.
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&&

.AVIATION /07Z MONDAY THROUGH FRIDAY/...
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VFR conditions are expected today and tonight as high pressure over
the region brings mostly dry and hot conditions. A few showers and
storms are possible around MRB late this afternoon, though coverage
is too low to include in TAF at this time.

A cold front will cross the area Tuesday afternoon and evening,
bringing scattered showers and thunderstorms to all terminals. Some
storms will be capable of producing wind gusts over 35 knots and
lightning strikes, as well as brief periods of reduced visibility.
Most convection dissipates Tuesday evening, though some shower
activity could linger across the area Tuesday night.

A second reinforcing upper trough moves across the area Wednesday,
causing scattered showers to develop. Some thunderstorms are also
possible Wednesday afternoon east of the Blue Ridge. This activity
quickly moves east of the area by Wednesday evening.

Outside of shower/storm activity, VFR conditions are expected
Tuesday and Wednesday.

No sig weather is expected Thu or Fri.
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&&

.MARINE...
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Favorable marine conditions likely today through Tuesday morning as
high pressure brings mostly dry and warm conditions to the local
waters.

A cold front will cross the waters Tuesday late afternoon to
evening, bringing scattered showers and thunderstorms. Some of these
storms will be capable of producing wind gusts of 35 knots or
greater and lightning strikes. Special Marine Warnings may be needed
as these storms cross the waters. Most of the shower and storm
activity dissipates by late Tuesday evening.

Southerly channeling is possible Tuesday afternoon and evening ahead
of the front, which could produce a period of SCA conditions in the
open waters of the Chesapeake Bay.

Winds are forecast to remain below SCA criteria Wednesday.

SCA conditions possible Friday into the weekend.
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&&

.CLIMATE...
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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
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&&

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

&&

$$

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