483
FXUS61 KLWX 200754
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
354 AM EDT Thu Jun 20 2024

.SYNOPSIS...
High pressure will remain in place offshore through this weekend. A
cold front will progress through on Monday, with high pressure
building back in by Tuesday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Strong upper level ridging will remain centered overhead today.
Large scale subsidence will keep conditions capped, resulting in dry
conditions across the entire forecast area. A mix of sun and high
clouds is expected throughout the day. While it will be yet another
hot day, onshore flow around an area of high pressure offshore will
keep it a bit cooler and less humid than one might expect given the
very strong upper ridge overhead. High temperatures today should
reach into the upper 80s and lower 90s for most, with low-mid 80s in
the mountains. Dewpoints will be in the low-mid 60s. High pressure
will remain in control tonight, leading to continued dry conditions.
Overnight lows will be in the mid-upper 60s for most, with lower 70s
in DC and Baltimore.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY NIGHT/...
Upper level ridging will start to break down a bit by Friday. As
this occurs, the 850 hPa high will shift a bit further south,
lessening the easterly component of the wind and resultant oceanic
influence. Temperatures will be a few degrees warmer as a result,
with highs in the mid 90s for most. As the upper ridge starts to
weaken, a few afternoon thunderstorms may form over the higher
terrain of the Potomac Highlands and Allegheny Front in response
to daytime heating and resultant terrain circulations. These
thunderstorms could potentially drift as far east as the
Shenandoah Valley before dissipating in the evening hours. Dry
conditions are expected further east. Friday night will feature
warmer temperatures compared to preceding nights, with
overnight lows generally in the low-mid 70s.

Mid-level heights will continue to slowly decrease on Saturday.
Meanwhile, flow at 850 hPa will turn westerly to southwesterly,
allowing a more continental airmass to work into the region.
This will result in even hotter temperatures, with highs in the
mid-upper 90s. It will also turn more humid, with dewpoints
increasing into the lower 70s. Peak heat indices of 100-105
appear likely across much of the forecast area, and Heat
Advisories may potentially be needed as a result.

Guidance hints that a weak southwest to northeast oriented
surface trough may develop across the center of the forecast
area. A few thunderstorms may form during the afternoon hours
along this surface trough and slowly progress eastward through
the evening hours. Mid- level flow (and as a result, shear)
will be relatively weak, at around 15 knots, but instability
will be plentiful (MLCAPE values over 2000 J/kg) within the hot
and humid airmass. While the activity should be somewhat
disorganized, storms may be capable of producing localized
downbursts, given high levels of CAPE and DCAPE in place.

Thunderstorm activity should gradually wind down through the
evening hours, with dry conditions expected through much of the
night. Saturday night will be warmer still, with overnight lows
in the mid-upper 70s to the east of the Blue Ridge, with lower
80s even possible in DC and Baltimore.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
Hot weather continues Sunday with highs likely in the mid 90s to
near 100. Dew points are also forecast to be peaking during this
time, so much of the area may need Heat Advisories. There will be a
greater chance of showers and thunderstorms than the preceding days
due to height falls ahead of a Great Lakes trough along with a lee
surface trough. Even though NBM PoPs currently favor the evening
hours, subtle timing differences could easily result in
thunderstorms at any point during the afternoon. A localized severe
weather risk could materialize with ample instability, although the
local area will be on the southern periphery of stronger flow to the
north.

Cold front will push south into the area Monday. There are still
some timing differences which would affect the temperature forecast
as well as the coverage of showers and thunderstorms. Surface high
pressure will build over the area by Tuesday. The post-frontal
airmass won`t bring a huge relief in temperatures, with most areas
still forecast to top 90 degrees. It will be less humid however.

Model spread increases by mid-week with differences in how the next
trough evolves. It does appear to heat back up as southwesterly flow
resumes, along with some risk for a shower or thunderstorm.

&&

.AVIATION /08Z THURSDAY THROUGH MONDAY/...
Prevailing VFR conditions and light southerly winds are expected at
the terminals through Saturday. An afternoon thunderstorm can`t be
ruled out at MRB Friday afternoon, and then at any of the terminals
on Saturday.

Thunderstorms are possible Sunday afternoon through Monday as a cold
front approaches.

&&

.MARINE...
Persistent southerly flow is expected over the waters through
Saturday. Winds may near low-end SCA levels in channeled southerly
flow during the afternoon and evening hours on both Friday and
Saturday.

South to southwest winds may require Small Craft Advisories Sunday
into Sunday night. Thunderstorms are possible Sunday afternoon into
Sunday night as well. A cold front will push through Monday with a
wind shift to the northwest. Additional thunderstorms are possible
depending on the timing of the front.

&&

.CLIMATE...
Hot temperatures are expected much of this week and especially
this coming weekend. The hottest days appear to be Friday through
Sunday when several records could be in jeopardy. Below is a list
of record high temperatures for Jun 21st, 22nd, and the 23rd
and the year the record was set, and the current forecast high
temperatures for those days. RERs are only issued for DCA, IAD,
BWI, and MRB, but other sites are shown for reference.

                                     Friday Jun 21st
Climate Site                  Record High     Forecast High
Washington-National (DCA)     99F (2012)          96F
Washington-Dulles (IAD)       98F (1988)          96F
Baltimore (BWI)              100F (2012+)         95F
Martinsburg (MRB)            102F (1931)          93F
Charlottesville (CHO)         99F (1933)          94F
Annapolis (NAK)              100F (1988)          90F
Hagerstown (HGR)              97F (1923)          95F

                                    Saturday Jun 22nd
Climate Site                  Record High     Forecast High
Washington-National (DCA)    101F (1988)          99F
Washington-Dulles (IAD)       99F (1988)          99F
Baltimore (BWI)              100F (1988)          97F
Martinsburg (MRB)            102F (1933)          95F
Charlottesville (CHO)        101F (1933)          98F
Annapolis (NAK)              101F (1988)          93F
Hagerstown (HGR)             100F (1988)          97F

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

&&

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

&&

$$

SYNOPSIS...KJP
NEAR TERM...KJP
SHORT TERM...KJP
LONG TERM...ADS
AVIATION...KJP/ADS
MARINE...KJP/ADS
CLIMATE...LWX