274
FXUS61 KLWX 171805
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
205 PM EDT Mon Jun 17 2024

.SYNOPSIS...
High pressure will remain anchored offshore through the week. A
warm front will lift northeastward across the Mid-Atlantic
through the evening, marking the beginning of a prolonged
period of heat.

&&

.NEAR TERM /THROUGH TONIGHT/...
Latest mesoanalysis shows heat/instability building near a lee
pressure trough along the I-81 corridor in the Shenandoah
Valley. Latest CAMs continue to show scattered
showers/thunderstorms in this area on the backside of the
departing surface high. Given weak low and mid- level flow,
convection will move slowly and/or lock to nearby terrain,
resulting in a localized heavy rainfall threat. FFG is
relatively high (2.5-4" in 1-3 hours), though slow storm motions
and higher PWs could result in totals close to these values in
a reasonable high-end scenario. Given the dry antecedent
conditions and the somewhat conditional nature of the threat, no
Flood Watch has been issued at this time. The increased heat
and steepening low-level lapse rates could also aid in a few
localized strong downbursts/gusty to perhaps damaging surface
winds. Convection chances are highest near and west of the Blue
Ridge Mountains and south of US-50 from around midday through
early this evening. Some guidance also has convection in and
around KCHO toward Nelson County, VA.

Elsewhere, a dry and hot day is expected. Humidity will
increase, but won`t be quite oppressive by early summer Mid-
Atlantic standards. This should result in heat index values
around or a degree or two higher than the air temperatures -
generally in the lower to middle 90s.

Low temperatures tonight will be in the 60s to lower 70s under
a partly to mostly clear sky.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
Ridging will build aloft Tuesday into Wednesday. Subsidence
could be weak enough to allow a few isolated showers or
thunderstorms to develop near the Appalachians Tuesday
afternoon, but most of the time/area will just be dry and hot.
Latest HREF highlights the far western Alleghenies with an area
of showers and thunderstorms drifting north along the periphery
of the ridge.

Temperatures will trend upward a bit Tuesday, then decrease
slightly Wednesday as the center of the ridge reorients itself
to the north and low-level flow pivots to off relatively cooler
water. Have issues a Heat Advisory for parts of western Maryland
into the eastern Panhandle of West Virginia given the overlap of
heat and high humidity. There remains uncertainty on how much
mixing there will be tomorrow afternoon, especially towards
Petersburg into the Shenandoah Valley, so have left out that
area from the advisory for now.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
Highly anomalous upper level ridging along the East Coast will
slowly start to break down during the second half of the week, with
flow aloft becoming more zonal in nature next weekend. As this
occurs, the 850 hPa high to our northeast will also start to break
down, allowing 850 hPa flow to shift from east-southeasterly on
Thursday, to southwesterly next weekend. As 850 hPa flow gains a
westerly component, an increasingly continental airmass will move
over the region, leading to an increase in temperatures, despite the
falling heights aloft.

The strong upper ridge should suppress any convection on Thursday
and Friday, leading to sunny skies both days. As temperatures rise
at the surface and cool aloft, chances for popup afternoon and
evening thunderstorms will return this coming weekend. Thunderstorm
activity looks to remain relatively isolated on Saturday in the
absence of appreciable large scale forcing for ascent. By Sunday,
height falls associated with a trough tracking through the Great
Lakes may lead to greater chances for thunderstorms.

The main story through the long term period will be the heat.
Temperatures are expected to reach into the lower 90s on Thursday.
The hottest temperatures of this week`s heat wave are expected to
occur on Friday, Saturday, and Sunday. High temperatures those days
should make it into the mid-upper 90s, with around 100 possible in
some spots. Overnight lows will also increase from the upper 60s to
near 70 on Thursday night, to the mid-upper 70s by Saturday
night.

&&

.AVIATION /18Z MONDAY THROUGH SATURDAY/...
VFR conditions are expected to prevail at the TAF sites through
at least the first half of the week. A shower or thunderstorm
could approach KCHO/KMRB this afternoon or early evening. If it
does, brief restrictions would be possible (as would patchy fog
later tonight into early Tuesday morning). Winds will generally
be southerly to southeasterly at 6-12 kts with occasional
daytime gusts to around 18 kts. Eastern terminals likely
experience some river/bay breeze influence during the afternoon
and early evening hours each day.

VFR conditions and southerly winds are expected at the terminals on
Thursday and Friday.

&&

.MARINE...
South to southeast winds will prevail through much of the
upcoming week. Southerly channeling combined with bay/river
breeze enhancements likely result in SCA level gusts each
afternoon and evening. Otherwise, dry and hot weather is
expected through the week.

Low-end SCA level winds appear possible in channeled southerly flow
during the afternoon/evening hours of Thursday and Friday.

&&

.TIDES/COASTAL FLOODING...
Persistent southerly flow continues, and tidal anomalies are
hovering near one to one and a half feet above normal. This is
enough to result in near minor flooding, particularly during the
overnight high tide cycle near Annapolis the next couple of
days.

&&

.CLIMATE...
Hot temperatures are expected much of this coming week and
especially this coming weekend. We could see a few records
broken on Tuesday, but 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 June 18th, 21st, and 22nd,
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.

                                     Tuesday Jun 18th
Climate Site                  Record High     Forecast High
Washington-National (DCA)     97F (1944)          93F
Washington-Dulles (IAD)       94F (2018+)         93F
Baltimore (BWI)               97F (1957+)         92F
Martinsburg (MRB)             99F (1943)          93F
Charlottesville (CHO)         96F (2014+)         94F
Annapolis (NAK)               96F (1957)          88F
Hagerstown (HGR)              95F (1957)          94F

                                     Friday Jun 21st
Climate Site                  Record High     Forecast High
Washington-National (DCA)     99F (2012)          97F
Washington-Dulles (IAD)       98F (1988)          98F
Baltimore (BWI)              100F (2012+)         96F
Martinsburg (MRB)            102F (1931)          95F
Charlottesville (CHO)         99F (1933)          97F
Annapolis (NAK)              100F (1988)          91F
Hagerstown (HGR)              97F (1923)          97F

                                    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)          98F
Martinsburg (MRB)            102F (1933)          96F
Charlottesville (CHO)        101F (1933)          99F
Annapolis (NAK)              101F (1988)          93F
Hagerstown (HGR)             100F (1988)          97F

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

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Heat Advisory from noon to 8 PM EDT Tuesday for MDZ003-502.
VA...None.
WV...Heat Advisory from noon to 8 PM EDT Tuesday for WVZ051>053-504.
MARINE...Small Craft Advisory until midnight EDT tonight for ANZ530-538-
     539-542.
     Small Craft Advisory until 2 AM EDT Tuesday for ANZ531>534-537-
     540-541-543.

&&

$$

SYNOPSIS...DHOF/CPB
NEAR TERM...CPB/DHOF
SHORT TERM...CPB
LONG TERM...ADM
AVIATION...ADM/CPB
MARINE...ADM/CPB
TIDES/COASTAL FLOODING...LWX
CLIMATE...LWX