501
ACUS01 KWNS 230603
SWODY1
SPC AC 230602

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0102 AM CDT Sun Jun 23 2024

Valid 231200Z - 241200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
OF NEW ENGLAND...

...SUMMARY...
Scattered damaging winds and a few tornadoes are likely across parts
of the Northeast into the OH/TN valleys, this afternoon and evening.
Isolated severe storms are also possible over parts of the central
and northern Plains.

...Synopsis...
Mostly zonal mid-level flow is forecast to remain over the northern
third of the US as a shortwave trough moves east across parts of WA
and the southern Canadian Rockies. To the east, a low-amplitude
shortwave trough embedded within broader zonal flow aloft over the
Great Lakes and southern Ontario is expected to consolidate and
strengthen as flow aloft increases over much of New England. A
secondary trough over the upper MS River Valley is also expected to
amplify as zonal flow aloft becomes southwesterly over the
Northeast. Height falls and increasing DPVA will aid in strong
surface cyclogenesis over the lower St Lawrence Valley. To the east
of the deepening surface cyclone, a warm front will extend eastward
across New England to the Atlantic coast, while a cold front and
surface trough trails toward the southwest into the OH valley.

...New England to the Mid Atlantic...
At the start of the forecast period, scattered thunderstorms are
likely to be ongoing near the warm front from southern Quebec
southeastward to southern New England. Insentropic ascent along the
front from a 30-40 kt LLJ will continue to support scattered storms
near the frontal zone through the morning hours as rich
boundary-layer moisture (dewpoints in the upper 60s to low 70s F)
are advected northward. In the wake of the early morning convection,
filtered solar heating will allow for moderate destabilization over
much of New England. Most guidance shows 1500-2000 J/kg of MLCAPE
developing by early to mid afternoon despite only modest low and
mid-level lapse rates. More than sufficient for strong updrafts,
scattered storm development is expected first near the warm front
and subsequently along the trailing surface trough. Deep-layer shear
profiles of 45-60 kt support both supercells and short line
segments. With a favorable parameter space for organized storms,
damaging winds, isolated hail and a few tornadoes are possible.

Confidence in a corridor of locally greater severe risk remains
highest across portions of southern ME, VT, NH and west-central MA.
Here, area model soundings show large curved hodographs with ESRH of
250-350 m2/s2 and STP values of 1.5-3, near the climatological
maximum for the region. With the potential for a mix of supercells
and line segments, the risk for tornadoes appears somewhat higher.
Eventual upscale growth into a linear cluster may also support a
locally greater risk of damaging winds toward the coast later this
evening. Additional storms are possible as the cold front moves
through later this evening, though multiple rounds of prior
convection may limit the severity of any subsequent convection later
this evening.

Across the Mid Atlantic, more isolated storm coverage is expected
with southward extent. Displaced from the main lobe of ascent from
the passing shortwave trough, convection may take longer to organize
owing to the warmer mid-level temperatures and weaker synoptic
forcing. Still, deep-layer shear and buoyancy are favorable for
organized multi-cell clusters and a few supercells. Damaging winds,
and occasional hail are the most likely threats, though a tornado or
two will remain possible with any sustained supercell.

...Upper OH to the Mid TN Valleys...
Ahead of the trailing cold front, scattered thunderstorm development
is expected during the afternoon. Despite veered surface flow west
of the surface trough over the Mid Atlantic, rich boundary-layer
moisture will support a broad plume of moderate instability. Several
bands of thunderstorms should track east southeast along the
southern periphery of the enhanced flow aloft. Sufficient for some
storm organization, 20-30 kt of effective shear should support a few
clusters capable of damaging gusts and isolated hail.

...Northern Plains...
Accompanying the wave over southern Canada and the Northwest, a
deepening surface cyclone with a cold front trailing southward into
MT will serve as a focus for isolated storm development this
afternoon and evening. Low-level southeasterly flow will transport a
confined plume of modest low-level moisture into parts of east MT,
resulting in a corridor of MLCAPE from 500-1500 J/kg. Deep-layer
shear will be favorable for organized convection capable of isolated
damaging winds and hail, but large-scale ascent attendant to the
shortwave trough may tend to remain north of the international
border. Development of a severe storm or two across east MT is
possible by early evening, which would then potentially spread into
northwest ND later into the evening and overnight hours.

...Central Plains...
Very warm temperatures are expected along a lee trough across the
central Plains this afternoon. With temperatures near 100 F,
scattered high-based thunderstorms are likely over parts of eastern
CO, southwest NE and western KS. Deep inverted-v profiles will
support a risk for severe gusts with strong downdrafts. Located on
the southern periphery of the stronger upper-level flow, these
storms may persist into early evening despite the lack of stronger
forcing for ascent.

..Lyons/Wendt.. 06/23/2024

$$