161
ACUS01 KWNS 300548
SWODY1
SPC AC 300547

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1247 AM CDT Sun Jun 30 2024

Valid 301200Z - 011200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS
AFTERNOON/EVENING FROM EASTERN AND SOUTHERN NEW ENGLAND INTO THE
MID-ATLANTIC...AND THIS EVENING INTO EARLY TONIGHT ACROSS MT...

...SUMMARY...
Scattered damaging winds will be possible across parts of the
Northeast and Mid-Atlantic States this afternoon/evening. Hail and
damaging winds may also occur from eastern Montana into western
North Dakota.

...New England into the Mid-Atlantic this afternoon/evening...
A midlevel shortwave trough over Lower MI will progress eastward
toward NY/PA by early tonight, while an associated surface cold
front moves eastward across New England and southeastward across the
central Appalachians.  A corridor of boundary-layer dewpoints in the
low 70s and surface heating in cloud breaks will support diurnal
destabilization ahead of the cold front/pre-frontal trough which
will focus thunderstorm development by early-mid afternoon.  Though
midlevel lapse rates will not be particularly steep, MLCAPE is
expected to increase to 1500-2000 J/kg as midlevel flow also
increases with largely straight, but sufficiently long hodographs.
The net result will be a favorable environment favorable for
organized storm clusters/line segments, as well as a few supercells,
capable of producing damaging winds, isolated large hail and perhaps
a tornado into the evening across southern and eastern New England.

Deep-layer vertical shear will weaken with southwestward extent into
VA/NC, where the storm mode is expected be predominately multicell
clusters.  Still, thermodynamic profiles will support the potential
for occasional wind damage with downbursts.

...Northern/central High Plains this evening into tonight...
A midlevel shortwave trough over WA/OR will move eastward over the
northern Rockies by tonight, with downstream lee cyclogenesis
expected across WY/MT.  Though the richer low-level moisture will be
confined to KS southward along a baroclinic zone, there will be a
modest increase in low-level moisture across the central/northern
High Plains on southeasterly low-level flow.  The somewhat larger
buoyancy and weaker convective inhibition are expected closer to the
high terrain, with the more likely area for storm-cluster
development over the mountains of southern MT in the zone of ascent
preceding the midlevel trough.  The storms will subsequently spread
east-northeastward toward eastern MT with an accompanying threat for
severe outflow winds of 60-70 mph.  Large hail (mainly 1-1.75 inches
in diameter) will also be possible with any embedded supercell
structures.

Farther south, isolated thunderstorm development will be possible
immediately east of the higher terrain from WY into CO.  Forecast
wind profiles will be at least marginally favorable for supercells,
though storm coverage is in question.  The southern fringe of the
stronger midlevel flow and the northwest edge of the monsoonal
moisture plume may support an isolated wind-damage threat into
western CO.

...Southern AZ this afternoon/evening...
Around the southwestern periphery of a midlevel high over the
southern Plains, low-midlevel moisture has been gradually increasing
from southern NM into AZ.  In the wake of scattered overnight
storms, cloud breaks will allow surface heating/destabilization
across southeast/south central AZ into the afternoon, which will
drive moderate buoyancy (MLCAPE up to 1000 J/kg).  Convection will
form over the high terrain of southeast AZ and spread westward
through late afternoon/evening in response to east-southeasterly
midlevel flow of 20-25 kt.  A typical/deep mixed boundary layer
coupled with the moderate buoyancy will support a few strong outflow
gusts (50-60 mph) with precipitation-loaded downdrafts.

..Thompson/Squitieri.. 06/30/2024

$$