864
ACUS01 KWNS 200554
SWODY1
SPC AC 200552

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1252 AM CDT Thu Jun 20 2024

Valid 201200Z - 211200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE
NORTHEAST AND OVER THE CENTRAL HIGH PLAINS...

...SUMMARY...
Storms may produce scattered damaging gusts over parts of the
Northeast on Thursday. Scattered severe storms are also expected
over parts of the central High Plains.

...Northeast...

Upper anticyclone currently centered over the middle Atlantic will
gradually build west across the CONUS during the day1 period. As
this occurs, some flattening of the height field is expected over
southern QC into New England. Modest 500mb flow will extend along
the international border, but much weaker mid-level winds will be
noted over the lower Great Lakes into southern New England. This
stronger flow over Canada will encourage a surface cold front to
advance south into northern ME, arcing west along the international
border into southern lower MI by 18z, with subsequent southeast
movement expected across the Northeast into the early evening. This
boundary will serve as the focus for convection later today as
surface temperatures quickly soar through the 80s into the lower
90s. Additionally, while deep-layer shear will not be particularly
strong along the northern fringe of the upper High, PW values are
seasonally moist with 1.5-2 inches expected south of the frontal
zone. Damaging winds are the primary risk with convection today.

...Central High Plains...

Weak 12hr mid-level height rises are forecast across much of the
interior western US through early evening as an upper trough
repositions itself from WA/OR into CA. This will ensure a corridor
of modest southwesterly flow at mid-levels from the Four Corners
region into the central High Plains. Within this flow a few weak
disturbances may track across the central Rockies into the Plains.
Each of these features could encourage robust convection. Latest
guidance suggests a weak lee cyclone will evolve over northeast CO
by late afternoon in response to one of these features. LLJ is also
forecast to respond across western KS into SD. As a result, an
easterly boundary-layer component will be noted across the NE
Panhandle into eastern WY. NAM forecast sounding for CYS at 22z
exhibits negligible inhibition but MLCAPE on the order of 2000 J/kg
with 35kt surface-6km bulk shear. HREF guidance strongly suggests
convection will evolve over the higher terrain of south-central
WY/CO fairly early, then propagate downstream, growing upscale into
a possible MCS within the warm-advection zone. Convection should
advance into the central Plains after sunset aided by strengthening
LLJ. Initial storm mode should be supercellular and large hail is
expected. Severe wind gusts could materialize along the leading edge
of the MCS if it matures as expected.

..Darrow/Thornton.. 06/20/2024

$$