863
ACUS01 KWNS 212000
SWODY1
SPC AC 211959

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0259 PM CDT Fri Jun 21 2024

Valid 212000Z - 221200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE NORTHERN
HIGH PLAINS TO THE UPPER MISSISSIPPI VALLEY...THE FOUR CORNERS
REGION...AND SOUTHERN NEW ENGLAND...

...SUMMARY...
Scattered strong to severe storms are expected from parts the upper
Mississippi Valley into the northern High Plains, and into the Four
Corners vicinity. A few strong storms may occur from parts of the
Lower Great Lakes to southern New England.

...Discussion...
Only two notable changes were made to the previous convective
outlook.  Otherwise the previous forecast thinking remains on track.

1) Have increased severe-wind probabilities to 15 percent and a
categorical Slight Risk over southern portions of New England.
Despite modest deep-layer westerly flow, steep 0-3 km lapse rates
(7.5 to 8.5 deg C/km) and around 2 inches PW have yielded an
environment that will favor multicells sporadically capable of
strong to locally severe gusts (50-65 mph) and wind damage.  A
linear cluster near the NY/MA/CT border will likely push eastward
over the next 2-4 hours and reach the CT/RI coast, and this area has
been highlighted with recently issued Severe Thunderstorm Watch
#444.

2) Included southwest NE in Slight-Risk equivalent severe wind
probabilities based on the latest satellite/observational trends.
Storms that potentially develop over the next few hours within
southwest NE may yield a severe-wind hazard given the steep lapse
rate environment.

..Smith.. 06/21/2024

.PREV DISCUSSION... /ISSUED 1052 AM CDT Fri Jun 21 2024/

...Four Corners into WY...
Water vapor imagery shows a well-defined upper trough over NV, with
an associated 40+kt mid-level speed max tracking from northern AZ
into UT/CO.  Beneath this strengthening wind field and large-scale
ascent, considerable low-level moisture is present today with
dewpoints in the 50s across much eastern UT/western CO and southwest
WY.  Pockets of strong daytime heating will lead to scattered
afternoon thunderstorms.  Vertical shear profiles will promote
supercell storm structures capable of hail and damaging winds for
several hours this afternoon and evening.

...MT/WY...
Several weak shortwave troughs are noted this morning moving
east-northeastward across the northern Rockies.  These features,
combined with persistent easterly low-level winds across
central/eastern MT will result in scattered afternoon thunderstorm
development.  Relatively isolated supercells are expected over MT,
with more convective coverage farther south into eastern WY and
western SD/NE.  Storms will be capable of large hail and damaging
winds, along with the possibility of a tornado or two (mainly over
parts of MT).

...Central Plains...
A well-defined surface boundary extends across northern NE into
southern MN.  Considerable heating to the south of this boundary,
along with strengthening southerly low-level winds/convergence by
late afternoon, will result in scattered thunderstorms in vicinity
of the front.  Sufficient flow aloft and ample CAPE will promote a
risk of a few severe storms capable of damaging winds and hail.

...Lower MI...
Pockets of strong heating will lead to scattered afternoon
thunderstorms over parts of central and southern Lower MI.  This
area is along the southern fringe of stronger westerlies, with 25-30
knots of flow at 500mb.  This might be sufficient for a few strong
storms capable of gusty winds and hail.

...NY/PA/Southern New England...
Hot and humid conditions are expected today across much of PA/NY and
southern New England, with dewpoints in the 70s and temperatures
well into the 80s and 90s.  Mid level lapse rates are rather weak,
so MLCAPE values will be <2000 J/kg.  Given relatively weak winds
aloft, thunderstorm organization is expected to be marginal.
Nevertheless, a few strong storms capable of locally gusty/damaging
winds are possible through the afternoon.  Please refer to MCD #1352
for further details.

$$