ACUS03 KWNS 160719
SPC AC 160718

Day 3 Convective Outlook  
NWS Storm Prediction Center Norman OK
0218 AM CDT Wed Jun 16 2021

Valid 181200Z - 191200Z


Scattered severe storms will be possible Saturday across Illinois,
Indiana and Ohio, and toward the Ohio River. A few strong to severe
storms may also occur into western New York and Pennsylvania, and
across northern Missouri and Kansas.

A strong shortwave trough will move from the upper MS Valley across
the upper Great Lakes through 00Z, and into the northeastern states
by Saturday morning. Cooling aloft will occur through the period
across these areas, with increasing midlevel westerlies enhancing

The primary surface low will move from eastern Ontario into western
Quebec, with lowering pressures extending south to the OH Valley.
Southwest surface winds will result in an expanse of 65-70 F
dewpoints from the lower MO Valley eastward toward western PA by 12Z
Saturday. Several areas of severe storm potential are expected to
develop over this broad zone from IL to PA, beginning over IL and IN
early Friday.

Elsewhere, a tropical low is forecast to move north across the
western Gulf of Mexico, with increasing moisture and shear affecting
southern LA and surrounding states.

...Midwest/OH Valley...
Storms, possibly with wind threat, may be ongoing Friday morning
across IN, but are expected to wane with time. By afternoon, new
development is expected in this region, as large-scale ascent
increases. Initiation points may depend on outflow boundaries from
early convection, but storms could develop with heating anywhere
from IL to OH where 2000-3000 J/kg MUCAPE is possible. Increasing
deep-layer mean wind speeds will favor forward propagating bows
capable of damaging wind. Additional storms will be possible later
in the day and overnight in the warm advection regime into NY and
PA, where a cold front will eventually overtake the unstable air by
morning. Portions of the Slight Risk may be upgraded categorically
in later outlooks as predictability increases.

Farther west across MO and into northeast KS, a front will stall,
with moderate instability developing during the day. Lift will be
weak, but deepening of the moist boundary layer may result in storms
between 00-06Z, and localized strong gusts cannot be ruled out.

...Coastal LA and upper TX Coast...
A low is forecast to move north across the western Gulf of Mexico,
approaching the TX/LA coast by Saturday morning. Coincident with the
low, wind fields and shear will also increase, along with tropical
moisture aiding instability. A substantial amount of convection is
possible from southeast TX into LA, and a couple tornadoes will also
be possible should shear be as strong as currently forecast.

..Jewell.. 06/16/2021