NOAA Storm Prediction Center
The convective outlooks serve as guidance to the local NWS forecast offices and are used by emergency managers, private sector meteorologists, media, and other weather customers concerned with public safety. Three separate risk areas (slight, moderate, and high) are used to describe the expected coverage and intensity for the categorical severe weather threat on days 1-3 along with severe weather probabilities for the potential threat.
Images courtesy of the NWS Storm Prediction Center
Categorical Day1 1200Z Outlook
Probability of a tornado within 25 miles of a point.
Hatched Area: 10% or greater probability of EF2 - EF5 tornadoes within 25 miles of a point.
Probability of one inch diameter hail or larger within 25 miles of a point.
Hatched Area: 10% or greater probability of two inch diameter hail or larger within 25 miles of a point.
Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point.
Hatched Area: 10% or greater probability of wind gusts 65 knots or greater within 25 miles of a point.
ACUS01 KWNS 290538
SPC AC 290537
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1237 AM CDT Sat Apr 29 2017
Valid 291200Z - 301200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM CENTRAL
TEXAS TO SOUTHERN MISSOURI...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM SOUTH CENTRAL
TEXAS TO SOUTHWEST OHIO...
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM SOUTH TEXAS
TO THE NORTHERN MIDDLE ATLANTIC...
Severe thunderstorms are expected from parts of south central Texas
northeastward to portions of the Ohio Valley/northern Middle
Atlantic region Saturday into Saturday night. These storms will be
capable of large hail, damaging winds, and a few tornadoes.
Early-morning water vapor imagery depicts a well-defined upper low
near the 4-Corners region, drifting slowly southeast in line with
the latest model guidance. This feature is forecast to shift into
the southern High Plains region by the end of the day1 period as
strongest mid-level flow finally rotates through the base of the
trough into northwest TX/western OK. Given this scenario, strongest
mid-level height falls will not spread into west TX until late
afternoon. As a result, large-scale forcing, for ascent, will be
negligible across much of the warm sector through the period. It
appears widespread convection will concentrate along a stationary
frontal zone oriented from eastern OK into the OH valley and along
the cold front as it surges eastward across OK/TX then into the
lower MS Valley Saturday night.
At 29/05z...a narrow corridor of widespread thunderstorms has
evolved along the aforementioned frontal zone from northern OK,
northeast into southern OH. Warm advection should maintain this
zone of convection through sunrise Saturday morning. Hail may be
the greatest severe risk with this activity, though very heavy rain
may ultimately become an issue along this front as training
thunderstorms allow the surface boundary to oscillate a bit through
the period. By 12z Saturday, strong/severe squall line is expected
to evolve along the cold front as it surges across OK/northwest TX.
Damaging winds could evolve with this activity, in addition to some
Given the slow eastward movement of the upper low, and the lack of
meaningful forcing across the warm sector, linear convection should
be the primary storm mode along the cold front, though strong shear
profiles do favor sustained rotating updrafts, especially
immediately ahead of the surface low/warm front. Even so, warm
frontal convection may struggle to maintain supercell
characteristics across the mid MS Valley due to extensive
precipitation/storm mergers. It appears an extensive frontal MCS
will advance across the southern Plains into the mid/lower MS Valley
region during the latter half of the period. Large hail and
damaging winds are the primary threats, though a few tornadoes can
not be ruled out if embedded supercells evolve along the squall
line, or warm front.