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Day 1 Outlook Convective Tornado Hail Wind

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.

  
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ACUS01 KWNS 280602
SWODY1
SPC AC 280600

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0100 AM CDT Sat Mar 28 2020

Valid 281200Z - 291200Z

...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FROM EASTERN
IOWA INTO CENTRAL AND NORTHERN ILLINOIS...

...SUMMARY...
A significant severe weather outbreak is expected for portions of
the Midwest this afternoon and evening. Threats include tornadoes, a
few which may be significant, large to very large hail, and severe
wind gusts.

...Synopsis...

Upper trough now situated over the southern Rockies will eject
northeast today, reaching the middle MS Valley and Midwest region
later this afternoon. Surface low in southwest KS will deepen as it
develops northeast within exit region of a strong upper jet, and
should reach southwest IA by early this afternoon. A warm front will
extend eastward from the low through northern IL into northern
portions of the OH Valley. Trailing cold front initially from
eastern KS through eastern TX will advance through the MS, TN and OH
Valleys. By the end of the period this front should extend from a
surface low in WI southeast through the OH Valley, TN Valley and
central portion of the Gulf Coast states.  

...Midwest through Ohio Valley region...

Areas of elevated thunderstorms will be ongoing north of warm front
from northern MO, IA, IL and eastward into the OH Valley and Great
Lakes. This activity will gradually shift northward during the day
with a gradual destablization of the boundary layer promoted by the
northward advection of mid 60s F dewpoints through the warm sector.
Widespread multi-layer clouds will slow the destabibliztion process
somewhat. However, back edge of cirrus associated with subtropical
moisture plume should shift east of this region and partial cloud
breaks will contribute to at least modest diabatic warming of the
surface layer. MLCAPE from 1500-2000 J/kg is expected across the
Midwest by middle to late afternoon. The process of destabilization
and deeper forcing for ascent within the upper jet exit region will
likely contribute to development of storms along warm conveyor belt
from northeast MO, eastern IA into western IL. Vertical wind
profiles with 50+ kt effective bulk shear will support supercells.
These storms will move northeast through central and northern IL
during the late afternoon and evening within an environment
characterized by a strengthening low-level jet which will promote
large 0-1 km hodographs (300-500 m2/s2 storm-relative helicity).
This parameter space along with low LCLs will support potential for
supercells capable of producing long-track, strong tornadoes and
very large hail. Assuming sufficient destabilization occurs, other
supercells might develop in an arcing band within zone of ascent
accompaying the primary vorticity maximum and just east of the
surface low across central IA. These storms will also pose a risk
for large hail and tornadoes. An upgrade to high risk will be
considered in later day 1 updates for a portion of this region.

Elsewhere, additional storms will develop east through the OH Valley
and southern Great Lakes during the evening with all severe hazards
possible.

...Lower Mississippi through Tennessee Valley region...

Storms will likely develop along and ahead of an eastward-advancing
cold front and will likely gradually intensify as the boundary layer
destabilizes during the day. While low-level hodographs will not be
as large as farther north, deep-layer shear in excess of 50 kt and
moderate instability will be more than sufficient for organized
storms including a few bowing segments and supercells capable of
damaging wind, large hail and a few tornadoes. Activity will
continue east into the TN Valley area into the overnight with a
continued severe threat.

..Dial/Dean.. 03/28/2020

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