SPC 0100Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0655 PM CST Tue Feb 27 2024
Valid 280100Z - 281200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER NORTHERN
ILLINOIS AND NORTHWEST INDIANA...AND FROM SOUTHEAST MISSOURI ACROSS
MUCH OF THE OHIO VALLEY...
...SUMMARY...
Severe thunderstorms producing tornadoes, damaging hail and wind
remain likely over parts of northern Illinois this evening, and
through tonight into parts of the Ohio Valley.
...Northern Illinois and Vicinity...
Supercells, some tornadic, have developed near the surface low just
ahead of the cold front over northern IL, and along the east-west
boundary which separates the greater theta-e to the south. Very
steep lapse rates aloft exist across the warm sector, where mid to
upper 50s F dewpoints are contributing to MUCAPE to 2000 J/kg.
As the surface low continues to deepen, the low-level jet will
strengthen across much of eastern IL, IN, and points south,
enhancing shear. As such, hodograph enlargement should support a
continued, and possibly increasing, significant-tornado threat
across parts of northern IL and eventually northwest IN later this
evening. The tornado threat may extend into southern Lower MI as
well, coincident with the surface low.
For more information, see mesoscale discussion 166.
...Southern IL and IN across much of the OH Valley Tonight...
A dryline currently extends from central IL southwestward into
northern AR, within the low-level lapse rate plume. Although farther
south from the surface low, midlevel temperatures remain quite cool,
resulting in steep lapse rates. In addition, boundary-layer theta-e
remains robust with lower 60 F dewpoints, contributing to around
1000 J/kg MLCAPE.
Several more hours of potential boundary-layer moistening will occur
ahead of the cold front from AR toward the lower OH Valley tonight,
as 850 mb winds increase to 60 kt. Although low-level winds may
veer, forecast storm motions are expected to be over 50 kt which may
allow for storms to remain just on or even ahead of the cold front.
And, effective SRH is forecast to remain over 300 m2/s2. The end
result will be storms focused along the front, possibly with linear
segments or broken with discrete supercells, with tornado,
damaging-wind, and hail potential. Strong-tornado potential will
exist with any activity remaining along or just ahead of the cold
front.
For more information in the near term, see mesoscale discussion 165.
..Jewell.. 02/28/2024
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