|Mesoscale Discussion 847|
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Mesoscale Discussion 0847
NWS Storm Prediction Center Norman OK
0431 PM CDT Fri May 26 2017
Areas affected...East-central Illinois and western/northwestern
Concerning...Tornado Watch 269...
Valid 262131Z - 262230Z
The severe weather threat for Tornado Watch 269 continues.
SUMMARY...A localized tornado threat appears to be increasing across
east-central Illinois in the short term.
DISCUSSION...An earlier line of storms over central Illinois (with a
history of hail and wind damage) has evolved into supercell
structures over portions of Livingston and McLean counties recently.
These storms are on the north edge of an area of moderate
instability (1500-2000 J/kg MUCAPE), with strongly veering wind
profiles with height and localized vorticity ingest along the warm
front aiding in updraft rotation with these storms. It appears that
the tornado threat with this activity is on the increase in the near
term, with hail/damaging wind gusts also possible near the strongest
Farther west, convective overturning has stabilized portions of
west-central Illinois north of an outflow boundary, although some
lingering mid-level instability (evidenced by convective towers atop
the cool low-level airmass on satellite imagery) suggests the severe
threat may not be completely over. Additional activity may form
along the aforementioned outflow boundary in southwestern portions
of the watch and also in east-central Illinois south of the ongoing
supercells (Macon, Piatt, and Champaign counties). This activity
will pose a threat for all severe modes into the evening, and
spatial southward and eastward extensions of WW 269 may be needed to
account for any evolving severe threat with this activity.
...Please see www.spc.noaa.gov for graphic product...
LAT...LON 40169040 40559040 40799002 41138931 41268815 41278735
41228654 41058608 40728595 40478595 40238632 40108724
39928767 39788819 39798876 39928929 39909002 39999023
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