MD 0225 CONCERNING TORNADO WATCH 42… FOR PORTIONS OF CENTRAL AND NORTHERN ILLINOIS
Mesoscale Discussion 0225
NWS Storm Prediction Center Norman OK
0806 PM CST Tue Feb 28 2017
Areas affected...Portions of central and northern Illinois
Concerning...Tornado Watch 42...
Valid 010206Z - 010330Z
The severe weather threat for Tornado Watch 42 continues.
SUMMARY...The severe threat is shifting back to western portions of
Tornado Watch 42. An ongoing threat for damaging winds, large hail,
and a few tornadoes is expected. In turn, new watch issuance will
likely be required prior to the 04Z expiration of Watch 42.
DISCUSSION...A second round of convection is organizing across
northern Missouri, far southeastern Iowa, and western Illinois in
response to large-scale forcing for ascent with the approaching
trough. Steepening mid-level lapse rates (observed upstream in the
00Z TOP and SGF soundings) and low-level convergence along the
surface front will promote further blossoming of convection this
evening. While cells may initially struggle due to modest low-level
moisture (e.g., low 50s dew points in western Illinois), a corridor
of higher dew points to the east will likely yield around 1000 J/kg
of MLCAPE late this evening. While some persisting convective
inhibition may partially temper a greater severe threat, effective
storm-relative helicity on the order of 300-400 m2/s2 will be
favorable for low-level mesocyclogenesis. Uni-directional
southwesterly flow above 850-mb suggests storms will evolve into
small bowing segments, with perhaps embedded supercell structures.
Therefore, a renewed threat for damaging winds, a few tornadoes, and
large hail will likely evolve across the region late this evening
into the overnight. New watch issuance is anticipated prior to the
04Z expiration of Watch 42.
..Picca.. 03/01/2017
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...LOT...ILX...LSX...DVN...
LAT...LON 39279091 39479139 40149177 40519177 41179121 41678951
41768775 41578748 40158759 39678815 39329064 39279091
from SPC Mesoscale Discussions http://bit.ly/2mqKBfP
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