Day 1 Severe Weather Outlook

Valid 031200Z – 041200Z


Severe storms may occur today from parts of Lower Michigan
southwestward into Illinois, Indiana, and Ohio. Isolated damaging
winds and large hail should be the main threats, but a couple
tornadoes will also be possible.

…Midwest into the Great Lakes and Mid MS Valley…
A long-lived MCS over far southeastern MN and western/central WI
early this morning will likely continue southeastward across WI for
at least the next several hours along an instability gradient. This
line of storms should continue to gradually weaken with
southeastward extent this morning as it encounters a less unstable
airmass. However, strong low/mid-level flow associated with a
shortwave trough over the northern Plains may allow these storms to
persist for longer than most model guidance suggests. An isolated
hail/wind threat may be ongoing at the start of the period across
parts of northern IL and vicinity if these storms can maintain their
intensity, especially on the southwestern flank of the line where
instability is relatively greater.

The convective scenario for today remains rather uncertain given the
potential for this morning MCS to delay/disrupt diurnal
destabilization, particularly with northward extent into Lower MI. A
relatively greater chance for moderate to strong instability to
develop may occur along a trailing outflow boundary from these
morning storms across parts of northern IL/IN into far southern
Lower MI. Strong large-scale forcing for ascent attendant to a
southeastward-moving shortwave trough will overspread these areas by
this afternoon. Additional convective development appears likely
along or just ahead of a surface cold front by peak afternoon

The presence of a 50-70 kt mid-level westerly jet will support
strong effective bulk shear values over this region. Any storms that
can form in this environment will likely become organized and pose
an isolated large hail and damaging wind threat. Initially
semi-discrete storms will probably grow upscale fairly quickly along
the cold front or remnant outflow boundary, with a damaging wind
threat potentially continuing into the evening across parts of
central IL/IN and northwestern OH. The degree of the tornado threat
will be dependent on storm mode, but a southwesterly low-level jet
will overspread much of the warm sector through the afternoon.
Isolated tornadoes will be possible given the strong low-level shear
that will be present. Greater severe probabilities may be needed
across some part of the Midwest into southern Lower MI, but too much
uncertainty exists regarding morning storms to introduce them at
them at this time.

Latest forecast from the National Hurricane Center shows Hurricane
Dorian should remain just offshore the east coast of the FL
Peninsula today through tonight. However, low-level convergence and
banded convection within the western half of the system will spread
slowly northward. While tornadoes are generally not favored along
the west side of the track, effective SRH around 200 m2/s2 during
the day increasing to over 300 m2/s2 into early Wednesday morning
may support a couple rotating storms with a brief/weak tornado risk.

..Gleason/Squitieri.. 09/03/2019


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