MD 0577 CONCERNING SEVERE POTENTIAL…TORNADO WATCH LIKELY FOR FAR EASTERN IA…NORTHERN IL…SOUTHERN WI
Mesoscale Discussion 0577
NWS Storm Prediction Center Norman OK
0150 PM CDT Thu Apr 20 2023
Areas affected...Far eastern IA...Northern IL...Southern WI
Concerning...Severe potential...Tornado Watch likely
Valid 201850Z - 202015Z
Probability of Watch Issuance...80 percent
SUMMARY...Thunderstorms capable of all severe hazards, including
tornadoes, are expected to develop across far eastern IA, northern
IL, and southern WI this afternoon and evening.
DISCUSSION...Recent surface analysis places a low about 45 miles
east-northeast of ALO in far northeast IA. A warm front extends
eastward from this low across southern IL, while a cold front
extends southwestward across eastern IA through northeast, central,
and southwest MO. Temperatures have climbed into the upper 60s/low
70s ahead of this front, with dewpoints generally in the upper 50s.
Convective inhibition currently remains in place, but is expected to
gradually erode as additional heating increases surface temperatures
and modest low-level moisture advection persists. This low-level
moisture advection may not result in an increase in dewpoints, but
should help offset the effects of boundary-layer mixing.
Most forecast soundings suggest temperatures in the mid 70s and
dewpoints in the upper 50s, combined with modest mid-level
cooling/moistening, will sufficiently reduced the convective
inhibition enough to allow for thunderstorm initiation. Whether or
not these conditions occur across far east IA before the front moves
through remains uncertain, given the lower temperatures and greater
cloud cover. Once initiation occurs, strong vertical shear should
result in organized storms, including some initially discrete
supercells. In addition to strong deep-layer flow, DVN VAD has
already sampled 50 kt at 1 km AGL. This intense low-level flow
supports the potential for supercells capable of producing
tornadoes. Large hail and damaging gusts are also possible.
Given the linear forcing, uncertainty exists regarding the duration
of truly discrete storms, with a trend towards a more cell-in-line
mode or even purely linear possible with time. Even so, embedded
tornadoes would still be possible, in addition to damaging gusts and
isolated hail.
..Mosier/Grams.. 04/20/2023
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...LOT...ILX...MKX...DVN...ARX...
LAT...LON 42519140 43059106 43599006 43658898 43558834 43148786
41428783 40758955 40559158 42519140
