Mesoscale Discussion 0469
NWS Storm Prediction Center Norman OK
0253 PM CDT Fri Apr 18 2025
Areas affected...swrn through much of ern MO...cntrl and nrn IL
Concerning...Severe potential...Watch possible
Valid 181953Z - 182230Z
Probability of Watch Issuance...40 percent
SUMMARY...The initiation of thunderstorms probably will begin to
increase by 5-7 PM, but this may be slow and rather widely scattered
in nature, resulting in uncertainty concerning severe weather watch
issuance. Storms that do develop may include supercells with severe
hail, locally strong surface gusts, and at least some risk for a
tornado.
DISCUSSION...Much of the region remains beneath strong, but broadly
anticyclonic mid/upper flow, on the northwestern periphery of
prominent large-scale ridging within a stagnant to slowly
progressive regime. However, one weak embedded mid-level
perturbation has been slowly shifting into/across the middle
Mississippi Valley vicinity, with associated lift contributing to a
gradual erosion of mid-level inhibition associated with elevated
mixed-layer air across Missouri into Illinois.
This is coinciding with diurnal destabilization of a modestly moist
boundary layer within lee surface troughing across the region.
Although this has been slowed by broken layers of cloudiness,
mixed-layer CAPE appears on the order of 1000-1500 J/kg, with at
least some further increase through 22-00Z. At the same time,
low-level hodographs may enlarge beneath southwesterly 850 mb flow
forecast to strengthen to 30-40+ kt.
As the environment becomes conditionally supportive of supercell
development across a sizable area, the focus for and extent of
thunderstorm initiation remains more unclear. Guidance suggests
that inhibition will become weakest within a relatively narrow
corridor near/just ahead of the cold front now still west of the
Rockford and Quincy IL, Columbia and Joplin MO, vicinities.
However, better mid/upper forcing for ascent continues to spread
ahead of the front across parts of northern/central Illinois and
east central into south central Missouri. Currently, it appears
that thunderstorm initiation will be gradual and rather widely
scattered into late afternoon.
..Kerr/Smith.. 04/18/2025
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...LOT...ILX...MKX...LSX...DVN...SGF...EAX...
LAT...LON 37419464 38309378 39779206 41979026 42578840 41888716
40268803 39338896 37639076 36699384 37419464
MOST PROBABLE PEAK TORNADO INTENSITY...UP TO 95 MPH
MOST PROBABLE PEAK WIND GUST...65-80 MPH
MOST PROBABLE PEAK HAIL SIZE...1.00-1.75 IN
Category: Watches, Warnings, Advisories, & Hazards