SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0258 PM CDT Wed May 18 2022
Valid 182000Z - 191200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE UPPER MIDWEST...CENTRAL/SOUTHERN PLAINS...AND KENTUCKY...
...SUMMARY...
A couple tornadoes along with scattered damaging winds and severe
hail remain possible across Kentucky and vicinity late this
afternoon and early evening. Scattered severe winds, a couple of
which may be significant, may occur from southeast Colorado to the
Kansas/Oklahoma border area from late afternoon into tonight.
Isolated to scattered large hail and damaging winds are also
possible across northeast/east-central Minnesota into northwest
Wisconsin during the late afternoon to early evening.
...20Z Update...
Have trimmed severe probabilities behind an MCV with associated
small cluster of thunderstorms ongoing along the IN/KY border area.
If this activity can become surface based, then it would pose a
threat for damaging winds, hail, and perhaps a tornado. The
potential for additional severe thunderstorms to develop on the
southwest flank of the MCV in western/central KY remains unclear.
See Mesoscale Discussion 812 for more details on the near-term
severe threat across this area.
Elsewhere, generally minor changes have been made to the outlook to
account for latest observational trends and short-term model
guidance. Still, overall forecast reasoning remains unchanged.
Mesoscale Discussion 813 contains more information on the short-term
severe risk across MN, while Mesoscale Discussion 814 details
expected convective evolution across eastern CO and vicinity this
afternoon. Mesoscale Discussion 815 has additional details on the
isolated wind threat across north-central NE over the next couple of
hours.
..Gleason.. 05/18/2022
.PREV DISCUSSION... /ISSUED 1127 AM CDT Wed May 18 2022/
...KY vicinity to the MO/AR border...
A pronounced MCV over southern IL will track east across the OH
Valley towards the central Appalachians through this evening.
Primary severe potential should eventually emanate out of the
south-southwest flank of the MCV where some cloud breaks should
support surface-based destabilization in tandem with a plume of low
to mid 60s boundary-layer dew points spreading east. A fairly tight
gradient in MLCAPE is anticipated from west to east by late
afternoon. A couple supercells should develop in this time frame
amid enhanced low to mid-level flow attendant to the MCV. A threat
for all severe hazards is possible, although the overall spatial
distribution will likely remain isolated and temporally confined, in
addition to delays in low-level destabilization which could limit
intensity. Some west/east-oriented clustering may linger during the
evening, but the severe threat should wane after the MCV outpaces
the plume of diurnal destabilization.
Farther west, isolated thunderstorm development will be possible
this evening along the effective baroclinic zone near the MO/AR
border. Forcing for ascent will be weak/shallow and confined to the
front, so storm development/coverage is uncertain. However,
mid-level lapse rates of 8-9 C/km, MLCAPE greater than 3000 J/kg,
and mid-level flow near 40 kt will support a conditional threat for
large hail and damaging winds.
...Southeast CO to northern OK...
A cluster of high-based storms appears probable across southeast CO
by mid to late afternoon, immediately east of the mountains in a
zone of weak upslope flow and strong surface heating/deep mixing.
Rather deeply mixed, inverted-V thermodynamic profiles with DCAPE
greater than 1200 J/kg, will favor strong downdrafts and the
potential for a storm cluster with occasional severe outflow gusts
of 60-75 mph from southeast CO into the OK Panhandle this evening.
Guidance is fairly consistent that the MCS will impinge on a plume
of richer low-level moisture arcing westward across northern OK.
This should help sustain a convectively generated MCV and maintain
the surface cold pool eastward along the southern KS/northern OK
border area. At least an isolated severe wind and some hail risk
should linger overnight in northern OK.
...Northeast/east-central MN and northwest WI...
A shortwave trough near the ND/Manitoba border will progress towards
the Upper Great Lakes through tonight. Attendant surface cyclone
should largely track along the MN/Ontario border with a reinforcing
cold front to its south-southwest sweeping east. Despite limited
low-level moisture on the larger scale, a corridor of low to mid 50s
surface dew points combined with abundant boundary-layer heating
beneath steep mid-level lapse rates and cooling mid-level
temperatures (colder than -20 C at 500 mb) will support MLCAPE
approaching 1000 J/kg with minimal convective inhibition. Effective
bulk shear of 40-50 kts with mainly straight hodographs and the
modest buoyancy will be sufficient for at least a few supercells
capable of large hail and isolated damaging winds. This threat will
diminish rapidly after dusk.
...Central NE and far south-central SD...
Convergence along the trailing portion of the aforementioned
reinforcing cold front may be sufficient for isolated thunderstorms
during the late afternoon to early evening. While buoyancy will be
weak, adequate deep-layer shear and a steep low to mid-level lapse
rate environment will support potential for isolated, marginally
severe hail and wind.
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