SPC AC 210059
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0759 PM CDT Mon May 20 2024
Valid 210100Z - 211200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS IN THE CENTRAL
HIGH PLAINS ACROSS SOUTHERN NE...
...SUMMARY...
Scattered severe thunderstorms are expected through tonight from the
central High Plains to parts of the Upper Midwest. The greatest
concentration of tornadoes, large hail, and severe wind is expected
over northeast Colorado into southern Nebraska, and far northwest
Kansas. This will include potential for a strong tornado, very large
hail, and significant severe gusts.
...01Z Update...
Primary concern is with ongoing convection developing across
northeast CO into the southwest NE Panhandle. With a current of east
to southeast 0-1 km winds expected to increase during the next few
hours, afternoon CAM guidance along with recent WoFS runs are
insistent on long-lived supercell development along the southern
flank of the thunderstorm plume. This appears likely to emanate out
of the Akron, CO vicinity and move east towards the CO/KS/NE border
area. With low 60s surface dew points across northwest KS marking
the northwest extent of MLCAPE in excess of 1500 J/kg, a supercell
or two impinging on the increasingly buoyant airmass downstream, may
become intense. In addition to the risk for very large hail,
enlarging low-level hodographs will support potential for cyclic
tornadogenesis, especially in the 02-05Z time frame. Transition from
tornadic supercell to a bow will likely occur during the late
evening to early morning, with probable movement along the
pronounced MLCAPE gradient into at least south-central NE.
Increasingly large MLCIN is anticipated overnight across KS,
suggesting that the severe wind swath will remain latitudinally
confined. Downstream convection, ongoing across southeast NE,
suggests the upstream severe wind threat may wane somewhat near dawn
as the MCS approaches the Mid-MO Valley. But the potential for a
well-organized MCS to persist across much of southern NE is apparent
and warrants expansion of the level 3-ENH risk.
Elsewhere, scattered large hail and sporadic severe wind gusts
should occur this evening into the early overnight from southeast NE
to southeast MN. A lower-end QLCS across Lower MI into northwest IN
may produce locally damaging winds with strong gusts through the
rest of this evening. But this convection will likely diminish
overnight.
..Grams.. 05/21/2024
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0600Z
SPC AC 201758
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1258 PM CDT Mon May 20 2024
Valid 211200Z - 221200Z
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS SOUTHERN
IOWA...NORTHWEST ILLINOIS AND FAR NORTHEAST MISSOURI...
...SUMMARY...
Severe storms are expected Tuesday across the Midwest, especially
including portions of Iowa and Missouri into Wisconsin and
western/northern Illinois. Tornadoes (a few strong), damaging wind
gusts, and large hail are expected.
...Lower/Middle Missouri Valley to the Upper Great Lakes...
A notably strong belt of cyclonically curved westerlies (70+ kt 500
mb) will extend from the south-central Great Plains to the Upper
Midwest and Upper Great Lakes on Tuesday, with a lead/convectively
augmented shortwave trough likely to spread from the central High
Plains toward the Lake Superior vicinity late Tuesday night. An
elongated surface low over eastern Nebraska Tuesday morning will
deepen and lift northeast to northern Wisconsin/Upper Michigan by
evening, with a surface warm front lifting northward ahead of the
surface low, although its effective position will likely be
influenced by the early day precipitation. Meanwhile, a trailing
cold front will surge east across Iowa/eastern Kansas/northern
Missouri from mid-afternoon into the evening.
Remnant clusters of storms will likely be ongoing Tuesday morning
across central/eastern Nebraska, with the possibility of additional
storms farther east across southern Iowa/northern Missouri in
association with a warm-advection regime. Some key uncertainties
persist about the influences of this early day convection, but
trends will be for quick air mass recovery given a
progressive/highly dynamic pattern.
Very steep mid-level lapse rates will overspread the increasingly
moist warm sector, supporting aggressive diurnal destabilization
especially on the southern fringe of lingering convection/cloud
cover. Significantly strengthening mid-level winds and a diurnally
persistent strong low-level jet will support initial supercells
capable of large hail and a few tornadoes, including strong (EF2+)
tornado potential. But a mixed/transitional mode is expected
overall, as upscale growth occurs given the degree of forcing for
ascent, with likely evolution into a well-organized/fast-moving QLCS
capable of increasingly widespread/intense damaging winds and a
continued QLCS-related tornado risk. This scenario currently appears
to be most probable across southern/eastern Iowa into northwest
Illinois and nearby far northern Missouri. The severe risk will
persist into the Upper Great Lakes region and middle Mississippi
Valley overnight.
...Southern Plains...
Convective coverage will likely decrease with southward extent as
large-scale ascent focuses northward toward the Great Lakes.
Nevertheless isolated storms are possible into northeast
Oklahoma/northwest Arkansas by late afternoon/evening, and more
conditionally with southwest extent near a dryline from central
Oklahoma into central Texas. Large hail and severe gusts will be
possible with this activity.
...Northeast States...
A weak upper shortwave trough will move across southern Quebec and
northern New England. This will result in a band of enhanced
westerly deep-layer flow from northern New York into Maine. A
seasonally moist airmass will be in place with surface dewpoints
into the low 60s F, with strong heating and steepening low-level
lapse rates. MLCAPE to around 1000 J/kg and effective shear
magnitudes around 35 kt will support organized cells. Elongated
hodographs and favorable vertical shear suggest marginally severe
hail will be possible along with locally damaging wind gusts.
..Guyer.. 05/20/2024
WUUS02 PTSDY2
NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 0600Z
SPC AC 200734
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0234 AM CDT Mon May 20 2024
Valid 221200Z - 231200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM CENTRAL TEXAS
TO THE OHIO VALLEY...
...SUMMARY...
Severe thunderstorms posing a risk for damaging gusts and hail will
be possible from central Texas into the Ohio Valley vicinity on
Wednesday.
...Southern MO/IL into western NY...
An upper shortwave trough over the northern/central Plains will
shift east to the Upper Midwest/Great Lakes vicinity on Wednesday.
This feature, coupled with a southeast-sagging surface front, and
convectively enhanced vorticity maxima floating through
southwesterly deep-layer flow, will focus thunderstorm potential
from portions of southern MO/IL northeast toward the Ohio
Valley/lower Great Lakes vicinity.
Ahead of the surface boundary, a moist and unstable airmass will be
in place (surface dew points in the mid/upper 60s F). Modest
midlevel lapse rates around 7 C/km will also overlap this moist
boundary layer, aiding in moderate destabilization (MLCAPE to 2000
J/kg). Vertical shear will be modest with northeast extent from IN
into western NY, but isolated to widely scattered storms capable of
damaging gusts and perhaps some hail will be possible from afternoon
into the evening.
A corridor of somewhat greater potential may develop across southern
MO/IL during the late afternoon into the nighttime hours.
Instability and vertical shear will likely be stronger here.
Better-organized diurnal convection could congeal into an MCS during
the nighttime hours. However, confidence in this scenario is low,
precluding higher probabilities at this time.
...OK/TX into AR...
An area of broad southwesterly flow will persist across the southern
Plains to the Mid-South. A surface front will extend northeast from
a low over west-central TX into southern MO. Additionally, a dryline
will extend southward from the TX low to the Rio Grande. The
evolution of the surface front is a bit uncertain, but this
boundary, along with the dryline, may focus thunderstorm
development. Capping may suppress convection, but an increasing
low-level jet by evening could result in scattered thunderstorms.
This activity would pose a risk for hail and damaging gusts, with
more conditional tornado risk given capping concerns. One or more
clusters or an MCS may spread southeast with time during the
evening/overnight.
..Leitman.. 05/20/2024
WUUS03 PTSDY3
NOTE: THE NEXT DAY 3 OUTLOOK IS SCHEDULED BY 0730Z
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