LIVE MAP (ABOVE) ... SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1253 AM CDT Sun May 07 2023
Valid 071200Z - 081200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS FAR
EASTERN NEBRASKA...EXTREME NORTHEAST KANSAS...MUCH OF IOWA...FAR
NORTHERN MISSOURI...AND EXTREME WESTERN ILLINOIS...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF
NORTHWEST TEXAS INTO FAR SOUTHWEST OKLAHOMA...
...SUMMARY...
Severe storms with very large hail, hurricane force gusts, and
isolated tornadoes will be possible across parts of the Mid Missouri
Valley today. Severe wind/hail producing storms will also be
possible in parts of the central and southern Plains, perhaps
extending into parts of the southern Great Lakes and Ohio Valley
into the Tennessee Valley and central Appalachians.
...Synopsis...
An upper ridge will remain in place east of the MS River as a
mid-level trough slowly traverses the Interior West today. Multiple
mid-level impulses will crest the ridge through the period,
supporting the development of multiple MCSs across the Mid MS Valley
into the OH/TN Valleys and central Appalachians. Meanwhile, surface
lee troughing and northward low-level moisture advection will
persist across the Plains states. A dryline will gradually push
eastward through the afternoon, initiating strong to severe
thunderstorms in a very unstable environment.
...Mid MS Valley...
Ahead of the surface lee trough, a diffuse warm front will stall
across eastern NE into IA and western IL by afternoon. Along and
south of the warm front, mid to upper 60s F surface dewpoints
overspread by 8.5+ C/km mid-level lapse rates (resulting in over
4000 J/kg MLCAPE) will characterize the warm sector. Veering and
strengthening vertical wind profiles along the warm front will also
support sizable, curved hodographs, especially in central IA. The
approach of a mid-level impulse and strong surface heating will
support isolated supercell development by late afternoon along the
warm front. Very large hail and a few tornadoes will be the initial
threats with these storms, and a strong (EF2+) tornado cannot be
ruled out.
Around and just after sunset, several thunderstorms are expected to
initiate along the surface lee trough/warm front intersection in
eastern NE/extreme northeast KS. While large hail may accompany
these storms, rapid upscale growth should result in the development
of an intense MCS, with severe winds becoming the main threat. It is
possible that a classic bow-echo MCS may develop by evening,
supporting widespread severe winds (with a few gusts exceeding 65
kts possible). However, confidence in this scenario is too low for
the introduction of higher wind probabilities at this time.
...OH/TN Valleys into the central Appalachians...
Multiple MCSs will track across areas east of the MS river into the
OH/TN Valleys through the forecast period. At the start of the day
(12Z), an MCS is poised to be moving southeast across the OH Valley.
This MCS will approach the central Appalachians by early afternoon,
preceded by 6.5-7.5 C/km low-level lapse rates, contributing to
500-1000 J/kg MLCAPE. Given modest line-normal speed shear, the MCS
may remain organized enough to produce a couple of damaging gusts
through the morning/early afternoon hours before dissipating. Latest
guidance consensus depicts a second MCS developing along the eastern
fringes of a low-level warm-air advection regime somewhere along the
MS river into the OH/TN Valley areas by mid-afternoon, when surface
heating will have boosted surface temperatures to near 80 F amid
upper 60s F dewpoints, overspread by 8 C/km mid-level lapse rates.
2500 J/kg SBCAPE amid 30+ kts of effective bulk shear will precede
this second MCS, supporting a threat for at least isolated damaging
gusts. The primary mitigating factor for introducing higher wind
probabilities this outlook over the OH/TN Valleys is the uncertainty
of placement and timing of the second MCS.
...Southern Plains...
Rapid thunderstorm development is likely by afternoon peak heating
ahead of the dryline across portions of western TX. Initial updrafts
will benefit from over 4000 J/kg MLCAPE, driven by steep low and
mid-level lapse rates. Effective bulk shear should remain modest
(i.e. under 30 kts), with multicells and perhaps a few supercells
likely initially. Large hail will be the main threat early on.
However, storms should quickly become outflow dominant given weak
low-level shear, with cold pool mergers anticipated. Upscale growing
clusters will support severe wind gusts as the primary threat.
Similar to the previous day, northward surging outflow from decaying
storms will promote damaging gust potential into southern and
central OK by evening.
...Northern High Plains...
Boundary-layer mixing and upslope flow along the Black Hills of
western SD will support thunderstorm development by afternoon peak
heating. These storms will progress eastward amid 7.5-8.5 C/km
low-level lapse rates and modest speed shear, contributing to
elongated, straight hodographs. Any storms that can mature and
sustain themselves may take on multicellular or transient
supercellular characteristics with the potential to produce a severe
gust or two before nocturnal cooling/boundary-layer stabilization
sets in around sunset.
..Squitieri/Lyons.. 05/07/2023
Read more CHECK UPDATE ZOOM GRAPHIC
http://dlvr.it/SnfTVl
