Severe Storm Outlook Narrative (AC)
Issued by NWS
Issued by NWS
986 ACUS02 KWNS 200601 SWODY2 SPC AC 200600 Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 0100 AM CDT Mon May 20 2024 Valid 211200Z - 221200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM THE LOWER MISSOURI VALLEY TO CENTRAL WISCONSIN... ...SUMMARY... A broad area of severe-thunderstorm potential is expected from the southern Plains to the upper Great Lakes. The highest concentration of severe storms is expected from eastern Kansas to southwest Wisconsin. Tornadoes (a few strong), damaging gusts, and large hail are possible through Monday night. ...Lower Missouri Valley to the Upper Great Lakes... An upper shortwave trough over the central High Plains Tuesday morning will spread northeast to the upper Great Lakes through the forecast period. This will result in strong height falls (particularly across IA/MN/WI) and strengthening surface cyclogenesis. An elongated surface low over eastern NE Tuesday morning will deepen and lift northeast to northern WI/Upper MI by evening. A surface warm front will lift north ahead of the surface low, becoming positioned across central WI by 00z. Meanwhile, a trailing cold front will surge east across IA/eastern KS/northern MO from mid-afternoon into the evening. The cold front will continue east overnight, becoming positioned from western Lower MI to central MO and northwest OK by Wednesday morning. One point of uncertainty on Tuesday is expected morning convection across IA into southeast MN and WI. Most guidance quickly moves this activity northeast with airmass recovery occurring quickly in a strong warm advection regime and progressive/dynamic large-scale pattern. An EML plume, characterized by midlevel lapse rates greater than 8 C/km, will overspread the region along with an increase 850-700 mb jet (50-70 kt) by afternoon and into the evening. This should support airmass recovery in the wake of morning convection. A broad warm sector, with surface dew points in the mid/upper 60s F will be in place. The moist boundary layer beneath steep to very steep midlevel lapse rates will result in a corridor of strong instability (greater than 2000 J/kg MLCAPE) from eastern KS into southwest WI. Large and favorably curved low-level shear profiles will be present as indicated by forecast hodographs. While supercell wind profiles are evident, a mixed mode scenario is possible with discrete supercells developing initially with potentially rapid upscale growth into a QLCS given both strong large-scale ascent and frontal forcing. Regardless, tornadoes will be possible with either convective mode, and a few strong tornadoes are possible. Severe-gust potential will increase a upscale growth ensues, with some potential for significant gusts (greater than 65 kt). Large hail will also be possible with any more discrete or line-embedded supercells. 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 OK/northwest AR by late afternoon/evening, and more conditionally with southwest extent near a dryline from central OK into central TX. Large hail and severe gusts will be possible with this activity. A QLCS will likely continue through the overnight hours into parts of Lower MI, northern IN, and central IL/MO. Damaging gusts will become the primary risk overnight, but a couple of tornadoes also will be possible. ...Northeast... A weak upper shortwave trough will move across southern Quebec and northern New England through Wednesday evening. This will result in a band of enhanced westerly deep-layer flow from northern NY into ME. A seasonally moist airmass will be in place with surface dewpoints into the low 60s. Strong heating will result in 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 gusts. ..Leitman.. 05/20/2024 $$