SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0754 AM CDT Wed Jun 18 2025 Valid 181300Z - 191200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF SOUTHEAST MISSOURI INTO SOUTHERN/EASTERN ILLINOIS...WESTERN KENTUCKY...INDIANA...WESTERN OHIO...AND SOUTHERN LOWER MICHIGAN... ...SUMMARY... Severe thunderstorms are expected today from parts of southern Missouri northeastward to the southern Great Lakes. Scattered to numerous damaging winds, isolated large hail, and a few tornadoes all appear possible. Strong to severe thunderstorms may also develop across parts of the southern Plains, northern Plains/Upper Midwest, and Mid-Atlantic. ...Mid Mississippi/Ohio Valleys to the Southern Great Lakes... Embedded within large-scale upper troughing, a well-defined MCV evident on radar and visible satellite imagery over MO this morning will quickly advance northeastward today across the mid MS Valley into the Midwest, and eventually the southern Great Lakes this evening. This feature will likely aid robust thunderstorm development across parts of eastern IL into IN and vicinity by late morning/early afternoon. Sufficient low-level and deep-layer shear will exist across the Midwest for updraft organization, including supercells. However, convection may quickly become linear; so, it remains unclear how long a supercell hail/tornado threat will exist. Regardless, filtered daytime heating of a rather moist low-level airmass will aid the development of at least moderate instability downstream of any convection that develops. With 40-50 kt of low/mid-level southwesterly flow forecast across parts of the mid MS Valley into the OH Valley/Midwest and steepening low-level lapse rates through the day, scattered to perhaps numerous damaging winds appear likely with organized clusters/bows spreading east-northeastward across these regions through the afternoon and early evening. The severe wind threat should extend as far north as parts of southern Lower MI, along/near a surface front. Some risk for line-embedded tornadoes may also exist. By mid to late evening, these clusters should gradually weaken as they continue eastward into a less unstable environment across the OH Valley. But, they may still pose some threat for damaging winds for as long as they can remain surface based. ...Southern Plains to the Mid-South... Ongoing convection across central OK may continue to pose an isolated hail/wind threat in the short term this morning, before eventually weakening as the nocturnal low-level jet aiding this activity slowly subsides. In the wake of these early-day thunderstorms, ample daytime heating of a seasonably moist airmass is anticipated along/south of a convectively reinforced cold front, with moderate to strong instability expected. The southern Plains will be on the southern periphery of upper troughing across the mid/upper MS Valley today, but enhanced mid-level winds should still be present from parts of OK eastward into AR and the Mid-South. Multiple bands/clusters should form this afternoon along/south of the front in a favorable thermodynamic environment given the continued presence of steep mid-level lapse rates, especially across OK/TX. While deep-layer shear is not forecast to be overly strong, it should still be sufficient for updraft organization, including the potential for a few supercells. Initial development this afternoon may pose more of a severe hail threat, before clustering occurs and the risk for severe/damaging winds increases with eastward/southward extent later in the afternoon and continuing into the evening. ...Northern Plains/Upper Midwest... Behind upper troughing over the mid/upper MS Valley, northwesterly mid-level flow around 25-40 kt should be present today over portions of the northern Plains and Upper Midwest. Low-level moisture is expected to remain fairly limited, with surface dewpoints mostly in the 50s. Even so, steepened low/mid-level lapse rates are anticipated through the afternoon, along with weak to moderate instability. While large-scale ascent should remain weak, widely scattered thunderstorms may still form and spread east-southeastward, with some threat for isolated severe wind gusts and marginally severe hail this afternoon and early evening. Modest deep-layer shear should keep the overall severe threat fairly isolated/marginal. ...Mid-Atlantic... Within modestly enhanced mid-level southwesterly flow, an embedded weak perturbation is forecast move northeastward today from the southern/central Appalachians across the southern Mid-Atlantic. A moist low-level airmass in place across this region, with surface dewpoints generally in the upper 60s to low 70s. Ample daytime heating will likely foster moderate to locally strong instability along/east of the Blue Ridge Mountains by mid afternoon. Current expectations are for thunderstorms to develop initially over the higher terrain and move eastward in a modest deep-layer shear environment. Some thunderstorm organization should occur, with multicells as the main convective mode. This activity may pose some threat for damaging winds this afternoon and evening until it moves off the Atlantic Coast or weakens with the loss of daytime heating. ..Gleason/Kerr.. 06/18/2025