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SPC Jul 16, 2025 2000 UTC Day 1 Convective Outlook

2 months ago

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0229 PM CDT Wed Jul 16 2025 Valid 162000Z - 171200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF THE GREAT LAKES AND CENTRAL HIGH PLAINS... ...SUMMARY... Scattered severe thunderstorms remain possible this afternoon and evening over parts of the Midwest and central High Plains. ...20Z Update... The previous forecast (see below) remains largely on track. The main changes made to the 20Z Day 1 Convective Outlook update was to trim severe probabilities behind the main band of convection across the Upper MS Valley, and to trim thunderstorm probabilities over parts of the north-central CONUS, amid waning buoyancy. ..Squitieri.. 07/16/2025 .PREV DISCUSSION... /ISSUED 1127 AM CDT Wed Jul 16 2025/ ...Midwest/Great Lakes... Late morning radar/satellite imagery shows an MCV over northeast IA co-located with a 1007-mb surface low. A front is draped from northeast to southwest and is forecast to gradually push eastward during the day. The frontal segment east-northeast of the low will remain quasi-stationary and serve as the northern delimiter of a surface-based warm sector. Continued heating of a moist boundary layer will contribute to 1000-2500 J/kg of MLCAPE across central WI into northern/central IL. The modestly enhanced low/mid-level winds associated with the MCV will yield 30-40 kt of effective shear---supporting rotation with a few of the stronger updrafts this afternoon. Semi-discrete thunderstorms developing in a north-south band will likely continue to intensify as ascent overspreads the warm sector over WI and far northern IL. A few supercells are possible with an attendant risk for all hazards. With time late this afternoon and evening, gradual upscale growth into a bowing cluster should occur, with a greater risk for severe/damaging winds towards Lake Michigan and parts of southern Lower MI. ...Central High Plains to Northern Missouri... Indications late this morning are that a convectively reinforced surface front will become stationary across KS into eastern CO with moist, upslope flow into the central High Plains north of the boundary. The southern periphery of stronger mid-level westerly flow will glance the central High Plains where strongly veering flow will result in deep-layer shear supporting storm organization. Although heating will be partially thwarted by persistent low-level cloud cover through at least the early afternoon, sufficient heating is expected to result in scattered to widespread thunderstorms eventually developing during the late afternoon. A few supercells are possible with an accompanying threat for large hail and localized severe gusts. As storm coverage increases, upscale growth into an organized cluster is probable during the evening. Severe gusts will likely become the primary hazard during the evening as the mode becomes more linear and outflow dominant. Farther east across KS into northern MO, isolated convection may develop through peak afternoon heating along the front. While deep-layer shear is forecast to remain fairly modest, strong instability and steep mid-level lapse rates could still support occasional severe hail/wind with the more robust cores that can be sustained. Additional convection may develop along/north of the front this evening in a low-level warm advection regime, while also posing an isolated severe threat. ...Ohio Valley/Mid-Atlantic... A couple of MCVs will focus scattered strong to locally severe thunderstorms mainly this afternoon and early evening. Relatively weak lapse rates and modest deep-layer shear will tend to limit storm organization. Nonetheless, sporadic and isolated bouts of strong to damaging gusts are possible with the stronger thunderstorms through early evening. ...Central Gulf Coast... Modest strengthening of the low-level wind field is expected as a weak tropical disturbance migrates westward over the northern Gulf of America. However, model guidance shows hodographs generally remaining diminutive in size, implying disorganized storm modes (mainly outflow dominant structures in the form of bands and small clusters). Read more