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Day 2 Outlook Categorical Probabilistic
Categorical Day2 0700Z Outlook
 Forecast Discussion

000 ACUS02 KWNS 151727 SWODY2 SPC AC 151726 Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1226 PM CDT Wed Aug 15 2018 Valid 161200Z - 171200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF THE CENTRAL PLAINS... ...SUMMARY... Isolated strong to severe storms will be possible Thursday over parts of the central Plains into the mid Mississippi Valley. Other strong storms may occur from the lower Mississippi Valley into the Tennessee and Ohio Valleys. ...Synopsis... A mid/upper-level trough over the OH Valley Thursday morning will move northeastward across the Lower Great Lakes and southern Ontario through the period. An upstream upper trough/low across the northern/central Plains will develop southeastward to the mid MS Valley by Thursday evening. Farther west, an upper trough will overspread parts of the Pacific Northwest as upper ridging remains prominent over much of the western states. At the surface, a weak cold front should develop slowly southeastward across the OH Valley, with the trailing portion of this front becoming nearly stationary across the southern Plains. A weak secondary cold front will also advance southward across the central Plains through the day. ...Central Plains into the Mid MS Valley... A moist low-level airmass, with surface dewpoints generally in the mid to upper 60s, will reside across southeastern NE into eastern KS and western MO along and south of a weak cold front. Modestly steepened mid-level lapse rates will also encourage moderate instability to develop as diurnal heating occurs. Storms may be ongoing across eastern NE at the start of the period, but additional convective development will likely occur along the front by Thursday afternoon in northeastern KS and vicinity. Strengthening west-northwesterly mid-level flow and related effective bulk shear of 30-40 kt should allow for a mix of supercells and multicells across this region. Isolated large hail and damaging winds should be the primary threats. There will be some potential for one or more small clusters to continue southeastward into southeastern KS and western/central MO Thursday evening, with at least a marginal hail/wind threat persisting. ...OH/TN Valleys into the Lower MS Valley and Southern Plains... A belt of 30-40 kt low-level southwesterly flow will accompany the shortwave trough across the OH/TN Valleys through Thursday afternoon. However, winds are forecast to weaken with height at mid levels, which will tend to limit deep-layer shear and the potential for thunderstorms to become organized on more than a transient/isolated basis. Still, enough low-level flow coupled with pockets of instability that should develop along/ahead of morning convection will probably support some potential for isolated strong to locally damaging winds with multicells and short line segments developing northeastward across the OH/TN Valleys. Along the trailing portion of a weak front across OK/AR into the Mid-South, shear is forecast to remain weak, although a front will probably act as a focus for renewed convective development Thursday afternoon. The airmass across this region is forecast to become at least moderately unstable, with MLCAPE of 2000-2500 J/kg probable. Convective evolution remains uncertain across OK/AR in particular, with some guidance suggesting a bowing cluster with strong/damaging winds may develop over eastern OK into western AR in the afternoon. However, given the weak low and mid-level flow expected, will maintain Marginal risk across this region. ...Central/Eastern OR... Mid-level south-southwesterly flow will likely increase into the 25-35 kt range across much of OR as an upper trough approaches from the west. Similar effective bulk shear values should encourage some updraft organization as thunderstorms develop along the Cascade crest and spread northeastward across parts of central/eastern OR Thursday afternoon and evening. Forecast soundings across this region show a deeply mixed boundary layer, and strong/gusty downdraft winds may occur. Limited low-level moisture and generally weak instability should keep the severe threat isolated/marginal. ...MAXIMUM RISK BY HAZARD... Tornado: 2% - Marginal Wind: 15% - Slight Hail: 15% - Slight ..Gleason.. 08/15/2018 $$