Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0800 PM CDT Mon Aug 21 2017 Valid 220100Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS NORTHEAST KS AND THE LOWER MO VALLEY TO WEST-CENTRAL IL... ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE SLIGHT RISK FROM EASTERN PORTIONS OF THE CENTRAL PLAINS THROUGH SOUTHERN IA TO IL... ...SUMMARY... The potential for severe storms continues across northeast Kansas into northern Missouri this evening, with a risk for damaging winds, hail, and perhaps a tornado. Otherwise, sporadic strong to locally damaging wind gusts will be possible through tonight from eastern Nebraska through western and southern Iowa into Illinois and northern Missouri. ...Eastern KS/northern MO/southern IL... Early evening surface analysis and visible satellite imagery showed a boundary extending from southern IL west-northwestward through northern MO (near or just north of STL to near COU to in vicinity of Kansas City metro) into northeast KS (north of TOP). Despite weak mid-level lapse rates, the presence of a high moisture-content airmass (surface dew points in the mid 70s) and steeper low-level lapse rates (prior to boundary layer cooling) are maintaining strong instability (MLCAPE exceeding 2000 J/kg). A shortwave trough (of southwest monsoonal origin) evident in water vapor imagery early this evening in central KS will continue to track east/northeast across northern MO to IL. Forcing for ascent attendant to this trough and ahead of the amplifying trough into the upper MS Valley should support additional storm development across northeast KS into northern MO this evening to the early overnight. Vertically veering wind profiles per area WSR-88D VADs suggest organized storms will remain possible with locally strong/damaging wind gusts possible, along with hail, and perhaps a tornado threat near the aforementioned boundary (where low-level shear is enhanced). ...Eastern NE/IA to parts of northern and central IL... Strengthening deep-layer westerlies are expected from MO/IA into the lower OH Valley and the Lower MI region through tonight, as strong height falls occur across the upper MS Valley/Upper Great Lakes region with the approach of an amplifying shortwave trough from south-central Canada. Associated westerly deep-shear vectors parallel to generally west-east oriented outflow boundaries from central NE to central IA suggest a continued likelihood for multiple line segments developing and advancing to the south/southeast across eastern NE and central/southern IA through tonight/early Tuesday morning. Residual abundant moisture and strong instability extending from NE into western IA suggest some of these lines could attain more robust updrafts/greater storm intensities. However, given weak mid-level lapse rates and the loss of daytime heating, the potential for stronger line segments may only be short-lived into the evening, as much of the ongoing activity was generally elevated north of the aforementioned outflow boundaries. Otherwise, storm coverage is expected to increase through tonight and spread to the south/southeast, given the increasing large-scale ascent with the amplifying trough and some increase of warm advection along the strengthening low-level jet. An isolated strong or damaging wind gust will be possible with the storms through later tonight. ..Peters.. 08/22/2017Read more
from SPC Forecast Products http://ift.tt/rxAC6Z
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