000 ACUS02 KWNS 161732 SWODY2 SPC AC 161732 Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1232 PM CDT Tue Jul 16 2019 Valid 171200Z - 181200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER A PORTION OF THE UPPER MISSISSIPPI VALLEY... ...SUMMARY... Strong/severe thunderstorms are possible across portions of the upper Mississippi Valley. Isolated strong storms may also be noted across parts of the Plains and over portions of the northeastern US. ...Synopsis... Upper pattern will change little through Wednesday with belt of stronger westerlies confined to the northern third of the country. A low amplitude shortwave trough currently moving through the northwestern U.S. will undergo further deamplification as it moves through the mean ridge position across the northern Plains and into the upper MS valley. Farther east, remnants of Barry will become absorbed within slightly stronger westerlies and weaken further as it continues through the central Appalachians and Middle Atlantic region. By 12Z Wednesday a quasi-stationary front should extend from the upper Great Lakes to a weak surface low over SD. A cold front will trail southwest from the low through western NE with a pre-frontal trough from the eastern CO into southwestern NE. Farther east a cold front will advance southeast into the Northeast States during the day. ...Upper MS Valley region... A very moist boundary layer will with 70 F dewpoints will reside along and south of the quasi-stationary front from eastern SD into southern MN and WI. It is likely that an MCS will be ongoing north of this boundary on nose of a modest southerly low-level jet posing some risk for strong to damaging wind gusts. Future evolution of this MCS is somewhat uncertain, and model solutions including the CAMS differ significantly. It is possible that MCS could reorganize and intensify while continuing east as the boundary layer in vicinity of the front destabilizes and especially since at least a modest low-level jet is forecast to persist within the exit region of a mid-level jet. Another possibility is that the MCS could weaken or dissipate, and additional storms develop upstream later in the afternoon or early evening along/north of the front as the low-level jet strengthens. If this occurs, strong vertical shear and instability in vicinity of the convectively enhanced but modifying stationary front would support supercells capable of large hail and possibly a few tornadoes. This activity would subsequently grow upscale and move east through southern MN and WI during the evening and overnight with a continuing threat for mainly damaging wind. Given these uncertainties regarding the mesoscale and convective scale evolution, will maintain SLGT risk this outlook, but an enhanced might be required for a portion of this region in future day 1 updates. ...Central and northern Plains region... Within a modest post-frontal upslope regime, dewpoints at least in the 50s F will persist beneath steep lapse rates contributing to moderate instability over the central High Plains. This region will reside beneath belt of stronger winds aloft and vertical shear will support supercells as storms develop and move off the higher terrain. Will maintain the MRGL risk category this update given uncertainty regarding storm coverage, but an upgrade to SLGT risk may be needed in later updates. Other storms with multicell characteristics are expected to develop within the more deeply mixed regime along the pre-frontal trough from western KS into south central NE with downburst winds the main threat. ...Northeast States... A moist, weakly capped warm sector will reside across the pre-frontal warm sector over the northeast U.S. and the atmosphere may become moderately unstable as the boundary layer destabilizes during the afternoon, south of any ongoing convection/clouds. Mid-level lapse rates will be very weak along with weak vertical shear. Nevertheless, storms are expected to intensify south of the cold front in association with remnant boundaries as well as over the higher terrain and spread east into the destabilizing boundary layer. A few locally strong wind gusts will be possible as storms merge into line segments and clusters, but modest winds aloft and the overall marginal thermodynamic environment may serve as limiting factors for a more robust threat. ...MAXIMUM RISK BY HAZARD... Tornado: 5% - Slight Wind: 15% - Slight Hail: 15% - Slight ..Dial.. 07/16/2019 $$