MD 1998 CONCERNING HEAVY SNOW FOR NORTHERN IOWA…ADJACENT SOUTHERN MINNESOTA AND SOUTHEASTERN SOUTH DAKOTA
Mesoscale Discussion 1998 NWS Storm Prediction Center Norman OK 1136 PM CST Thu Dec 08 2022 Areas affected...northern Iowa...adjacent southern Minnesota and southeastern South Dakota Concerning...Heavy snow Valid 090536Z - 090930Z SUMMARY...Heavy snow rates on the order of 1-2 inches per hour, with occasional heavier convective bursts accompanied by lightning, may continue to develop through 1-4 AM CST. DISCUSSION...Strong differential cyclonic vorticity advection associated with a short wave impulse migrating east-northeastward across the middle Missouri Valley is beginning to contribute to intensifying mid-level lift and cooling in a corridor across northern Iowa, roughly from north-northeast of Sioux City toward the Mason City area. This is supporting increasing precipitation and embedded convection, in the wake of an initial northeastward advancing convective band. Although temperatures in a layer around 850 mb are still near and above freezing across northwestern into north central Iowa, models suggest that this will change with further dynamic and latent cooling during the next few hours. Through 07-10Z, Rapid Refresh forecast soundings indicate that lift will become maximized within the 700-500 mb layer, where temperatures will become favorably cold for large dendritic ice crystal growth. This may contribute to a consolidating band of heavy snow rates on the order of 1-2 inches per hour, in the presence of precipitable water on the order of .6-.7 inches. With steepening mid-level lapse rates also contributing to sufficient destabilization for weak CAPE (and convection capable of producing lightning), even higher rates are possible in occasional convective bursts. ..Kerr.. 12/09/2022 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...ARX...MPX...DMX...FSD... LAT...LON 42819652 43859626 43429235 42539305 42449382 42819652
