SPC AC 181952 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0252 PM CDT Tue Mar 18 2025 Valid 182000Z - 191200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS TONIGHT ACROSS PARTS OF SOUTHEASTERN NEBRASKA THROUGH SOUTHWESTERN AND CENTRAL IOWA... ...SUMMARY... Isolated, marginally severe hail is possible by late tonight in a corridor from north central Kansas through central Iowa. ...20Z Update... The Marginal risk area was expanded slightly eastward into east-central Iowa. Any elevated thunderstorm clusters that evolve and track east-northeastward along the warm front (as indicated by the latest MPAS runs) will pose an isolated severe-hail risk into this area. For additional details, see the previous discussion below. ..Weinman.. 03/18/2025 .PREV DISCUSSION... /ISSUED 1123 AM CDT Tue Mar 18 2025/ ...Discussion... Much of the nation remains under the influence of one prominent belt of westerlies emanating from the northern mid-latitude Pacific. Within this regime, mid-level troughing is in the process of digging across the Intermountain West and Rockies. This includes one significant embedded smaller-scale perturbation approaching the southern Rockies, which is forecast to accelerate east-northeastward across the south central Great Plains by late tonight. Models indicate that this will be accompanied by a strong mid/upper jet streak, including a core intensifying in excess of 100 kt around 500 mb, nosing across the Texas Panhandle vicinity through the lower Missouri Valley from early this evening through 12Z Wednesday. It appears that this may be accompanied by substantive further deepening of a developing low across central through northeastern Kansas, within already deep surface troughing now present across the central/southern Great Plains into lower/middle Missouri Valley. In the wake of the prior cyclone which impacted much of the central and eastern U.S. and Gulf Basin late last week into the weekend, boundary-layer moistening across the western Gulf is underway, but still only supportive of rather modest low-level moistening across the Texas Gulf coast into southeastern Great Plains (including low to mid 50s F surface dew points). It appears that this will reach portions of the lower central Great Plains into Upper Midwest late this evening through early Wednesday. However, relatively warm and dry air in the lower/mid-troposphere, associated with a broad plume of elevated mixed-layer air overspreading the central/southern Great Plains and middle/lower Mississippi Valley, will tend to impede an appreciable risk for thunderstorm development. ...Central Great Plains toward the Upper Midwest... Perhaps as early as late this evening, into the overnight hours, model output continues to indicate that strengthening mid/upper forcing for ascent, coupled with better low-level moisture return, will overcome the inhibition and support a corridor of thunderstorm development. This likely will be focused within strengthening lower/mid-tropospheric warm advection, along a frontal zone extending to the east-northeast of the surface cyclone, across southeastern Nebraska through central Iowa by late tonight. Based at least on the latest NAM, it appears that the more sustained and stronger thunderstorm development may initiate as early as late evening near/east-northeast of the Concordia KS vicinity, before spreading northeastward. This seems likely to occur as convection begins to become increasingly rooted below the 700 mb level, closer to 850 mb, with soundings perhaps becoming characterized by "loaded gun" thermodynamic profiles above the near-surface stable layer. Although most unstable CAPE may mostly peak in the 500-750 J/kg range, stronger cells may become conducive to marginally severe hail, aided by strong shear in the convective layer. The potential for strong surface gusts is somewhat more uncertain. Although the risk for strong downdrafts to reach the surface appears negligible, gravity wave induced surface pressure perturbations supportive of gusty winds may not be entirely out of the question. CLICK TO GET WUUS01 PTSDY1 PRODUCT NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z
Category: Watches, Warnings, Advisories, & Hazards