1PM Day 1 Convective Outlook for Wednesday, February 25. THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PARTS OF THE CENTRAL HIGH PLAINS
SUMMARY
Isolated severe gusts are possible across parts of the central High Plains late this afternoon into the early evening.
20z Update
The previous forecast largely remains on track with only minor adjustments made - namely a slight northward expansion of 5% wind probabilities to better align with developing convection across west/southwest NE. Although this convection is fairly weak, severe wind gusts have been observed across far western NE within the past hour associated with convectively-augmented downward mixing of strong flow aloft. The potential for additional severe gusts should continue through the next several hours downstream. See the previous discussion below and MCD #118.
Central High Plains
Water-vapor imagery this morning shows a mid-level shortwave trough/speed max over southern MT/northern WY as it crests an upper ridge over the West and moves quickly east-southeastward to the MS Valley through tonight. Morning visible-satellite imagery shows a cirrus shield extending eastward across parts of the central High Plains atop a relatively dry boundary layer (surface dewpoints around 30 deg F). A dearth of observed data sampling boundary layer moisture above the surface lends to some uncertainty for this forecast. Yet, westerly downslope flow is leading to warming surface temperatures (mid 50s deg F) with additional mixing/warming likely resulting in nearly dry adiabatic lapse rates in the 0-3 km layer by mid afternoon. As the upper disturbance approaches and a cold front --roughly delineated by low cloud cover across northern WY/western SD-- pushes southward into the central High Plains late today, isolated high-based convection is forecast to develop. Forecast soundings show upwards of a few hundred SBCAPE and strong west-northwesterly flow within a steep-lapse-rate environment. A few of the stronger evaporatively cooled downdrafts may yield an isolated risk for severe gusts (60-65 mph) primarily during the 21-01 UTC period.
Elsewhere, thunderstorm potential will otherwise develop east-southeastward toward the Ozarks/Mid-South/Tennessee Valley tonight as warm/moist advection interfaces with a southward-spreading front, with weak buoyancy expected to limit hail potential with this mostly elevated convection.