SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1259 AM CDT Sat May 13 2023 Valid 131200Z - 141200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE MID MISSOURI VALLEY AND TEXAS COASTAL PLAIN... ...SUMMARY... Thunderstorms associated with a few tornadoes, wind damage and large hail will be possible today in parts of the upper Mississippi Valley. Storms with wind damage and isolated large hail will also be possible along the Texas Coastal Plain. ...Mid to Upper Mississippi Valley... An upper-level ridge will build slowly northward across the mid Mississippi Valley today, as an upper-level low moves northward into the northern Plains. At the surface, a low will gradually weaken across the mid Missouri Valley, with a warm front extending from northwest-to-southeast from Iowa into western Missouri. Surface dewpoints near this boundary will be in the mid to upper 60s F, contributing to a moderately unstable airmass in most areas by midday. As surface temperature warm and low-level convergence increases, thunderstorms will develop along and near the front. Convective coverage will markedly increase during the mid to late afternoon, with a severe threat developing and persisting into the evening. Although flow will be relatively weak across much of the north-central U.S., a small zone of stronger low-level flow is forecast across eastern Iowa this afternoon. Forecast soundings in eastern Iowa at 21Z have MLCAPE in the 1000 to 2000 J/kg range, with 0-6 km shear near 40 knots, mostly due to directional shear. This profile will be sufficient for supercell development. The stronger updrafts could have an isolated large hail threat. Low-level hodographs are looped and long, but lack speed shear in the low to mid-levels. Still, this should be enough to support a tornado threat with rotating storms that develop in the mid to late afternoon. During the late afternoon and early evening, storms are expected to congeal into a line segment, which could be associated with an isolated wind-damage threat. ...Southern Plains... An upper-level low is forecast to move northward across far southeast New Mexico today. Flow at low to mid-levels will be relatively weak across much of the southern Plains. At the surface, a moist airmass will be in place from the Texas Coastal Plain northward into the Ark-La-Tex. A severe threat could be ongoing along the western edge of this moist airmass around daybreak, with the threat gradually moving eastward toward the Texas coast during the day. Surface dewpoints in the mid to upper 70s F will contribute to strong instability, with MLCAPE peaking around 2500 J/kg during the afternoon. As low-level lapse rates become steep, isolated damaging wind gusts will be possible along the leading edge of the more organized multicell line segments. Isolated large hail could also occur in and around the stronger downdraft cores. Further north into Oklahoma, forecasts have a moist airmass in place across much of the state. As surface temperature warm today, thunderstorms are forecast to develop on the western edge of this airmass. Although some of this convection could remain as showers, moderate instability and gradually veering wind profiles with height could be sufficient for a marginal tornado threat. ..Broyles/Weinman.. 05/13/2023
