SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0748 AM CDT Sun May 25 2025 Valid 251300Z - 261200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE SOUTHERN PLAINS... ...SUMMARY... Severe thunderstorms, including the risk for very large hail, swaths of severe winds with isolated 75+ mph gusts, and a few tornadoes, are expected across parts of the southern Plains this afternoon and evening. Scattered severe thunderstorms with large hail and damaging winds will also be a concern across the lower Mississippi Valley into the Deep South. ...Synopsis... A weak upper trough will advance slowly eastward today across the Southwest and southern Rockies, while upper ridging gradually becomes more suppressed over the southern/central Plains by a low-amplitude shortwave trough moving northeastward from northern Mexico. A belt of enhanced mid-level flow associated with upper troughing over the Northeast is expected to remain mostly displaced to the north of the warm sector in place across the Ozarks into the lower MS Valley and Southeast. At the surface, a convectively reinforced front extending eastward from a weak surface low over the southern High Plains will likely serve as a focus for renewed severe thunderstorm development this afternoon and evening. The northward advance of this front with eastward extent into the lower MS Valley/Mid-South and TN Valley remains somewhat uncertain. But, most guidance still shows it generally draped from northwest to southeast across these regions by this afternoon. ...Central/Southern Plains into the Lower Mississippi Valley and Southeast this Morning/Afternoon... A 30-35 kt south-southwesterly low-level jet will continue to aid mostly elevated thunderstorms across southern KS into the Ozarks this morning. With strong deep-layer shear in place, some of this convection may continue to pose an isolated threat for hail/wind over the next few hours, even with greater low-level moisture and related instability confined farther south along the outflow-reinforced boundary. As filtered diurnal heating occurs downstream of this morning activity, an increasingly unstable airmass is likely to exist from parts of eastern OK into AR and the Mid-South/lower MS Valley, along and south of the front. Various NAM/RAP forecast soundings across this region suggest that stronger deep-layer shear will tend to remain to the north of the surface boundary. Still, there will likely be sufficient shear to foster some updraft organization, with both clusters and embedded supercell structures possible. One or more well organized clusters/bowing line segments may eventually develop across the lower MS Valley/Mid-South vicinity this afternoon/evening, possibly related to the ongoing convection this morning across south-central KS and northeast OK/northwest AR. Regardless of its origin, the overall environment should support at least scattered severe/damaging winds and occasional large hail as these thunderstorms spread east-southeastward through the afternoon and early evening. Consideration was given to including higher wind probabilities across part of this region, but confidence was not high enough in a more concentrated corridor of severe wind gusts to do so at this time. Severe probabilities have been expanded southward across the lower MS Valley to account for one or more thunderstorm clusters with associated damaging wind threat spreading southeastward this evening into the early overnight hours, before eventually weakening. ...Southern High Plains into the ArkLaTex this Afternoon through Tonight... A low-amplitude mid-level shortwave trough over northern Mexico this morning will move northeastward across the southern High Plains by this afternoon/evening. Ahead of this feature, ample daytime heating will likely aid in the development of moderate to strong instability by mid afternoon amid a moist low-level airmass. A surface front will extend from eastern NM across northwest TX and the TX Panhandle into parts of western/central OK, with a dryline extending southward from the front across west TX. Both of these surface boundaries will likely prove instrumental, in combination with modest large-scale ascent associated with the shortwave trough, to focus intense thunderstorm development later today. While mid/upper-level winds are not expected to be overly strong, veering and gradual strengthening with height should support around 30-45 kt of deep-layer shear. Stronger shear is forecast near the front. Convective temperatures will likely be reached by 20-22Z, and explosive thunderstorm development is expected in this time frame across west/northwest TX along the front and dryline. A mix of supercells and clusters will likely form and spread east-northeastward across the southern High Plains through the late afternoon and early evening. Very large hail (2-3 inches in diameter) will be possible with any initial supercells given favorably steep mid-level lapse rates and relatively long/straight hodographs at mid/upper levels. By early evening, consolidation into a bowing complex appears likely across northwest TX and vicinity. An increasing threat for scattered to numerous severe winds will exist with this cluster as it develops generally eastward into western north TX and southwest OK through the evening. Given steepened low-level lapse rates and the presence of strong to locally extreme instability, some wind gusts of 75+ mph appear possible with the bowing cluster. The potential for supercells to develop separately farther east along the front in western/central OK remains unclear. If thunderstorms can form here, they would likely become severe quickly, and pose a threat for very large hail. Some risk for a few tornadoes may also exist this evening (either embedded with the bow or with semi-discrete supercells) as a southerly low-level jet and related 0-1 km SRH gradually strengthens. A continued threat for severe/damaging winds may continue into the early overnight hours across parts of OK and north/central TX. Severe probabilities have been expanded southward some to account for latest guidance trends showing the potential for the bow to persist with some intensity farther south/east in TX. A somewhat separate area of at least isolated supercell potential is also evident across northeast to east-central NM this afternoon in a modest low-level upslope flow regime along and north of the front. Large hail should be the main threat with this activity. The eastward extent of the severe threat will likely be confined by weaker instability into the OK Panhandle and northern TX Panhandle. ...Florida... Compared to the prior couple of days, mid/upper-level winds appear somewhat weaker across the FL Peninsula today. Mid-level temperatures are also slightly warmer per area 12Z soundings. Even so, another day of scattered thunderstorm development is anticipated over much of the FL Peninsula, with various sea breezes acting as foci for initiation. Moderate instability coupled with modest deep-layer shear may still support an isolated threat for marginally severe hail and gusty winds with the stronger cores that can develop this afternoon. ..Gleason/Leitman.. 05/25/2025