SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1115 AM CST Thu Nov 26 2020 Valid 271200Z - 281200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FRIDAY ACROSS PARTS OF SOUTHEASTERN TEXAS...SOUTHERN LOUISIANA AND SOUTHERN MISSISSIPPI... ...SUMMARY... Strong thunderstorms may impact parts of the northwestern Gulf coastal plain Friday, and could pose at least some risk for severe hail and strong wind gusts. ...Synopsis... Stronger mid-latitude westerlies are forecast to remain confined to the central/northern tier of the U.S. northward, but a strong high-level jet emerging from the subtropical eastern Pacific appears likely to remain influential across the Gulf Coast region and Southeast through this period. Within this regime, one mid-latitude wave, in phase with the subtropical stream, is forecast to progress east of the New England coast by 12Z Friday, followed by another perturbation digging into and across the Great Lakes region by late Friday night. Another upstream perturbation, currently splitting off of the belt of mid-latitude westerlies across the Great Basin, may evolve into a mid-level low over Arizona, before gradually accelerating eastward in phase with the subtropical westerlies, into/across the southern Rockies. Although spread among the various model output remains largest concerning the Southwestern perturbation, there is little suggestion within the guidance that it will provide support for substantive wave development along a frontal zone expected to slowly continue advancing into the northwestern Gulf coastal plain. This frontal motion is forecast in response to the progression of the preceding mid-latitude short waves, which may also contribute to a southeastward advancement of the front off the southern Atlantic Seaboard, while the front becomes quasi-stationary across the eastern Gulf Coast states vicinity. A plume of seasonably moist air will linger along and just south of this frontal zone, though generally weak mid/upper lapse rates are expected to temper the potential instability. ...Southeast Texas into southern Louisiana/Mississippi... Near/just south of the surface front, it does appear that CAPE rooted within/just above the boundary-layer may reach 500-1000 J/kg across the coastal plain. Deep-layer shear is also expected to become strong, as the core of the high-level jet emerging from the subtropics begins to overspread the region, with 30-50+ kt westerly flow as low as the 700-500 mb layer. However, guidance generally indicates that low-level wind fields and forcing for ascent will remain modest to weak through this period. Models do suggest that a coupling of speed maxima within the mid/upper jet may contribute to a region of strong, focused high-level divergence overspreading southeast Texas into the lower Mississippi Valley during the day Friday. Perhaps aided by weak mid-level warm advection, this is expected to contribute to thunderstorm development which could eventually become rooted within the modestly unstable boundary layer. If this occurs, stronger cells may briefly become capable of producing marginally severe hail. One or two small organizing clusters of storms might not be out of the question, which could pose a risk for potentially damaging wind gusts while propagating southeastward into Friday evening. ..Kerr.. 11/26/2020
There’s more click here.