SPC 0600Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 0100 AM CDT Thu Apr 08 2021 Valid 091200Z - 101200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FOR NORTH-CENTRAL TEXAS EASTWARD INTO NORTHERN LOUISIANA AND MISSISSIPPI... ...SUMMARY... Scattered severe thunderstorms are forecast on Friday from parts of Oklahoma and Texas eastward through the lower Mississippi Valley. Large to giant hail is possible across parts of Texas, and a swath of damaging gusts and several tornadoes are possible from Texas east into Mississippi. ...Synopsis... A mid-level low will weaken and meander northward over the western Great Lakes. A more potent, upstream mid-level trough will move from WY southeastward into eastern KS/OK by early Saturday morning. A lower-amplitude disturbance in the southern stream will move eastward from southwest Texas into the lower MS Valley. In the low levels, an area of low pressure over western north-central TX will develop eastward and reach the AR/MS/TN vicinity by daybreak Saturday. A dryline will extend southward near the I-35 corridor in north-central TX. A residual front will advance northward across much of AR and western TN. ...Southern Great Plains... A seasonably moist/unstable airmass sampled by Wednesday evening raobs along the TX Gulf Coast, and an elevated mixed layer, will overlap and result in a very unstable airmass developing across TX east of the dryline with 3000 J/kg MLCAPE forecast. Rather cold 500 mb temperatures (-15 to -16 deg C) will result in very large CAPE in the -10 to -30 deg C layer. A strong capping inversion will weaken with localized erosion of the cap by the late afternoon via strong heating, convergence near the dryline, and the aforementioned disturbance moving east across TX. Explosive updraft growth is expected with isolated to widely scattered storms developing from southern OK southward into east-central TX. A veering and increasing wind profile with height will strongly favor discrete supercells, before additional storm development occurs during the evening as storms move east into the Arklatex. In addition to hail and a tornado risk, the threat for damaging gusts will probably increase during the evening as this activity moves east into the Arklatex. ---model discussion--- The 08/00z and 07/18z NAM runs exhibit a too-cool bias with surface temperatures east of the dryline across north-central TX (low to mid 70s near DFW metro), specifically near the I-35 corridor. Moreover, it is likely strong heating will occur across central and north TX during the day with temperatures at least 90 F west of the dryline and into the middle 80s to the east in the warm sector. As a result, ARW-based convection-allowing models (based on the parent ARW model) are likely misrepresenting thunderstorm potential across TX during the 21z-03z period. Conversely, the 08/00z and 07/18z GFS runs are showing excessive boundary-layer mixing and a too-warm bias across north-central TX with the dryline likely displaced too far east compared to its likely position near I-35 by late afternoon. The 07/12z ECMWF appears superior to the NAM/GFS in this regard with adequate boundary-layer mixing implied by the warmer surface temperatures (mid 80s F). This forecast across the southern Great Plains coincides with model output similar to the ECWMF in recent model runs. ...Northern Gulf Coast states... A complex forecast is seemingly evident for this region and concerning mainly the after-dark severe threat expected to develop from LA eastward into MS/AL. Models indicate a moisture-rich boundary layer beneath steep lapse rates will be present during the day. Despite the presence of a capping inversion, isolated to widely scattered storms are possible during the day with mainly an associated hail hazard. The stronger updrafts may acquire supercell characteristics with some conditional tornado risk over southern AL. However, the primary severe threat will likely develop as the low- to mid-level wind field strengthens during the evening into the overnight. Storms developing within the WAA regime and/or a thunderstorm cluster growing upscale into an MCS are seemingly the favored scenarios for storm development. Severe gusts (some significant; 65+ kt) and tornadoes will likely become the main hazards as storms move east across northern LA eastward into MS and into western AL by early Saturday morning. ...Southern Appalachian states... The northeastern periphery of richer low-level moisture (60s F dewpoints) will probably include GA and perhaps extend northward into the western Carolinas during the day. Isolated to widely scattered multicells are forecast to develop during peak heating with an isolated hail/wind risk with the stronger storms. This activity will likely diminish by early evening. ..Smith.. 04/08/2021
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