SPC 0830Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0225 AM CST Sun Nov 22 2020 Valid 241200Z - 251200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE SOUTHERN/CENTRAL PLAINS INTO THE OZARKS...MID-SOUTH...AND LOWER MISSISSIPPI VALLEY... ...SUMMARY... Isolated strong to severe thunderstorms appear possible Tuesday into Tuesday night across portions of the southern/central Plains, Ozarks, Mid-South, and lower Mississippi Valley. ...Southern Plains into the Ozarks and Lower Mississippi Valley... An upper trough/low initially centered over the southern/central Rockies should eject eastward across the southern/central Plains on Tuesday, eventually reaching the lower/mid MS Valley by the end of the period. Enhanced (50-60+ kt) mid-level southwesterly winds will likely overspread much of the developing warm sector across the southern/central Plains by Tuesday evening. A surface low over the vicinity of western KS/NE Tuesday morning is forecast to develop eastward towards the mid MS Valley through the period. Pronounced low-level warm/moist advection will likely be ongoing across the southern/central Plains Tuesday morning, with a 40-50+ kt south-southwesterly low-level jet present over this region. As this low-level jet shifts eastward across the Ozarks and lower/mid MS Valley through the day, partially modified Gulf moisture will likewise return northward. Elevated convection may be ongoing Tuesday morning across the southern/central High Plains associated with low-level warm advection. As mid-level temperatures cool with the approach of the upper trough and low-level moisture continues streaming northward across the southern Plains, at least weak instability should develop by late Tuesday afternoon along and east of a surface cold front and dryline. Somewhat steepened mid-level lapse rates and strong deep-layer shear may support isolated, marginally severe hail with any initially discrete storms across OK and perhaps south-central KS. By Tuesday evening, any storms that do form will likely grow upscale into a line along the advancing cold front. Given the predominately linear mode and enhanced low-level wind field, isolated strong to damaging winds should become the main threat across the Ozarks, Mid-South, and lower MS Valley region Tuesday night into early Wednesday morning. There is uncertainty regarding the quality and northward extent of greater low-level moisture return, with the 00Z GFS/ECMWF suggesting mid to perhaps upper 50s surface dewpoints may reach as far north as south-central/southeastern KS into southern MO and the Mid-South. The 00Z NAM shows less low-level moisture return across these areas. Regardless, there will probably be enough low-level moisture and related weak instability to support surface-based storms and isolated strong/gusty wind potential with a low-topped convective line. Farther south into parts of central/eastern OK, AR, northeast TX, northern LA, and MS, the presence of somewhat higher dewpoints along with enhanced low-level shear may support a slightly greater tornado threat compared to locations farther north. Model differences regarding the degree of low-level moisture return and weak forecast instability suggest there is too much uncertainty to include more than a broad Marginal risk area at this time. ..Gleason.. 11/22/2020
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