SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1250 AM CDT Sun Aug 22 2021 Valid 221200Z - 231200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE CENTRAL AND NORTHERN PLAINS INTO THE MID MISSOURI VALLEY... ...SUMMARY... Isolated severe thunderstorms will be possible this afternoon and evening across parts of the central and northern Plains into the mid Missouri Valley, where wind-damage, large hail and an isolated tornado threat is expected. A brief tornado will also be possible across parts of the southern New England. ...Central and Northern Plains/Mid Missouri Valley... An upper-level trough will move northeastward across the western Dakotas this afternoon. Ahead of the system, a low-level jet will be located across the central and northern Plains. Elevated convection should form near the low-level jet across eastern South Dakota early this afternoon. Hail could occur with this activity as it moves eastward into the western Minnesota during the late afternoon. Further to the southwest, the strong low-level flow will result in moisture advection across central Nebraska and central South Dakota, with surface dewpoints increasing into the 60s F by mid afternoon. This should enable moderate instability to develop along the moist axis as surface temperatures peak in the late afternoon. MLCAPE is forecast to reach the 1200 to 1500 J/kg range across east-central South Dakota by 00Z/Monday. This combined with large-scale ascent associated with the upper-level trough and strong deep-layer shear, should be favorable for supercells. Storm coverage should remain relatively isolated due to a capping inversion that will strengthen across the northern Plains early this evening. Any supercell that can develop in spite of the cap, should be able to produce large hail and wind damage. A tornado threat will also be possible with supercells, especially as the low-level jet strengthens early this evening. The threat may extend into eastern North Dakota, but weaker instability should could marginalize the severe threat there. Further to the south, across the eastern half of Nebraska and northern Kansas, moderate to strong instability will be in place by afternoon. In spite of this, a capping inversion should keep storm coverage very isolated this afternoon. If the cap can weaken enough during the late afternoon, then a supercell with wind damage and isolated large hail will be possible. ...Southern New England... The National Hurricane Center is forecasting Hurricane Henri to move northward into southern New England today. The center of Henri is forecast to move across western Rhode Island by late afternoon and into east-central Massachusetts by late this evening. Bands with heavy rainfall will overspread southern New England today. RAP forecast soundings across southern New England increase 0-1 km shear to near 30 kts as Henri moves inland, suggesting that a marginal tornado threat could develop this afternoon. ..Broyles/Jirak.. 08/22/2021 Read more LIVE: spc.noaa.gov
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