SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0758 AM CDT Tue Sep 14 2021 Valid 141300Z - 151200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE MIDWEST/GREAT LAKES AND SOUTH-CENTRAL HIGH PLAINS... ...SUMMARY... Isolated to widely scattered severe storms are possible today into tonight across parts of the Midwest and Great Lakes into the Northeast States. Other severe storms may develop across the south-central High Plains this afternoon and evening. A brief tornado risk is also possible in association with Nicholas from southeast Texas into southern Louisiana. ...Midwest/Great Lakes... Initially, a band of thunderstorms is ongoing over northern Lower Michigan this morning. Although an initially cool/stable boundary layer will limit severe potential, a localized early day severe risk is a possibility, with moderate instability and ample cloud-layer shear noted in the 12Z observed sounding from Alpena, MI. Meanwhile, a surface low will continue to quickly move from Upper Michigan into Ontario. A cold front will trail south from the low, oriented roughly from southeast Lower Michigan into northern Indiana/central Illinois by 00Z. Ahead of the front, mid to upper 60s F dewpoints will be common, along with strong heating resulting in 2000+ J/kg MUCAPE by late afternoon. Deep-layer shear will be most favorable over northern parts of Michigan. However, instability will be greatest farther south where vertical shear will be less. The greatest overall severe threat will be with storms along the front after 21Z from central Lower Michigan into Illinois. Linear forcing along the front suggests wind may be the primary concern, but hail will also be possible. ...Northeast States... Shortwave ridging will occur today, with a warm front otherwise shifting north-northeastward across New York and southern New England. Heating will contribute to instability south of the front, from western New York into Pennsylvania and New Jersey. A capping inversion is expected to generally hinder development during the day, although a few isolated late-afternoon storms could occur over north-central/northeast New York with some severe risk. Otherwise, storm coverage will increase tonight as the front approaches after 03Z into western and northern New York, where 500-1000 SBCAPE may remain. Strong westerly flow with 40-50 kt mid-level winds may support a few severe wind gusts across western New York, but eventual nocturnal thermodynamic influences should keep the overall severe risk somewhat limited. ...Colorado Front Range to Central Plains... Late-afternoon storms are likely along the stalled front across Missouri into southern Kansas, with localized severe wind gusts and/or hail a possibility. Some potential for a few supercells will exist across southern Kansas where vertical shear should be stronger. Although some questions exist regarding storm coverage and the downstream thermodynamic environment across the Plains, other potentially severe storms are expected to develop, at least on an isolated basis, near the Colorado Front Range this afternoon. Although the boundary layer will not be overly unstable, ample effective shear (40+ kt) and steep mid-level lapse rates will support some supercells capable of large hail. These storms may gradually merge/organize as they progress southeastward from east-central/southeast Colorado into southwest Kansas this evening with an isolated severe hail/wind risk. ...Louisiana/southeast Texas... Nicholas will continue to weaken and drift east-northeastward along the upper Texas Coast toward southern Louisiana through tonight. Lower 70s F surface dewpoints reside in coastal areas coincident with moderately strong low-level shear, accentuated by low-level easterly winds near the coast. The scenario will support the possibility of a brief tornado risk mainly across southern Louisiana. ..Guyer/Smith.. 09/14/2021
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