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Archives for the SPC Convective Outlook are updated daily (approximately) with a live map at the beginning of each article. Follow the link at the end of the article to check for current updates on the NOAA/NWS Storm Prediction Center website. Also, see Archives for Chicago's hourly weather data on CARDINAL NEWS Magazine.

Tuesday, November 29, 2022

SPC Nov 29, 2022 0600 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 1200Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1109 PM CST Mon Nov 28 2022 Valid 291200Z - 301200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS FAR EAST-CENTRAL LOUISIANA INTO CENTRAL MISSISSIPPI... ...SUMMARY... Severe thunderstorms capable of producing tornadoes, very large hail, and a few severe wind gusts are expected this afternoon into the overnight period across parts of the lower to mid Mississippi Valley and parts of the Southeast. A few strong tornadoes will be possible. ...Synopsis... A surface low will deepen while tracking from Kansas to the Great Lakes today, accompanied by an eastward advancing upper trough. A strong mid-level jet stream will overspread an intense low-level jet across the OH/TN Valleys into the Southeast. As such, strong deep-layer flow and shear will overlap with a moistening, destabilizing airmass from late morning to early evening from the lower MS Valley east-northeastward. Several strong to intense thunderstorms are expected to organize and promote a relatively robust severe threat, particularly across the Southeast, where regionally higher instability should reside. ...Portions of the Lower MS Valley today into early tonight... Strong warm-air advection should be underway across the Lower MS Valley at the start of the period (12Z), with rich boundary-layer moisture being transported northward by a 40-50 kt southwesterly low-level jet. Through the day, at least modest surface heating should support surface temperatures rising into the lower 70s F amid upper 60s F dewpoints within the warm-air advection regime, where an increase in thunderstorms is also expected. 50-70 kts of west-southwesterly 500 mb flow and 6.5+ C/km lapse rates will overspread the lower MS Valley and the warm-air advection regime by early afternoon, contributing up to 1500 J/kg MLCAPE, which is adequate in supporting a severe threat. Storms should eventually root into a gradually deepening boundary layer during the afternoon, taking advantage of the strong deep-layer and low-level speed/directional shear provided by the overlapping southwesterly low-level and westerly mid-level jets. Large, curved low-level hodographs with mid/upper-level elongation will support well over 50 kts of effective bulk shear, and 300-400 m2/s2 effective SRH. Supercell structures are expected initially, with large hail, tornadoes, and a few severe gusts all likely. A few instances of 2+ inch diameter hail and/or strong tornadoes are possible with the more robust supercells. Should a more dominant supercell develop, remain discrete, and traverse an axis of locally stronger surface heating/buoyancy, a long-tracked and intense tornado may occur. The latest high-resolution guidance consensus suggests this scenario would be most likely across central MS, where a Category 4/Moderate risk is in place. Later at night, storms should grow upscale into more linear segments as the surface cold front and greater low-level convergence approaches. Damaging gusts should then become the main threat, though a few tornadoes remain possible. ...Parts of the OH/TN Valley into early evening... A strong surface cold front should sweep across the OH/TN Valleys through the late afternoon and evening hours as the deepening surface low tracks across the Great Lakes. Strong convergence along the cold front should force a low-topped band of convection. Ambient tropospheric wind fields will be strong, with 55+ kts of flow likely just 1 km AGL. Downward momentum transport within this line may foster strong, occasionally damaging gusts, with a couple of severe gusts also possible, warranting the introduction of Category 1/Marginal probabilities this outlook. ..Squitieri/Darrow.. 11/29/2022 Read more CHECK UPDATE ZOOM GRAPHIC