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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.


Wednesday, September 6, 2023

SPC Sep 6, 2023 1300 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 1300Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0732 AM CDT Wed Sep 06 2023 Valid 061300Z - 071200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM NORTHERN LOUISIANA TO PARTS OF THE TENNESSEE VALLEY REGION... ...SUMMARY... Severe thunderstorms capable of damaging gusts and isolated hail are possible from northern Louisiana to parts of the Tennessee Valley region. ...Synopsis... A mid/upper-level anticyclone is building over the NM/far west TX region, with ridging northward across WY to the northern Plains. A progressive shortwave train will be maintained on the anticyclone's northern and northeastern periphery, from the Pacific Northwest to the Appalachians. The currently strongest of the shortwave troughs -- apparent in moisture-channel imagery over the mid/upper Mississippi Valley -- will shift eastward to an axis from western Lake Superior to western IN through 00Z, before weakening and slowly moving eastward across the remainder of the Upper Great Lakes. Meanwhile, an upstream perturbation -- initially over WY -- will pivot eastward then southeastward away from the mean-ridge position and strengthen as it traverses downstream northwest flow. By 00Z, this feature should reach western IA, southeastern NE and northern KS. By 12Z tomorrow, the trough should extend over the Wabash River area and southwestward across parts of the Mid-South region, with a 500-mb low developing near EVV. At the surface, 11Z analysis showed frontal-wave lows over the Keweenaw Peninsula and western WI, collected by a cold front that extended across northern/southwestern IL, southeastern MO, southeastern OK, to a weak low over northwest TX, then quasistationary across the Llano Estacado into central NM. By 00Z, the front should reach eastern Upper/northern Lower MI, southern IN, the DYR area, south-central AR, and the Red River Valley. The western segment of the front should stall over north TX today into tonight, and return northward diffusely across the TX Panhandle and northeastern NM tonight. Meanwhile, by the end of the period, the rest of the front should reach eastern portions of OH/KY/TN, northern AL, central MS, and southern AR. ...Lower Mississippi Valley to Great Lakes... Scattered thunderstorms are expected to develop this afternoon along/ahead of the cold front, and near any remaining prefrontal outflow/ and differential-heating boundaries from prior/morning convection. The most-favorable shear/instability parameter space, and best-organized severe potential, should be in and near the 15%/"slight" area, where damaging to severe gusts will be the main threat, with large hail also possible. Isolated, marginal severe potential extends northward from there past the Ohio Valley into portions of the Great Lakes. The strongest winds aloft and associated deep shear will remain largely behind the leading mid/upper trough -- with one important exception: a channel of enhanced 500-250-mb layer flow extending from the central Plains across the Ozarks toward the Mid-South by 00Z. The leading edge of intensifying gradient winds aloft will extend over parts of the warm sector from northern LA into the Mid-South today, even as the strongest mid/upper flow lags the surface front/outflow. This will increase deep shear enough to aid in multicellular organization from northern LA to the Tennessee Valley, with effective-shear magnitudes relatively maximized at around 25-35 kt, compared to 15-25 kt farther north across the Great Lakes States. The southern corridor also will correspond to the greatest preconvective buoyancy, with a combination of steep low-level lapse rates (from diurnal heating) and rich moisture (70s F surface dewpoints) -- each of which will be weaker northward into the Great Lakes. This should result in a plume of 2000-3000 J/kg MLCAPE (locally higher) over the lower Mississippi Valley region, diminishing to around 1000-1500 J/kg north of the Ohio Valley. A secondary, weaker relative max in buoyancy (contributing to MUCAPE near 2000 J/kg) may be noted over parts of western/northern Lower MI, under stronger cooling aloft, though low/middle-level flow and vertical shear will be weak there. ..Edwards/Leitman.. 09/06/2023 Read more CHECK UPDATE ZOOM GRAPHIC
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CHICAGO UTC-6 during CST (Central Standard Time, e.g., winter)
CHICAGO UTC-5 during CDT (Daylight Savings Time, e.g., summer)