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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.


Sunday, August 6, 2023

SPC Aug 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 0748 AM CDT Sun Aug 06 2023 Valid 061300Z - 071200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS MID-MS AND LOWER OH VALLEYS TO THE MID-SOUTH AND SOUTHEAST... ...SUMMARY... A few tornadoes along with scattered damaging winds and large hail will be possible from late afternoon into tonight from the Mid-Mississippi to Lower Ohio Valleys. Scattered damaging winds will also be possible, mainly from midday into early evening across parts of the Mid-South and Southeast. ...Mid-MS to Lower OH Valleys... In the wake of decaying convection over northeast MO and AR/OK, a plume of at least moderate buoyancy should develop towards peak heating across the Mid-MS Valley. Guidance is fairly consistent that an arc of thunderstorms will develop during the mid to late afternoon across southeast IA into northeast MO downstream of the eastward-drifting shortwave trough and attendant surface cyclone over the Mid-MO Valley. The impinging of a 700-mb speed max across MO into IL will enhance 0-3 km SRH and foster supercell development despite predominantly west-southwesterly low-level flow. Modest mid-level lapse rates (especially with eastern extent) may curtail greater updraft intensity. But with at least a few supercells expected, there will be potential for large hail up to around 2 inches and a couple tornadoes. Towards late evening, upscale growth into one or two organized clusters seems plausible, with potential for an MCS to evolve along the northern extent of the surface-based instability plume. An elongated swath or two of damaging winds with embedded severe gusts, along with a couple brief tornadoes may be sustained into the early overnight into the Lower OH Valley. ...Mid-South to the Southeast... There is uncertainty whether a decaying MCS near the AR/OK border will completely subside by late morning owing to nearly cloud free insolation underway downstream of its remnant outflow. This boundary will likely serve as a focus for renewed thunderstorm development from midday through the afternoon as it spreads east of the Lower MS Valley into the Southeast. While the leading outflow will outpace stronger mid-level flow attendant to the slow-moving trough over the Mid-MO Valley, impinging of 25-35 kt 700-mb westerlies from the TN Valley northward should be adequate to support semi-organized multicell clusters amid an extensive plume of large buoyancy across the Deep South. Scattered damaging wind swaths from water-loaded downbursts will be possible through early evening. Have expanded both the cat 1 and 2 risks southward to account for a more southern evolution of clusters. During the evening, low-level warm theta-e advection should strengthen along the trailing outflow/effective baroclinic zone over the Mid-South. This activity should pose an isolated threat for severe hail initially before likely clustering into a localized damaging wind threat overnight. ...Central/southern Rockies... The presence of 50s surface dew points will support potential for isolated but regenerative thunderstorms to develop along the Front Range during the late afternoon and evening. While the NAM appears much too cool across the adjacent plains, MLCIN should steadily increase with eastern extent. This should yield a rather confined corridor for weak buoyancy with MLCAPE of only 500-1000 J/kg. Nevertheless, deep-layer wind profiles will be quite favorable for supercells and large hail potential given near-perfectly straight-line hodographs. After collaboration with WFOs PUB/BOU have held at upgrading to a cat 1-MRGL risk for now, but a meso-beta scale corridor of cat 2-SLGT risk for hail may be warranted in later outlooks. Downstream of a minor shortwave trough over the interior Northwest, isolated to scattered afternoon thunderstorms are anticipated around the UT/WY/CO border area within a weak buoyancy plume. Adequate deep-layer shear will exist for a threat of marginally severe hail and wind centered on the late afternoon. ...Central/southern Appalachians to Lake Erie... A trio of MCVs, one over northern IN and the others over eastern KY/TN, will aid in scattered thunderstorm development downstream of these features from midday through the afternoon. Instability will be substantially weaker relative to the TN Valley region, owing to both weaker mid-level lapse rates and buoyancy. Pockets of stronger low to mid-level flow attendant to these MCVs may support sporadic localized damaging winds. ..Grams/Broyles.. 08/06/2023 Read more CHECK UPDATE ZOOM GRAPHIC
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