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Saturday, June 12, 2021

SPC Jun 12, 2021 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0250 PM CDT Sat Jun 12 2021 Valid 122000Z - 131200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE SOUTHERN HIGH PLAINS... ...SUMMARY... Isolated significant severe wind and hail are possible late this afternoon through evening across parts of the southern High Plains. Sporadic localized damaging winds should also occur through this evening in an arc from the South to Mid-Mississippi Valley to Lower Michigan. ...20Z Update... Only minor changes have been made to the Marginal Risk across parts of the Southeast based on recent radar and observational trends. Sporadic strong to damaging wind gusts should remain the primary threat with loosely organized convection given the presence of moderate to strong instability, weak deep-layer shear, and steepened low-level lapse rates. Farther north, other isolated strong to severe storms will remain possible through the afternoon across parts of northeastern IL and vicinity along a weak surface trough. For more information on the near-term severe threat across this area, see Mesoscale Discussion 936. Across the southern/central High Plains, convective initiation still appears likely across the higher terrain of eastern NM and southeastern CO by 21-22Z. Isolated supercells should initially pose a threat for large to very large hail given the presence of very steep mid-level lapse rates and generally 30-35 kt of effective bulk shear. It still appears possible that a small cluster posing more of a severe wind threat may eventually evolve this evening across the southern High Plains. However, this activity will encounter increasing convective inhibition with eastward extent, and a general weakening trend will likely occur with any storms by late this evening across the TX Panhandle and vicinity. ..Gleason.. 06/12/2021 .PREV DISCUSSION... /ISSUED 1129 AM CDT Sat Jun 12 2021/ ...Southern High Plains... Low-level upslope flow will remain established to the north of a weak surface boundary that arcs across a portion of the Permian Basin and TX South Plains. Surface dew points in the 60s are common north of this boundary which will support strong buoyancy amid steep mid-level lapse rates with MLCAPE in excess of 3000 J/kg across eastern NM and the TX/OK Panhandles. Despite the presence of a mid-level anticyclone near El Paso, modest west-northwesterly flow aloft atop the low-level easterly flow will result in sufficient deep-layer shear/hodograph length for a few supercells. Initial cells near the higher terrain of eastern NM to the Raton Mesa vicinity will be most likely to produce large hail. Strong downdraft potential and strengthening low-level southeasterlies will result in outflow mergers and upscale growth this evening. This will yield a risk for isolated significant severe wind gusts. There is greater-than-average latitudinal variation in storm-scale guidance with the track of an evening MCS into the Panhandles. Have broadened the cat 2/SLGT risk to account for this uncertainty. ...The South to Lower MI... Between a low-amplitude shortwave impulse over GA/SC and the mid-level anticyclone near El Paso, a broad swath of weak to moderate north-northwesterly flow will persist atop very rich boundary-layer moisture characterized by 70s surface dew points from IL/IN south. Scattered thunderstorms are expected in a broad arc across the Southeast to the Midwest to the east of steeper mid-level lapse rates over the south-central states. The latter may effectively yield sufficient MLCIN to curtail renewed storm development associated with a remnant MCV over northeast TX. Vertical shear profiles will generally favor pulse to loosely organized multicell clusters, with sporadic wet microbursts and small hail expected with the strongest storms through this evening. Farther north across Lower MI, somewhat strong vertical shear profiles should compensate for weaker buoyancy, which may result in a couple transient supercell structures. But given weak mid-level lapse rates, steep low-level lapse rates will be the primary driver of a locally damaging wind and small hail threat. Read more LIVE: spc.noaa.gov
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