SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0306 PM CDT Fri Jul 09 2021 Valid 092000Z - 101200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS CENTRAL/WESTERN NE AND FAR NORTH-CENTRAL KS...SOUTHERN IA/NORTHERN AND EASTERN MO/WESTERN IL... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF THE MID ATLANTIC... ...SUMMARY... Thunderstorms, some with potentially significant severe weather, are expected this afternoon into tonight across parts of the lower Missouri Valley westward into the parts of the north-central High Plains. ...20Z Update... The primary change has been to add an Enhanced Risk across western/central NE and adjacent portions of northern KS. Multiple intense thunderstorm clusters are expected late this afternoon into the evening, within an unstable and favorably sheared environment. Very large hail will be the initial threat, with an increasing threat of wind damage this evening as outflows consolidate and move east-southeastward with time. The Slight and Marginal Risks have also been adjusted slightly southward and westward across the High Plains, based on latest guidance and observational trends. See MCD 1213 for more information regarding the short-term threat in the High Plains. Uncertainty remains regarding the timing of redevelopment across IA/MO later this afternoon/evening, but another intense cluster is expected to eventually develop and move southeastward with time tonight. Elsewhere, no substantial changes have been made to the outlook. See the previous discussion below for more details. ..Dean.. 07/09/2021 .PREV DISCUSSION... /ISSUED 1134 AM CDT Fri Jul 09 2021/ ...IA/IL/MO... Residual clouds/showers and thunderstorms persist across the area from overnight convection, however strong heating this afternoon of a very moist air mass is expected to result in strong instability south of a developing warm front. Elevated thunderstorms may develop this afternoon over northern IA and pose a risk for large hail, however the primary concern is with supercell storm development near the warm front late this afternoon or perhaps early evening. Steep mid-level lapse rates and 40-45 kts of effective shear will result in a risk for all hazards, including the potential for very large hail and isolated tornadoes. These storms should evolve into a southeast-moving complex during the evening with an increasing risk of widespread damaging winds, with potentially significant severe gusts. ...WY/NE... Thunderstorm development is expected this afternoon near the higher terrain of WY/northeast CO, with very steep mid-level lapse rates and moderate MLCAPE supporting a supercell storm mode with a risk for very large hail and damaging winds, and perhaps a couple of tornadoes. Aided by a developing low-level jet, storms are expected to move east/southeast across much of NE and northern KS tonight with a continued severe wind/hail risk. ...Mid-Atlantic/Northeast U.S.... Tropical Storm Elsa was located over eastern Long Island and continuing to move northeast. The risk for a tornado or two over southeast New England should end by mid afternoon as the more favorable environment for brief tornadoes shifts northeast and offshore. A cold front will move east across the northeast and mid-Atlantic states this afternoon and tonight as a shortwave trough over the Great Lakes also shifts east. Scattered thunderstorms are expected to develop ahead of the front in a moderately unstable air mass this afternoon/evening. Effective shear averaging around 25-30 kts will promote organized storms in the form of multicells, and eventually a few clusters with a risk for mainly damaging winds. Have introduced a focused SLGT Risk for this afternoon over portions of the mid-Atlantic region where a higher concentration of storm coverage may exist. Read more LIVE: spc.noaa.gov
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