SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0259 PM CDT Fri Jul 30 2021 Valid 302000Z - 311200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS CENTRAL/EASTERN NE TO SOUTHWEST IA AND NORTHWEST MO... ...SUMMARY... A couple tornadoes along with scattered damaging winds and large hail are possible across portions of the central Great Plains to the Lower Missouri Valley from late afternoon into tonight. ...Discussion... No change was made to the previous convective outlook. ..Smith.. 07/30/2021 .PREV DISCUSSION... /ISSUED 1128 AM CDT Fri Jul 30 2021/ ...Central Great Plains and Lower MO Valley... Late afternoon to evening thunderstorm development will be focused along and north of a quasi-stationary front arcing from northeast CO to central NE to southwest MO. The temperature and dew point gradient will be largest in the NE portion of the baroclinic zone. Here, organized severe storms should initiate along a corridor of moderate to large buoyancy supported by upper 60s to mid 70s boundary-layer dew points. Initial storms in the central NE vicinity will be on the fringe of modest deep-layer westerlies (with stronger flow east; weaker west). This should tend to foster mainly outflow-dominated cells. However, convection will likely intensify as it spreads towards eastern NE this evening with effective shear around 40 kts. Although lower-level lapse rates should progressively weaken with northern extent from the surface boundary, enlargement to the low-level hodograph may yield a couple tornadic storms prior to broader clustering of convection that spreads east-southeast. Regenerative warm-advection-driven storms should persist across the Mid to Lower MO Valley through much of the night, although the overall severe threat will gradually subside during late evening to early morning as instability diminishes. ...Southeast VA and central/eastern NC... A southeast-sagging cold front should be the focus for at least isolated thunderstorms later this afternoon. In the mid-levels, relatively warm temperatures and weak lapse rates will be limiting factors, as well as drier air spreading from west to east. A moderate buoyancy plume should still develop along the coastal plain where boundary-layer dew points will be largest. With west-southwesterly low-level flow, moderate speed shear through the cloud-bearing layer should foster mainly cellular convection capable of small hail. This should augment downdraft strength and yield a threat for locally damaging winds from sporadic downbursts.
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