SPC 0600Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1142 PM CDT Tue Oct 06 2020 Valid 081200Z - 091200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Aside from low probabilities for thunderstorms inland of the northwestern Gulf coast, the risk for thunderstorms appears negligible across much of the rest of the nation Thursday through Thursday night. ...Synopsis... Downstream of a strong, zonal jet propagating across the northern mid-latitude Pacific, a low-amplitude short wave trough may progress across the Canadian Prairies during this period, within the main belt of branching flow. Otherwise, it appears that this regime will remain broadly anticyclonic and confluent across much of southern Canada and the northern tier of the U.S., into large-scale negatively tilted troughing gradually shifting east of the north Atlantic coast. In a separate stream to the south, broad troughing may begin to progress inland of the California coast, but an embedded closed low probably will remain well offshore. As this occurs, weak troughing evolving in somewhat lower latitudes, across the southern Great Plains/lower Rio Grande Valley, may begin progressing slowly eastward. At the same time, at least a couple of tropical perturbations will continue to slowly migrate within the low/mid-level easterlies, on the southern and southwestern periphery of lingering mid-level ridging across the subtropical western Atlantic into parts of the Southeast. This will include Hurricane Delta, which is forecast to migrate northwestward, then northward, into the northwestern Gulf of Mexico Thursday through Thursday night. Preceding Delta's approach of the northwestern Gulf coast, beneath the confluent mid-level flow in the wake of the negatively tilted trough in the westerlies, the center of a fairly expansive area of cold surface ridging is forecast to shift from the Upper Midwest into the Mid Atlantic Coast region. It appears that this probably will reinforce a relatively dry/potentially cold boundary-layer air mass as far south as the Gulf Coastal plain by 12Z Thursday. There may be little modification through Thursday night, except perhaps across parts of the northwestern Gulf coast into parts of the southern Great Plains, where at least a weak southerly return flow may commence. ...Gulf States... It still appears that moisture return will initially occur above a stable boundary layer. However, this may contribute to weak/modest CAPE in lower to mid-levels. In the presence of large-scale ascent, aided by forcing in the right entrance region of an anticyclonic high-level jet, this is expected to support increasing precipitation and embedded convection. With mid/upper levels moistening, relatively warm and characterized by weak lapse rates, it remains unclear whether thermodynamic profiles will become conducive to convection capable of producing lightning. However, it may not be out of the question. ...Upper Great Lakes region... Models indicate a zone of steepening lower/mid tropospheric lapse rates and strengthening lift associated with warm advection, with perhaps sufficient elevated moistening to support weak thunderstorm activity late Thursday night across the western upper Michigan/Lake Superior vicinity. ..Kerr.. 10/07/2020
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