Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0333 AM CDT Tue Oct 06 2020 Valid 091200Z - 141200Z ...DISCUSSION... Medium-range models continue to indicate substantial amplification within a belt of westerlies emanating from the mid-latitude Pacific this coming weekend into early next week. This still appears likely to include the evolution of large-scale mid/upper troughing across and east of the Canadian and U.S Rockies by Sunday. This likely will be accompanied by deepening surface troughing and embedded cyclogenesis across the Canadian Prairies and U.S. Great Plains, before shifting northeastward and eastward, toward Hudson Bay and across the Mississippi Valley by late Monday. This is expected to be preceded by the inland migration of Hurricane Delta Friday night, which will pose the most substantive initial potential for severe weather (in the form of tornadoes) during this period. However, as is typically the case with features the scale and nature of tropical cyclones, the extent of this risk, at this extended range, remains unclear due to a number of uncertainties. One in particular concerns relatively dry/potentially cool low-level air associated with surface high pressure, which appears likely to encompass much of the East and Gulf Coast states prior to landfall of Delta. An elevated influx of moisture and associated rain falling into this air mass may further reinforce stable boundary-layer conditions preceding Delta. And this could mitigate the risk for tornadoes inland of perhaps a small corridor near coastal areas, before Delta weakens. Thereafter, the most appreciable severe weather potential associated with the extratropical cyclogenesis is probably Sunday into Monday, before diminishing by Tuesday. The high latitude nature of the stronger cyclogenesis (i.e. across the northern Great Plains/Canadian Prairies into the west of Hudson Bay), and the likely dependence on substantive moisture return from the Gulf of Mexico for appreciable destabilization, contribute to uncertainty which remains sizable concerning the extent of this risk.
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