Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0325 AM CST Mon Nov 16 2020 Valid 191200Z - 241200Z ...DISCUSSION... The period will begin with a positively tilted trough over the U.S./Canadian West Coast -- a degraded remnant of the substantial cyclone now over the northeastern Pacific. Downstream and in low levels, a slow-moving cold front will extend from the Great Lakes to the southern High Plains days 4-5/22nd-23rd, largely parallel to and south of the faster flow aloft. Strong low-level ridging over the Southeast and Gulf Coast will be slow to retreat, precluding robust moisture return into this regime, with organized severe potential too low for an outlook area days 4-6. Though details differ some at shortwave scales, operational GFS/ECMWF/CMC, and available ensemble guidance, generally agree that the positively tilted synoptic trough will cross the western/central CONUS and amplifying days 5-6, with the front sagging southeastward through the Appalachians and western Gulf Coast States. Considerable spread occurs at mid/upper levels from day 6 onward. Still, the general pattern of front-parallel flow aloft suggests weak lapse rates and abundant clouds/precip near the front that should keep severe potential generally marginal and conditional. One exception may be near the end of the period (days 7-8/23rd-24th) in the upper Ohio Valley to Mid-Atlantic/Northeast, if a more intensely amplified northern-stream cyclone, as forecast by operational ECMWF (but not deterministic GFS/CMC nor several EC ensemble members), verifies over the southern ON/lower Great Lakes region. Such a scenario would strengthen frontal forcing under intense flow aloft for potential low-topped convective band(s). However, at such a long time range, predictability is very low for such a solution.
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