Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0315 AM CST Mon Feb 22 2021 Valid 251200Z - 021200Z ...DISCUSSION... Blocking may linger within the large-scale pattern across the southern mid-latitude and subtropical eastern Pacific late this week into the beginning of next week. However, the latest medium-range guidance indicates that prominent/amplified mid-level ridging, forecast to evolve across the eastern Pacific during the middle to latter portion of this week, will become increasingly suppressed by a series of significant short wave perturbations emerging from the upstream westerlies. Mid-level flow inland of the Pacific coast appears likely to become increasingly split, with a number of embedded progressive short wave perturbations. The northern branch is currently forecast to maintain a relatively low amplitude with a west-northwesterly component, to the southwest of an elongated deep vortex centered just north of Hudson Bay. Within the southern branch, it appears that relatively amplified mean troughing will develop across the Pacific Coast into the Great Plains. At the same time, subtropical ridging may become increasingly prominent across much of the Gulf of Mexico into the Southeast. This regime may become increasingly conducive to significant surface cyclogenesis to the lee of the southern Rockies by next Sunday/Monday, as boundary-layer moistening continues over the Gulf of Mexico (particularly the southwestern Gulf). Associated large-scale forcing for ascent and destabilization could support increasing severe thunderstorm potential across parts of the southern Great Plains into the middle/lower Mississippi Valley. However, much will hinge on the shorter wavelength developments, which are still fairly uncertain at this extended range. One particular concern is the timing of the northern branch short waves, and their associated southward surges of colder air to the lee of the Rockies, relative to the emerging southern branch short waves, which could displace and/or mitigate the risk for severe storms.
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