Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0342 AM CST Sat Jan 23 2021 Valid 261200Z - 311200Z ...DISCUSSION... Medium-range models are in reasonable agreement with respect to evolution of large-scale features through Day 6, after which divergence in solutions increases through the end of the period. Even early on in the period, however, differences at smaller scales -- particularly with an upper short-wave trough ejecting from the Southwest across the southern tier of the U.S. during the first half of the period -- complicate assessment of convective potential. Models generally agree in the maintenance of persistent western U.S. upper troughing, with the aforementioned short-wave feature progged to eject eastward, crossing the Four Corners states and eventually emerging into the central/southern Plains Day 4 (Tuesday). By Day 5 (Wednesday), as the feature shifts across the Mid and lower Mississippi Valley and then the Mid South and central Gulf Coast states, surface cyclogenesis is expected to occur. With the GFS stronger/sharper with the upper feature, stronger surface cyclogenesis is depicted, with a deepening low over the Tennessee Valley area by Wednesday evening, while the weaker ECMWF solution places a much weaker low over the southern Alabama/southern Georgia vicinity. In either case however, it appears likely that the boundary layer will remain stable, as a strong baroclinic zone over the northern Gulf of Mexico just ahead of this system will likely be slow to retreat northward. Thus, severe weather is not expected with this system. As the system moves offshore Day 6 (Thursday), large-scale ridging will prevail over much of the country, ahead of re-establishment of western U.S. troughing. Therefore, severe weather is not expected Thursday, and then beyond which pattern predictability diminishes steadily through the end of the period.
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