Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0544 AM CST Sun Jan 24 2021 Valid 271200Z - 011200Z ...DISCUSSION... Latest runs of the medium-range models show fair model-to-model agreement with respect to large-scale features into Day 6 (Friday Jan. 29), though even larger-scale similarities between models fade further into the second half of the period. This increasing large-scale disagreement centers around timing of the ejection of a short-wave trough across the southwestern U.S. Day 6, and then into/across the central U.S. Day 7. Depending upon evolution of this feature, convective potential could increase over the south central and later the southeastern U.S. during the second half of the period. However, predictability concerns in this time frame preclude any further assessment of convective potential. Prior to this, through the first half of the period, a short-wave trough is forecast to move from the central/southern Plains region at the beginning of the period (Wednesday Jan. 27), to the East Coast states by the start of Day 5. Slight differences in the strength of this feature between the GFS and ECMWF result in more notable deviations in depiction of associated surface low intensity, with the GFS more aggressive in terms of surface cyclone development over the southern Appalachians area, and thus more bullish with respect to convective potential. With the ECMWF showing a much more muted frontal wave much farther south -- shifting from the Gulf Coast to the southeast Georgia coast -- confidence remains too low to render a more thorough assessment. As this upper feature moves offshore Day 5, strong cyclogenesis is progged over the Gulf Stream/western Atlantic, with cold high pressure building southward in its wake, across the eastern half of the country -- in tandem with large-scale ridging/anticyclonic flow across most of the CONUS.
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