Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0358 AM CDT Fri Oct 16 2020 Valid 191200Z - 241200Z ...DISCUSSION... ...Monday/Day 4 to Tuesday/Day 5... An upper-level trough is forecast to move eastward across the central United States on Monday as a cold front advances southeastward into the mid Mississippi and Ohio Valleys. The medium-range models are suggesting potential for thunderstorm development ahead of the front Monday afternoon and evening. At this time, instability is forecast to be weak ahead of the front which would limit the potential for severe storms. On Tuesday, the central U.S. upper-level trough is forecast to move into the Mississippi Valley as the front advances southward into the Southeast. As a large area of high pressure moves into the eastern states, moisture return will be possible across the southern Plains. Although the models are forecasting moderate instability across parts of Texas, capping and weak deep-layer shear should keep any severe threat marginal across Texas Tuesday afternoon and evening. ...Wednesday/Day 6 to Friday/Day 8... On Wednesday, the medium-range models maintain a large-scale upper-level trough across the Mississippi Valley. A moist airmass is forecast to advect northward from the Arklatex to the lower Ohio Valley. Convective development will be most likely along the instability gradient from the central Plains east-northeastward into northern sections of the Ohio Valley. An isolated severe threat will be possible along this corridor. The same general area is forecast to have a continued chance of storms on Thursday as an upper-level trough moves into the Great Plains. The ECMWF and GFS are in good agreement with the timing of the system and placement of the moist axis. Thunderstorms would be most likely Thursday evening from Oklahoma northeastward into Missouri, Illinois and Indiana. Although a severe threat will be possible Thursday afternoon and evening, the models suggest that the strongest instability will be located to the southwest of the stronger mid-level flow. For this reason, predictability is low concerning the magnitude and spatial distribution of a severe threat Thursday afternoon and evening. On Friday, the models move an upper-level trough eastward across the Great Lakes as a cold front advances quickly eastward into the eastern U.S. Thunderstorm development will be possible along the front during the day extending into the overnight period. However, instability is forecast to be weak which should keep any severe threat isolated. In any case, uncertainty is substantial late in the day 4 to 8 period.
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