SPC Mar 20, 2017 Day 4-8 Severe Weather Outlook

By Newsroom America Feeds at 20 Mar 2017

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0328 AM CDT Mon Mar 20 2017 Valid 231200Z - 281200Z ...DISCUSSION... ...Day 4 to Day 6... The medium-range models begin the day 4 to 8 period with an upper-level ridge in the central U.S. and an upper-level trough over Baja California. This system is forecast to move quickly northeastward across the Desert Southwest and into the southern Rockies on Thursday/Day 4. A dryline is forecast to setup in the southern and central High Plains by late afternoon where isolated severe thunderstorms will be possible into the evening. However, will not add a severe threat area yet due to uncertainties concerning the quality of moisture return and exact timing of large-scale ascent entering the high Plains Thursday evening. The dryline is forecast to sharpen on Friday/Day 5 and move eastward across the southern Plains during the day. The best chance for thunderstorm initiation would be in the late afternoon from east-central Oklahoma south southwestward into the north-central to northeast Texas. The ECMWF and GFS solutions are in good agreement with this scenario and the models provide support for the idea of a line of thunderstorms organizing into a wind producing linear MCS. If this where to occur based on the timing of the models, a line of storms would move east southeastward across the Arklatex Friday evening, into the lower Mississippi Valley overnight crossing the central Gulf Coast States during day on Saturday/Day 6. Based on this scenario, will maintain a 15 percent contour from eastern parts of the southern Plains into the Arklatex. Will expand this area eastward into the lower Mississippi Valley and add a new 15 percent contour in the central to eastern Gulf Coast States for Day 6. ...Day 7 to Day 8... On Sunday/Day 7 and Monday/Day 8, large differences exist between the ECMWF and GFS solutions. The ECMWF emphasizes the development of a negatively tilted upper-level trough in the southern and central Plains while the GFS emphasizes the upper-level trough just upstream from the Carolinas. A severe threat could develop ahead of either of these two systems. However, due to large model differences, uncertainty is too great to warrant adding a 15 percent area late in the forecast period. Read more



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