SPC Apr 21, 2017 Day 4-8 Severe Weather Outlook

By Newsroom America Feeds at 21 Apr 2017

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0346 AM CDT Fri Apr 21 2017 Valid 241200Z - 291200Z ...DISCUSSION... ...Monday/Day 4... The medium-range models begin the Day 4 to 8 period with an upper-level low over northern Georgia and move this feature to the east coast on Monday/Day 4. Thunderstorm development will be possible during the day across parts of the eastern Carolinas. ...Tuesday/Day 5... Both the ECMWF and GFS advect moisture into eastern parts of the Great Plains on Tuesday/Day 5 and move a relatively low-amplitude upper-level trough across the region. Although a localized severe threat would be possible across parts of the southern Plains Tuesday afternoon and evening, any convective development should remain very isolated. ...Wednesday/Day 6... Both the ECMWF and GFS continue moisture advection across the south-central U.S. as an upper-level trough moves into the Four Corners region on Wednesday/Day 6. Both models place an axis of instability by afternoon across east Texas extending north northeastward into the Ozarks. If this pattern materializes, severe thunderstorms will be possible along the northern part of the instability corridor in the Ozarks and mid Mississippi Valley on Wednesday afternoon and evening. ...Thursday/Day 7... The ECMWF and GFS differ in their solutions on the shortwave trough positions for Thursday/Day 7. The ECMWF develops a negatively tilted shortwave trough over the central Plains while the GFS maintains southwesterly flow across the central U.S. If the ECMWF were to verify, a cluster of severe storms would be possible across eastern parts of the central Plains eastward into the mid Mississippi Valley. Predictability remains low due to differences in model solutions concerning smaller-scale features. ...Friday/Day 8... The ECMWF and GFS are in better agreement in the western U.S., developing a vigorous upper-level trough in the Four Corners region. This coincides with strong moisture advection across the Great Plains. The synoptic setup which the medium-range models have been forecasting for a couple days, could result in a significant severe weather event on Friday into Friday night across parts of the southern and central Plains with tornadoes, large hail and wind damage possible. Due to the potential for a higher-end event on Friday, have added a 15 percent contour where model consensus places the greatest chance of severe weather. Read more



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