Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0350 AM CDT Sun Apr 18 2021 Valid 211200Z - 261200Z ...DISCUSSION... Low/mid-level winds will likely strengthen across the Mid-Atlantic and Northeast on Day 4/Wednesday as an upper trough moves eastward across these regions. There is still some uncertainty regarding how much low-level moisture will be present ahead of a cold front. If enough boundary-layer instability develops by Wednesday afternoon, then strong/damaging winds appear possible with any storms that can develop along or ahead of the quickly moving front. At this point, confidence in organized severe convection producing a swath of damaging winds remains too low to introduce 15% severe probabilities. Still, some severe risk appears possible from roughly eastern NC to southern NY, and this region may need to be included in low severe probabilities in a subsequent outlook. Low-level moisture return should begin to occur on Day 5/Thursday across parts of the southern Plains as another upper trough develops eastward across the Southwest and northern Mexico. There are still substantial differences in medium-range guidance regarding the evolution of this upper trough as it ejects over the southern Plains on Day 6/Friday. Depending the on quality and northward extent of the low-level moisture return, enough instability may be present to the east of cold front and dryline to support organized severe storms Friday across part of the southern Plains. If a more progressive and amplified upper trough develops eastward as indicated by some deterministic guidance, then a severe risk may also occur across parts of the Southeast next weekend. Regardless, far too much uncertainty remains regarding the timing/amplitude of the upper trough and placement of related surface features to include any severe probabilities at this extended time frame.
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