SPC Mar 7, 2018 Day 4-8 Severe Weather Outlook

By Newsroom America Feeds at 7 Mar 2018

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0356 AM CST Wed Mar 07 2018 Valid 101200Z - 151200Z ...DISCUSSION... Models indicate that the persistent blocking will continue this weekend into the middle of next week, and another deep closed low may eventually form over parts of the Northeast into the Canadian Maritimes. Upstream, it appears that there may be considerable amplification within a southern branch of split westerlies emanating from the mid-latitude Pacific, with large-scale troughing evolving across the eastern Pacific into the western U.S. and large-scale ridging across the Rockies into the Mississippi Valley. Preceding these developments, models continue to indicate that several short waves within the split streams will progress east of initial broad western U.S. upper ridging, before digging across the Plains toward the Southeast (to the west and south of an initial closed low departing the Northeast). There remains considerable spread among the model output concerning these features and possible associated frontal wave development across the interior southern United States. The GFS/GEFS continue to indicate a more amplified initial frontal wave developing near the southern Plains Red River Valley by early Saturday. However, even this guidance has trended toward suggesting little further deepening until the wave progresses off the south Atlantic coast. The ECMWF/ECENS maintain the forecast of a considerably lower amplitude wave, particularly after initial development over the southern High Plains. Given the evolving pattern, the more subdued wave development across the lower Mississippi Valley into the Southeast seems more probable at this time. Guidance does continue to indicate a rapid and fairly substantive return flow of moisture across the Texas coast into the Ark-La-Tex vicinity by Saturday. And it appears likely that this will contribute to a plume of weak to modest warm sector boundary layer instability beneath rather steep mid-level lapse rates due to differential thermal advection. However, it also appears that the bulk of the forcing for ascent may remain to the cool side of the developing warm front to the east of the low. And some model guidance continues to indicate that convective development near/offshore of the Gulf Coast could impact potential warm sector destabilization east of the Mississippi Valley. All of this leads to considerable lingering uncertainty concerning the location and/or extent of any severe weather potential. While it certainly remains at least possible that severe probabilities could increase across parts of the southeastern Plains into the Southeast in later outlooks for Saturday/Sunday, for now severe probabilities still appear to remain less than 15 percent. Read more



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