Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0759 AM CDT Sat Apr 29 2017 Valid 291300Z - 301200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS CENTRAL/NORTHEAST TX AND EASTERN OK TO OZARKS... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE SOUTHERN PLAINS TO THE OHIO VALLEY... ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE SOUTHERN PLAINS TO THE OHIO VALLEY AND MID-ATLANTIC STATES... ...SUMMARY... Severe thunderstorms are expected from parts of south central Texas northeastward to portions of the Ohio Valley and northern Middle Atlantic region, especially this afternoon and evening. These storms will be capable of large hail, damaging winds, and a few tornadoes. ...Synopsis... Within a highly amplified branch of southern-stream westerlies, a slow-moving closed trough over the southern Rockies will continue east-southeastward before turning more east-northeastward tonight as it spreads toward the southern High Plains. Ahead of this system, an increasingly moist air mass will continue to develop northward to the south of a convectively reinforced front extending from OK to the Ohio Valley and to the east of a southeastward-moving cold front across TX. ...Central/northeast TX and eastern OK/Ark-La-Tex... Extensive showers and thunderstorms will persist early today particularly along and north of a frontal zone across the region. Particularly given current advancing outflow across OK, there are some questions in regards to how many storms will form this afternoon within the pre-frontal/pre-outflow warm sector across eastern OK into AR and neighboring Ark-La-Tex vicinity. Although the boundary layer will be increasingly moist (lower 70s F surface dewpoints) with considerably eroding CINH, background forcing atop the warm sector will be weak while some mid-level warming may also occur through the afternoon, prior to the arrival of somewhat stronger forcing for ascent late this afternoon into tonight via the upstream trough. However, at least some pre-frontal development is plausible. If/where semi-discrete storms do form ahead of the front, low-level/deep-layer shear, characterized by strong (40+ kt) and modestly backed low-level winds beneath southwesterly mid-level winds, could support supercells capable of a tornado/large hail risk, particularly across eastern OK and northeast TX into parts of western AR/northwest LA. A more certain scenario will be for an intensification of storms along the cold front (augmented by outflow across parts of OK into north TX) by mid/late afternoon. Especially given a tendency for backing mid-level winds, any window for semi-discrete supercellular development should remain short-lived as a more mixed linear mode with embedded bows should evolve. Large hail and damaging winds will be possible, but some mixed-mode-related tornado risk may exist as well given the strength of low-level winds. Other severe storms capable of mostly severe hail/wind are expected by early/mid-evening as far south-southwest as the Edwards Plateau and Hill County vicinity of TX near the advancing front. ...Ozarks/Ohio Valley to Mid-Atlantic States/Delmarva... Corridors of eastward-moving precipitation including heavy rainfall and a few strong storms early this morning will continue to reinforce a generally west/east-oriented frontal zone from the Ohio Valley to the coastal Northeast States. A gradually abating low-level jet and moist conveyor, along with prevalent rising upper heights, may allow for some northward shift of the effective boundary and increasingly moist warm sector this afternoon. Regardless, one or more storm clusters ongoing across the lower/middle Ohio Valley early today could persist or reinvigorate in vicinity of the effective frontal zone toward PA/Delmarva vicinity with mainly a damaging wind risk. Other storms should diurnally intensify near the effective warm front from MO into IL with damaging winds and severe hail as the primary severe risks. ..Guyer/Dial.. 04/29/2017Read more
from SPC Forecast Products http://ift.tt/rATNzD
No comments:
Post a Comment