SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1129 AM CST Fri Jan 29 2021 Valid 301200Z - 311200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SATURDAY AFTERNOON INTO SATURDAY EVENING ACROSS PARTS OF EASTERN OKLAHOMA THROUGH NORTHERN ARKANSAS AND SOUTHERN MISSOURI... ...SUMMARY... An isolated strong thunderstorm or two may impact a narrow corridor across parts of eastern Oklahoma through northern Arkansas and southern Missouri Saturday afternoon and evening, accompanied by at least some risk for severe weather. ...Synopsis... Ongoing amplification within the westerlies across the central into eastern mid-latitude Pacific appears likely to begin translating inland across western North America during this period. This is forecast to include the continuing evolution of deep large-scale mid-level troughing across the eastern Pacific (generally just west of the Pacific coast), and building large-scale ridging across the U.S. Intermountain West and Rockies. As this occurs, an initially vigorous short wave impulse, to the lee of the southern Rockies by 12Z Saturday, is forecast to continue an east-northeastward acceleration. However, models indicate at least some weakening is possible as it progresses into a broadly confluent regime between low amplitude downstream ridging overspreading the south Atlantic coast and the western flank of remnant large-scale troughing shifting east of the Atlantic Seaboard. It does appear that the perturbation will be accompanied by a significant surface cyclone emerging from the high plains of southeastern Colorado. And guidance indicates that this may include a period with at least some further deepening as it migrates across the Kansas/Oklahoma border vicinity into the lower Missouri Valley. In the wake of a recent cold intrusion, boundary-layer moistening may be underway across much of the southwestern Gulf of Mexico by early Saturday, and continue through the period across much of the remainder of the Gulf. However, this may still be fairly modest, with deepest inland boundary-layer moistening confined to southeast Texas through the lower Mississippi Valley, with surface dew points in the mid 50s to around 60F. ...Southern Great Plains into Ohio Valley... Potential for thunderstorm activity is expected to initially be in association with elevated moisture return (of lower latitude eastern Pacific origin) and destabilization, supported by strong large-scale forcing for ascent downstream of the progressive short wave trough. Lower/mid tropospheric warm advection, beneath divergent high-level flow, may be contributing to this early, across Oklahoma and adjacent portions of the Great Plains/Ozark Plateau. It appears that this may diminish during the day, with probabilities for renewed thunderstorm development becoming focused near the compact mid-level cold core (including 500 mb temps of -20 to -25 C). This is expected to spread across parts of the lower Missouri Valley and Ozark Plateau by Saturday evening. It might not be out of the question that convection capable of producing lightning could continue east-northeastward in a corridor along the Ohio River Saturday night, but this potential becomes more unclear due to model spread. The stronger mid-level cooling, to the north of an initially intense mid-level jet (around 100 kt at 500 mb), appears likely to spread to the north of the better warm sector boundary-layer moistening, with warm mid-levels to the south of the jet capping convective development. However, early day precipitation will contribute to boundary-layer moistening in advance of the cold pool, and forecast soundings suggest potential for weak boundary-layer destabilization with some insolation beneath a developing dry slot. Current model output suggests this is most probable along a corridor across east central Oklahoma through north central Arkansas/south central Missouri Saturday afternoon into early Saturday evening. However, given spread evident among the model output, this axis could be displaced at least somewhat to the north or south. Regardless, given the potential for a developing narrow corridor of at least weak boundary-layer destabilization, vigorous thunderstorm development appears possible in the presence of strong deep-layer mean wind fields and vertical shear. It appears that this will include 50-70 kt southwesterly to westerly flow in the 850-700 mb layer, which could support a small organized cluster and/or isolated supercell structure or two, accompanied by the risk for damaging wind gusts and perhaps an isolated tornado. ..Kerr.. 01/29/2021
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