SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0131 PM CST Tue Dec 29 2020 Valid 292000Z - 301200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS CENTERED OVER PORTIONS OF NORTHWESTERN TEXAS AND SOUTHWESTERN OKLAHOMA... ...SUMMARY... A couple storms producing marginally severe hail are possible this evening into early tonight across a portion of northwest Texas into southwest Oklahoma. ...Discussion... No changes to the ongoing outlook are necessary at this time. ..Goss.. 12/29/2020 .PREV DISCUSSION... /ISSUED 1012 AM CST Tue Dec 29 2020/ ...Northwest TX and far southwest OK... A shortwave trough just off the southern CA coast will dig southeast and reach the southern Gulf of CA overnight, while a northern-stream shortwave trough moves east-southeast from southern Saskatchewan to MN. In the wake of the northern-stream wave, a cold front will surge into the southern Great Plains this evening through the overnight. The northwest extent of low to mid 50s boundary-layer dew points are already prevalent from the Permian Basin into southwest OK, and will gradually moisten into the mid to upper 50s amid persistent surface south-southeasterlies. By late afternoon, a dryline should take shape across west TX, intersecting with a slow-moving warm/quasi-stationary front near the southern TX Panhandle that should extend northeast across western OK. The HRRR appears more aggressive than other CAM guidance with convective development along the dryline and front during the early evening as its parent RAP depicts greater surface-based buoyancy than the NAM. A somewhat more probable scenario is for convective development tonight as the High Plains frontal surge impinges on the richer low-level moisture, predominately rooted above the surface. Strong speed shear within the cloud-bearing layer may prove favorable for at least transient mid-level updraft rotation in a few cells. Weak MUCAPE and moderate mid-level lapse rates will probably limit hail size between small to marginally severe magnitudes.
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