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Friday, May 14, 2021

SPC May 14, 2021 1630 UTC Day 1 Convective Outlook

SPC 1630Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1125 AM CDT Fri May 14 2021 Valid 141630Z - 151200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON AND EVENING ACROSS PARTS OF EASTERN COLORADO INTO SOUTHWESTERN NEBRASKA...WESTERN KANSAS AND THE TEXAS/OKLAHOMA PANHANDLE VICINITY... ...SUMMARY... Strong to severe thunderstorm development is expected this afternoon and evening, east of the southern Rockies into parts of the central and southern Great Plains. Some of these may pose a risk for large hail and strong wind gusts. ...Synopsis... Much of southern Canada and the U.S. remains under the influence of split branches of west-northwesterly mid/upper flow, and models indicate that a more prominent split will continue to evolve inland of the Pacific coast through this period. To the east of building ridging over the eastern Pacific, a short wave trough (in the southern branch) is forecast to amplify and dig toward the California coast, to the south of ridging (in the northern branch) building inland across British Columbia. Downstream of the digging trough, broad mid-level ridging will be maintained across the eastern Great Basin into the central Great Plains. However, mid-level troughing within a branch of westerlies emanating from the subtropical eastern Pacific is forecast to progress across Baja, northwestern Mexico and adjacent portions of the Southwest, preceded by a more subtle perturbation or two across the southern Rockies and southwestern Texas. 

Downstream, flow remains broadly confluent, but models indicate that the most pronounced confluence will begin to shift east of the Atlantic Seaboard. As this occurs, the center of expansive surface ridging is forecast to continue to slowly weaken while shifting east of the Mississippi Valley, into the vicinity of the Appalachians by late tonight. However, potentially cold/dry air associated with this feature will continue to spread southeast of the northern/eastern Gulf of Mexico, and through much of the remainder of the Florida peninsula by the end of the period. 


In response to the evolving upstream mid/upper flow, surface troughing is forecast to deepen to the immediate lee of the southern Rockies through tonight. Various model output suggests that strongest pressure falls may become focused either side of the Raton Mesa vicinity, where a low may develop by late tonight. In response to associated strengthening southerly low-level flow across the southern high plains, seasonably modest moisture return is expected to continue to gradually develop northward from the lower Rio Grande Valley. This may include surface dew point increases into the mid/upper 50s as far north as the western Kansas vicinity by late this afternoon. Beneath steep lower/mid tropospheric lapse rates associated with elevated mixed-layer air advecting east of the southern Rockies, the moisture return probably will become sufficient to contribute to thermodynamic profiles supportive thunderstorms capable of producing large hail and strong surface gusts. ...

Southern Rockies into adjacent Great Plains... A combination of moistening upslope flow, broad low-level convergence and low/mid-level warm advection appear likely to focus the most widespread thunderstorm development from the Front Range vicinity into the adjacent central Great Plains late this afternoon into tonight. This may be aided by a number of smaller-scale perturbations progressing around the broad mid-level ridging. A couple of fairly prominent impulses are already progressing east of the middle Missouri Valley, with another couple shifting east of the northern Rockies/Front Range. In response to these developments, there may be some southward shift of the leading (northeastern) edge of the plume of elevated mixed-layer air emanating from the southern Rockies/Plateau region. A developing zone of stronger differential surface heating beneath this feature may provide one, if not the primary, focus for upscale growing convection by this evening, from parts of northeastern Colorado into northwest and west central Kansas. Despite the seasonably modest, though improving, low-level moisture return, the steep lapse rates may support mixed-layer CAPE on the order of 1000-1500 J/kg by late afternoon. Aided by favorable vertical shear beneath 30-40+ kt northwesterly flow around 500 mb, the environment probably will become conducive to widely scattered to scattered storms capable of producing severe hail and locally strong surface gusts. Congealing surface cold pools may contribute to upscale growing, southeastward propagating storm clusters, with strong wind gusts becoming the primary hazard before diminishing around mid evening with the loss of daytime heating. ..Kerr/Lyons.. 05/14/2021 Read more LIVE: spc.noaa.gov
http://dlvr.it/RzfK4x


NWS SPC Convective Outlook provided by Arlingtoncardinal.com/weather

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