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Sunday, July 11, 2021

SPC Jul 11, 2021 0730 UTC Day 3 Severe Thunderstorm Outlook

SPC 0730Z Day 3 Outlook Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0225 AM CDT Sun Jul 11 2021 Valid 131200Z - 141200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS TUESDAY INTO TUESDAY NIGHT ACROSS PARTS OF SOUTHEAST LOWER MICHIGAN...NORTHERN OHIO AND PENNSYLVANIA...INTO WESTERN AND CENTRAL NEW YORK STATES...AS WELL AS PARTS OF SOUTHEASTERN WYOMING...MUCH OF NEBRASKA AND ADJACENT PORTIONS OF SOUTHERN SOUTH DAKOTA... ...SUMMARY... Strong thunderstorms may impact parts of the lower Great Lakes region, and parts of the central Great Plains through adjacent portions of the middle Missouri Valley, Tuesday into Tuesday night, accompanied by at least some risk for severe weather. ...Synopsis... Prominent mid-level ridging may maintain considerable influence along much of the Atlantic Seaboard through this period, while another mid-level high, initially centered over the southern Great Basin, undergoes considerable weakening. The more prominent westerlies will remain confined to latitudes near/north of the Canadian/U.S. border, and generally zonal. One of the more significant embedded perturbations is forecast to gradually dig east-southeastward across southern Hudson Bay and northwestern Ontario Tuesday through Tuesday night. As it does, the increasingly sheared remnants of troughing emerging from the Mississippi Valley are forecast to gradually shift across and northeast of the Great Lakes region. Forcing for ascent associated with a remnant embedded cyclonic circulation may support modest surface cyclogenesis south through southeast of James by the end of the period. In its wake, another modest short wave trough may dig to the east of the northern Rockies, into a more zonal remnant weaker belt of westerlies extending across the north central and northeastern tier of the United States. ...Parts of central Great Plains and adjacent mid Missouri Valley... In the wake of the short wave within the main belt of westerlies, and ahead of the trailing wave digging across/east of the northern Rockies, a plume of steep lapse rates associated with elevated mixed-layer air may become suppressed southward across northern portions of the central Great Plains. However, beneath it, during the day Tuesday, a zone of stronger differential surface heating may become a focus for destabilization and increasing thunderstorm development, somewhere across northern/central Nebraska into southeastern Wyoming. Aided by forcing for ascent and strengthening shear associated with the approaching short wave and mid-level speed maximum, the environment may become conducive to evolution of one or two east-southeastward propagating storm clusters. Isolated supercells appear possible initially, particularly across parts of southeastern Wyoming into the Nebraska Panhandle. These may be accompanied by a risk for severe hail and perhaps a couple of tornadoes, before strong wind gusts become the more prominent hazard in upscale growing convection. ...Lower Great Lakes vicinity... The southern periphery of the lower/mid-level troughing generally shifting to the north of the international border may become a focus for scattered strong to severe storm development Tuesday afternoon and evening. Lapse rates will likely remain generally weak, but a deep moist boundary layer may still support moderate CAPE (1000-2000 J/kg), in the presence of at least modest shear associated with a belt of 30+ kt southwesterly flow in the 700-500 mb layer. ..Kerr.. 07/11/2021 Read more LIVE: spc.noaa.gov
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