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Archives for the SPC Convective Outlook are updated daily (approximately) with a live map at the beginning of each article. Follow the link at the end of the article to check for current updates on the NOAA/NWS Storm Prediction Center website. Also, see Archives for Chicago's hourly weather data on CARDINAL NEWS Magazine.

Sunday, June 27, 2021

SPC Jun 27, 2021 1300 UTC Day 1 Convective Outlook

SPC 1300Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0741 AM CDT Sun Jun 27 2021 Valid 271300Z - 281200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE OZARKS TO PORTIONS OF LOWER MICHIGAN...AND OVER THE SOUTHERN NEW MEXICO/FAR WEST TEXAS REGION AROUND EL PASO... ...SUMMARY... Isolated severe thunderstorms may develop this afternoon into evening from the Ozarks to portions of Lower Michigan, and over the southern New Mexico/far west Texas region around El Paso. Damaging to severe gusts are the main threat in each area. ...Synopsis... The mid/upper-level pattern will continue to be characterized by an omega block over the West Coast States -- featuring a roughly 598-dm high at 50-mb over southern BC -- and an extensive, positively tilted mean trough from Hudson Bay across the northern Plains to NM and northwestern MX. A strong ridge will extend from another high offshore from the Mid-Atlantic region west-southwestward over the Tennessee Valley to the southern Plains' Red River region. Several convectively generated/enhanced vorticity lobes and small shortwaves will traverse the southwesterly flow between the southern High Plains and upper Great Lakes. At the surface, a low was analyzed at 11Z over the northern Lake Michigan area, with quasistationary to slow-moving cold front southwestward across southeastern IA, western MO, and the TX South Plains region, becoming a cold front over far west TX and northwestern Chihuahua. Except for minor mesobeta-scale oscillations, the front should move little through the period, outside backing westward across portions of AZ and adjoining northern MX. A series of outflow boundaries will persist south of the synoptic front from the southern Plains to Great Lakes. These boundaries and the front will combine to form a messy, ragged baroclinic zone aligned nearly parallel to the flow aloft, and continuing to support scattered to locally numerous thunderstorms. ...Ozarks to southern MI... Scattered thunderstorms are expected to develop today in this near- frontal corridor, offering locally damaging to marginally severe gusts from the most intense downdrafts. A couple of MCVs are apparent over western OK, in an ongoing area of clouds/precip extending into the western Ozarks. These should move northeastward toward/near the outlook area through the evening in support of additional convective potential. Also, though stronger mid/upper-level winds will lag the frontal zone to the west, the southeastern edge of at least marginally favorable flow aloft and deep shear will overlap the baroclinic zone across this corridor, perhaps with some reinforcement on smaller scales by weak southwest- flow perturbations. As such, a supercell or two may develop. Though diurnal heating will be muted somewhat by patchy cloud cover, a boundary-layer corridor characterized by upper 60s to low 70s F surface dew points still should warm enough to remove already weak MLCINH through early-mid afternoon. This will offset modest midlevel lapse rates enough to support 1000-1500 J/kg MLCAPE (locally/briefly peaking near 2000 J/kg). Any severe potential that does develop through the afternoon should wane with gradual evening diabatic cooling, given the lack of substantial deep forcing. ...Borderlands of far west TX/southern NM... Thunderstorms are expected in a wide swath southwest of the Ozarks area across much of OK, and northwest/west TX into the Desert Southwest. A severe gust cannot be ruled out anywhere in that corridor. However, a pocket of relatively maximized deep-layer instability and seasonally rich moisture may favor a better- organized threat of locally strong-severe gusts across parts of the Borderlands region surrounding ELP and LRU. Relatively cool midlevel temperatures are expected over this area, near the essentially collocated thermal and height troughs at 500 mb, with -9 to -10 deg C at that level and steep midlevel lapse rates. Under that, boundary-layer moisture will continue to be transported into this region from the east and northeast following frontal passage, with lower-elevation surface dew points commonly in the 50s to low 60s F. Diurnal heating will strengthen low-level lapse rates and foster a well-mixed subcloud layer -- despite the air mass being post-frontal -- while maintaining enough moisture for peak/preconvective MLCAPE to reach the 1000-1500 J/kg range. Though midlevel winds will be weak, the easterly low-level component, beneath 40-60-kt southwesterlies around 300 mb, will enable favorable cloud-layer shear for some storm organization. ..Edwards/Broyles.. 06/27/2021 Read more LIVE: