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Weather conditions on bar directly above are near Lakefront. Tabs under Moon Phases refer to O'Hare (official).

Archives for SPC Convective outlook are updated daily with a live map a the beginning of the article. Touch or click map to get possible update, and follow link at end of article for referral to NOAA/NWS Storm Prediction Center. Archives for Chicago's hourly weather data were updated 24-48 hours after end of each day prior to Dec. 2020.

Tuesday, July 12, 2022

SPC Jul 12, 2022 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0243 PM CDT Tue Jul 12 2022 Valid 122000Z - 131200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM EASTERN PENNSYLVANIA SOUTHWESTWARD TO NORTHERN VIRGINIA... ...SUMMARY... Thunderstorms capable of producing locally damaging winds are expected to continue from New England through the Mid-Atlantic States into the central Appalachian region and Tennessee Valley, this afternoon and early evening. A few strong storms may also be noted across the Upper Midwest and over the central High Plains. ...Discussion... Convection continues to evolve as expected/forecast per prior outlooks, with the only appreciable changes that appear necessary at this time are to adjust western portions of the thunder/severe risk areas to account for eastward advance of the cold front/convective initiation zone. Otherwise, severe risk remains greatest from New England across the central Appalachians, where a zone of storms continues to evolve at this time. Lesser risks persist across the Upper Mississippi Valley/western Upper Great Lakes area, and over parts of the central High Plains. ..Goss.. 07/12/2022 .PREV DISCUSSION... /ISSUED 1117 AM CDT Tue Jul 12 2022/ ...Appalachians/Mid-Atlantic/Northeast this afternoon/evening... No changes to the previous outlook. Within a broad midlevel trough over the Great Lakes, an embedded speed maximum will eject eastward/northeastward from the central Appalachians/lower Great Lakes to the Mid-Atlantic and New England this afternoon/evening, as an associated surface cold front likewise moves eastward/southeastward from the upper OH Valley and western PA/NY. Destabilization will proceed from west-to-east through the afternoon in advance of the front in conjunction with low-level moisture advection and surface heating, and visible satellite imagery suggests that multiple cells/small clusters will form along and ahead of the cold front by early-mid afternoon from central PA/NY eastward. MLCAPE of 1000-2000 J/kg and relatively long/straight hodographs with effective bulk shear of 35-50 kt is expected from the Mid-Atlantic northward, along with DCAPE near 1000 J/kg. The near-storm environment and expected convective mode will favor clusters and supercells capable of producing damaging winds, though isolated large hail and an isolated tornado or two may also occur with the strongest storms. Some upscale growth into line segments will be possible, which would favor damaging winds as the primary threat. ...Ozarks to TN Valley this afternoon through late evening... Vertical shear will weaken with southwestward extent along a cold front moving slowly southward into TN/AR. Surface temperatures will warm into the 95-100 F range by late afternoon, with steep low-level lapse rates and moderate buoyancy immediately ahead of the front. Widely scattered thunderstorm development is expected by late afternoon/evening along the front, and the strongest storms will be capable of producing isolated strong/damaging downburst winds from late afternoon into this evening. ...Central High Plains this evening... Boundary-layer dewpoints in the mid-upper 50s reside across eastern CO as of mid morning, though some vertical mixing is expected this afternoon along with strong surface heating. A few high-based storms are expected to form late this afternoon/evening immediately east of the higher terrain, along a developing surface lee trough from southeast WY into northeast CO. Deep-layer northwesterly shear will be sufficient for some storm organization/supercell structures, while the steep lapse rates and modest buoyancy support the threat for isolated strong-severe outflow winds and marginally severe hail for a few hours late this afternoon/evening. ...MN/WI this afternoon/evening... An embedded shortwave trough will move southeastward from southern MB/far western ON across northern MN and WI through this evening. Surface heating and residual low-level moisture, beneath cool midlevel temperatures (near -15 C at 500 mb), will result in MLCAPE of 500-1000 J/kg this afternoon with minimal convective inhibition. Thus, scattered thunderstorm development is expected from northeast MN into northern WI, where the modest buoyancy and deep-layer west-northwesterly shear will be sufficient for clusters and low-end supercells capable of producing marginally severe hail and outflow gusts for a few hours later this afternoon/evening. Read more CHECK UPDATE ZOOM GRAPHIC