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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.


Friday, April 28, 2023

SPC Apr 28, 2023 0600 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 1200Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1255 AM CDT Fri Apr 28 2023 Valid 281200Z - 291200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS CENTRAL TEXAS... ...SUMMARY... Scattered storms are forecast to produce damaging hail and severe winds from late afternoon through evening from north-central Texas to the middle and lower Rio Grande Valley. Isolated strong to severe storms may also occur over parts of the Southeast into the central Appalachians. ...Synopsis... Latest water-vapor imagery and analyses depict a mid-level shortwave trough undergoing slight deepening over the central Rockies. This is within a strong cold advection regime, behind a southward-surging cold front over the Rockies and central High Plains. Both of these features are expected to continue southward over the next 24 hours, with the upper trough likely reaching northern Mexico and the attendant cold front sweeping into central TX by around 21 UTC this afternoon. Additionally, a second, less intense, upper perturbation is noted over the mid-MS Valley migrating to the east/northeast. A weak surface low associated with this feature is forecast to lift into parts of the upper OH Valley, with modest lee cyclogenesis east of the Appalachians. Thunderstorm development under the upper low and in the vicinity of the lee low appears probable around peak heating. ...Central to southern Texas... 00 UTC soundings from across the High Plains/Rockies sampled steep mid-level lapse rates in excess of 8 C/km. This corroborates recent RAP analysis that show the lapse rate plume extending over NM into west TX. Northwesterly 700-500 mb mean flow will advect these lapse rates into central TX over the next 12-18 hours. At the surface, modest moisture advection is occurring over central TX to the coastal plain, amid weak surface pressure falls over west TX. Mid 50s to low 60s dewpoints should migrate into central TX by early afternoon. This moisture return will become more pronounced through the morning hours as the surface low deepens, and shifts eastward in tandem with the approaching upper wave. This combination of increasing low-level moisture and steepening mid-level lapse rates should establish a corridor of 3000-3500 J/kg MLCAPE from southern to central TX by early to mid afternoon. The positive tilt of the upper trough over southern NM will spread 50-60 knot zonal mid-level winds over the warm sector, with effective bulk shear values approaching 50 knots. Diurnal warming, combined with broad ascent in the vicinity of the surface low over central TX, may allow for convective initiation as early as 18-20 UTC, near a diffuse triple point and/or along a sharpening dryline roughly parallel with the I-35 corridor. Initial storm modes will likely be discrete supercells, given favorable flow orientation away from the zone of initiation and elongated hodographs. These early cells will pose a risk for large to very large (2+ inch) hail as well as a tornado threat - especially in the vicinity of the surface warm front where low-level helicity will be maximized. However, the window/longevity for discrete supercells is uncertain. Recent surface observations across the High Plains show a faster frontal progression than depicted by most guidance. As such, the arrival of the cold front into central TX may foster rapid upscale growth into a squall line faster than expected by 00z CAMs. The primary hazard is expected to quickly transition to severe wind once the MCS becomes established and propagates southeastward towards the TX Coastal Plain. A strong line-orthogonal deep-layer shear component suggest this MCS may be fairly progressive and capable of a few 75+ mph wind gusts. However, the eastward and westward extent of the wind threat is uncertain, given a tight buoyancy gradient across east TX and the potential for frontal undercutting across south-central TX. ...Upper OH River Valley to the Mid-Atlantic... Daytime heating under the upper-low should bolster MLCAPE values to 500-1000 J/kg across the upper OH Valley region and into the Mid-Atlantic by peak heating this afternoon. While mid-level lapse rates will be meager, deep-layer shear values on the order of 25-30 knots should support some storm organization with an attendant hail/damaging wind threat. Damaging gusts may be more common across parts of the Mid-Atlantic where daytime highs in the mid 70s will support steep lapse rates in the 0-1 km layer that may allow for more efficient downdraft acceleration. ...Florida... A convective cluster ongoing over the central Gulf of Mexico is forecast to migrate eastward, reaching the FL Peninsula by around 12 UTC. Diurnal warming ahead of this cluster of storms should support increasing buoyancy with MLCAPE values reaching near 1500 J/kg by mid-afternoon. 30-40 knot mid-level flow on the southern periphery of the eastern wave will allow for some elongation of the deep-layer hodograph conducive for some organization of semi-discrete cells/clusters. The threat for severe hail/damaging winds will likely be greatest across the eastern FL coast, where diurnal warming will be maximized ahead of any convection. ..Moore/Darrow.. 04/28/2023 Read more CHECK UPDATE ZOOM GRAPHIC
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