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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.

Saturday, July 31, 2021

SPC Jul 31, 2021 1630 UTC Day 1 Convective Outlook

SPC 1630Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1129 AM CDT Sat Jul 31 2021 Valid 311630Z - 011200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PORTIONS OF THE MID-MS VALLEY... ...SUMMARY... Scattered damaging wind gusts and a brief tornado are possible across a portion of the Mid-Mississippi Valley through this afternoon. A tornado and locally damaging winds are possible during the early morning tomorrow in the central to southeast Virginia vicinity. ..Mid-MS/Lower OH Valleys to south-central Great Plains... Southwest portion of a remnant MCS over southeast MO may intensify as it spreads southeast along the instability gradient across the Mid-MS/Lower OH Valleys. This cluster should be fed by an influx of rich boundary-layer moisture from the west across southern MO and AR. The STL VWP sampled 45-60 kt 3-6 km AGL flow attendant to the MCV that is currently centered south of SPI. As further boundary-layer heating and moistening occurs, potential will exist for intensification of this cluster which could result in a spatially confined swath of damaging winds into parts of western KY/TN. CAM guidance varies greatly with evolution of this cluster, rendering below-average confidence in this scenario occurring. Farther west, isolated to scattered thunderstorms should develop along the trailing outflow/effective cold front across southwest MO and southern KS to a weak upslope regime near the Raton Mesa. While deep-layer shear will be weak, deeply mixed thermodynamic profiles with hot temperatures south of the front will support sporadic severe wind gusts from downbursts. Have maintained cat 1/MRGL risk given the limited potential for storm- to meso-scale organization. ...Central to southeast VA... At least isolated thunderstorms should develop across the region between 09-12Z tonight. Some of this activity may pose a threat for a tornado and locally damaging winds, constituting the earliest stage of the following convective day's severe threat regionally; see the SWODY2 for more details past 12Z. The MCV/embedded mid-level speed max over IL should quickly progress east towards the Lower Mid-Atlantic region overnight with weak height falls spreading overhead. Meanwhile, low-level lift will increase during the early morning, near an inverted trough and northward-bulging, surface frontal inflection area. Along and south of the front, moisture advection will yield upper 60s to low 70s surface dew points yielding potential for surface-based inflow parcels. However, low to mid-level lapse rates should remain weak, resulting in only thin buoyancy. Nevertheless, pronounced veering with height of wind profiles should yield around 35-45-kt effective-shear magnitudes, along with a modestly enlarged low-level hodograph. ...Western Upper Great Lakes... Isolated to scattered thunderstorms should develop later this afternoon along/ahead of a reinforcing southeast-moving cold front. While boundary-layer temperatures/dew points will be seasonally subpar, relatively cool mid-level temperatures should yield a plume of modest MLCAPE from 500-1500 J/kg by late afternoon. Low-level winds will remain predominately westerly, limiting effective shear magnitudes. But sufficient speed shear with height should prove favorable for multicell clustering through about sunset, offering a risk of marginally severe hail and isolated damaging wind gusts. ...Coastal Carolinas... At least isolated thunderstorms should develop along sea-breeze boundaries and an area of weak confluence upstream across central SC. Rather rich boundary-layer moisture characterized by 75-80 F surface dew points will support large buoyancy. However, weak deep-layer flow and lack of substantial vertical shear should limit both duration and organization of the severe threat. As such, sporadic wet microbursts producing locally damaging winds will be the primary threat. ..Grams/Mosier.. 07/31/2021 Read more LIVE: spc.noaa.gov