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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.

Monday, July 17, 2023

SPC Jul 17, 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 1241 AM CDT Mon Jul 17 2023 Valid 171200Z - 181200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE BLACK HILLS VICINITY INTO NEBRASKA...AND ACROSS THE LOWER OHIO VALLEY... ...SUMMARY... Severe storms producing large hail and damaging gusts are expected from the Black Hills area southeastward into northern Nebraska this evening into tonight, and across portions of the Lower Ohio Valley vicinity this afternoon. More isolated strong to severe thunderstorms are possible across parts of the northern Great Basin/northern High Plains vicinity, the Ozark Plateau, and the Upper Ohio Valley. ...Synopsis... An upper ridge centered over the northern Rockies this morning will deamplify as it shifts east in response to a Pacific Northwest shortwave trough progressing eastward along the international border through Tuesday morning. Further east, an upper trough oriented over the Midwest to the TN Valley will pivot slowly east. Moderate west to northwest mid/upper flow will overspread the northern/central Plains and much of the Midwest vicinity, while numerous vorticity maxima migrating through this broad area of northwest flow will provide focus for areas of strong to severe thunderstorms. The most likely area of organized severe storms existing across parts of northeast WY into SD/NE and the Lower OH Valley vicinity. ...Ohio Valley vicinity... A seasonally moist airmass will be in place beneath moderate mid/upper west/northwesterly flow. A surface cold front is forecast to sag southward across MO/IL/IN/OH during the afternoon and evening. The sagging surface front and convectively enhanced vorticity maxima migrating through the mid/upper trough will focus thunderstorm development as diurnal heating aids in moderate to strong destabilization from southeast MO to southwest OH. Low-level winds are expected to mostly be southwesterly, limiting directional shear. However, speed shear will result in effective bulk shear magnitudes around 40 kt. A mix of discrete cells and clusters are expected. Steep low-level lapse rates will aid in strong outflow and damaging gusts are expected, especially with any organizing clusters. Otherwise, isolated cells may be capable of producing large hail with forecast soundings indicated midlevel lapse rates around 7-7.5 C/km and elongated hodographs. With east and northward extent along the Upper Ohio Valley vicinity, effective shear and instability weakens. However isolated strong storms producing marginal hail and strong gusts are possible across much of Ohio into western PA. ...Black Hills into Nebraska... A deepening lee trough ahead of the northern Rockies upper trough will result in moist upslope flow into the Black Hills/northeast WY/southeast MT vicinity. Thunderstorms are expected to develop by late afternoon in a moderately unstable and strongly shear environment. These initial supercells may be elevated. However, steep midlevel lapse rates and long, straight hodographs suggest large to very large (greater than 2 inch diameter) hail is possible. With time, and as a low-level jet strengthens during the evening, upscale development into a bowing MCS is possible as convection track southeast into northern/northeastern NE. A swath of damaging gusts may accompany this MCS during the evening and overnight hours. ...Northern Great Basin into Central/Eastern Montana... Moderate to strong west/southwest mid/upper flow will overspread the region ahead of the northern Rockies trough. Meanwhile, steep midlevel lapse rates and pockets of midlevel moistening will support MLCAPE around 500-1250 J/kg. A well mixed boundary-layer will result in mostly high-based, low-precipitation convection capable of sporadic strong dry microburst winds from far northeast NV/northern UT into central MT. With eastward extent into parts of eastern MT, deeper boundary-layer moisture will result in potential for isolated strong gusts as well as hail. ...Eastern KS/OK into MO/AR... Convection may be ongoing at the start of the period as a continuation of nighttime storms from the prior Day 1 period. If this activity persists through the morning, some strengthening could occur as the boundary layer destabilizes through midday. Strong gusts and marginal hail could accompany these storms, but confidence in this scenario is low. ..Leitman/Wendt.. 07/17/2023 Read more CHECK UPDATE ZOOM GRAPHIC