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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.

Saturday, May 20, 2023

SPC May 20, 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 1236 AM CDT Sat May 20 2023 Valid 201200Z - 211200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF THE SOUTHEAST...LOWER RIO GRANDE VALLEY OF TEXAS...SOUTHERN NEW MEXICO REGION...AND INTERIOR OREGON AND WASHINGTON... ...SUMMARY... Strong to isolated severe thunderstorms are possible Saturday across much of the Southeast, lower Rio Grande Valley in Texas, southern New Mexico region, and parts of central Oregon and Washington. ...Discussion... Seasonally weak mid-level flow regime continues across much of the CONUS. Even so, modest 500mb flow is expected across the mid-South/northern Gulf States due to an upper trough digging southeast across the Great Lakes. This flow regime will encourage a surface front to advance into middle TN-northern AL-central MS/LA by 18z, with subsequent movement toward the central Gulf Coast by the end of the period. Early this morning, scattered convection persists across much of eastern AR, immediately ahead of the aforementioned surface front. This activity may persist into the pre-dawn hours then possibly increase in areal coverage/intensity by mid day as buoyancy improves due to low-level heating. Forecast soundings exhibit modest instability but poor lapse rates. While mid-level flow should increase during the day, it's not clear how intense this convection will ultimately be due to weak lapse rates. Some organization is possible, along with a few weak supercells. Will maintain MRGL Risk at this time due to instability issues. Isolated damaging winds/hail are the expected threats. Trailing front has surged into south-central TX. The majority of convection remains post-frontal and should gradually propagate toward the international border early in the period. Latest model guidance suggests the strongest boundary-layer heating will be west of the Rio Grande, thus the primary concern for robust updrafts will initially be over northeast Mexico. Some of this activity may spread into the lower Rio Grande Valley of deep south TX later in the day. Gusty winds and isolated severe hail are possible. Upstream, easterly low-level component will strengthen across far west TX into southwestern NM. Strong boundary-layer heating will contribute to instability and isolated-scattered convection should easily develop across this region as temperatures warm through the mid 70s. Gusty winds/marginally severe hail are the primary concerns. Strong surface heating east of the Cascades, along the western periphery of an upper ridge, will contribute to steep surface-3km lapse rates later this afternoon. Isolated convection should once again develop over interior WA/OR by mid-late afternoon. This activity will not be strongly sheared, but adequate flow should contribute to some organization. Gusty winds/hail are the primary concerns with this late afternoon/evening convection. ..Darrow/Thornton.. 05/20/2023 Read more CHECK UPDATE ZOOM GRAPHIC