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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.


Tuesday, April 18, 2023

SPC Apr 18, 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 1240 AM CDT Tue Apr 18 2023 Valid 181200Z - 191200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS MUCH OF THE GREAT PLAINS REGION INTO WYOMING... ...SUMMARY... Isolated severe thunderstorms are possible from parts of the southern Great Plains northward into the Mid Missouri Valley and westward into Wyoming. Severe gusts and large hail will be the hazards with the stronger storms Tuesday afternoon into Tuesday night. ...Discussion... Upper ridge is forecast to shift across the Great Plains into the MS Valley by 19/00z as a significant short-wave trough ejects across the Great Basin to a position from eastern ID-western CO by early evening. In response to this feature, lee surface low should migrate from southeast WY into central NE Tuesday evening before tracking into northeast NE by sunrise Wednesday. LLJ is forecast to strengthen in a couple of segments before focusing over the central Plains Tuesday night with speeds in excess of 60kt. Large-scale pattern appears favorable for dryline convection shortly after peak heating and overnight convection within the warm-advection corridor. One concern regarding the prospect for more widespread convection is the limited moisture currently observed across the Plains, especially the southern Plains. Early this morning, lower 60s surface dew points were suppressed into deep south TX while leading surge of 50F dew points extended as far north as Fort Stockton/Pecos in west TX. Latest model guidance suggests 60s dew points will advance across western OK prior to sunset and strong surface heating west of the dryline should allow surface parcels to reach their convective temperatures by late afternoon. In the absence of meaningful forcing, convection should remain quite isolated along this boundary from KS into west TX. Slow-moving supercells that materialize could produce damaging winds/hail. During the latter half of the period, increasing low-level moisture should advance into a corridor of strong low-level warm advection (mostly north of I80). Latest guidance suggests elevated convection should easily develop along/north of a warm front as it advances across NE/IA toward the MN border ahead of the aforementioned surface low late in the period. Hail is the primary risk with elevated storms and while gusty winds may also accompany near-surface-based storms across the warm sector. Additionally, strong forcing ahead of the short wave should enhance scattered convection across WY by mid afternoon. Forecast soundings exhibit very steep lapse rates through 8km with strong southwesterly flow through a deep layer. While PW values are quite low, vertical mixing may contribute to wind gusts with this activity as it spreads toward the Black Hills region. The lack of significant moisture across the Plains is the main limiting factor for potentially more widespread/organized severe. For this reason will maintain MRGL Risk. ..Darrow/Squitieri.. 04/18/2023 Read more CHECK UPDATE ZOOM GRAPHIC
SUNRISE AND SUNSET TIMES IN UTC (if you're not logged in to Google)
CHICAGO UTC-6 during CST (Central Standard Time, e.g., winter)
CHICAGO UTC-5 during CDT (Daylight Savings Time, e.g., summer)