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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, March 24, 2023

SPC Mar 24, 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 1256 AM CDT Fri Mar 24 2023 Valid 241200Z - 251200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF THE MID-MISSISSIPPI VALLEY... ...SUMMARY... An outbreak of severe weather is expected from the Lower Mississippi Valley toward the lower Ohio Valley Friday afternoon and evening. Tornadoes, strong to potentially intense, as well as damaging winds and hail are expected. ***Tornado Outbreak Possible Across Portions of the Mid Mississippi Valley Friday Evening*** ...Synopsis... A mid-level trough can be seen on water vapor east of the northern Baja Peninsula this morning. This trough will move quickly across the southern Plains through the day and into the Mid Mississippi/Lower Ohio Valley by Saturday morning. A very strong mid-level jet (90-100 knots) will develop as this wave impinges on a strong upper-level High across the Southeast. Broad warm air advection is expected across the Mid-Mississippi Valley during the day Friday with a strengthening low-level jet through the day. Significant mass response is expected across this area by early evening as the mid-level trough approaches the area. As a result, the surface low will deepen rapidly between 00Z to 06Z to around 992-994mb in the southern Illinois/Indiana vicinity. During this period of rapid deepening, a warm front which is forecast to be mostly stationary from northeast Arkansas to central Tennessee during most of the day, will start to move quickly north during the late afternoon with the northern extent of the warm sector depicted by the approximate path of the surface low. ...Mid Mississippi Valley... Thunderstorms will be ongoing at the beginning of the period across eastern Oklahoma and western Arkansas. Some embedded supercells are possible with the threat for a few weak tornadoes. Most guidance is consistent with the convectively enhanced cold front drifting south into north-central/northeast Arkansas in the morning. Therefore, this early activity will likely wane as it interacts with this southward moving front by late morning. A pocket of drier air can be seen on water vapor moving north in the west-central Gulf early this morning. This is associated with a relative minimum in PWAT which will overspread eastern Louisiana and much of Mississippi during the late morning and through the afternoon. This seems to be responsible for the significant mixing and surface dewpoint reductions seen my much of the guidance across Mississippi in the afternoon where temperatures warm into low 80s. However, despite this drier air further east, deep moisture will remain across the western Gulf and will advect northward into Louisiana during the afternoon as low-level mass response increases. By mid to late afternoon, upper 60s to potentially low 70s dewpoints are expected across northern Louisiana and eastern Arkansas, spreading into northern Mississippi by the evening. This will lead to an uncapped warm sector featuring MLCAPE of 500-1000 J/kg up the Mississippi River to near Memphis and 1500-2000 J/kg farther south across northern Louisiana and west-central Mississippi. Expect storms to strengthen during the afternoon as the better moisture advects northward and destabilizes the airmass ahead of ongoing activity. CAM guidance is in agreement for a strong QLCS to develop from central to northern Arkansas during the afternoon. This line of storms will pose a threat for damaging wind and QLCS tornadoes given the long, curved low-level hodographs with the best overlap of favorable shear and instability in the vicinity of the Mississippi River. This line of storms will eventually outrun the better instability as it moves toward Middle Tennessee/southern Kentucky, but the strong low-level jet (~70 kts), and strong forcing with the deepening surface cyclone will help to maintain some severe threat well into the overnight despite progressively more meager instability. Across southeast Arkansas, northern Louisiana, and northwest Mississippi, a more volatile environment will develop Friday evening/early overnight. More discrete convection is anticipated on the southern periphery of the aforementioned QLCS. The more discrete mode, combined with greater instability and strong shear should allow for multiple supercells to develop across northern Louisiana and southern Arkansas and move northeastward. Low-level hodographs are very favorable in this region with 0-500m SRH around 200 m2/s2 and 0-1km SRH 300+ m2/s2. Therefore, any sustained supercells will be capable of producing strong to intense (EF3+) tornadoes, with long-track tornadoes possible with any longer-lived, undisturbed supercells. 00Z HREF members showed a variety of solutions which cast some uncertainty on the forecast. WRF members are notably less bullish with warm sector supercell development from northeast Louisiana into northern Mississippi while the HRRR was most aggressive with convective coverage and environment. After further investigation it appears the more aggressive HRRR solution can be attributed to a more robust mass response during the afternoon/early evening hours. This results in a pronounced shortwave trough which can be seen at 700 and 850mb and reflected as a significant confluence zone at the surface. Not only does this act as a forcing for storm development, but it also acts as moisture convergence with a more broad region of 70+F dewpoints. In this scenario, numerous strong tornadoes would be likely, with the potential for several intense tornadoes. Despite being the most aggressive, this solution does not seem unreasonable as similar low-level confluence features can been on both the 00Z GFS and the 18Z ECMWF. As is often the case, the severity of the tornado threat across the moderate risk will be modulated by mesoscale influences in the region. As the event approaches, these mesoscale effects may become more clear and allow the greatest risk corridor to become better defined. ..Bentley/Weinman.. 03/24/2023 Read more CHECK UPDATE ZOOM GRAPHIC