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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

Wednesday, March 22, 2023

SPC Mar 22, 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 1259 AM CDT Wed Mar 22 2023 Valid 221200Z - 231200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM PORTIONS OF NORTHEASTERN KANSAS EASTWARD TO NORTHERN INDIANA... ...SUMMARY... Isolated/elevated strong to severe thunderstorms -- capable of large hail -- are possible from far northeast Kansas eastward to northern Indiana late tonight. ...Synopsis... An upper trough across the western U.S. will move gradually eastward with time, with the broader cyclonic flow field to encompass roughly the western half of the country through the period. As this trough advances, downstream ridging centered over the Gulf of Mexico will amplify a bit, with a trend toward a bit of anticyclonic curvature within the westerlies across the central and eastern U.S. with time. At the surface, a low initially over the northern Minnesota vicinity is forecast to shift quickly northeastward into -- and then across -- Ontario through the period. Meanwhile, the trailing cold front will become an increasingly west-to-east quasi-stationary front from the central Plains into the Midwest. This boundary -- or more specifically, a zone of warm advection focused to the cool side of the front -- will focus a zone of elevated convection through the period. ...Northeastern Kansas to northern Indiana... Elevated showers and isolated/embedded thunderstorms are forecast to be ongoing at the start of the forecast period across the northern Missouri vicinity -- i.e. portions of the MRGL risk area. This convection is forecast to shift eastward across the Midwest region through the day. Meanwhile, as a southwesterly low-level jet redevelops later this evening, a gradual increase in new, elevated convection is expected, in tandem with the increase in low-level warm advection atop a surface-based stable layer. With continued low-level theta-e advection within the 900 to 700 mb layer, and some steepening of lapse rates aloft, the elevated destabilization will likely be sufficient to support locally strong/vigorous updrafts. This, combined with favorably strong speed shear through the cloud-bearing layer, will likely support locally severe storms, capable of producing large hail. With time, an expanding convective cluster is forecast to spread eastward, crossing central Illinois and eventually northern Indiana through the end of the period. ..Goss/Lyons.. 03/22/2023 Read more CHECK UPDATE ZOOM GRAPHIC

Sunday, March 19, 2023

SPC Mar 19, 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 1153 PM CDT Sat Mar 18 2023 Valid 191200Z - 201200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Severe thunderstorms are not expected on today. ...Discussion... As an upper low crosses Quebec and shifts into the Canadian Maritimes today, remnant troughing extending southwestward across the eastern U.S. will weaken/advance slowly through the period. Upstream, ridging will generally prevail over the West, though short-wave troughing over the West Coast states early will be replaced by a stronger short-wave trough that should approach/reach the Pacific Northwest Coast overnight. At the surface, a cold front is forecast to continue moving southward across Florida early in the period, clearing the southern coast/Keys by early afternoon. Meanwhile, in the wake of the front, high pressure will shift eastward across the south-central and into the southeastern U.S. through the period. Little lightning potential is evident onshore through Monday morning. A few flashes may occur across southern Florida or the Keys early, as the front progresses southward. A couple of flashes will also be possible over portions of the Sierra of central/northern California. No severe weather is expected. ..Goss/Lyons.. 03/19/2023 Read more CHECK UPDATE ZOOM GRAPHIC

Saturday, March 18, 2023

SPC Mar 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 1232 AM CDT Sat Mar 18 2023 Valid 181200Z - 191200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Severe thunderstorms are not forecast Saturday. ...Florida... Strong northern-stream upper trough will shift east across the Great Lakes during the day1 period as 100+kt 500mb speed max translates off the southern New England Coast, increasing to near 140kt by 19/12z. In the wake of this feature, strong surface anticyclone will build south across the Plains, ultimately dominating the CONUS east of the Rockies. Leading edge of this air mass will force a cold front into the central FL Peninsula later this afternoon, then to the Keys by the end of the period. Early this morning, most concentrated convection extends ahead of the front across southeast GA along with a nearly north-south band approaching the central FL Gulf Coast. Scattered convection will likely persist along/ahead of the boundary into the early part of the period, but aside from a few strong updrafts, this activity is not expected to be severe. Latest model guidance suggests modest boundary-layer heating ahead of the cold front by late morning with surface temperatures forecast to rise into the lower 80s by 18z. Convective temperatures will be breached shortly thereafter and isolated thunderstorms should develop along the boundary. While SBCAPE values could exceed 1000 J/kg, modest lapse rates and seasonally weak surface-6km bulk shear do not favor organized updrafts, especially given the expected weak low-level convergence. While a few robust updrafts could evolve, the prospect for severe wind, and/or hail appear too low to warrant severe probabilities. ..Darrow/Lyons.. 03/18/2023 Read more CHECK UPDATE ZOOM GRAPHIC