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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.


Wednesday, May 11, 2022

SPC May 11, 2022 1300 UTC Day 1 Convective Outlook

SPC 1300Z Day 1 Outlook Day 1 Convective Outlook CORR 1 NWS Storm Prediction Center Norman OK 0831 AM CDT Wed May 11 2022 Valid 111300Z - 121200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PARTS OF CENTRAL/SOUTHERN MINNESOTA AND SURROUNDING STATES... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE SOUTHERN HIGH PLAINS...AND SURROUNDING THE ENHANCED RISK IN THE UPPER MIDWEST... CORRECTED FOR INCORRECT WIND PROBABILITY LINE ...SUMMARY... Severe thunderstorms are expected this afternoon/evening over the north-central states. Very large hail, wind, and a threat for tornadoes is expected. Additionally, widely scattered severe thunderstorms are anticipated across the southern High Plains. Wind/hail are the primary threats. ...Synopsis... The large-scale mid/upper-level pattern will continue to feature mean troughing over western North America, a lengthy and positively tilted ridge from west of the central MX Pacific Coast across the Arklatex to the St. Lawrence Valley, and a retrograding/cutoff synoptic-scale cyclone offshore from the Carolinas and GA. For this period, the two most convectively crucial features aloft will be ejecting northeastward from or ahead of the mean trough, in southwesterly flow: 1. A strong shortwave trough -- now including a compact closed cyclone over the Sierra of northern CA and NV. This feature will pivot slowly eastward over the Great Basin today, then turn northeastward tonight, reaching the Star Valley area of western WY and south-southeastward near the CO/UT line by 12Z tomorrow. 2. A former southern-stream shortwave trough that ejected northeastward out of northwestern MX yesterday, with convectively induced vorticity supplementation last night into early this morning over the southern High Plains. A primary/embedded MCV is evident in satellite and especially composited radar-reflectivity animations over west-central/southwestern KS, with a vorticity lobe and lesser MCV(s) across western OK. This perturbation, as a whole, will move northeastward across the central Plains this morning, reaching southwestern MN, western IA and northeastern KS by 00Z. The trough should reach Lake Superior and western Upper MI by the end of the period. At the surface, 11Z analysis showed a low over southeastern CO near the KS line, with wavy warm front northeastward across northeastern KS, south-central/eastern NE, central IA, and southern WI. A dryline was drawn from the low across the northwestern TX Panhandle, southeastern NM and far west TX, and this boundary should move little today before retreating deeper into NM overnight. The low should merge with another initially drawn over southeastern WY, then migrate erratically around northeastern CO, extreme southeastern WY and the southwestern NE Panhandle through 06Z, before moving northeastward to the western Sandhills by 12Z. The warm front should move northward through the remainder of eastern NE and IA, and into eastern SD, southern/central MN and western/southern WI by 00Z. This boundary then should decelerate over northeastern SD and central MN before being overtaken by convection. ...Upper Midwest... See SPC mesoscale discussion 719 for near-term coverage of isolated/elevated convection with hail risk over southeastern SD. Otherwise, scattered thunderstorms are expected to develop mainly this afternoon, in an arc, over southwestern parts of the outlook area, and move northward to northeastward, offering all severe hazards, including at least a few tornadoes and some large to very large hail. Early-stage supercells are expected, with evolution to an MCS over parts of southern/central MN late this afternoon into this evening. As the upscale growth occurs, the hail hazard will diminish (especially in magnitude), while the wind threat increases and becomes more dense. The severe threat will increase with time and northward extent this afternoon across eastern NE, western IA, the Siouxland area, and southwestern MN as the MCV and its accompanying wind/UVV fields impinge on a very moist, well-heated, increasingly weakly capped boundary layer, along and south of the warm front. Accompanying the ejecting shortwave trough/MCV will be mesoscale midlevel speed maxima -- roughly 55-65 kt at 500 mb and 55-65 kt at 700 mb, as evident in regional VWP and reasonably progged by models that resolve the perturbation best. These features should contribute to a corridor of enhanced vertical shear, both directly via strengthening/veering wind profiles with height, and through low-level mass response along the warm front and nearby warm sector. As these winds shift into the convective transition regime, they may enhance the damaging-gust threat with the upscale clustering across southern/central MN as well, near and south of the warm front where large CAPE still will remain available to storm inflow. Supercellular tornadoes will be possible in the warm sector, where LCLs may be lower than forecast by RAP-based models that tend to overmix a bit. However, this threat is more probable close to the warm front for any relatively discrete cells and/or QLCS segments that can interact with the front's backed flow, larger hodographs and enhanced low-level vorticity. Surface dew points in the upper 60s to low 70s F will support MLCAPE in the 3500-4000 J/kg range along and south of the warm front, with 40-50-kt effective-shear magnitudes and 200-400 J/kg effective SRH. The transition toward more-clustered convective mode should occur as flow aloft backs in response to the passing perturbation, becoming less orthogonal to the orientation of the axis of convective lift. The resulting MCS should have the potential for downward momentum transfer from strong midlevel flow, while being maintained by forced ascent of very moist inflow air along and south of the warm front. Activity should diminish overnight farther east across parts of central/northern WI and perhaps western Upper MI as inflow-layer instability gets weaker. ...Southern High Plains... Widely scattered to scattered thunderstorms are forecast to develop this afternoon near the dryline, with large hail expected. The potential also exists for a few smaller-scale clusters to evolve upscale for a few hours and offer localized concentrations of damaging gusts. Initiation and maturation of this convection should be strongly tied to diurnal heating/lift processes, and should diminish after about 03Z as the boundary layer stabilizes downshear from the convection. Strong boundary-layer heating/mixing, and resultant presence of steep low-level lapse rates and favorable DCAPE, will support maintenance of hail and acceleration of downdrafts to ground. Peak/preconvective MLCAPE in the 1000-1500 J/kg range will be attained beneath modest mid/upper-level flow, but amidst enough veering with height in the wind profile to support 30-35-kt effective-shear magnitudes. Mostly multicells, with some transient supercellular structures, are possible, also supporting the threat for large hail. ...WY/MT/western to central Dakotas... Isolated to widely scattered thunderstorms are possible late this afternoon into evening, beginning over areas of modest but sustained upslope lift in northeastern WY, and spreading/developing northeastward in sporadic fashion, potentially as far northeast as the western/central ND/SD border region overnight. The main threats will be isolated large hail and strong/briefly severe gusts. Large-scale ascent will increase this evening and overnight across the region, as the strong shortwave trough pivots out of the Great Basin and approaches. This will destabilize midlevels, and by extension with an improved warm-advection response, low levels as well. Areas of surface heating/mixing may permit surface-based development late this afternoon over northeastern WY north/northwest of the surface low, with additional/elevated initiation probable thereafter. Though buoyancy will be meager (MUCAPE generally 300-800 J/kg), favorable deep shear (effective-shear magnitudes around 50-65 kt) will favor supercell potential. Any late-developing activity overnight near the SD/ND line will have access to somewhat richer low-level moisture, in an elevated warm-advection plume extending westward from the regime related to the ENH outlook described above. Elevated MUCAPE may reach 1500-2500 J/kg amidst 50-60-kt effective-shear magnitude, suggesting a large-hail threat, conditionally risking significant-severe (2+ inches) hail in any sustained activity. Convective coverage concerns and elevated-initiation uncertainties preclude an upgrade for that region at this time. ..Edwards/Gleason.. 05/11/2022 Read more CHECK UPDATE ZOOM GRAPHIC
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