Quincy Vagell
EF4
As upper level heights begin to at least slowly fall across the central U.S. in response to a trough making eastward progress across the Intermountain West, a broad area of severe thunderstorm potential should return to the High Plains vicinity by late in the day on Thursday. Although upper level flow does not look particularly strong, the models show some enhancement of wind fields toward 00z Sat from the High Plains into the Dakotas, resulting in at least 30-35 knots of 0-6km shear from portions of the Texas panhandle/West Texas, northward into the central High Plains. Somewhat stronger deep layer shear may be realized over the Dakotas.
In terms of thermodynamics, a persistent south to southeasterly low-level flow should transport at least upper 50s to lower 60s dew-points into parts of Kansas, Oklahoma and the Texas panhandle, as well as a secondary area over the Dakotas vicinity, based on good model agreement. There is potential for somewhat higher dew-points on a local scale, while portions of the central High Plains (eastern Colorado into southeastern Wyoming and the Nebraska panhandle) may only see dew-points rise into the mid-50s. Nonetheless, this low-level moisture coupled with fairly steep mid-level lapse rates, i.e. 7.5 to 8.5 C/km throughout most, if not all of the risk zone, would result in a broad area of 1500-3000 J/kg MLCAPE from Texas to the Dakotas, based on a consensus of overnight/early morning model data. Modest height falls coupled with boundary layer heating should prove sufficient to erode most convective inhibition by mid to late afternoon, resulting in convective development over much of the region.
I would argue that this broad area can be broken down into three, somewhat more specific, threat zones, with the first being across the central High Plains (main SPC focus), another around the Texas panhandle vicinity and the third up in the Dakotas.
Central High Plains vicinity:
Upslope flow should aid in convergence near a lee trough, situated along the Front Range Thursday afternoon. While boundary layer moisture may not be as impressive as in the other threat areas, dew-points should rise into the mid-50s by peak heating, supporting moderate instability. Deep layer wind shear may be marginal for supercellular development and there are concerns that convection on the north edge of this area, into southeastern Wyoming/western South Dakota/Nebraska panhandle may evolve into clusters, casting some uncertainty with the longevity of any discrete storms there. Otherwise, enhanced convergence and more isolated storm coverage in northeastern Colorado suggests that this area may be the most favorable in this regime. Large hail appears to be the dominant threat, with damaging winds increasingly possible, especially if storms do form into clusters or one or more MCSs. The Denver convergence zone is a climatologically favored area for a modest tornado threat as well.
Texas panhandle and vicinity:
Greater boundary layer moisture should build into portions of the Texas panhandle area Thursday afternoon with lower 60s dew-points expected. While large scale forcing may be minimal, convergence along the dryline on the edge of a moisture plume may be sufficient for at least isolated thunderstorm development. Like areas of the central Plains, deep layer shear looks to be relatively marginal for supercells, but strong surface heating should result in 2000-3000 J/kg MLCAPE, which may help offset the relative lack of shear. Large hail appears to be the main threat at this time, given large CAPE profiles. Temperature/dew-point spreads suggest that any tornado threat is minimal, while DCAPE should also be large, which may result in a few damaging surface gusts, despite relatively modest wind fields.
Dakotas vicinity:
A frontal boundary near the North Dakota/South Dakota border early Thursday may lift northward somewhat during the day as a warm front, working as the northern extent of favorable moisture/instability. Here, the models are in good agreement with moisture pooling beneath the front and dew-points near or a couple of degrees above 60F. This moisture, combined with heating in the warm sector, should result in 1500-2500 J/kg MLCAPE from northern South Dakota into parts of southern North Dakota. The models suggest somewhat stronger wind fields should impact this area as well, with 0-6km shear of at least 30-40 knots, along with a low-level jet of 40+ knots already in place by 00z. Although this region appears to have the best shear/instability parameter space (compared to areas farther south), there is concern that convective modes over the western Dakotas may become messy quickly, with the potential for MCS development. While all modes of severe weather remain possible, substantial convective development may limit the tornado threat. On the other hand, the warm front farther east across North Dakota (possibly far northern/northeastern South Dakota) may be the focus for an elevated, albeit somewhat conditional, tornado threat.
I don't think Thursday looks like a widespread, significant severe weather day, as wind fields should be relatively modest (outside of the Dakotas) and storm modes may tend to be messy across a broad area from eastern Wyoming into the central/northern Plains. With that said, the broad area targeted gives chasers many possibilities to choose from.
In terms of thermodynamics, a persistent south to southeasterly low-level flow should transport at least upper 50s to lower 60s dew-points into parts of Kansas, Oklahoma and the Texas panhandle, as well as a secondary area over the Dakotas vicinity, based on good model agreement. There is potential for somewhat higher dew-points on a local scale, while portions of the central High Plains (eastern Colorado into southeastern Wyoming and the Nebraska panhandle) may only see dew-points rise into the mid-50s. Nonetheless, this low-level moisture coupled with fairly steep mid-level lapse rates, i.e. 7.5 to 8.5 C/km throughout most, if not all of the risk zone, would result in a broad area of 1500-3000 J/kg MLCAPE from Texas to the Dakotas, based on a consensus of overnight/early morning model data. Modest height falls coupled with boundary layer heating should prove sufficient to erode most convective inhibition by mid to late afternoon, resulting in convective development over much of the region.
I would argue that this broad area can be broken down into three, somewhat more specific, threat zones, with the first being across the central High Plains (main SPC focus), another around the Texas panhandle vicinity and the third up in the Dakotas.
Central High Plains vicinity:
Upslope flow should aid in convergence near a lee trough, situated along the Front Range Thursday afternoon. While boundary layer moisture may not be as impressive as in the other threat areas, dew-points should rise into the mid-50s by peak heating, supporting moderate instability. Deep layer wind shear may be marginal for supercellular development and there are concerns that convection on the north edge of this area, into southeastern Wyoming/western South Dakota/Nebraska panhandle may evolve into clusters, casting some uncertainty with the longevity of any discrete storms there. Otherwise, enhanced convergence and more isolated storm coverage in northeastern Colorado suggests that this area may be the most favorable in this regime. Large hail appears to be the dominant threat, with damaging winds increasingly possible, especially if storms do form into clusters or one or more MCSs. The Denver convergence zone is a climatologically favored area for a modest tornado threat as well.
Texas panhandle and vicinity:
Greater boundary layer moisture should build into portions of the Texas panhandle area Thursday afternoon with lower 60s dew-points expected. While large scale forcing may be minimal, convergence along the dryline on the edge of a moisture plume may be sufficient for at least isolated thunderstorm development. Like areas of the central Plains, deep layer shear looks to be relatively marginal for supercells, but strong surface heating should result in 2000-3000 J/kg MLCAPE, which may help offset the relative lack of shear. Large hail appears to be the main threat at this time, given large CAPE profiles. Temperature/dew-point spreads suggest that any tornado threat is minimal, while DCAPE should also be large, which may result in a few damaging surface gusts, despite relatively modest wind fields.
Dakotas vicinity:
A frontal boundary near the North Dakota/South Dakota border early Thursday may lift northward somewhat during the day as a warm front, working as the northern extent of favorable moisture/instability. Here, the models are in good agreement with moisture pooling beneath the front and dew-points near or a couple of degrees above 60F. This moisture, combined with heating in the warm sector, should result in 1500-2500 J/kg MLCAPE from northern South Dakota into parts of southern North Dakota. The models suggest somewhat stronger wind fields should impact this area as well, with 0-6km shear of at least 30-40 knots, along with a low-level jet of 40+ knots already in place by 00z. Although this region appears to have the best shear/instability parameter space (compared to areas farther south), there is concern that convective modes over the western Dakotas may become messy quickly, with the potential for MCS development. While all modes of severe weather remain possible, substantial convective development may limit the tornado threat. On the other hand, the warm front farther east across North Dakota (possibly far northern/northeastern South Dakota) may be the focus for an elevated, albeit somewhat conditional, tornado threat.
I don't think Thursday looks like a widespread, significant severe weather day, as wind fields should be relatively modest (outside of the Dakotas) and storm modes may tend to be messy across a broad area from eastern Wyoming into the central/northern Plains. With that said, the broad area targeted gives chasers many possibilities to choose from.
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