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Archives for SPC Convective outlook are updated daily with a live map a the beginning of the article. Touch or click map to get possible update, and follow link at end of article for referral to NOAA/NWS Storm Prediction Center. Archives for Chicago's hourly weather data were updated 24-48 hours after end of each day prior to Dec. 2020.

Sunday, July 24, 2022

SPC Jul 24, 2022 1300 UTC Day 1 Convective Outlook

SPC 1300Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0755 AM CDT Sun Jul 24 2022 Valid 241300Z - 251200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER A CORRIDOR EAST OF THE LOWER GREAT LAKES IN PENNSYLVANIA AND NEW YORK... ...SUMMARY... Severe thunderstorms are expected to develop across the lower Great Lakes vicinity into St. Lawrence Valley by late this afternoon, with a threat for damaging gusts and a couple tornadoes. ...Synopsis... A belt of cyclonic flow will persist across the Upper Midwest, Great Lakes and Northeast, south of a persistent and large cyclone wobbling erratically around the James Bay/southern Hudson Bay area. An embedded, convectively enhanced shortwave trough -- initially located over Lower MI -- is expected to eject east-northeastward across southern ON to southern QC through the period. That process will be encouraged by the progression of a much stronger shortwave trough -- apparent in moisture-channel imagery over parts of far northwestern ON and adjoining central/southern MB. That trough should pivot southeastward over Lake Superior, Upper MI and northern WI around 00Z, then eastward across Lake Huron and nearby sections of ON. Upstream, a shortwave trough and intermittently closed/small cyclone are evident over the northern Rockies. This feature should move slowly eastward over western/southern MT and adjoining parts of ID/WY through the period, while gradually weakening. Meanwhile, farther south -- in the face of repeated incursions of vorticity lobes from the lower-latitude easterlies turning northwestward over the Desert Southwest, the persistent anticyclone previously anchored over the Four Corners States should erode eastward. Ridging will remain over the southern Rockies, southern Plains and eastward past the Tennessee Valley. The 11Z surface analysis showed a cold front from near the east end of Upper MI southwestward across southern WI, southern IA, to a low over southwestern KS, to northeastern NM. By 00Z, this front should advance to southeastern Lower MI, central IL, south-central MO and south-central KS, becoming a stationary to warm front westward to a hybrid frontal-wave/lee-side low over southeastern CO. By 12Z, that low should migrate eastward along the front to near ICY, with a nearly stationary boundary segment eastward over the MO Ozarks to extreme southern IL. The cold front should resume from there across southern OH, northern PA and northern NY. ...Lower Great Lakes and vicinity... Scattered thunderstorms are expected today into this evening, along/ahead of the cold front from the Lower Great Lakes region to the Ohio Valley. Convection in the northern/northeastern parts may include a few supercells, and will pose a risk of scattered severe gusts and a few tornadoes. The "enhanced" area may represent an aggregate coverage of multiple strong-severe convective episodes crossing the region, as much as for the intensity of any one of them. The convective environment will be supported by the glancing/southern influence of the ejecting MI shortwave trough -- both in terms of large-scale DCVA/ascent, and enhancement of deep shear through tightening of the height gradient aloft. Modest low/middle-level lapse rates will offset favorable low-level moisture enough to keep MLCAPE maximized at 1000-1500 J/kg in a narrow corridor east of the Lower Great Lakes, but with 40-50-kt effective-shear magnitudes and 150-300 J/kg effective SRH in support of mixed supercell/multicell modes and possible some bowing segments. In the higher-moisture, more strongly heated, but weaker shear environment farther southwest across IN/IL, clustered multicells (with a few small MCSs possible) will be the dominant modes, with sporadic damaging to severe wind possible. Forecast soundings suggest a deep troposphere supporting 2000-2500 J/kg MLCAPE, but with only about 25-35 kt effective-shear magnitudes. Overall frontal lift and deep shear each will weaken further with southwestward extent from there, though isolated pulse/multicell severe may be noted. ...Central/northern Rockies and adjoining High Plains... Isolated to scattered thunderstorms are forecast to develop this afternoon, along a lengthy expanse of the interface between the eastern Rockies front and the High Plains. Activity should move roughly eastward onto the Plains, with more longevity/persistence likely in middle and southern segments of the outlook area (hence, its broadening southward). The main concern will be at least isolated severe gusts. Diurnal heating will steepen lower/middle-tropospheric lapse rates in the presence of sufficient/residual low-level moisture advecting into the region in the post-frontal boundary layer. This should lead to a well-mixed low-level thermodynamic profile, beneath minimal MLCINH, with a plume of 500-1000 J/kg peak/preconvective MLCAPE that generally narrows northward. Though low-level moisture and theta-e should be somewhat lower on the northwest end, large- scale ascent ahead of the northern Rockies perturbation should overlie surface heating to contribute to very steep low/middle-level lapse rates. Continued easterly flow component north of the front/low should contribute to both favorable storm-relative boundary-layer winds for activity moving off the higher terrain, and strong veering of flow with height. Several loosely organized bands or clusters of convection may aggregate cold pools for a few hours in support of gust potential. Depending on subsequent mesoscale trends and convective guidance, some subset of this area may gain enough spatial certainty to warrant greater probabilities. ...AZ... The onset of diurnal convective potential today may be delayed somewhat by passage/dissipation of a band of morning clouds/ convection and a few embedded thunderstorms now crossing parts of southern AZ. Still, strong heating is expected, in the clearing evident in satellite imagery behind the early activity, especially of higher terrain in the east and south. Loftier areas from the Mogollon Rim to the Chiricahuas and westward across higher terrain south through east of TUS should support initial, widely scattered to scattered thunderstorms this afternoon. This activity should evolve into clusters and move roughly westward to west-northwestward over the deserts, with damaging/isolated severe gusts possible into the evening as still more convection develops atop assorted outflows emanating from the afternoon activity. Low-level moisture will remain favorable with PW around 1.5-inches, with lower/desert-elevation surface dewpoints in the 50s to low 60s F, supporting around 1000 J/kg MLCAPE. A deep layer of easterly to southeasterly flow is expected to persist in the middle/upper troposphere, maintained by perturbations now over parts of Chihuahua and northern Sonora, despite some weakening of the ridging to the north. This will occur atop a well-heated/mixed boundary layer, encouraging locally strong-severe convective gusts and discrete westward propagation of convection and successive outflows. ..Edwards/Gleason.. 07/24/2022 Read more CHECK UPDATE ZOOM GRAPHIC
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