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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.

Friday, July 22, 2022

SPC Jul 22, 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 Fri Jul 22 2022 Valid 221300Z - 231200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM PARTS OF THE CENTRAL AND NORTHERN PLAINS INTO THE UPPER MIDWEST...SEPARATELY OVER PARTS OF NORTHERN UTAH...AND THE UPPER OHIO VALLEY/NORTH-CENTRAL APPALACHIANS REGION... ...SUMMARY... Isolated strong to severe thunderstorms may occur from parts of the central and northern Plains into the Upper Midwest, separately over parts of northern Utah, and the upper Ohio Valley/north-central Appalachians region. ...Synopsis... In mid/upper levels, the persistent anticyclone will remain anchored over the Four Corners region, but with height falls and more zonal flow to its north, as a series of shortwaves traverse the westerlies. Downstream, the eastern mean trough also will deamplify gradually, but with broadly cyclonic flow lingering from the upper Mississippi Valley across the Great Lakes, Ohio Valley and Northeast. The most prominent northern-stream shortwave trough is evident in moisture-channel imagery over portions of WA/OR. This perturbation should move eastward to the northern Rockies by 00Z, with slight deamplification. By 12Z, it should extend from northern ND southwestward over western MT. At the surface, 11Z analysis shows a weak cold front across northern parts of ME and NY, becoming warm to a triple point over southern Lower MI, with an occluded front northward to northern ON. A cold front was drawn from there across northern/western IN, becoming warm to quasistationary over west-central IL, northern MO, eastern NE, and eastern SD, to a low near PIR. The front then curved back southwestward across the NE Sandhills to eastern WY. The SD low should migrate eastward to IA by 00Z, while the trailing frontal segment becomes nearly stationary over eastern to southwestern NE and weakens somewhat. An area of surface cyclogenesis and frontogenesis is expected over northern ND by 00Z, with the resulting front extending east-southeastward and southwestward from a southeastward-shifting low. ...Northern Plains... At least isolated thunderstorms are possible this afternoon and evening near the surface low and the frontal segment to its east/southeast, as strong diurnal heating minimizes MLCINH. Additional development may occur overnight farther east and southeast as a LLJ intensifies to 35-45 kt, with accompanying theta-e advection above the surface. Any sustained convection will offer strong-severe gusts and hail. The environment across the region will be characterized by a well-mixed subcloud layer with enough moisture to support about 500-1500 J/kg MLCAPE, highest near the warm front (which will correspond closely with a low-level moist axis). Forecast soundings suggest 45-55-kt effective-shear magnitudes, strengthening northward under stronger mid/upper winds and more-backed frontal-zone flow in the boundary layer. A conditional threat for organized severe exists near the international border north of the front, with favorable moisture and enlargement of both hodographs and low-level shear vectors. Any convection that can develop near the front -- perhaps across parts of southeastern SK or extreme southern MB -- accordingly may become supercellular and potentially grow upscale into a small, eastward to southeastward-moving MCS on either side of the international border. However, progs that do overcome MLCINH and develop such convection (some still do not) remain inconsistent on timing by a few hours, as well as initiation/track location. Any such activity that does form will have access to a corridor of around 1000-1500 J/kg MLCAPE above a well-mixed subcloud layer, even with or without a stable nocturnal or frontal layer near the ground. If progs initialized from 12Z onward, and/or mesoscale trends, impart more confidence in such development/maintenance on the U.S. side, a corridor of greater hail/wind probabilities would be needed. ...Central Plains, Corn Belt... Isolated to scattered thunderstorms are possible this afternoon and evening in a broad, poorly focused convective regime, with any sustained activity posting a risk of strong-severe gusts and isolated large hail. Intense surface heating along the northwestern rim of favorable warm-sector moisture, and near the weak frontal segment, should reduce CINH enough by mid/late afternoon to support an area of high-based convection over parts of southwestern/NE and perhaps northwestern KS. Activity then should move southeastward over a deep/well-mixed subcloud layer suitable for strong/damaging gusts. Buoyancy and MLCINH each should increase with eastward extent. Initial thunderstorms may access around 1000-2000 J/kg MLCAPE, with not much less DCAPE below. Light but backed near-surface winds will underlie around 25-35-kt 500-mb flow, contributing to effective-shear magnitudes around 30-40 kt. Outside the more-confident but weaker-buoyancy scenario over the southwestern parts of the outlook area, confidence is low (and guidance highly variable in any specific initiation/propagation scenario in or near the frontal zone. That said, activity may develop near the front across eastern NE and/or IA this evening, and as late as 04Z-07Z tonight over eastern parts, west of Lake Michigan and somewhat northeast of the surface warm front, with marginal severe hail/wind potential. ...Upper Ohio Valley, north-central Appalachians... Widely scattered to scattered thunderstorms are expected to develop from midday through the afternoon over this area and move predominantly eastward, offering sporadic damaging gusts. Isolated, marginally severe convective gusts may occur in the most intense cells. Satellite and radar imagery indicates two low-amplitude but still potentially influential perturbations: 1. Over northwestern PA and extreme western NY, with an MCV evident south of BUF, forecast to move eastward astride the PA/NY line and over southern New England today. 2. A convectively enhanced shortwave trough over the upper Mississippi Valley, poorly depicted by most synoptic models and CAMs, and forecast to reach southern ON, Lake Erie and OH by 00Z. Combined, these features should help to maintain a sufficiently tight height gradient to maintain strong-magnitude and somewhat cyclonic mid/upper flow over the area. Development should be aided by diurnal heating, orographic lift, and the residual outflow/ differential-heating boundary from clouds/convection related to the leading perturbation/MCV. Moisture advection/transport from the Ohio Valley region should combine with that heating to yield 1000-1500 J/kg peak/preconvective MLCAPE. Effective-shear magnitudes around 30-35 kt will support organized multicells. ...UT... Widely scattered high-based thunderstorms are possible this afternoon across much of northern through south-central UT, with activity over northern deserts into the Wasatch Range (and perhaps slightly farther east) posing a threat for isolated strong-severe gusts. Although lower-elevation surface dew points are commonly in the 40s to low 50s at this time, those values should decrease to the 30s to low 40s amidst intense diurnal heating and mixing. Nonetheless, that still supports around 300-800 J/kg of MLCAPE, starting in the 500-600-mb layer, atop a dry-adiabatic/inverted-V thermodynamic profile with large DCAPE. Though low-level winds and shear will be weak, some increase in mid/upper flow is expected this afternoon as the shortwave trough to the northwest and north tightens the height gradient, leading to around 35-40-kt cloud-layer shear. ..Edwards/Gleason.. 07/22/2022 Read more CHECK UPDATE ZOOM GRAPHIC
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