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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.

Thursday, May 4, 2023

SPC May 4, 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 1241 AM CDT Thu May 04 2023 Valid 041200Z - 051200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS CENTRAL TEXAS TO OKLAHOMA AND FAR SOUTHERN KANSAS... ...SUMMARY... Severe thunderstorms capable of large hail, strong/damaging wind gusts, and a couple of tornadoes are possible across parts of the southern Great Plains this afternoon and evening. More isolated strong to severe storms capable of severe wind and large hail are possible across parts of the central Plains and the Pacific Northwest. ...Synopsis... Omega blocking over the southern/central Plains is expected to break down over the next 24 hours as a sub-tropical shortwave trough, noted over Baja California and northwest Mexico in latest water-vapor imagery, shifts northeast. This will result in modest lee cyclogenesis over the TX Panhandle and northwest OK this afternoon, which will help northward moisture advection through the day, and the establishment of a warm sector ahead of the approaching ascent. A weak surface trough/stationary front across the central Plains will likely focus thunderstorm development this afternoon within an otherwise weakly forced environment. Across the Pacific Northwest, broad ascent over eastern WA and northern ID may support a few isolated strong to severe thunderstorms. ...Southern Plains... Mid 50s to upper 60s dewpoints, currently spread across central to southern TX, are expected to gradually advect north into central OK as the lee cyclone deepens through the day. Broad ascent ahead of the approaching shortwave trough is noted in recent satellite imagery, and is expected to maintain a swath of high-level cloud cover over the region. This will modulate diurnal warming over much of TX/OK/KS to some degree, but temperatures warming into the upper 70s should be adequate to support a corridor of around 1000 J/kg MLCAPE across central OK with increasing buoyancy into central TX. 40-50 knot mid-level flow associated with the wave should overspread much of the region, and somewhat weak low-level flow will result in elongated, nearly straight, hodographs across the warm sector. While the environment appears adequate to support organized convection, storm coverage and mode remain uncertain, especially across north TX into OK and far southern KS. Overnight convection ongoing across the TX Panhandle may persist into central OK/north TX by the start of the period. This could reinforce the existing diffuse warm frontal zone across north TX, which could then be a focus for convective initiation this afternoon. Several CAMs also depict sufficient isentropic ascent ahead of the wave for broad rain showers/isolated elevated thunderstorms during the morning hours, which may hinder destabilization. Predictability of these scenarios is low given spread in high-res model solutions. Thunderstorm initiation appears most probable along a sharpening dryline across western OK to central TX where initial storm modes should be discrete to semi-discrete supercells given off-boundary storm motions/deep-layer shear vectors. While confidence in exact evolution of the warm sector is somewhat low across OK/KS, backed low-level winds in the vicinity of the surface cyclone may support adequate low-level shear for a couple of tornadoes if discrete supercells can be achieved. ...Central Plains... Although moisture advection into the central Plains is expected to be modest, ensemble guidance shows a reasonably strong signal for dewpoints in the low 50s to reach NE by late afternoon. This, coupled with 8 C/km mid-level lapse rates, should be adequate for a swath of MLCAPE values approaching 1000 J/kg. The central Plains will be well displaced from stronger synoptic ascent to the south, but focused lift along a surface trough/stationary front should support thunderstorm development by late afternoon. Effective bulk shear values near 25-30 knots will allow for organized convection, but mean-wind vectors and storm motions roughly along the initiating boundary may favor upscale growth, limiting the coverage/duration of the severe threat. ...Pacific Northwest... Recent surface observations are sampling a pocket of dewpoints in the upper 40s to low 50s across eastern WA into adjacent areas of OR/ID. This moisture will support a regional pocket of 500-1000 J/kg MLCAPE this afternoon, which may allow for a few more intense cells as lift ahead of a broad West Coast low overspreads the region. While the spatial coverage of this threat is expected to be limited, adequate deep-layer shear may allow for robust convection capable of posing a hail/wind risk. This scenario appears to be captured well by latest CAM ensembles, which show a somewhat stronger UH signal across the region compared to previous days. ..Moore/Broyles.. 05/04/2023 Read more CHECK UPDATE ZOOM GRAPHIC