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Monday, June 7, 2021

SPC Jun 7, 2021 1300 UTC Day 1 Convective Outlook

SPC 1300Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0756 AM CDT Mon Jun 07 2021 Valid 071300Z - 081200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM NORTH-CENTRAL TEXAS INTO THE ARKLATEX REGION...AND PORTIONS OF THE DAKOTAS INTO NORTHWEST MINNESOTA... ...SUMMARY... Severe thunderstorm winds and hail will be possible this morning and perhaps into the afternoon over parts of north-central Texas into the Arklatex region, as well as late this afternoon into evening across portions of the Dakotas into northwest Minnesota. ...Synopsis... A fairly static large-scale pattern will persist across most of the Lower 48, with southwest flow in the northern stream from the Pacific Coast across the northern Rockies, and a slow-moving trough in the central CONUS. That trough, accompanied by an intermittently closed 500-mb low now located over southeastern KS -- will continue to drift northeastward and gradually lose amplitude through the period. By 12Z tomorrow, the low - or its remnant vorticity max -- should be located over northern MO or southern IA, with trough southward to the lower Sabine River region. Meanwhile, a formerly cut-off low -- now evident in moisture-channel imagery west of northern Baja -- will accelerate northeastward as a weakening open- wave trough, reaching the LAS/SGU area by the end of the period. Ahead of that, a weak shortwave trough -- noted over parts of southern UT and AZ -- should move northeastward across the central Rockies. By 12Z, this perturbation may reach western SD and the NE Panhandle. Surface analysis at 11Z showed a wavy stationary to slow-moving warm front from Lake Superior southwestward to southwestern NE, which will move northward over the north-central Plains through the period. A low over northeastern WY should meander erratically in a net eastward direction to western SD, with another frontal zone extending northeastward across ND. ...Southern Plains/Arklatex... A complex of thunderstorms is apparent north through west of the DFW Metroplex, with some lingering severe wind/hail potential and later re-intensification possible. See the remainder of watch 241 and accompanying mesoscale discussions for near-term details. Severe-convective scenarios for today are rather messy and conditional, but mostly involve: 1. As noted above, a re-invigoration of the ongoing activity later this morning into midday, along the leading edge of the associated pressure/thermal perturbation, as it encounters diabatically destabilizing boundary layer across the rest of north/northeast TX, and/or 2. Additional development along the outflow boundaries from that complex, and from convection that has crossed southern AR. Midlevel lapse rates will diminish gradually with eastward extent. However, strong surface heating, weak MLCINH and rich low-level moisture will be common, including a deep moist layer with 1.75 to 2-inch PW and surface dewpoints commonly in the 70s F. This will support peak preconvective MLCAPE in the 2000-3000 J/kg range. Though mid/upper winds will be modest, strong directional shear and enhanced low-level convergence/vorticity near older outflow boundaries will augment storm-organization potential locally, in addition to that related to forced ascent along the leading thrust of cold pools. ...Northern Plains/MN... Isolated to scattered thunderstorms in clusters may develop late this afternoon, or more likely this evening, near the frontal segment northeast of the surface low, with the potential for large hail and strong-severe gusts. Large hail also is possible from elevated convection overnight behind any MCS cold pool that may develop. A conditional, low-end tornado threat also exists, the main uncertainty being whether any mature supercells can evolve away from more-clustered activity before too much nocturnal cooling occurs to stabilize the near-surface layer. Although the AZ/UT shortwave trough will approach this area late overnight, most of the period will be characterized by neutral to rising heights aloft, and a lack of substantial upper-air support. This casts uncertainty on timing/coverage of convection, though the thermodynamic and shear environment will become favorable. Moisture and warm advection will destabilize the low-level air mass over the outlook area from south to north beneath steep middle-level lapse rates, with surface dew points expected to increase into the upper 50s to mid 60s this evening and tonight. Accordingly modified forecast soundings yield MLCAPE into the 2000-3000 J/kg range. Lack of stronger mid/upper flow limits deep shear, with effective-shear magnitudes generally in the 25-35-kt range, locally higher near the warm front. ..Edwards/Kerr.. 06/07/2021 Read more LIVE: spc.noaa.gov