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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.

ARLINGTON HEIGHTS WEATHER

Friday, October 29, 2021

SPC Oct 29, 2021 1300 UTC Day 1 Convective Outlook

SPC 1300Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0732 AM CDT Fri Oct 29 2021 Valid 291300Z - 301200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PARTS OF COASTAL NORTH CAROLINA INTO THE MID-ATLANTIC... ...SUMMARY... Isolated strong to severe storms may occur today over parts of coastal North Carolina into the Mid-Atlantic. Marginally severe wind gusts will be the primary threat. ...Synopsis... The main feature for convective potential this period will remain a large, deep-tropospheric cyclone covering much of the eastern CONUS, and initially centered over western KY in mid/upper-level moisture- channel imagery. Associated cyclonic flow covers areas from the coastal Carolinas to the central/southern Plains, and the upper Great lakes to the Gulf. The cyclone aloft is forecast to fill slowly through the period, as its core region (with multiple, intermittent 500-mb lows possible) pivots east-northeastward to the central/southern Appalachians. At the surface, 11Z analysis showed the low -- related to the mid/upper cyclone -- over west-central KY, with occluded front arching across northeastern KY, southern WV, southwestern VA and northwestern/north-central NC to an ill-defined triple point over east-central/southeastern NC. The cold front extended from there across Atlantic waters to south FL, with warm front over the southern Outer Banks. The occluded/warm front will move northward and northeastward over the Mid-Atlantic region today. ...Eastern NC/Mid-Atlantic... A marginal convective-wind/tornado threat will develop today in an arc of convection (with isolated to widely scattered embedded thunderstorms) in and near the occluded/warm frontal zone. This activity will move northward to northeastward over the region. With time this evening, the area of strongest convection-supporting lift will outrun any favorable surface-based instability, with weakening convection expected. A narrow slot of superposition of relatively maximized boundary- layer moisture (and minimized MLCINH) with backed near-surface winds is apparent on the surface chart and in mesoscale diagnostics from the southern Outer Banks region west-northwestward to north-central NC. Buoyancy does -- and should continue to -- diminish gradually with westward/inland extent, as this regime shifts north- northeastward across the outlook area, largely in keeping with available theta-e in the prospective inflow layer. Abundant clouds/precip will preclude development of large low-level lapse rates, but convergence in and near the baroclinic zone should combine with continuing weak CINH and minor surface heating to boost convective coverage/intensity later this morning. MLCAPE of 200-800 J/kg is possible, though a pronounced stable layer between 650-700 mb (evident in the 12Z MHX RAOB) may limit development/coverage on the east end for at least a few hours. As the deep-layer cyclone moves toward the Appalachians, a long, cyclonically curved mid/upper-level jet streak will shift eastward across the NC/Mid-Atlantic region, bringing parts of the outlook area beneath its left-exit region for some additional large-scale ascent. Favorable deep shear is forecast, with 0-6-km vectors around 50-75 kt, though weak and somewhat shallow CAPE-bearing layers will keep effective-shear magnitudes smaller than that (30-50 kt). Downdrafts may transfer enough momentum from aloft to yield a localized, isolated threat for damaging to severe gusts. In the sliver where surface-based buoyancy and optimally backed surface winds may develop, effective SRH of 250-350 J/kg is possible, followed by quickly veering surface flow that will yield much less favorable hodographs. Any sustained/discrete activity that persists in that small, conditional, yet favorable environment may become supercellular, with a tornado possible given the favorable shear and low LCL. ..Edwards/Mosier.. 10/29/2021 Read more LIVE: spc.noaa.gov
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SUNRISE AND SUNSET TIMES IN UTC (if you're not logged in to Google)
CHICAGO UTC-6 during CST (Central Standard Time, e.g., winter)
CHICAGO UTC-5 during CDT (Daylight Savings Time, e.g., summer)