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Weather conditions on bar directly above are near Lakefront. Tabs under Moon Phases refer to O'Hare (official).

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.

Thursday, May 12, 2022

SPC May 12, 2022 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0259 PM CDT Thu May 12 2022 Valid 122000Z - 131200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF NORTHEAST NEBRASKA...EASTERN SOUTH DAKOTA...SOUTHEAST NORTH DAKOTA...AND WESTERN MINNESOTA... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE LOWER MISSISSIPPI VALLEY... ...SUMMARY... Scattered to numerous severe thunderstorm gusts (some 75+ mph), large hail and a few tornadoes are expected over parts of the eastern Dakotas, eastern Nebraska, western Iowa, and central/southern Minnesota this afternoon into tonight. Other severe storms are expected across the southern Plains and Lower Mississippi Valley. ...Discussion... Only two notable changes were made to the previous convective outlook and are listed below. 1) Upgraded severe wind probabilities from 30% to 45% for northern portions of NE and southeast SD immediately ahead of an evolving bow that is forecast to quickly move north-northeast at 55 kt. Severe gusts ranging from 60-100 mph are possible in the short-term over NE into southeast SD over the next several hours. See MCD #737 for short-term details. 2) Reduced hail probabilities from 30% to 15% for NE and focused the significant hail area to be over eastern SD where supercell convective mode is most likely. ..Smith.. 05/12/2022 .PREV DISCUSSION... /ISSUED 1156 AM CDT Thu May 12 2022/ ...Northern/central Plains and Upper Midwest... Have made spatial (westward) adjustments to the categorical Moderate Risk along with some increased potential for initial severe-discrete storms, which includes the potential for a strong tornado, across South Dakota. In general, scattered to numerous thunderstorms are expected to develop in an arc near the surface low and cold front by mid/late afternoon, from central/eastern South Dakota southward across central/eastern Nebraska and into at least northern Kansas. A brief interval, early in the convective cycle, may support discrete to semi-discrete supercells before the convection becomes quasi-linear. The most common severe type should evolve quickly to thunderstorm gusts through early evening -- some of which may be significant (65+ kt) strength, especially from parts of eastern South Dakota and southeast North Dakota into western Minnesota. The warm sector is forecast to destabilize throughout the day, with a combination of at least weak large-scale ascent (increasing northward), diurnal heating and related lift from below, and ultimately frontal convergence, eliminating a basal EML inversion and supporting convection initiation. Activity is expected to intensify quickly as it impinges on a narrow but very favorable prefrontal corridor where 60s to near 70 F surface dewpoints contribute to MLCAPE in the 3500-4500 J/kg range in and near the "moderate" area, decreasing gradually with southward extent as more low-level moisture is mixed out. Low-level and deep shear will be greatest near the triple point and warm front across South Dakota, with 300-500 m2/s2 effective SRH and 45-55-kt effective-shear magnitudes. A substantial component of mid/upper winds parallel to the axis of convective forcing indicates potential for fairly fast merging of early discrete and sporadically supercellular convection. Surges of wind from resulting LEWP/bowing segments will pose the greatest overall severe hazard, with line-embedded mesovortices and perhaps a few associated tornadoes also possible. With the warm sector's not being very broad, the convective event should diminish late this evening into early overnight hours as it outruns the most favorable instability. ...Eastern Minnesota/northern Wisconsin/northern Michigan today... An ongoing linear complex of storms may persist eastward today in vicinity of the warm front and nearby moist/unstable air mass. For additional details, see Mesoscale Discussion 733. ...Portions of Mississippi/Louisiana and western Alabama... Have upgraded portions of the region to a categorical Slight Risk. Morning upper-air data reflects moderately strong north-northeasterly mid/high-level winds across the region to the west of the low centered in the Atlantic off the coastal Southeast. Ample insolation/heating is occurring in conjunction with a moist air mass across the region. This will contribute to scattered thunderstorm development this afternoon with gradual clustering and some potential for upscale evolution into multiple southwestward-moving semi-organized clusters. Isolated wind damage is expected to the primary severe hazard. Read more CHECK UPDATE ZOOM GRAPHIC
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