SPC Convective Outlooks

SPC Aug 20, 2019 0600 UTC Day 1 Convective Outlook (Di, 20 Aug 2019)
SPC 1200Z Day 1 Outlook Day 1 Outlook Image Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0102 AM CDT Tue Aug 20 2019 Valid 201200Z - 211200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF THE MIDDLE MS VALLEY... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS NORTHERN MN... ...SUMMARY... An organized cluster of thunderstorms capable of severe wind gusts and hail will overspread portions of the middle Mississippi and lower Ohio Valleys today. Hail and isolated strong winds are also possible across portions of Minnesota this morning. ...Mid MS Valley eastward across the OH Valley... An organized MCS will likely be moving through south-central/southeast IA early this morning. Expectation is for this MCS to be near its mature phase at this point with a well-developed rear-inflow jet and strong cold pool resulting in strong wind gusts. A few of these gusts could be greater than 75 mph. As the MCS continues southeastward through northwest MO and central IL later this morning and into the early afternoon, it is expected to gradually lose intensity as its cold pool accelerates and loses depth. By the time the MCS reaches IN and western KY, it is expected to be characterized by weakly organized multicells along the cold pool. Even with this anticipated weakening, strong wind gusts are still possible. ...Central High Plains/Central Plains... A cold front is expected to push into the Upper Midwest and central Plains, likely extending from western WI southwestward into northeastern CO during the late afternoon. Moist upslope flow is anticipated into eastern WY/northeast CO behind this front, with the resulting convergence along the lee trough expected to result in thunderstorm initiation. Downstream environment characterized by strong buoyancy and at least moderate vertical shear will support supercell storm structures capable of very large hail and strong wind gusts. These storms are expected to continue eastward into NE during the evening. A strengthening low-level jet will lead to a reinvigoration of any ongoing storms and/or development of new storms, primarily across central and eastern NE. Given the presence of ample low-level moisture and steep mid-level lapse rates, large hail is probable with these storms. Isolated very large hail (i.e. greater than 2" in diameter) is possible. Dry mid-levels could also contribute to strong wind gusts. ...Upper Midwest... Ample low-level moisture and steep mid-level lapse rates will result in strong buoyancy ahead of the approaching cold front this morning across northern/central MN. Stable low-levels (below 850 mb) will likely limit storm strength but large hail and occasional strong gusts through the stable layer are possible. ...Northern Mid-Atlantic... Showers and thunderstorms will likely develop during the afternoon within the moist and diurnally destabilized air mass across the region. Vertical shear will be weak, leading to predominately disorganized, outflow-dominant multicells. Even so, the very moist air mass and steep low-level lapse rates support water-loaded downbursts capable of damaging wind gusts. ..Mosier/Nauslar.. 08/20/2019 Read more
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SPC Aug 20, 2019 0600 UTC Day 2 Convective Outlook (Tue, 20 Aug 2019)
SPC 0600Z Day 2 Outlook Day 2 Outlook Image Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1254 AM CDT Tue Aug 20 2019 Valid 211200Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE NORTHEAST... ...SUMMARY... Scattered storms, some severe, are possible Wednesday over parts of the Northeast, and over much of the central Plains into the mid Mississippi Valley. Damaging wind gusts and marginal hail are possible in both regions. ...Synopsis... An upper low will move from Ontario into Quebec, with a leading shortwave trough moving across the Great Lakes during the day and New England overnight. A cold front will stretch from southwest Ontario to IL by late afternoon, with mid to upper 60s F dewpoints spreading into the Northeast. Aiding moisture advection as well as low-level shear will be southwesterly 850 mb winds increasing to 25-30 kt, while mid to upper level winds increase throughout the period. To the west, a convectively reinforced boundary is expected across northern MO, KS, and into eastern CO, with a very moist and unstable air mass to the south. Bouts of thunderstorms are likely throughout the period near this boundary, with the greatest concentration over MO, closer to the Great Lakes trough influence. ...Northeastern states... Heating will lead to numerous thunderstorms across the moist sector by 18Z over much of NY and northeast PA, expanding across New England during the afternoon. Around 30-35 kt of deep-layer shear and 100-150 m2/s2 effective SRH will be sufficient to sustain severe storms, including isolated supercells capable of marginal hail, a brief/weak tornado, or damaging wind. Due to the expected large number of storms, mergers are likely, and a few line segments may form as well. Storms may persist well into the evening and overnight into northern New England when the stronger height falls occur. ...Central Plains into the Mid MS and lower OH Valley... Storms are expected to be ongoing from NE across MO and into IL Wednesday morning along an east-west oriented front, and where substantial instability will exist. This outflow-reinforced front will likely translate south during the day, with continuous areas of storms over KS, MO, and IL. Winds aloft will generally be westerly and below 20 kt, thus disorganized storms are most likely. However, a few small bows are possible, with localized areas of wind damage. Given such strong instability, the strongest storms may produce hail. To the west, east/northeast surface winds will bring a moist air mass into east-central WY and CO, where capping will be a concern. Storms are likely to form over the higher terrain, with a narrow north-south zone of hail or wind threat. Other storms are likely farther south in the well-mixed and hot air, from northeast NM across northern OK and AR, with localized downbursts possible. ...MAXIMUM RISK BY HAZARD... Tornado: 2% - Marginal Wind: 15% - Slight Hail: 5% - Marginal ..Jewell.. 08/20/2019 Read more
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