SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1229 PM CDT Fri Sep 13 2019 Valid 141200Z - 151200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF MID MO AND UPPER MS VALLEYS...THE EASTERN FL PENINSULA...AND CENTRAL/SOUTHERN AZ... ...SUMMARY... Strong to severe storms may impact parts of the mid Missouri and upper Mississippi Valleys Saturday afternoon and evening. A few thunderstorms associated with a tropical system may also pose a risk for strong wind gusts and isolated tornadoes across parts of the east central Florida peninsula. Strong wind gusts are also possible across central and southern Arizona Saturday afternoon and evening. ...Synopsis... Moderate, predominantly zonal upper flow is expected across the northern tier of CONUS on Saturday with flattened ridging remaining in place over the southern CONUS. A low-amplitude shortwave trough embedded within the stronger westerly flow will move from its early period position over the northern Plains eastward through the Upper MS Valley and Upper Great Lakes. At the same time, a weak surface low associated with this shortwave is expected to move from central SD northeastward into southern MN. A cold front attendant to this surface low will move across the northern Plains for much of the day Saturday. However, the southern portion of this front is expected to slow down and eventually stall late Saturday night/early Sunday morning. Farther south, a tropical cyclone will likely be centered over the northern Bahamas early Saturday morning. This storm is expected to move gradually northwestward throughout the period. ...Mid MO Valley into the Upper MS Valley... Strong moisture advection is anticipated across the central and southern Plains on Saturday, bringing upper 60s dewpoints in the Mid MO and Upper MS Valleys by late Saturday afternoon. As a result, a moist and moderately buoyant warm sector beneath moderate vertical shear. The strongest forcing for ascent will likely remain north of the region and convergence along the front will be limited by pre-frontal veering of the surface winds. These factors are expected to keep the overall storm coverage isolated. Even so, the few storms that do develop will likely be capable of large hail and damaging wind gusts. Additionally, any robust storms near the warm front may also pose a risk for a tornado or two. Anticipated storm coverage currently precludes higher severe probabilities but upgrades may be needed in subsequent outlooks if higher storm coverage appears more likely. ...Eastern FL Peninsula - Potential Tropical Cyclone Nine... Recent intensity guidance from the National Hurricane Center suggests the cyclone will have reached Tropical Storm intensity by the beginning of the Day 2 period (i.e. 12Z Saturday). Latest forecast track keeps the center about 60-70 mi off the east-central FL coast, which keeps the strongest winds (and highest wind/tornado risk) offshore. Best chance for any damaging wind gusts and/or a tornado is currently along the immediate coastal areas of the eastern FL Peninsula during the afternoon when thunderstorms are most likely. However, any westward shift in the storm's path could result in damaging wind gusts/tornado risk farther inland. ...Central/Southern AZ... Scattered thunderstorm coverage is anticipated across central and southern AZ as low-level moisture surges northward into the region and a weak vorticity maximum approaches from northern Mexico. Expectation is for thunderstorms to develop during the early afternoon across the higher terrain, with some potential propagation into the lower deserts thereafter. Mid-level flow will be very weak but the deeply mixed boundary layer is still expected to support a few strong wind gusts and low severe probabilities have been introduced as a result. ...MAXIMUM RISK BY HAZARD... Tornado: 2% - Marginal Wind: 5% - Marginal Hail: 5% - Marginal ..Mosier.. 09/13/2019
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