SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0100 AM CDT Wed Jul 17 2019 Valid 171200Z - 181200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF THE MID-UPPER MS VALLEY...NORTHERN MN...NORTHERN HIGH PLAINS...AND NORTHEAST... ...SUMMARY... Severe thunderstorms capable of severe wind gusts and large hail are possible across portions of the northern High Plains and mid-to-upper Mississippi Valley through tonight. Storms capable of damaging wind gusts will be possible across portions of the Northeast this afternoon and evening. ...Minnesota/Iowa into the mid MS Valley... A great deal of uncertainty remains regarding convective evolution leading into the Day 1 period across portions of MN/IA and vicinity, but a substantial severe threat may evolve later today somewhere in the vicinity of IA and southern MN, and potentially further south into the mid MS Valley. Substantial midlevel flow will move into MN and northern IA in conjunction with a shortwave trough, while a seasonally strong low-level jet will impinge on this region from the SSW. Strong to extreme buoyancy will develop south of any convective outflow this afternoon, as steep midlevel lapse rates over spread a very warm and moist boundary layer. The timing, intensity, and location of any early morning thunderstorm clusters and subsequent redevelopment remain highly uncertain, however. Possible scenarios include one or more progressive MCSs capable of damaging wind swaths, and also supercell development along outflow boundaries, capable of large hail and possibly a couple of tornadoes. An upgrade to severe probabilities in subsequent outlooks is possible if the potential scenarios become clearer. Further north across northern MN, shear profiles will be quite favorable for organized convection, but the amount of available instability will largely depend on convective development (or lack thereof) further south. If a substantial MCS impacts southern MN during the day, that will likely limit destabilization further north, but if the environment across northern MN remains mostly undisturbed, then there is some potential for organized clusters and perhaps a couple of supercells capable of large hail, damaging wind, and perhaps a tornado. ...Northern High Plains... While the northern High Plains will generally be between shortwave troughs for most of the day, a belt of stronger midlevel westerly flow will persist across this region, with some potential for winds to veer to southeasterly during the afternoon, maintaining sufficient low-level moisture for moderate buoyancy by late afternoon into the Black Hills and eastern WY. Some uncertainty remains regarding storm coverage remains in this region, but there is some potential for a couple of supercells with an attendant risk of large hail and severe wind gusts. ...Central High Plains... Widely scattered thunderstorm development is possible late this afternoon across in the hot and well-mixed regime from southwest NE into western KS. Shear will be weaker compared to areas further north, but sufficient to support some modest storm organization. Steep low-level lapse rates will support a threat of isolated severe wind gusts. ...Ohio Valley into the Mid Atlantic and Northeast... As the remnants of T.C. Barry get caught up in the westerlies, some enhancement to the low/mid-level flow is expected later today. Midlevel lapse rates will be weak throughout the region, but substantial heating of a moist airmass (PW values generally between 1.5 - 2 inches) will result in the development of moderate buoyancy from the OH Valley into the Mid Atlantic and portions of the Northeast. Widespread convection will move across this region this afternoon into this evening, with thunderstorm clusters capable of locally damaging wind possible. The best overlap of shear and buoyancy is forecast to occur from PA into southern New England, where the greatest relative threat of damaging wind is currently forecast. Flow/shear will be weaker into the Mid Atlantic, but still sufficient for wet microburst potential given strong heating and steep low-level lapse rates. ..Dean/Squitieri.. 07/17/2019
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