11PM Day 2 Convective Outlook for Tuesday, February 17. NO SEVERE THUNDERSTORM AREAS FORECAST
SUMMARY
Scattered thunderstorm activity is possible across Pacific coastal areas and the Central Valley of California Tuesday into Tuesday night, as well as across parts of the mid Missouri Valley into Upper Midwest Tuesday night. However, the risk for severe storms appears low.
Discussion
Models continue to indicate that a lower/mid-tropospheric cyclone will weaken while migrating inland of the Pacific Northwest coast Tuesday. However, an initially intense offshore jet is forecast to continue digging south-southeastward across California coastal areas to the south of San Francisco Bay, toward the lower Colorado Valley through late Tuesday night, contributing to the maintenance of amplified larger-scale troughing across and inland of the U.S. Pacific Coast.
Downstream, a broad swath of seasonably strong west-southwesterly mid/upper flow is forecast to continue developing east of the southern Rockies, across the south central Great Plains and Ohio Valley, as the remnants of preceding inland migrating troughing pivot across the northern Rockies and much of the middle/lower Missouri Valley into the Upper Midwest by late Tuesday night. Models continue to indicate that initially deep surface troughing accompanying this perturbation will begin to slowly weaken, but a broad belt of strong southwesterly low-level flow (including 40-50 kt around 850 mb) may be maintained while spreading from the central/southern Great Plains into the Ohio Valley by 12Z Wednesday.
To the west/northwest of the low-level jet axis, a plume of rather modest low-level moisture, including surface dew points in the mid 40s to lower/mid 50s F, may advect from parts of the central Great Plains across and northeast of the lower/mid Missouri Valley, beneath a warm/dry elevated mixed-layer initially overspreading much of the central and southern Great Plains through middle and lower Mississippi Valley. However, substantive Gulf boundary-layer modification and inland return flow still appears unlikely through this period and beyond.
Pacific Coast
Low probabilities for thunderstorm activity may linger into early Tuesday nearly southern California coastal areas. However, the primary convective potential, including scattered thunderstorm development, seems likely to become focused across northern and central California coastal areas into the Central Valley Tuesday afternoon into Tuesday night. This will accompany strong mid-level cooling and forcing for ascent associated with the digging mid/upper jet, which may provide support for stronger cells becoming capable of producing gusty winds and small hail, particularly near coastal areas around San Francisco Bay as early as midday Tuesday. It still appears that the lack of steeper lower/mid-tropospheric lapse rates, and more substantive CAPE, may minimize the potential for storms to reach severe criteria, but this will continue to be monitored in later outlooks for this period.
Mid Missouri Valley into Upper Midwest
Given at least limited low-level moisture return, it still appears that forcing for ascent may contribute to a corridor of thunderstorm development as strong mid-level height falls overspread the region late Tuesday afternoon through Tuesday night. Based on the latest forecast soundings and other model output, the potential for severe hail and strong surface gusts still appears rather low, but perhaps not entirely out of the question. This will continue to be monitored in later outlook updates for this period.