11PM Day 1 Convective Outlook for Tuesday, February 17. NO SEVERE THUNDERSTORM AREAS FORECAST
SUMMARY
Thunderstorms are possible across Pacific coastal areas much of California Tuesday, and across parts of the mid Missouri Valley into the Upper Midwest late. The risk for severe storms appears low.
Pacific Coastal States
An upper low will drop south toward the coastal Pacific Northwest today as a strong upper speed max noses into central CA by 00Z. This feature will translate southward overnight and into southern CA by 12Z Wed. North of the upper jet, very cold temperatures aloft will exist which will result in a few hundred J/kg SBCAPE despite cool surface conditions. While favorable shear profiles will develop southward through the central valleys, surface temperatures will largely be in the 40s to perhaps lower 50s F, with generally limited heating. Very small hail cannot be ruled out in the strongest convection given long hodographs and such cold temperatures aloft, but severe storms are not currently forecast.
Mid MO Valley / Upper Midwest
A leading shortwave trough will move into the Plains today, with a strong speed max aloft from NM into KS by 00Z. The strongest cooling aloft and lift will occur from NE into the Dakotas, and into western MN/IA be evening. Low pressure will develop into SD during the afternoon, with a cold front pushing toward the mid MO Valley. While surface heating as well as boundary-layer mixing will steepen low-level lapse rates in the veered flow, it appears capping may hold atop the plume of 40s F dewpoints ahead of the wind shift. An isolated thunderstorm cannot totally be ruled out through 00Z, but a greater chance will exist as minimal elevated instability develops near the nose of the 850 mb jet with lift focused across MN and WI. Instability does not appear strong enough to support severe hail with this elevated activity.