1PM Day 1 Convective Outlook for Wednesday, February 18. NO SEVERE THUNDERSTORM AREAS FORECAST
SUMMARY
Organized severe weather is not expected today or tonight.
20Z Update
Only minor changes were made to the ongoing thunderstorm forecast based on recent observational trends. See the previous discussion for additional information.
Synopsis
Recent satellite imagery shows a very active upper pattern with numerous shortwave troughs embedded within the broad troughing that covers the CONUS. Lead shortwave in this series is currently maturing over the Upper Midwest, with evolution into a cyclone expected by this evening. A pair of lower amplitude shortwaves exist farther west, one entering the central Plains and another over the southern Great Basin. Lastly, a strong shortwave is currently dropping quickly southward through the northeast Pacific, preceded by yet another low-amplitude shortwave moving into the central CA Coast.
All of these waves are displaced either north or west of the better low-level moisture, which is in place from central TX to the central Gulf Coast. This displacement will mitigate the overall severe potential, although thunderstorms are still expected across several areas, including the central Intermountain West into the central Rockies ahead of the southern Great Basin shortwave, and along the West Coast as the northeast Pacific shortwave drops south along the coast. Highest coverage ahead of the Great Basin wave will likely occur along the UT/CO this evening. Highest coverage along the West Coast is anticipated along OR coast where multiple bands should move through during the period. A secondary max is likely farther south in the Monterey Bay Vicinity late tonight/early tomorrow morning.
Isolated elevated thunderstorms also remain possible this afternoon from Lower MI into northeast OH/northwestern PA as the vorticity max currently over OH moves into the region. Mid-levels will be dry but lapse rates will be steep, and there could be just enough low-level moisture to support limited buoyancy and a few thunderstorms as the vorticity max moves through.
Lastly, strengthening low-level flow within the moistening low-level airmass could support a few isolated thunderstorms across Middle TN and adjacent far south-central KY tonight.