Threat for Tornadoes Increasing Wednesday Afternoon & Evening
Wind shear is defined as winds in the atmosphere that change direction and speed with height. Shear values are forecast to increase across the DC Region Wednesday afternoon & evening as the remnants of Fred move through West Virginia. The image below shows shear values increasing above 40 knots across the Metro Area on Wednesday afternoon increasing the odds of some super cells developing that will be capable of producing large destructive hail, damaging winds and tornadoes.
Tropical Systems and Wind Shear
Land falling tropical systems begin to weaken as their circulation in the lower-levels of the atmosphere begin to interact with ground friction. However, the mid and upper level winds remain stronger allowing for increasing wind shear along/east of the system’s main center of circulation, increasing the threat for rotating updrafts and tornadoes.
Energy Helicity Index (EHI) Values Impressive on Wednesday
0-1 km AGL EHI values greater than 1-2 have been associated with significant tornadoes in super cells. The blue and especially yellow colors in image below suggest that the threat of some storms becoming tornadic will remain elevated Wednesday afternoon continuing through the late evening.
Timing Wednesday’s Thunderstorms
A broken line of thunderstorms (some potentially becoming rotating super cells) will move through during the peak heating of the afternoon, likely approaching the western suburbs after 3pm and clearing the eastern shore after midnight. (time stamp in upper left corner of image below).
Have a plan on Wednesday, know what to do during a tornado and have a weather radio or local media outlet available in case tornado warnings are issued for your area.