There's been a lot of debate the past 24 hours about whether the system that went from Wisconsin to Tennessee was actually a derecho. By the definition below from the SPC, the derecho yesterday met all the requirements. While not as big as the June 29 Super Derecho, the derecho yesterday was moving over 50 mph, had wind damage all along its path and moved over 240 miles. The highest wind speed was 80 mph at Crown Point Lake, Ind.
To point things in perspective, we typically see these types of derechos at least 3-5 times a summer. The Super Derechos, we see every 5-10 years on average, so you can see how some might think yesterday's was not one.
Food for thought.
Definition of a derecho
A derecho (pronounced similar to "deh-REY-cho" in English, or pronounced phonetically as "") is a widespread, long-lived wind storm that is associated with a band of rapidly moving showers or thunderstorms. Although a derecho can produce destruction similar to that of tornadoes, the damage typically is directed in one direction along a relatively straight swath. As a result, the term "straight-line wind damage" sometimes is used to describe derecho damage. By definition, if the wind damage swath extends more than 240 miles (about 400 km) and includes wind gusts of at least 58 mph (93 km/h) or greater along most of its length, then the event may be classified as a derecho.
Severe weather today will be across the Great Lakes as shown on the map below. Main impacts will be gusty winds and some hail. Thursday could be a big day for severe weather in New York and Pennsylvania to Ohio and West Virginia. The right rear quadrant of the jet will be over that area in the afternoon, and the front will be pressing southeast. Surface dew points will rise to near 70, and temps near 90 will only add fuel to the storms. I expect a line of storms to develop along the front with wind damage and hail being the main impacts. SPC may upgrade that area to a moderate risk later today or Thurs AM.
Heavy rains associated with the upper-level low will hit the Carolinas into Virginia. Some areas could get over a foot of rain by Monday!
The heavy rains are still coming and someone is going to have up to a foot of rain and flooding.
Major problems the end of the week and weekend as another round of flooding rains occur and Joaquin could impact the mid-Atlantic.
The Northeast will be the center for flooding rains through the weekend. Joaquin could bring troubles late in the weekend.
A stormy week for the Eastern part of the country. Heavy rains will be the main issue.
Stormy along the East coast this weekend and perhaps in the Gulf of Mexico late in the weekend and early next week.