Monday, July 23, 2012

Latest Model Forecast Highlights Derecho Concern


The latest 0z NAM model forecast continues to highlight the concern of another derecho in the Ohio Valley and Mid Atlantic regions tomorrow, with this latest forecast giving the two Virginias and Kentucky the brunt of this complex.
The image above is valid at 4:00 PM CDT, and highlights 3 hour precipitation in millimeters. Based on the above image, we see a bowing segment placed in West Virginia and Kentucky putting out potentially high precipitation. With any bowing segment comes the risk of damaging winds, but with a derecho this danger is greatly increased.
A derecho is a long-lived wind storm spanning a large area, while a bowing segment involves a small, weaker bow in a much smaller scale region. Considering the strength and span of this bowing segment, as well as the distance it will have travelled (origins from Chicago, IL), I believe that this has the characteristics of a derecho, and would most likely prompt damaging wind potential.

I will issue a special morning post on this matter tomorrow morning with a full model update.

For the initial derecho post, click here.


Derecho May Strike Ohio Valley Tomorrow

For the 9:55 PM CDT Update (7/23), CLICK HERE

There does appear to be potential for yet another derecho tomorrow into the Ohio Valley and Mid Atlantic regions, as the latest NAM model shows a strong bowing segment of storm cells storming through the Ohio Valley at around 4:00 PM CDT. With the potential for a second derecho, one begins to wonder, how does this happen? This summer, there has been a strong ridge of high pressure stationed over much of the Plains into other portions of the nation, and around this ridge is called the 'Ring of Fire' This Ring of Fire earns its name by being the hotspot for multiple complexes of showers and thunderstorms on an almost daily basis. This happens by a warm, moist and unstable air mass surging into an area. The Ring of Fire, which carries with it the Lower Level Jet stream, combines instability and wind shearing into the potential for potentially multiple complexes of showers and storms, also called a mesoscale convective system (MCS). This potential derecho situation looks to be part of this Ring of Fire. 
According to the latest 12z WRF run shown on the left, valid for tomorrow afternoon, there is also a derecho shown, but this one goes more into the Mid Atlanti than into the Ohio Valley. Either way, the potential remains for significant storms to fire tomorrow in the Ohio Valley and Mid Atlantic, and this could become a derecho. It will certainly have to be monitored.

Overnight Severe Weather Possible for the Midwest, Great Lakes

There is a slight risk of severe weather extending from the Northeast into the Midwest and Great Lakes.

A frontal boundary will move through the region late in the day today, and may provoke some isolated thunderstorms. The concern rests overnight, however, with the nocturnal lower level jet stream amping up and providing a safe haven for strong clusters of showers and storms to develop. Given the strengthened lower level jet stream, wind shear in the midst of elevated instability will most likely give way to storms capable of damaging winds and hail. Due to the shearing, a tornado has potential to form as well, but this is not a big concern.

Strong storms have developed in the Northeast and Ohio Valley and are expected to continue to develop and strengthen, with Round 2 possible overnight. Despite the loss of daytime heating, a disturbance with shearing will move into the area and promote severe weather overnight. Large hail and damaging winds are possible.