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A fast-moving and potentially powerful complex of thunderstorms could pass near or directly through the Washington area early Tuesday morning.
If the complex reaches its full potential and hits the area directly, it could unleash torrential rains and destructive gusts, creating dangerous conditions for Tuesday morning travel. However, it remains possible that the storms are not particularly intense or just bypass the Washington area, moving north or south.
The most likely time for any storms would be between about 6 and 10 a.m., arriving first on Corridor 81 Highway and last in Southern Maryland.
Early Monday afternoon, the storm complex was just beginning to take place in Wisconsin. By late afternoon, a storm zone was expanding near the Indiana-Ohio border.
Computer models typically design the complex to boost over the Ohio Valley on Monday night toward early Tuesday before heading southeast across the Appalachians to Pennsylvania, Maryland, northern and central Virginia and the county.
The complex is expected to develop on the northern periphery of a thermal dome, generating record high temperatures in the central United States. This area – where hot, unstable air meets cooler air and storms tend to erupt – is sometimes called the “ring of fire”.
The record heat wave is spreading east; over 100 million under signals
There is an external chance that the turbulent complex, known as the mesoscale convection system, will meet the criteria for a tree – a vast, fast-moving, long-lasting and violent bow-shaped gust. However, if a gorge forms, it is unlikely to be as strong as the scandalous event about a decade ago on June 29, 2012.
The National Meteorological Service’s Storm Forecasting Center put the region below level 2 of 5 at risk of severe storms on Tuesday. Areas in the north-west are at even higher risk – up to level 4 out of 5 – “pending a highly organized MCS / possible dereu development”.
The storm complex has the potential to generate widespread wind damage spanning multiple countries as it approaches the Mid-Atlantic region early Tuesday.
The complex will be traced along a stopped front along the top of the thermal dome as it moves from northwest to southeast. This front is depicted in the forecast meteorological map of the surface, valid at 8 am on Tuesday. The hard chestnut color over West Virginia indicates the probable location of the severe weather threat:
Whether this complex will continue in an intense and damaging state, east of the Appalachians, is very uncertain. The projections of the model show that this is a possibility, as shown in the simulation of the NAM high-resolution model below.
We define derecho as a fast-moving complex of thunderstorms that generates a destructive wind slope of at least 250 miles, with multiple continuous gusts above 58 mph, and sometimes higher (ie, in the range of 70-80 mph).
But not all derechos are the same, as they seem to exist in a spectrum of intensity and size. If this complex is considered a gorge, its intensity can be mitigated by the morning, when there was not enough sun to destabilize the atmosphere.
Derecho science: The debate over what is derecho and what is not
The heavy gorge arrived here late in the evening on June 29, 2012, one to two hours after sunset, in the afternoon, when the temperature reached 104 degrees – the highest temperature in Washington in June. This heat wave caused an extremely volatile air mass – among the most volatile ever measured in the region – which lasted several hours after sunset.
In contrast, the June 13, 2013, one of the two that hit the Mid-Atlantic that day managed to cross the Appalachians in the very early hours of the morning, but was in a rather torn state with minimal wind damage since reaching Washington.
In other words, the timing of the Appalachian crossing and the arrival on the eastern slopes of any storm complex seems to be important in terms of the outcome of the gorge. Chances may be for a less organized or weaker system when the storm complex arrives on Tuesday.
However, as some models continue to simulate an angry storm hitting the DC area on Tuesday morning, we need to take this threat seriously. Even if the mountains are really bitten by the storm complex and the atmosphere is slightly unstable, a vast and deep “cool pool” containing high-pulse air can allow the system to stay at an intense level for a while east of the mountains.
The CWG will monitor upward trends, updated models and early evening observations on weather balloons, and will publish updates on the situation at the top of this story.
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