Today’s serious threat, which I discussed in a blog post this morning, has just begun.

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At the time I am writing this blog, no storms are currently meeting or exceeding the critical threshold, but we can see convection shooting out of the shallows. Although tonight’s serious threat is not yet fully organized, we will still discuss the topic of tomorrow’s threat as it is potentially extremely impactful and is something to be aware of in advance.

Via SPC

By now, you’ve probably seen this image shared hundreds of times on social media, and for good reason. Severe storms are expected tomorrow with the potential to significantly affect a sizable portion of the Eastern United States.

But what exactly are the threats I’m referring to?

Unlike last week’s event, where the moderate risk (red) was primarily due to the possibility of a tornado, this week’s event was primarily wind driven.

  • Strong winds will occur not only in the middle levels but also in the lower levels. Based on this forecast sound, which is GFS and likely smooths things out a bit, ~40 kts shear will be available between the surface and 850 mb. That’s an amazing amount of low-end trim.
  • However, stability is somewhat limited, the over-cutting is supposed to fix that problem and serve to hold updates as they form.
  • Low shear forces will also enhance rotation, especially with surface winds from the SE. Therefore, tornadoes may occur within the line.
  • Dry air and strong currents in the middle layers present us with the threat of high winds. GFS estimates ~55 kts at 700 mb in this audio, but some CAMs suggest up to 75 kts at 700 mb. If those winds combine down to the surface, there could be gusts – 75 mph or greater -, making this a significant wind risk.

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As mentioned in the previous blog, the weaker version of QLCS will happen in the morning. As the day wears off and low-level jets begin to pump out warmth and moisture, that stream will eventually enter a much more favorable environment. By late morning or early afternoon, inclement weather flowers will begin to bloom.

Due to the linear nature of the threat, strong winds are likely to exceed or exceed hurricane force as the primary threat. However, low-level strong shear winds and surface winds from SE will enhance rotation and there may be some potential strong cyclones in the route.

It is important to note that this line will move very quickly. Since QLCS tornadoes have historically been harder to warn of because they sometimes come on quickly, you’ll want to be ready to act on your shelter plan as you may not have much time to do so. In addition, given the predicted strength of hurricane-related gusts, I highly recommend taking shelter during severe thunderstorm warnings the same way you would for tornado warnings. Straight winds can do as much damage as a tornado downstairs, if not more. Trees and power lines are expected to fall. Large-scale power outages may occur.

If you recheck that simulated radar loop, you’ll notice a few discrete cells forming in the deep South in front of the line. This is a possibility and would carry a high risk of tornadoes due to shear forces if they could form and persist. However, they are unlikely to last long because the stream of vehicles will move very quickly and can easily pass them. It remains unclear whether these discrete cells actually form. The volatility is expected to be relatively limited and perhaps not enough to spur growth in the open kettle manufacturing sector.

Another important note:

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Pre-arrival winds are forecast to be particularly strong. This could knock down power lines or trees before the storm arrives. Always charge your devices and make sure you have batteries for your weather radio so you can still receive alerts if the power goes out before a storm.

This is still a developing forecast as many of the mid-level details that can have a significant impact on the forecast (changes in instability, surface heat pockets, flow boundaries) will not become clear until tomorrow. Follow your local NWS and broadcast meteorologists for the latest information on your particular area.

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