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Halloween Week: The Ingredients for Scary Weather

October 30, 2013

When people think of severe weather, they probably think of springtime. But fall is another part of year when meteorologists expect hail, high winds, and even tornadoes.

As the last week of October finishes, severe weather will once again rear its head, bringing periods of thunder and lightning from the Plains to the Mississippi Valley.

(MORE: Tornadoes in October, November: Fall Considered Second Severe Season)

We’ve been telling you that severe thunderstorms will be rumbling, but what meteorological elements are coming together for this late season event?  Below is an analysis of the ingredients that could help create this week’s severe weather.

Thursday, Oct. 31

Weather on Halloween could be pretty scary from some in and around the lower Mississippi River Valley and the Ohio River Valley.  Hail, high winds and isolated tornadoes are all possible.

(MORE: TWC's Exclusive TOR:CON Index)

Background

Thursday's Severe Ingredients

Thursday's Severe Ingredients

Thursday's Severe Ingredients

Thursday's Severe Ingredients
Background

Thursday's Severe Threat

Thursday's Severe Threat

Thursday's Severe Threat

Thursday's Severe Threat

Here’s what we know:

  • Moisture: ?As a strong low-pressure ejects into the midsection of the country, moisture will continue to stream north. Moisture is a key component in determining the buoyancy – or how easily air can move up and down.  If the air is buoyant, it makes storm initiation much easier. A stream of moisture will continue pouring into the Southeast.  Dew points will be in the upper 60s area-wide. Dew points in the 70s, closer to the coast, aren’t out of the question.
     
  • Energy: Energy – more specifically CAPE, or Convective Available Potential Energy – is integrally linked to moisture and helps meteorologists determine the atmosphere’s instability.  Generally, the higher the moisture, the higher the CAPE. CAPE can also give us an idea of how strong thunderstorm updrafts might be, and that allows meteorologists to have insight into the robustness of potential storms that develop.At this point, CAPE looks pretty limited on Thursday, around 500 J/kg. If more sunshine is forecasted, instability could increase.
     
  • Forcing: ?Forcing is a general term that meteorologists use to describe how certain atmospheric features – like a front – will affect an air mass.  Think of it this way: A bulldozer uses force to move dirt forward.  A frontal feature, like a cold front or dryline, is a forcing mechanism that pushes air forward and up.The cold front will continue its eastward march as the parent low-pressure system pulls up to the northeast. The majority of the storm activity will focus on the front.
     
  • Mid-level Temperature: Around 700 millibars, or roughly 10,000 feet in the air, meteorologists focus on the atmosphere’s temperature.  More specifically, we’re looking at a temperature inversion.  That’s where this area of the atmosphere is warmer than parts above or below it. It acts as a barrier to rising air. Think of a lid on a pot of boiling water: the lid traps the hot air and when you remove the lid, hot air races up.  That’s kind of how an atmospheric capping inversion works.  If the cap is too strong, the severe weather potential is pretty limited. The capping inversion won’t have much of an impact on storm development.

(FORECAST: Memphis, Tenn. | Nashville, Tenn. | Paducah, Ky.)

It’s important that you remain weather-aware though Halloween night. Check back with us frequently. We’ve got all the forecast information you need at this link.

MORE: Mitch Dobrowner - Storms

San Juan County, N.M.

San Juan County, N.M.

'Shiprock', San Juan County, N.M., 2008 from 'Storms', photographs by Mitch Dobrowner (Aperture, 2013)

  • San Juan County, N.M.
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