11.2: Types of Thunderstorms
- Page ID
- 44878
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Severe Thunderstorms
As previously mentioned, thunderstorms are just a part of everyday life for many people, especially in the summertime, and are known as "air mass," or "ordinary" thunderstorms. However, many of the thunderstorms that were occurring in the United States at the time of Figure 11.1.1 were severe thunderstorms. Severe thunderstorms generally last longer than ordinary thunderstorms and can produce very strong winds, flooding, hail, and/or tornadoes. Ordinary thunderstorms are generally short-lived and do not produce very strong winds or large hail. For severe thunderstorms to develop, the following things are necessary:
- Fuel: The previously mentioned ingredients — heat and moisture — are fuel for thunderstorms.
- A layer of Convective Inhibition (CIN) near the surface of the earth, and Convective Available Potential Energy (CAPE) higher up in the atmosphere.
- A lifting mechanism, like a front, low-pressure system, or a mountain range. This "triggers" the lifting of air beyond the layer of CIN near the surface.
- Vertical wind shear: A change in the wind direction and wind speed with height prevents the fuel from running out, and can also provide rotation for thunderstorms.
Vertical wind shear can be of two types:
- Speed Wind Shear: Winds become faster as you rise in the atmosphere.
- Directional Wind Shear: Winds change directions as you rise in the atmosphere.
- Near the surface, winds typically blow from the south, allowing for warm, moist air from the Gulf of Mexico to be fed into the storms.
- A few thousand feet up (about 850 mb), winds begin to shift from south to southwest.
- By about 500 mb, winds shift from southwest to west.
- By about 300 mb, winds shift from west to northwest.
Before continuing, you may want to review the definitions of fuel (Section 11.1), CAPE and CIN (Investigation 5), Fronts (Investigation 10), and Upper-Level Maps (Investigation 8). Figure \(\PageIndex{1}\) shows upper-air data from a Radiosonde Launch at Topeka, Kansas, about 100 miles West of Kansas City, at 1200 UTC (7 am Central Daylight Time) on May 28, 2019.
The following are some True/False questions based on Figure \(\PageIndex{1}\).
- There is a layer of CIN near the surface of the Earth:
- True
- False
- Higher up, a layer of CAPE is present:
- True
- False
- Winds shift from South/Southeast to Southwest/West as you rise from the surface in the atmosphere. Hint: Check the wind barbs.
- True
- False
- Wind Speed does NOT generally increase from the surface to about 150 mb:
- True
- False
- Based on questions 11 and 12, there was adequate wind shear to support severe thunderstorm development.
- True
- False
- In Figure \(\PageIndex{1}\), there was no "trigger" present near the Kansas City/Topeka region:
- True
- False
- Putting all of this together, it was likely that at least some of the thunderstorms over the Kansas City region were severe thunderstorms:
- True
- False
Let’s verify this. Whenever conditions are favorable for severe thunderstorm formation, the National Weather Service will issue an outlook indicating how likely severe thunderstorms are for a particular region. Table \(\PageIndex{1}\) is the guide to how to interpret this information, and Figure \(\PageIndex{2}\) is the Severe Thunderstorm Outlook for the United States, Valid at 2000 UTC on May 28, 2019.
| Risk Category | Description | Threat Details |
|---|---|---|
| Thunderstorms (no label) | No severe thunderstorms expected | Lightning and/or flooding threats may exist with all thunderstorms. |
| 1 - Marginal (MRGL) | Isolated severe thunderstorms possible | Limited in duration, coverage, and/or intensity. |
| 2 - Slight (SLGT) | Scattered severe storms possible | Short-lived and/or not widespread. Isolated intense storms are possible. |
| 3 - Enhanced (ENH) | Numerous severe storms possible | More persistent and/or widespread. A few storms may be intense. |
| 4 - Moderate (MDT) | Widespread severe storms likely | Long-lived, widespread, and intense. |
| 5 - High (HIGH) | Widespread severe storms expected | Long-lived, very widespread, and particularly intense. |
- Based on Table \(\PageIndex{1}\) and Figure \(\PageIndex{2}\), severe storms were _______ at and near Kansas City during this time.
- isolated
- possible
- widespread and likely
- not expected
- This _________ that conditions over Kansas City were favorable for severe thunderstorms to form.
- cannot confirm
- confirms
So, the conditions appear suitable for severe thunderstorms, and the forecast is calling for them, but did they actually occur? The Storm Prediction Center (SPC) in Norman, Oklahoma, a branch of the National Weather Service, also produces maps that show storm reports for given days. Figure \(\PageIndex{3}\) shows Storm Reports over the United States for May 28, 2019. Severe Thunderstorms produce Tornadoes (red), High Winds (blue), and large hail (green).
- According to Figure \(\PageIndex{3}\), there ______ reports of Severe Thunderstorms produced events (such as tornadoes and hail) near Kansas City Area on May 28, 2019.
- were not
- were
- This _________ that conditions needed for severe thunderstorms were present, and that the weather forecasters accurately predicted severe thunderstorms for Kansas City on May 28, 2019.
- confirms
- disproves