Public Information Statement
Issued by NWS Paducah, KY

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NOUS43 KPAH 171626
PNSPAH
ILZ075>078-080>094-INZ081-082-085>088-KYZ001>022-MOZ076-086-087-
100-107>112-114-180100-

Public Information Statement
National Weather Service Paducah, KY
1126 AM CDT Thu May 17 2018

...Isolated Landspouts possible this afternoon over the Quad State
region...

The atmosphere this afternoon and into the early evening appears
to be conducive for the development of isolated landspouts across
parts of the Quad State Region. At this time, the best potential
appears to be over southeast Missouri and southern Illinois.

The National Weather Service in Paducah Kentucky received a
report of a landspout early Wednesday evening over Butler County
in southeast Missouri.

This weather phenomena is normally experienced across Southeast
Missouri this time of year and is usually referred to as
landspouts or gustnadoes. These landspouts may develop near
thunderstorm outflow boundaries from nearby thunderstorms.

An outflow boundary is commonly referred to as the leading edge
of colder air and gusty winds from thunderstorms. Depending on the
moisture content of the atmosphere, an outflow boundary may
generate a line of clouds and may even appear as a very thin
moving line on radar imagery.

Landspouts usually appear to the eye as very narrow, rope-like
tornadoes coming out of a rather benign cumulus or towering
cumulus clouds. Scientifically, it is a condensation funnel,
resembling a tube reaching from the base of the cloud to the
ground and is not associated with a wall cloud. They are usually
very short-lived and weak. Rarely, landspouts can produce some
minor damage.

Landspouts are NOT associated with supercell thunderstorms, which
are capable of producing deeper and more sustained rotation of air
parcels within a storm that yield a greater threat of severe
weather.

Although thought of as a weather phenomena of in the High Plains
of the United States, Landspouts periodically occur in the
Southern Plains and Mississippi Valley. They are more common
during the Spring and Summer months when there is extremely moist
and unstable air near the surface and changes in wind direction
and speed much higher in the atmosphere and are more subtle and
weak.

Around the Quad State region, the most likely location to see
landspouts is in the the Mississippi Delta region, such as in
parts of Southeast Missouri. These areas usually have a ready
reservoir of much deeper, warm and moist air near the ground.

Interestingly, the formation of landspouts can occur even before
any precipitation is observed or detected by radar. This makes it
difficult for even the most sophisticated radar systems to detect
these short-lived phenomena.

Sometimes, landspouts may develop on the leading edge of an
outflow of cold air that descend from thunderstorms, called a gust
front. A gust front is usually noticeable by a sharp increase in
winds and slightly cooler air that comes from a thunderstorm. Any
observable circulations seen to develop from clouds that develop
on the gust front are commonly referred to as gustnadoes.

$$

Smith



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