MET 4300/5355 Severe
Weather
Lecture 1
Introduction
Course Organization
• Tu/Th 11:00AM-12:15 PM, AHC5 Rm357
• Haiyan Jiang, 305-348-2984,
AHC5 Rm371, haiyan.jiang@fiu.edu
• Office Hours Tu 12:15-1:15 PM, or by
appointment
• Previous General or Introduction to MET course.
• On-line course materials at:
http://faculty.fiu.edu/~hajian/MET4300/MET4300.html
• WxChallenge (Local manager Alannah Irwin will
stop by on Thursday Jan 22 after class )…
Grades:
Grading Factors
Participation
10%
Term-paper
(Graduate)
10%
Exam #1
20%
Exam #2
20%
Final
50%(Under)
40% (Graduate)
Total
100%
Absence:
• Need a valid excuse (in-class
exercises are counted toward
your grade)
Text:
Textbook:
• 27 chapters: we’ll cover 22 of them
• Website: weather links and animations/photos
– http://severewx.atmos.uiuc.edu (for 3rd edition);
– http://webcom8.grtxle.com/severeweather (for 4th edition,
access code comes with the book)
• Special sections:
1). List of learning Objectives
2). Check your understanding
3). Test your understanding
4). Test your problem solving skills
5). Use the website (animations don’t work in my laptop??)
6). Focus box (case, advanced topics, etc.)
Suggestions
• Preview the chapter
• Read the text, start with learning
objectives
• Pay attention to “check your
understanning” questions while
reading
• ”Answer “Test your understanding”
questions after reading the chapter
• “Test your problem-solving skills”
Class Activities:
• From “Active Learning
Exercises” book or textbook “test
your problem solving skill”
questions
• Due in class, counting 10% of
your total grade
• No Make-ups
Exams:
• Total 3 exams: Exam 1, 2, and
final
• Final exam on Apr. 30 (Thursday)
9:45am-11:45am (same on
pathersoft)
• Your input about exam time?
Course Focus:
Severe & Hazardous Weather
Course Topics
• 1/3 of the whole course will cover some very
basic meteorology concept (lec 1-11;
textbook CH1-9)
• The rest: different types of severe &
hazardous weather including lee cyclone,
northeasters, ice storms, lake-effect snow,
cold waves, blizzards, mountain
snowstorms, mountain windstorms,
thunderstorms, tornadoes, hailstorms,
lightning, and downbursts.
What is severe weather?
• Large, damaging hail
(20 mm, or ¾ in)
• Damaging winds (60
mph, 50 kt, or 25 m s-1)
• Tornado
• Or all of the above
• Strong updrafts!
Severe Weather =
“MESOSCALE” Weather
• Meso = Middle, between Macro- and Microscale
• Or between “Synoptic” and “Convective”
• Actually includes Convective scale, too.
• Horizontal scale is determined by surface
properties or natural scales of convective
systems
• Vertical scale is defined by the depth of the
troposphere.
What is Hazardous Weather?
• The definition is much broader than severe
weather.
• Hazardous weather includes all types of
weather that has hazardous impacts.
• It includes almost all scales of weather
systems, not only mesoscale.
MET SCALES
Scales of Atmospheric Motion
Scale
Length
Time
Planetary
~6000 km (Re)
Weeks
Synoptic
~ 2000 km
days to a week
Meso-α
2000-200 km
A day or two
Meso-β
200-20 km
A day-hours
Meso-γ
20-2 km
Hours-minutes
Convective
5 km – 500m
Minutes
Micro
< 2 km
Minutes-seconds
Orlanski, 1975
Planetary
Waves
Synoptic-Scale
Weather in 1863
Synoptic-Scale
Weather
Meso- 
Radar, which maps hydrometeors
(primarily rainfall) is a key instrument
for understanding the mesoscale
Meso-Antiyclone
Gust Front
Gust front: the leading edge of cool air
rushing down and out from a thunderstorm.
Downslope wind (Chinook,
snow eater) is a wind directed down a slope,
often used to describe winds produced by processes
larger in scale than the slope.
Suction vortex are really substructures of
many, perhaps all, tornadoes but are not always
easily visible. These occur, usually, at the base of the
tornado vortex where the tornado makes contact with
the surface.
Dust devil is a
strong, well-formed, and
relatively long-lived
whirlwind, ranging from
small (half a metre wide
and a few metres tall) to
large (more than 10 metres
wide and more than
1000 metres tall). The
primary vertical motion is
upward. Dust devils are
usually harmless.
Summary
• Severe weather
– Large, damaging hail (20 mm, or ¾ in)
– Damaging winds (50 kt, or 25 m s-1)
– Tornado
– Or all of the above
• Hazardous weather: include all scales of weather
• Scales of motion
–
–
–
–
Planetary & synoptic—balanced > 2000 km
Mesoscale---nonbalanced, 2000-2 km
Convective—buoyant motions, 5-0.5 km (scale height)
Microscale---near surface < 1 km