forecastingmintemps

forecastingmintemps - Forecasting
Tmin
 ATMS 100 1...

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Unformatted text preview: Forecasting
Tmin
 ATMS 100 1 Nighttime
Cooling
 1.
Long
night
 2.
Calm
or
light
winds
 3.
Dry
air
 4.
Clear
sky
 5.  Surface
characteristics
 &
topography
 Results
in
a
radiation
inversion
 2 2.
Calm
or
light
winds
 •  Wind
favors
mixing
air
 3.
Dry
Air
 1.
Air
with
little
water
vapor
will
cool
faster
 than
air
with
high
water
vapor
content
 –  Example:
Las
Vegas
vs.
Miami
 2.  Overnight
low
rarely
drops
below

 dew
point
temperature
 Tmin
≥
Td
 Tmin
&
Moisture
Facts
 Dew
Point
Temperature
(Td)
 –  Temperature
to
which
air
must
be
cooled
for
 saturation
(condensation)
to
occur
 –  Units
°F
 –  Measure
of
actual
water
vapor
content
of
air
 •  •  High
Td
→
more
water
vapor
 Low
Td
→
little
water
vapor
 –  Good
indicator
of
overnight
low
temperature
 “The
Disappearing
Puddle”
 “The
Disappearing
Puddle”
 Liquid
water
+
energy
from
air
→
water
vapor
 EVAPORATION
 Temperature
≡
average
kinetic
energy
 –  If
air
has
less
energy,
then
T
↓
 Evaporation
is
a
cooling
process
 Formation
of
Dew/Clouds
 When
T
=
Td,
condensation
will
occur
 water
vapor
-
energy
→
liquid
water
 CONDENSATION
 Temperature
≡
average
kinetic
energy
 –  If
air
has
more
energy,
then
T
↑
 Condensation
is
a
warming
process
 So
What
About
Tmin?
 •  If
T
drops
to
Td
→
condensation

 •  Condensation
releases
heat
→
T
↑
 •  Tmin
will
hover
near
Td
value
 Tmin
and
Td
 So
what
does
this
say
about
the
value
of
 knowing
Td?
 If
you
know
Td,
you
can
forecast
Tmin
 But
will
this
always
work???
 No! 
 Why
not? 
 •  Winds
mix
the
air
near
the
surface
and
 change
the
moisture
content
(i.e.,
Td)
 •  Moisture
is
advected
in
or
out
of
the
 region
resulting
in
a
change
in
Td
 Diurnal
Cycle
of
RH
 4.
Clear
Sky
 •  Clouds
emit
Infrared
(IR)
energy
 ATMS 100 15 4.
Cloud
Height
 •  Height
of
Clouds
Affects
Temp.
 –  Nights
Warmer
with
Stratus
(low)
 –  Nights
Cooler
with
Cirrus
(high)
 5.
Surface
Characteristics
/
 Topography
 •  Cold
Air
is
More
Dense
Than
Warm
Air
 –  Cooler
in
Valley
 –  Warmer
on
Hillside
 Frost
Formation
 Deposition will occur when the dew point temperature is at or below freezing White crystals are called hoarfrost (white frost) Glass Warm and humid indoor air Cold air outside Heat transfer frost point temperature Is reached conduction Formation of frost on a glass window 18 Frost
Formation 
 When the atmosphere is relatively dry, the temperature may drop below freezing without reaching the frost point temperature – no visible frost forms Such conditions are called freeze frost or black frost Can cause severe damage to crops April 2007 - Widespread severe freeze over much of the east and Midwest causing 2 billion dollars in damage to agriculture How are crops protected from freezing? 19 Heaters set up convection… Turbines mix air from above… 20 ...
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This note was uploaded on 10/08/2010 for the course GEOG 1172 taught by Professor Snyder during the Summer '10 term at Minnesota Colleges.

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