Download Collected Rules of Thumb

Rules of Thumb
 Unsettled
weather (clouds and
precipitation) is typically associated
with Low pressure systems !
 Relatively tranquil weather is usually
found in the vicinity of high pressure
systems.
ATM OCN 100 Summer 2002
3
Rule of thumb
 When:
– Air temperature falls to within 2 to
3 Fahrenheit degrees of dewpoint
and
– Winds are light
 Then:
– Fog often forms.
ATM OCN 100 Summer 2002
4
Rule of thumb
 If
you can expect
– Clear skies
– Near Calm conditions
 Then:
– Afternoon dewpoint provides good
predictor of following morning’s
low temperature.
ATM OCN 100 Summer 2002
5
Rule of Thumb
 Tightly
packed isobars, means
stronger winds!
ATM OCN 100 Summer 2002
6
Rule of Thumb
 The
tighter the packing of the
isobars, the stronger the winds!
ATM OCN 100 Summer 2002
7
Rules of Thumb
Other
things being equal:
–Cloudy nights have higher
temperatures than clear nights.
–Cloudy days have lower
temperatures than clear days.
ATM OCN 100 Summer 2002
8
Rules of Thumb
 Unsettled
weather (clouds and
precipitation) is typically associated
with Low pressure systems !
 Relatively tranquil weather is usually
found in the vicinity of high pressure
systems.
ATM OCN 100 Summer 2002
9
Rules of Thumb
From Table 16.5 (p. 391) Moran & Morgan (1997)
 At
night, air temperatures will be
lower if the sky were clear thin if the
sky were cloud-covered.
 Why?
ATM OCN 100 Summer 2002
10
Rules of Thumb
From Table 16.5 (p. 391) Moran & Morgan (1997)
 Clear
skies, light winds and a fresh
snow cover favor extreme radiative
cooling and very low air temperature
by dawn.
 Why?
ATM OCN 100 Summer 2002
11
Rules of Thumb
From Table 16.5 (p. 391) Moran & Morgan (1997)
 Falling
air pressure may indicate the
approach of stormy weather,
whereas rising air pressure suggests
that fair weather is approaching.
 Why?
ATM OCN 100 Summer 2002
12
Rules of Thumb
From Table 16.5 (p. 391) Moran & Morgan (1997)
 The
appearance of cirrus,
cirrostratus, and altostratus clouds
(in that order) indicates overrunning
ahead of a warm front and the
possibility of precipitation.
 Why?
ATM OCN 100 Summer 2002
13
Rules of Thumb
From Table 16.5 (p. 391) Moran & Morgan (1997)
A
counterclockwise wind shift from
NE to N to NW (called backing) is
usually accompanied by clearing
skies and cold air advection.
 Why?
ATM OCN 100 Summer 2002
14
Rules of Thumb
From Table A.1 AMS Datastreme/OLWS (2002)
A
clockwise wind shift from E to SE
to S (called veering) is usually
accompanied by clearing skies and
warm air advection.
 Why?
ATM OCN 100 Summer 2002
15
Rules of Thumb
From Table 16.5 (p. 391) Moran & Morgan (1997)
A
wind shift from NW to W to SW is
usually accompanied by warm air
advection (and increasing clouds).
 Why?
ATM OCN 100 Summer 2002
16
Rules of Thumb
From Table 16.5 (p. 391) Moran & Morgan (1997)
 If
radiation fog lifts by late morning, a
fair afternoon is likely.
 Why?
ATM OCN 100 Summer 2002
17
Rules of Thumb
From Table 16.5 (p. 391) Moran & Morgan (1997)
 With
west or northwest winds, a
steady or rising barometer and
scattered cumulus clouds, fair
weather is likely to persist.
 Why?
ATM OCN 100 Summer 2002
18
Rules of Thumb
From Table 16.5 (p. 391) Moran & Morgan (1997)
 Towering
cumulus clouds by
midmorning may indicate afternoon
showers and thunderstorms.
 Why?
ATM OCN 100 Summer 2002
19
Rules of Thumb
For Large Scale Pressure Systems
From Chap.1 AMS Datastreme/OLWS (2002)
 Highs
are typically fair-weather
systems.
 Winds circulate in a clockwise
outflow from a surface high.
 Lows are usually stormy-weather
systems.
 Winds circulate in a clockwise
outflow from a surface high.
ATM OCN 100 Summer 2002
20
EJH: From as02-map.ppt
GENERAL RULES for ISOPLETHS
 Determine
appropriate isopleth interval;
 Maintain a particular convention
(e.g., working from highest to lowest);
 Isopleths never cross;
 Isopleths may form a closed loop;
 Isopleths do not end abruptly;
 Smooth isopleths with appropriate interpolation;
 Label isopleths with appropriate numbers.
ATM OCN 100 Summer 2002
21