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Southwest Climate
Bimodal and Unimodal rainfall
Winter precipitation
– Pacific frontal storms
– El Niño
Summer monsoons
Arid Foresummer
What SW climate (precipitation) means
– Vegetation
– Humans
Temperature less interesting for now
MAP (in.)
MAT (°F)
JFMAMJJASOND
Northern Hemisphere Winter
Northern Hemisphere Winter
Winter Pacific front
Maybe to SW
La Niña = normal
Upwelling of cold water to surface of Peruvian coast
Westward flow of warm surface water
Hot air rises over western Pacific
Clouds miss American SW
El Niño = abnormal
Upwelling of cold water slackens, fails
Warm surface water stalls over central Pacific
Hot air rises over central Pacific
Clouds hit the American SW
U.S. Temperature and Precipitation Departures During the Last 30 and 90 Days
Last 30 Days
30-day (ending 16 Jan 2011) %
of average precipitation
90-day (ending 16 Jan 2011) % of average
precipitation
30-day (ending 15 Jan 2011)
temperature departures (degree C)
Last 90 Days
90-day (ending 15 Jan 2011) temperature departures (degree C)
Watch these videos
http://www.youtube.com/watch?v=fN_NmCpr
y38&feature=related
http://www.youtube.com/watch?v=1oKIJIfpR
6U&feature=related
http://www.youtube.com/watch?v=OsYneLonQF
4&feature=related
http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/enso.shtml
Niño
Niña
North Hemisphere Summer
North Hemisphere Summer
6. Cooling air
condenses
1. Incoming
solar
2. Surface
absoprtion
7. Rain
4. Hot air
rises
5. Rising air
cools
3. Surface
emission
Tucson, Water Year-to-Date (2007)
We ended up ca. 1” below normal—few winter rains
Monsoon Rainfall & SW
• Some modern societal segments
“immune” to rainfall variation
– Stored, imported, or ground water
• Critical to non-irrigated agriculture
– Upland “dry” farming
– Ranching
• Flooding.
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Key Points
SW has bimodal (W) and Unimodal (E)
rainfall
Arid Foresummer—always (?)
Winter
– Frontal westerlies
– El Niño
– Decadal variability
Summer
– Monsoonal southerlies
– Fairly consistent