Summer Precipitation across New Mexico: Regimes and Variability

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Summer Precipitation across New MexicoRegimes
and Variability
Kerry Jones Deirdre KannNWS Albuquerque
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Topics Covered

• Summer Precipitation in New Mexico
• North American Monsoon System
• Backdoor Cold Fronts
• Variability of Summer Precipitation
• Summer 2003 vs. Summer 2004

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Summer Precipitation in NM
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Mechanisms Responsible for Summer Precipitation

• North American Monsoon System
• Backdoor Cold Fronts
• General Terrain Forced Convection
  (diurnally-driven)

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Precipitation across the U.S.July August
September ( of Annual)
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Average Summer Precipitation for New Mexico
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North American Monsoon System
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North American Monsoon System (NAMS)
Portions of the southwest United States,
including New Mexico, are influenced by the North
American Monsoon System (NAMS), which is also
referred to as the Southwest Monsoon. Many
locations in New Mexico receive 40 to 50 percent
of the annual precipitation during the period
from July 1 through August 31 and much, but not
all, of the summer rainfall can be attributed to
the Southwest Monsoon.
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North American Monsoon System (NAMS)

• Important elements of the NAMS include
• a temperature contrast between the land and
  adjacent sea surface,
• low pressure at the surface with high pressure
  aloft, and a transport of moisture at low levels
  of the atmosphere.  
• Monsoon climates have a distinct and dramatic
  increase in precipitation associated with the
  onset of monsoon circulations.

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North American Monsoon System (NAMS)
Although New Mexico is not impacted by the NAMS
until July, development of the system takes place
over Mexico during May and June.
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The switch from a westerly flow to a
southwest/southerly flow can be noted in
monthly-averaged sounding data.
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Clockwise circulation around the upper level high
transports moisture from Mexico to the SW U.S.
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Annual Distribution of Precipitation at Deming
In the SW corner of the state, onset is readily
apparent, with an average start date of July 3.
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Annual Distribution of Precipitation at
Albuquerque
The sudden onset is not as apparent at
Albuquerque, where the average start date is July
7.
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Areal Distribution of the North American Monsoon
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Moisture Source

• Numerous authors have attempted to identify the
  primary source of moisture for the monsoon in the
  SW U.S.
• While it remains unclear, there is a consensus
  that most of the low-level moisture arrives from
  the northern Gulf of California.
• The precipitation is enhanced by diurnal heating.
  

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Changes in Upper Level Circulations
Once the westerlies shift to the north and
moisture is in place, circulations associated
with the monsoon may change, but diurnally-driven
convection can still produce convective
precipitation.
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Lightning data illustrates both the onset of the
monsoon and the influence of terrain on summer
convection
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Lightning data also indicates the importance of
heating in our diurnal distribution of
precipitation
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Backdoor Cold Fronts
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Backdoor Cold Fronts

• At least 4 events in 2003, and 7 or 8 in 2004
• Most in 2003 were weak shallow, 2 stronger
  events in 2004 (moisture made it to eastern
  Arizona)
• Gap winds (ABQ)
• Low level convergent boundary between
  Continental Divide and Rio Grande Valley
• Generally favor Eastern Zones

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Significant Convective Events at Albuquerque in
2003
July 20 July 26 August 25 July 23 (mdt) August
14 (mdt) August 16 (weak) August 28-30 (stg)
No Backdoor Front
49 ABQ JJA Precip!!
Backdoor Fronts
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Significant Convective Events at Albuquerque in
2004
July 20 July 27 August 2 June 29 (mdt) July
11(weak) July 18 (strong) July 23-24
(strong) August 10 (weak) August 30 (strong)
No Backdoor Front
68 ABQ JJA Precip!!
Backdoor Fronts
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500 mb Analysis
12Z July 22, 2003
12Z July 23, 2003
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July 23, 200312Z Surface Analysis
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Albuquerque July 22-23, 2003
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July 23, 2003Sounding and Profiler
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Increased Afternoon/Evening Convection West
Central New Mexico
July 22, 2003
July 23, 2003
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KABX WSR-88D
-- Higher dew points spreading westward--
Enhanced low level convergence
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Precipitation Variability
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You know the routine
August 4, 2004 ABQ Sunport Trace ABQ Foothills
2.01 ABQ Sunport 10E 2.08
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Variability of Summer Precipitation
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July-August 2003 vs. 2004
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July-August 2003 vs. 2004Circulation Differences
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Summary

• While the NAM system is responsible for much of
  our summer precipitation, back door cold fronts
  as well as diurnally-driven convection contribute
  to summer precipitation events
• Precipitation across the Southwest, including
  the summer periods, exhibits substantial
  variability. While ENSO can explain some of this
  variability, much of the variance cannot be
  explained and is the topic of current research
  projects.