Anomalous Summer Precipitation over New Mexico during 2006: Natural Variability or Climate Change? Shawn Bennett, Deirdre Kann and Ed Polasko NWS Albuquerque David Gutzler University of New Mexico

Topics Covered 2006 – A Year of Extremes Variability of the Summer Precipitation Summer Precipitation Regimes in New Mexico 2006 Anomalies Was the record-breaking precipitation accompanied by an increase in frequency?

2006 – A Year of Extremes

The wet summer of 2006 followed an exceptionally dry winter. For the state, the 6-month period of November ’05 through April ’06 was the third driest on record.

July and August 2006 Precipitation Historical persistence of statewide rainfall from July to August is slightly negative (r  -0.16) or the lowest month-to-month correlation of the year, while 2006 was extremely persistent.

Variability of Summer Precipitation July + August

Do relationships exist between the spring snow extent and summer precipitation? Gutzler & Preston (1997) calculated a New Mexico statewide average of Jul-Aug precipitation (dashed line below) and compared it to snow extent across the central U.S. Rocky Mountains (Brown et al. 1985, solid line below) The time series are negatively correlated over the (short) period of record ( ) M-A-M snow

Additional Variability Studies Wet winter  dry summer Dry winter  wet summer Wet winter Dry winter Higgins et al. (1999) examined a slightly longer period and noted that wet (dry) winters were generally associated with wet (dry) summers. Additionally, late (early) onset was associated with dry (wet) summer.

Additional Variability Studies Using snow conditions limited to New Mexico, a local (ABQ) study showed that winters with snow pack less than 50% are generally followed by summers with above average precipitation.

Mechanisms Responsible for Summer Precipitation North American Monsoon System Diurnally-Driven Convection Backdoor Cold Fronts

What Patterns Dominated in 2006? JulyAugust 500 mb Heights

Persistence of the “Monsoon” Pattern in August 30 July through 31 August

August Precipitation Rate and Anomalies Moisture anomalies are confined to a regional scale.

Frequency of Precipitation Precipitation for July and August 2006 was 100% or greater for nearly all locations in New Mexico, but was close to 300% of the long term average at some locations. Were the high precipitation values accompanied by an increase in frequency of rain events?

Frequency of Precipitation In northeast New Mexico (Clayton), frequency and precipitation amounts are fairly well correlated values (red box) demonstrates the above average rain occurred with above average number of days with rain.

Frequency of Precipitation In the north central mountains (Chama), well above average precipitation was accompanied by only a modest increase in precipitation days.

Frequency of Precipitation At stations with record precipitation totals, the frequency of precipitation days did not show a corresponding record value.

Summary Precipitation in the summer 2006 was well-above average for New Mexico. Variability observed in previous studies was noted in 2006, that is, the wet summer followed a dry cool season with snow pack well below normal. Anomalies were confined to a regional scale, with positive precipitation anomalies limited to New Mexico and west Texas. Increases in precipitation amounts for July and August did not necessarily correspond to an increase in the frequency of precipitation.