NWS ABQ - 1941 Extreme NM Precipitation

This web feature is a summary of a project focused on an observational analysis of the wettest year on record in New Mexico, the year 1941. The overarching goal of this project was to explain how and why the year 1941 was so abnormally wet across all of New Mexico and if these conditions are likely to occur again. Many different variables and climatic indices were examined, including the Palmer Drought Severity Index (PDSI), monthly precipitation statistics, temperature, monsoon rainfall, sea surface temperature (SST) anomalies, historic weather map analyses, tropical storm remnants, synoptic-scale composites, analyses of individual conditions that produce certain storm events, and external factors such as El Niño-Southern Oscillation indices over various spatial and temporal extents.

The 1941 anomaly was initially quantified through an evaluation of the severity, area, and duration (SAD) of precipitation anomalies. The percent of normal precipitation for climate divisions (sub-regions of each state that have relatively uniform climate characteristics) ranged from 100 to 300 percent of normal when comparing monthly precipitation for the climate divisions for New Mexico and adjoining states for different time periods. Shown to the left are the climate divisions in Utah, Arizona, Colorado, New Mexico, and Texas with 1941 precipitation values compared to a 60-year (1951-2010) time scale. Divisions in eastern New Mexico, western Texas, and western Arizona have the largest percent of normal. Though not shown here, anomalies on 12-month, 24-month, water year, and 80-year (1931-2010) record time scales show little variation.

The anomaly ends north of Utah and Colorado, shows considerable variability in Arizona, is most pronounced in New Mexico, and affects west Texas but decreases across the eastern portion of the state. The northeast region of the United States received below normal precipitation in 1941 (not shown) while much of the Southwest was anomalously wet. This result alone could suggest the possibility of an El Niño event. Clearly, the 1941 precipitation anomaly was a regional precipitation event that mainly affected the southwestern United States with precipitation amounts above normal on many different time scales.

Highlights for the year obtained from these records include:

• Elephant Butte Reservoir was filled to its capacity for the first time!
• There were 28 weather-related deaths, with 24 of those due to flooding. In recent history, there is an average of 1 or 2 fatalities in New Mexico per year due to flooding.
• Property damage exceeded $3.5 million (approximately $55 million in today's dollars).
• The greatest amount of snowfall reported was 203.6" at Irvin's Ranch in San Miguel County, with 106.7" of snowfall reported in Cloudcroft where the average is about 70 inches per year.

This is an example of the daily local record for September 28, 1941. About half an inch of precipitation was recorded in Albuquerque on this day.

This is an example of the NOAA Central Library Daily Weather Map for September 23, 1941. Observed rainfall is shaded in grey. 

The NOAA Central Library has a collection of historic U.S. daily surface weather maps for the period from 1871 to 2002. (More recent maps are available via the NOAA/NWS Weather Prediction Center.) Though the format changed during 1941, these surface maps feature temperatures, barometric pressure with analyzed isobars, wind velocity and direction, precipitation, synoptic features, and forecast discussions for various cities across the continental United States.

The daily surface weather maps depict patterns at a synoptic scale. They also provide a written and visual analysis of the daily weather that occurred. These maps illustrate a limited number of weather observations in New Mexico, as well as observations and analyses across the continental United States. Examination of the daily maps indicates that a fairly high number days with precipitation in New Mexico during May and September, with associated surface low systems or moist upslope flow.

The wet conditions can be examined in finer detail using single station precipitation data. The historic nature of the 1941 precipitation anomaly comes from multiple months with large precipitation totals and a high frequency of days with precipitation, as shown in the graph to the left. Daily precipitation for Albuquerque is shown as bars while daily normals are connected by the green line. Note that precipitation occurs throughout the year, thus the precipitation anomaly cannot be attributed to an active monsoon or a strong wintertime ENSO anomaly alone.  On a long-term average, the rain gauge at the Albuquerque Weather Office (located at or near the Albuquerque airport) averages 24 days of precipitation greater than or equal to 0.1 inches in a year. Calendar years 1919 and 1992 (also wet years) reported 42 days of precipitation greater than or equal to 0.1 inches, while the year 1941 had 41 days of precipitation greater than or equal to 0.1 inches. Therefore, at Albuquerque, precipitation in calendar year 1941 was in the 99th percentile of the instrumental record. 

A comparison of precipitation statistics for New Mexico and the observed values for 1941 is illustrated in the graph below.  Box and whisker plots depict the characteristics of monthly precipitation while the light blue line represents the 1941 water year time series.

In New Mexico, maximum precipitation generally occurs in July and August associated with the North American Monsoon System. April is the driest month and September experiences the greatest variability in precipitation for New Mexico - it can be exceptionally dry but also has the record values for the state.  September 1941 is the wettest September on record, even overshadowing September 2013.

A comparison of 1941 precipitation values to normal shows the two wettest months of 1941 statewide were September and May with large amounts of precipitation spread across both months. Nine out of 12 months in 1941 were anomalously wet (in the upper quartile) and three months (March, May, and September) were the maximum precipitation values for all water years from 1931 to 2012. November was the only month in 1941 with below average precipitation, while August and December were close to average.

1941 had below normal temperatures for all wet months, except for May. As expected, the departure from normal for the minimum and maximum temperatures throughout the year were below normal due to anomalously high frequency of cloudiness (89 cloudy days in 1941) and precipitation, indicating multiple low-pressure systems. The year 1941 had a cool spring and summer and overall was the coolest year since 1932. Summer temperatures are particularly well-correlated negatively with precipitation, but significant precipitation in 1941 is mainly noticed outside the summer precipitation season. The temperature departures were not dramatic, as the anomalies were mostly due to precipitation.

The images above depict mid-atmospheric pressure anomalies (500 mb geopotential heights) generated by the 20th Century Reanalysis dataset for four major wet periods in 1941. The anomalies for three of the events, 1-5 May 1941, 21-25 May 1941 and 20-23 September 1941 (top left, top right and bottom left), indicate an amplified pattern with lower than average heights west of New Mexico associated with upper level troughs.  The fourth event, 27-29 September 1941 (bottom right) show anomalies associated with fairly strong upper level high pressure east of New Mexico, a pattern that can support a south to north transport of moisture into New Mexico.

The graphic to the left shows anomalies of low level moisture (2 meter specific humidity) for the month of May 1941. Note the swath of above normal moisture stretching from northern Mexico through eastern New Mexico and west Texas to the northern Plains while much of the eastern U.S. is dry.

Tropical remnants affecting New Mexico are most common in September with equal chances of occurrence in the first and latter parts of the month.

Tropical storm records for the eastern Pacific are not available for 1941, but historic records indicate that three tropical storms tracked along the west coat of Mexico in September of 1941. One broke a record for low barometric pressure and another caused considerable damage on the Baja Peninsula. It is possible that precipitation in September 1941 was enhanced by tropical storm remnants.

A recent visitor to NWS Albuquerque mentioned that he had lived in New Mexico during 1941 and offered to share the following description. "As a 10-year old,  I was lucky to be able to spend the summer of 1941 on a ranch in the Sacramento Mountains of Lincoln County.  The ranch house was nine miles from the nearest paved road.  Our south fence was the Lincoln County line - across the fence was Otero county and the beautiful Mescalero Apache reservation.  Snow and rain had been good all winter and spring, and the summer monsoon brought spectacular thunderstorms.  All plants were growing and blooming in splendid fashion, including the cacti.  Stock tanks with dirt dams were overflowing so we could go swimming if we accepted the cold water and the floating cow chips.  Grass was so tall in some meadow areas that we could not see the white-face calves even when they were standing.   Deep mud meant that the ranch pickup could not get us into town for weeks at a time.  Two bad-tempered old jersey cows provided milk and cream so we make ice-cream with hail from the tin roof,  the only ice available on a ranch with no electricity.  A sensational time in a gorgeous place.  Our nearest "town" with more than one house was the tiny Mescalero village of Whitetail,  8 miles away.  I understand that Whitetail holds the all-time New Mexico record for total precipitation in one year:  something incredible like 60 inches in that year 1941." (NWS Comment: The highest observed annual precipitation total for New Mexico is 62.45 inches in 1941.)

In conclusion, a widespread precipitation anomaly like the one that occurred in 1941 is a low-probability forced climatic episode based on the severity, area, and duration of the precipitation anomaly that was generated. Another positive ENSO/PDO in the future may lead to above average precipitation, but it is unlikely that we will see values equaling those of the 1941 precipitation anomaly. Precipitation associated with May and September anomalies were isolated storm events and occurred randomly in the same year as they had different moisture sources and storm tracks. The combination of the positive PDO and moderate El Niño may not entirely explain the high precipitation values for the year 1941, but could have contributed to multiple independent high-precipitation storm events region-wide as the pattern of some of the precipitation is consistent with an El Niño event. The annual precipitation anomaly in 1941 can be partially explained by external forcing, but unforced weather events are also added to the extreme anomaly. 1941 will forever stand out as a significant event in climatological history for New Mexico.