All-Time Moisture Records Pile Up as 2018 Draws to a Close

More than a dozen U.S. locations have seen their wettest year on record—and others are in their top-two wettest—as soggy 2018 enters its final days. Part of the blame goes to Hurricane Florence, which produced the heaviest single-location totals associated with any tropical cyclone in both North Carolina (35.93”) and South Carolina (23.63”). However, the year’s unusual wetness transcended any single event.

Take Wilmington, North Carolina, which was in the grip of slow-moving Florence for several days. Florence dumped a total of 23.02” of rain in Wilmington, by far the largest storm total in 148 years of recordkeeping at Wilmington. Yet the city’s yearly total through Friday was a phenomenal 102.26”, which is an incredible 18.61” above the previous annual record of 83.65”, notched way back in 1877. In other words, even if you took out the rains directly produced by Florence, 2018 still came close to dumping more precipitation on Wilmington than any other year!

The National Weather Service office in Wilmington noted: 

“Our local observations show the last five years (2014 through 2018) have all had above-normal rainfall in Wilmington, and are collectively the wettest five year period since records began in 1871. While it's never possible to attribute a single storm or even a particular year's weather events to climate change, the Fourth National Climate Assessment states ‘Across most of the United States, the heaviest rainfall events have become heavier and more frequent. The amount of rain falling on the heaviest rain days has also increased over the past few decades.’”

Single-site records

Here are some of the larger towns and cities that have already notched records for 2018, as tallied by weather.com through Friday, December 28, based on data from NOAA and the Southeastern Regional Climate Center. All of these locations have at least a 60-year period of record. Some of these new records will be bumped up even more by rains expected between Saturday and Monday. See the weather.com article for additional background on this very wet year.

Location + rainfall through Fri. 12/28 (old annual record + year)

Washington, DC (DCA):  65.80” (61.33”, 1889)
Mason City, IA:  49.98” (47.75”, 2016)
Waterloo, IA:  53.99” (53.07”, 1993)
Lexington, KY:  70.62” (66.35”, 2011)
Baltimore, MD (BWI):  70.05” (62.66”, 2003)
Asheville, NC:  79.17” (75.22”, 2013)
Elizabeth City, NC:  63.80” (62.13”, 1979)
New Bern, NC:  79.43” (72.70”, 2003)
Wilmington, NC:  102.26” (83.65”, 1877)
Elmira, NY:  57.57” (49.96”, 2011)
Atlantic City, NJ:  67.90” (66.38”, 1958)
State College, PA:  63.76” (59.30”, 1996)
Sioux Falls, SD:  39.12” (38.26”, 2010)
Danville, VA:  67.31” (62.78”, 2003)
Lynchburg, VA:  65.56” (59.71”, 1972)
Roanoke, VA:  62.39” (58.81”, 2003)
Green Bay, WI:  38.82” (38.36”, 1985)
Charleston, WV:  66.56” (61.01”, 2003)
Wheeling, WV:  56.94” (50.79”, 1950)

Another batch of cities had already secured their second wettest year on record as of Friday.

Wilmington, DE:  60.68” (61.05”, 1945)
Atlanta, GA:  69.48” (71.45”, 1948)
Louisville, KY: 67.35” (68.02”, 2011)
Columbus, OH:  54.17” (54.96”, 2011)
Raleigh, NC:  60.15” (64.22”, 1936)
Binghamton, NY:  56.04” (68.05”, 2011)
Pittsburgh, PA:  57.08” (57.41”, 2004)
Philadelphia, PA:  60.85” (64.33”, 2011)
Rapid City, SD (NWS):  26.95” (27.70”, 1946)
Dallas-Fort Worth, TX:  55.51” (62.61”, 2015)
Richmond, VA:  63.55” (72.02”, 1889)

Figure 1.  Statewide rankings for average precipitation for 2018 through November, as compared to each January-to-November period since records began in 1895. Darker shades of green indicate higher rankings for moisture, with 1 denoting the driest month on record and 124 the wettest. Image credit: NOAA/NCEI, via Wayback Machine. (Direct links to NOAA/NCEI were not available because of the ongoing government shutdown.)

State records

For the period January through November, every state east of the Rockies was wetter than average, and eight states had their wettest Jan.-to-Nov. period on record (see Figure 1 above). We can expect at least some of these states to end up with records for the year as a whole when NOAA’s National Centers for Environmental Information publishes the final data for 2018 in January. Note that the NOAA/NCEI website is offline for the time being because of the government shutdown.

At least six states have set preliminary all-time records for the wettest annual totals at any location, according to NWS and CoCoRaHS data. In some states, more than one station has apparently topped the previous record. Below are the highest preliminary totals observed through Friday, December 28. More rain is possible in some of these locations through the end of the year. Any state rainfall records need to be validiated and certified by NOAA’s State Climate Extremes Committee before they become official.

Maryland:  84.11”, Catonsville (1.2 mi NW, CoCoRaHS)
   Current annual record: 76.52” (Towson, 1971)
North Carolina:  139.38”, Mt. Mitchell (NWS/COOP)
   Current annual record: 134.40” (Lake Toxaway, 2003)
Pennsylvania:  98.85”, Hidden Valley (CoCoRaHS)
   Current annual record: 81.64” (Mt. Pocono, 1952)
South Carolina:  122.95”, Jocassee (8 mi WNW, NWS/COOP)
   Current annual record:  119.16” (Hogback Mountain, 1979)
Virginia:  97.34”, Montebello Fish Cultural Station (NWS/COOP)
   Current annual record: 83.70” (Philpott Dam, 1996)
West Virginia:  96.97”, Parsons (CoCoRaHS)
   Current annual ecord: 94.01” (Romney, 1948)

The final 2018 total at Mt. Mitchell, NC, is likely to be the highest annual precipitation ever reliably recorded at any U.S. location east of the Pacific Coast states.

Figure 2. Still more U.S. rain is expected during the final days of 2018, as shown in this outlook for the 72-hour period from 8 am Saturday, December 29, 2018, through 8 am Tuesday, January 1, 2019. Image credit: NOAA/NWS/WPC.

Natural variability within a warming climate

This year’s phenomenal U.S. precipitation was the result of several factors, including a series of slow-moving upper-level features that concentrated rainfall over several days at various locations. Unusual warmth also predominated across the northeast Pacific and northwest Atlantic/Caribbean/Gulf of Mexico. These warm sea surface temperatures pumped vast amounts of moisture into the atmosphere that flowed into U.S. storm systems and tropical cyclones.

This year offers a classic example of the pitfalls of simplistic “X causes Y” thinking in the context of a changing climate. Persistent large-scale features, plus the occasional tropical storm and hurricane, were the direct rainmakers in 2018. Yet the rainfall amounts in some places were larger than anything produced by natural variability in the last hundred-plus years. As noted above, many studies have found that the wettest short-term rainfall events have become even wetter in the U.S. and elsewhere as a result of climate change, as warmer oceans allow more water to evaporate and become concentrated within rain-producing systems.

The 2017 Climate Science Special Report (Part I of the Fourth National Assessment) reported that annual precipitation across the contiguous U.S. increased by about 4% over the period from 1901 to 2015. Most of that increase has been observed east of the Rockies. When droughts do occur, as in much of the Southwest during recent years, warming temperatures can worsen their impact. It stands to reason that a year like 2018, peppered with multiple intense rain events triggered by normal mechanisms, could become even wetter as those rain events are goosed by a warming climate.

“I will not say climate change ‘caused’ this year's weather,” said Weather Geeks podcast host Marshall Shepherd (University of Georgia). “In the same way, I would not say steroids ‘caused’ a MLB baseball player's 520th home run. However, I would say that I can see the influence of steroids in his overall statistics for [number] of homers and their length….A wet 2018 is consistent with what is expected in a warming climate.”

Thanks go to the weather.com team for the compilation of 2018 local precipitation records and to WU historian Christopher Burt for data on state rainfall records.