Borderline El Nino conditions arrive; Chicago, Detroit, and Milwaukee hit 102°

The odds of an El Niño event developing in time for the August - September - October peak of hurricane season have grown to 61%, said NOAA's Climate Prediction Center in their latest El Niño/Southern Oscillation (ENSO) diagnostic discussion, released on July 5. Ocean temperatures in the equatorial Pacific have increased to 0.6°C above average this week, which is just above the 0.5°C above-average threshold used to define a weak El Niño event. These temperatures must remain 0.5° or more above average for three consecutive months to qualify as an official El Niño. CPC advised that current conditions show a weakening of the east-to-west trade winds over the east-central equatorial Pacific, along with a reduction in heavy thunderstorm activity over Papua New Guinea, which "reflect a likely progression towards El Niño." However, the upper atmospheric winds and circulation patterns don't resemble what we expect of an El Niño yet. For example, in June over the North Pacific Ocean, there was an overall ridge of high pressure (more characteristic of La Niña) rather than a trough of low pressure (more typical during an El Niño). Thus, any development of El Niño during July is likely to be slow. El Niño events tend to suppress Atlantic hurricane activity by increasing the upper-level winds that create high wind shear capable of tearing storms apart.


Figure 1. Departure of sea surface temperature (SST) from average for July 5, 2012. In the equatorial Pacific, waters had warmed to 0.6°C above average, denoting the possible onset of an El Niño event. Image credit: NOAA/NESDIS.

Chicago, Detroit, Milwaukee, and Madison all hit 102° on July 4
The summer of 2012 continued its onslaught of record extreme heat on Wednesday, with the Midwest the focus of the most intense heat. Chicago hit 102°, just 3° below the city's all-time hottest temperature of 105°, set on July 24, 1934. Chicago hits 102° or more an average of once every 7.4 years, and last hit that mark on July 24, 2005. Detroit's high of 102° yesterday was its hottest day since 1988. Detroit's all-time hottest temperature is also 105°, set on July 24, 1934. Milwaukee, WI also hit 102° yesterday, which tied for the 4th hottest temperature in city history. Madison's 102° was their hottest day since 1988, and tied for the 6th warmest temperature ever measured in the city. Madison's all-time high is 107°, set July 14, 1936, and the forecast for today calls for a high of 104°. Other notable extremes from the 4th of July:

St. Louis hit 105°, the seventh consecutive day the city has hit triple digits. This streak is now the 4th longest such streak in city history; the only longer streaks occurred during the Dust Bowl summer of 1936 (streaks of 13 and 9 days) and the Dust Bowl summer of 1934 (an 8-day streak.) The current forecast for St. Louis calls for highs of 102 - 106° Thursday, Friday, and Saturday, which will likely bring the city's streak of 100°+ days to ten by week's end. St. Louis' all-time hottest temperature is 115°, set in 1954.

The high temperature in Pueblo Colorado reached 101 degrees on July 4th, bringing the number of consecutive days with high temperatures of 100 degrees or higher to a record thirteen. The previous record was 9 consecutive days, set in 1990. Record keeping began in 1888.

The low temperature in La Crosse, WI dropped to just 81° Wednesday. This tied July 21 1901 and July 13 1995 for the warmest low ever recorded. Temperature records date back to 1872.

Minneapolis, MN hit 101°, which is 7° below their all-time record high of 108° set 7/14/1936.

Highs of 100°+ are predicted to occur again on Thursday and Friday in Chicago, Detroit, Milwaukee, and Madison. A cold front will bring welcome relief on Saturday to the region, and the region of highest extreme heat will shift southeastwards to the Tennessee Valley. The models have backed off on their prediction of a strong ridge of high pressure bringing extreme heat to the Western U.S. next week, and more typical hot weather can be expected over most of the U.S. next week. Nevertheless, the extreme Midwest heat is causing havoc to the nation's corn crop, and multi-billion dollar drought disaster is taking shape. Today's New York Times details the drought concerns. I did a live interview Tuesday for Democracy Now discussing the recent extreme weather and how we can expect to see more weather like this in the future due to climate change.

Quiet in the Atlantic
There are no threat areas to discuss in the Atlantic, and none of the reliable computer models are developing a tropical cyclone over the next seven days.

Jeff Masters