WunderBlog Archive » Weather Extremes

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U.S. Temperatures Running Unusually Hot AND Unusually Cold this Year
U.S. Temperatures Running BOTH Unusually Hot AND Unusually Cold so far this Year

My previous blog dealt with the record summer warmth in the Pacific Northwest relative to the cool summer that much of the rest of the nation has enjoyed. An interesting report published in late August by NOAA’s climate portal Climate.gov states that for the January-July period the contiguous U.S. has never seen such “radically different temperature extremes as they have so far this year.” In other words, it has been BOTH unusually cold AND unusually warm across the country since January 1st.

The web site published an interesting map of minimum temperature ranks (compared to the average for the past 120 years) for the January-July 2014 period. I have added the maps for the maximum temperature and average temperature rankings as well. Data for August should be available next week (on September 11).

Minimum temperature ranks (top map), maximum temperature ranks (middle map), and average temperature ranks (bottom map) for January-July 2014 within the historical record of 1895-2014. Color-coded from record coldest (dark blue) to record warmest (dark red). Overall the January-July period has ranked as the 57th coolest on record (out of 120 years), so statistically, in aggregate, almost exactly normal! Map adapted from analysis by the NCDC.

The persistent ridge of high pressure that stagnated over the Eastern Pacific Ocean since last December has been responsible for this sharp contrast in temperature anomalies across the lower 48 states. The system caused the jet stream to flow over the top of the ridge and southward to the east of the high, thus funneling cold air into the central third of the nation. In itself this is not unusual, but what has been “unprecedented” (to quote NOAA) is how persistent this pattern has been over the past 7-8 months. As the NOAA article put it, “never before has the country experienced such large areas of simultaneous, opposing temperature extremes in the same January-July period.”

To put the quote above in an historical perspective they provided this graphic:

Graph of percent U.S. area affected by extremes in maximum temperature (red is warm, blue is cool) for January-July periods since 1910. Based on data from the U.S. Climate Extremes Index from the NCDC.

If you would like to see the chart for the extremes in minimum temperature follow the link above and click on the ‘Step 2’ indicator. Note that for this NOAA analysis the term ‘extreme’ is referring to temperatures that rank in the top or bottom 10% of the historical average. So far this year some 40% of the contiguous U.S. has fallen into one of these two extreme categories.

Guy Walton of The Weather Channel has used NCDC data to compile tallies of temperature-record reports since the 1920’s. In his most recent compilation (up to August 16th) we can see that since January 1, 2014 there have been almost twice as many ‘daily record lows’ as ‘daily record highs’ and yet the ratio between ‘monthly record lows’ and monthly record highs’ has been almost even.

Table of record temperature reports for each decade since 1920 and also for the 2014 year-to-date period. Table compiled by Guy Walton of The Weather Channel and based upon NCDC data.

The original NOAA report can be found here.

Christopher C. Burt
Weather Historian

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.