Monday, May 28, 2012

Fat Lady Preparing to Sing: U.S. Crushing Warmest Spring Record

May 30, 9 PM Update: As a check on the temperature estimate methodology described in the previous update, the same procedure was applied to a set of 247 stations for the month of April. The result was only 0.1°F different from the official U.S. April average from NCDC.

May 30, 5 PM Update: Preliminary data continue to confirm that the U.S. average spring temperature is likely to smash the old record high by a wide margin. The latest national average map, through May 28 (Monday) shows some cooling creeping into the Pacific Northwest and northern Rockies, compared with the month-to-date 4 days earlier (in original post below). However, the warmth has intensified from the Midwest eastward to the Atlantic coast, with maximum values exceeding 3.5°C above normal in central Kansas:

In order to estimate a numerical value for the national average May temperature departure, CapitalClimate compiled the weekly average temperature departures from normal for the 4 weeks ending May 27 at 215 major National Weather Service weather reporting locations across the 48 contiguous states. The final figures from the National Climatic Data Center (NCDC) will include many more stations and adjust for geographical distribution, but the estimate indicates a 4-week average of 4°F above normal. Even with somewhat cooler temperatures for the last 4 days of the month, it appears that the final spring average will come in at the high end of the range of estimates in the original post (near the "2012+2C" figure of 57.4°).

Original post:
As suggested last week, the U.S. is well on its way to crush the record for warmest spring since national temperature data began in 1895. Here's an indication of just how far that record could go. The previous record spring in 1910 had a national average temperature of 55.1°. However, the March 2012 temperature exceeded March 1910 by 0.5° to set a new record for the month. April 2012 then exceeded April 1910 by 1° (see the charts to the right).

At this point, May 2012 would have to be 1.5° cooler than May 1910 to avoid exceeding the record. What are the chances of that? Somewhere between slim and none. Here is the temperature departure from average for May 1-24:

Note that the chart is in °C. Nearly all of the country is above average, with large areas over 2°C higher. How did May 1910 compare?

Most of the country was below average. In fact, May 1910 was 1.8°F below the 1981-2010 average overall.

If the last 7 days of the month completely reversed the May 1-24 pattern shown above so that May averaged equal to the climatological mean, Spring 2012 would still be 1.1° warmer than the old record, as big a margin as the difference between the current record and the 10th place year of 1977. If May averages as much as 2°C above climatology, which looks quite plausible, the spring average would be an eye-popping 2.3°F above the old record (see the chart at the top of the post).

Meanwhile, daily high temperature records, while not at the incredible March rate, continue to outpace low records by a huge ratio (click to enlarge):

Counting Down to the Record: Washington Temperature Approaches Reaches Exceeds 1° Above Warmest Spring, Heads Higher

June 1, 2 PM Update: Charts updated above. Note that the May average of 71.4° was 5.4° above the climatological average and the 3rd warmest May on record, behind 1991 and 2004. It was only the 4th time in history that May averaged over 70°.

June 1, 1 AM Update: The midnight (standard time) temperature is 74°. The daily low remains 69°, and the new record for warmest spring stands at 62.2°. (Charts to be updated.)

May 31, 6 PM Update: Today's high of 85° has exceeded expectations by 3°, and the morning low of 69° is a whopping 11° above the forecast from last evening. That's enough to push the semi-final spring average up another 0.2° to 62.2°, an incredible 1.5° above the old record. With cooling temperatures this evening, however, it all comes down to the midnight temperature (1 am EDT). A reading of 63° or lower would shave off 0.1° and put the final average at 62.1°.

May 30, PM Update: Yesterday's high/low temperatures were 91°/70°. While today's high of 83° as of 5 pm was held down by persistent clouds, the spring average to date has been lifted to 62.0°, exceeding the old record by 1.3°. Tomorrow's cooler readings should still be enough to raise the final average by another 0.1°. (Charts updated above.)

Meanwhile, preliminary indications are still confirming that the U.S. 48-state average spring temperature will crush the old record. See here for the latest update.

May 28, PM Update: Today's preliminary high of 90° brings the month to date average temperature up to 61.7°, a full degree above the old record. The projection remains the same.

Original post:
As noted previously, Washington DC is headed to the record warmest spring by an unprecedentedly large margin. Following the low this morning of 70°, the high temperature so far today (through 1 pm) of 86° is enough to raise the March-May average to date to 61.6°, which is 0.9° above the old record from 1977. Given the forecast temperatures for the next 3 days, the projected final average will be 62.2°. Even without reaching the 90° levels predicted for this afternoon and tomorrow, the average will continue rising. In order to decline from the current level, the average for the next 3 days will have to be at least 8° below the historical average through the 31st. That would mean a high of 71° and a low of 53°. Although that's hardly impossible, it's fair to say: Ain't. Gonna. Happen. While it's bad form to predict records days before before they occur, this one is about as sure as you can get.

Stay tuned as we count down the record.

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