Tuesday, May 19, 2015

Eagle Record Heat

The COOP station in Eagle reported 86 °F for a daily maximum temperature yesterday.  This is a new record, by a margin of 1°F, for the hottest on record for so early in the season at Eagle; the previous earliest date with a temperature of 86+ was May 27 (1947).  However, the 1995 heat wave, which I mentioned the other day, was arguably more impressive as it brought 85 °F to Eagle more than a week earlier, on May 11.  Other than the 1995 event, yesterday's heat in Eagle appears to be the earliest on record for such a high temperature anywhere in Alaska.

The diurnal range of temperature in Eagle has been extreme in recent days, exceeding 50 °F at the airport where overnight minima are usually cooler.  While extreme intraday temperature variations are not too unusual in winter (especially late winter) with snow on the ground, it is rare to see such a large diurnal variation without snow cover.  The chart below shows the hourly temperature and relative humidity observations from the past 10 days; the relative humidity reached as low as 8% yesterday afternoon (temperature 84°F, dewpoint 16°F).


  1. It's been clear, sunny, and warm. I suppose the nearby Yukon River is still cold due to melting tributaries and likely the air above gets chilled in the early morning hours along with a humidity excursion.


    1. Gary, undoubtedly yes the river surface is still very cold. It appears the ASOS is about 2000 feet from the river, but I'm not sure of the precise elevation difference.

      It's interesting that the temperature only dropped to 49F last night; winds were no higher than previous nights and surface dewpoints were only a little higher; CLR reported all night of course. I suspect increased humidity aloft last night was the reason for the relative lack of net radiative cooling. And conversely the main reason for the cold nights earlier in the week was extreme dryness of the airmass.