Fig. 1: November 2013-2020 HDD vs. 20-year/10-year normal.
November OPTIMUM CLIMATE NORMAL: In 2013 the northeast Pacific Ocean turned extremely warm while south-southeast of Greenland the North Atlantic turned colder than normal. These conditions have been dominant since that time and affecting the North America climate more so than ENSO while also influencing the character of conventional climate signals (AO, NAO, PNA, WPO and EPO). The 2013-2021 (so far) prevailing climate is considered an optimum climate normal, i.e. having characteristics unique to that time and different from standard 10-year, 20-year, 30-year and 50-year climatology. An example is the HDD observations from 2013 to 2020 in November. Note that except for 2017 each year produces a cold or warm extreme (Fig. 1). A warm extreme is projected for November 2021 (Fig. 2). Note that during the cold season of 2013-14 to 2020-21 the warm and cold extremes have been impressive (Fig. 3). The 2013-14 to 2020-21 OCN makes the case for high risk of extremes!
Fig. 2: The most likely upper air pattern for November 2021.
Fig. 3: November 2013-2020 HDD vs. 20-year/10-year normal.
Midday 12Z GFS changes: The 12Z GFS trended somewhat cooler in the West the next 15 days while the already warm northeast quadrant of the U.S. trended warmer (Fig. 4).
Fig. 4: The temperature changes for the next 15 days across the U.S. using the midday 12Z GFS.
Population weight HDD/CDD forecast changes at midday: The 12Z GFS indicates CDD are higher than HDD through mid-October (Table 1-2). Keeping EXTREMES in mind is handy for the current climate pattern.
|Dates||HDD Forecast||12-Hr Change||24 Hours Ago||10-year NML||30-year NML|
Table 1: The 12Z GFS gas population weight HDD forecast compared to the 30-year/10-year normal and 12 and 24 hours ago.
|Dates||CDD Forecast||12-Hr Change||24 Hours Ago||10-year NML||30-year NML|
Table 2: The 12Z GFS population weight CDD forecast compared to the 30-year/10-year normal and 12 and 24 hours ago.