Saturday September 1st… Dear Diary. The main purpose of this ongoing post will be to track United States extreme or record temperatures related to climate change. Any reports I see of ETs will be listed below the main topic of the day. I’ll refer to extreme or record temperatures as ETs (not extraterrestrials)😊. Here is today’s main climate change related topic:
Fall Forecast For United States
In separate posts during the last week of August I alluded to models indicating that well above average heat will be occurring during the first half of September across most of the eastern United States. As I do at the start of every boreal season it’s time to make a seasonal forecast. What other clues can tell us about temperatures for the fall across the United States to come?
Well, here is my two cents for a broad, rough forecast for the U.S.
First, I like to look at water temperature anomalies surrounding North America just before the start of a season to get a sense of how much potential added heat can be added to the atmosphere across the continent. Here is what we see:
Leading off fall 2018 water temperature anomalies around North America are much warmer than those at the beginning of summer 2018, so I believe that SSTs will come into play, tending to make fall across the U.S. warm. Anomalies are extraordinarily warm off the Northeast coast.
Going out on a tangent, here is how remarkable those water temps are off the Northeast:
Second I like to look at the strength of the Hudson Bay low or the beginnings of the polar vortex forming at the start of fall:
A low around Hudson Bay has not formed yet and may not form for a considerable length of time going into the fall. Nevertheless, we do see cold anomalies building in Canada, so we should begin to see some shots of cool air moving into the CONUS, particularly in the West, the next few weeks. I’ll check the warm box here looking at the overall pattern.
Next, an El Nino is forecast to begin developing this fall. We don’t see too many signs of this yet on SST charts, but should we see it this phenomena is likely to warm November above climatological averages. We don’t know how strong this El Nino will be nor the time of its onset, though, if it occurs at all.
Last we can get another clue looking at prior ranking and temperature record count data. For this I like to drag out that “Record Scoreboard” (updated through 8/28/18):
Notice that nearly every month saw an above average ranking (from the median number of 62) since January 2015. The big monkey wrench in the warm works was April 2018, which turned out to be exceptionally cold from Montana into the Midwest. Indeed as you can see from my forecast for the summer, all three summer months verified with above average temperatures: https://guyonclimate.com/2018/06/01/extreme-temperature-diary-june-1-2018-hot-topic-summer-forecast/ So, I’m expecting all three months of fall 2018 to have above average temperatures with the caveat that October 2018 has the best chance for closer to an average ranking.
Seasonal forecasters are beginning to “chuck it” giving up on forecasting cool seasons simply because of what carbon pollution is doing to the planet. Here is what we see from the National Weather Service for this fall:
On the forecast chart we see a continuation of the temperature anomaly pattern over this summer. The “relatively coolest” portion of the country is forecast to be in the Southeast. I can’t disagree at all with this NWS outlook.
Can we get a tad more specific? I think so. Here are NCEI rankings for seasons through summer 2018:
Notice that the past three falls had a ranking at or above 114, but those of 2013 and 2014 were closer to average. I think that this fall will be ranked somewhere in between the last six. We remain way overdue to see an average or below average season across the U.S. Carbon pollution is definitely making below average seasons more rare. I’m going to guess that the fall 2018 ranking will be around 105 + or – 10, with fairly good confidence given all of the warm factors in this post. I think that September will see the highest monthly average ranking with October having the coolest relative averages, which is going out on a limb a little more. Let’s see if this forecast will be a bust or like the last few fairly decent.😅
Sunday we will see another hot day across the southern tier of states:
Pleasant temperatures will be felt across the northern tier.
(As usual, this will be a fluid post in which more information gets added during the day as it crosses my radar, crediting all who have put it on-line.)
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The Climate Guy