Very above normal temperatures dominating US to end November

Much above normal temperatures are dominating much of the United States right now. This is largely a product of a zonal or progressive jet stream moving along the northern tier states and southern Canada locking colder air over interior Canada and the Arctic (although, I note, the Arctic is seeing much above normal temperatures relative to what they should be seeing as well!).

My area…Eastern Nebraska…has been seeing many days of 60s and even mid-70s, including today. The average temperatures this time of year should be in the low to mid-40s for highs and near 20 for lows. Instead it’s been feeling like it’s around birthday time for me. My birthday is in May.

GFS-025deg_NH-SAT1_T2_anom
Global Forecast System model analysis of surface air temperature anomalies for November 27th. The GFS tends to have a minor warm bias from reality, but it is accurate is showing significant above normal temps over the western and central sections of the United States. The baseline normal period is 1979-2000, prior to the significant amplification of climatic warming in the Arctic (occurring because of anthropogenic global warming).
gfs_namer_048_250_wnd_ht
Global Forecast System model forecast depiction of upper-air wave pattern at 250 millibars (~10,200 meters/33,500 ft) valid Wednesday morning. The jet stream will remain largely over the northern tier and southern Canada this week with above normal temps of varying departures over the US.

As we move into the first week of December, trends point to some dip in the jet stream over the Western US early next week causing below normal temperatures. However, this will also amplify the jet stream over the eastern two-thirds, producing significantly above normal temperatures yet again.

One additional thing of note. Snow cover is virtually non-existent in the contiguous US today (Nov. 27th). Only 4% of the CONUS has snow cover today. Going back to 2003, this is lowest snow cover extent for this particular date. The second and third lowest for Nov. 27th were 8.7% (2009) and 10.2% (2011). The snow cover area extents on Nov. 27th in 2010, 2012-2015 were in the range of 20-35%. 2016 was fairly low at 15.4%. The data is available HERE.

nsm_depth_2017112705_National
Snow depth analysis map for the US and southern Canada for November 27, 2017.

I don’t know date prior to 2003, however it is known that climate change is reducing snow cover extent and depth in the US and the Northern Hemisphere beyond natural variability. The aforementioned trough in the West should increase that extent somewhat next week.

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Author: Meteorologist Nick Humphrey

Meteorologist and geoscientist in Lincoln, NE. Seattle, WA native. Love weather, storm chasing/photography and planetary science.

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