The sun is still fairly strong and clear skies allow maximum warming at the surface. Furthermore, the atmosphere above the surface is still relatively warm and that warmth mixes down during the day. As a result, there is often a large diurnal (daily) temperature range during this time of the year.
We can can a feeling for the diurnal variations by looking at Wednesday's high and low temps. First the highs. East of the Cascades and south of Olympia, 80sF were not rare and temperature variations were not huge.
In contrast, the minimum temps, were not only much colder (mainly 40s), but the range was huge, getting down into the 20s in much of eastern Oregon and around Spokane. It is cold over the high plateau of eastern Oregon, particularly in the valleys
There is an amazing example yesterday (Wednesday) of extreme behavior at a very reliable observation site to the southeast of Spokane (Turnbull National Wildlife Refuge). Here is a plot of the temperature variations at this site for Tuesday and Wednesday. Huge daily range, particularly yesterday, when the temperatures rose from the low 20s to the mid 70sF. Below freezing to shorts weather in only a few hours! A diurnal range of a bit more than 50F.
Perhaps you are not impressed with this. No problem. Now let's consider the change in temperature of the surface soil layer, as shown in the table below (TRNW1 is the identifier for Turnbull and TSFC stands for surface temperature).
WOW! The temperature of the surface ranged from 18F at 6 AM (1300 UTC) to 117F at 2 PM (2100 UTC). 99F change! Just stunning. From well below freezing to warm enough to cook some food.
Between 8 AM and 10 AM, the temperature rose from 34 to 81F! You would notice that. Don't like big temperature variations? Don't worry...clouds and rain are in store for this weekend and they suppress diurnal temperature changes.
Talk on Northwest Climate Surprises on September 28.
During the evening of September 28, I will be giving a talk in Seattle at at the Mountaineers in NE Seattle on Climate Surprises: Unexpected Impacts of Global Warming on the Pacific Northwest.
You think global warming will simply bring warmer temperatures, drought, less snow, and more storms?
Think again. The latest climate model simulations provide a far more nuanced prediction of what will happen here, with some of the results quite surprising. This talk is sponsored by CarbonWa and the Audubon Society. To find out more or to secure tickets, please go here.
And if you already secured tickets please not that the location has been shifted to the Mountaineers location in NE Seattle (in Magnuson Park). Parking will be easier and free. Right near Sand Point Way (lots of buses) and the Burke Gilman trail.