Warmer temperatures this week have been a nice reprieve from our recent bout of winter cold. The warmth is not isolated to just where we live near the ground, but also extends above us into the lower atmosphere. The featured chart presents mandatory level temperature percentiles from Omaha for the Wednesday evening sounding. These percentiles are calculated over all January evening soundings from the site on record. A value of 100 would indicated the warmest on record. You can see warm percentiles extend to quite high levels, but then reverse around the 250 hPa level. The reason is that these levels are above the tropopause and while this gets difficult to explain, when the lower atmosphere is warmer than average, heights increase and these above tropopause levels are thus at higher altitudes than average, which will imply colder temperatures.

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