Mighty cold start to our day as the first map on the right clearly shows. A number of records were set this morning, including the -2 for the official low here in Tulsa. The last time we had temperatures that cold was early Feb of 2011 at which time we also had an extensive snow pack. To show just how rare temperatures at or below zero actually are around here, we had 3 below zero readings during that Feb, 2011 event and the only other time we have been that cold this century was Dec 9, 2005 when the temperature made it to an even 0 degree reading. Prior to that, you have to go back to the winter of 1995-96 when it happened twice.
A closer examination of the frequency of such extreme cold suggests it was a little more common prior to 1990, but since then has occurred less often. And, to anticipate the question, what winter had the most occurrences of at or below zero temperatures, you have to go all the way back to the winter of 1917-18 when it happened 10 times, 7 of those in January 1918. By the way, that was not the coldest winter on record; that distinction belongs to the winter of 1978-79, one of only 3 winters in which the average temperature was below freezing.
Ok, now that we have some perspective on the unusual nature of such cold weather events; now what? Fortunately, we have a pattern change aloft taking place in which the cross polar component of the upper level wind pattern (the second map on the right) is shifting to a more zonal configuration, i.e. west to east (the third map on the right). That is a much more moderate pattern for us as it keeps the polar air bottled up in the arctic regions where it belongs. Meanwhile, at the surface that strong polar high pressure ridge that was sitting over us this morning will be moving on eastward. The clockwise flow around the ridge means our winds will be returning to a southerly direction which will help to moderate temperatures. Typically, the guidance tries to erode these shallow, cold air masses a little too quickly and I suspect that is the case this time as well.
With clear skies, light winds, and snow still on the ground, look for temperatures to be in the single digits to start the day Tuesday. What wind we do have will be southerly which should keep temperatures from totally bottoming out. Having said that, the more NE counties which have more snow on the ground and in particular the protected valley locations where the winds will be lightest could once again have some negative numbers Tuesday morning.
Lots of sunshine during the day Tuesday along with stronger southerly winds will help to moderate temperatures even more and some of the guidance has us reaching the lower 40s. As mentioned above, I think this cold, shallow air mass is being eroded too quickly and am thinking we will be lucky to make it into the mid 30s.
However, the rest of the week will see a continued moderation in temperatures. The more zonal flow aloft will also have some embedded disturbances which will bring more clouds our way and increasing chances of precipitation, particularly late Wednesday and again during the day Friday. Another cold front will also arrive Wed evening/night and with temperatures at or below freezing during that time frame, the vertical profile of temperature and moisture suggests we could be in for some additional freezing drizzle or light freezing rain. Accumulations should be minimal, but it does not take much of that to cause problems.
A cold rain looks to be a good bet on Friday, but by then temperatures at the surface and aloft will be above freezing so no wintry stuff is expected by then. That system should have cleared out in time for a much milder weekend with daytime highs generally running into the 50s.
Of course, this is only early January and we are bound to get some more very cold air down here eventually, so stay tuned and check back for updates.