December Warmth Breaks Records
I'm not going to lie – I love this warm weather. We'll have our time for true winter-like temperatures, but for now, I'm perfectly content to bask in the December sunshine and not worry about using my heater. However, it's unusual to have a full weekend in the holiday season where shorts and t-shirts are the way to go. I, for one, went to get a real Christmas tree while it was in the 70s and it did feel a bit… odd. If it wasn't for the rather barren trees, early sunsets and Christmas lights, I'd be almost convinced it was April!
Here are some remarkable stats about this warm spell. We tied a record high on Saturday at 77º. Today's morning low of 66º breaks an all-time record warm low for ALL of December (if it holds till midnight- the big question). That low was not only 13º WARMER than our average high for this date, but within 11º of a record high! Wow! We are track for this Monday afternoon to set another record. As the attached map shows, we are not alone. Record-breaking warmth expands well to the north into the Midwest and to the Eastern seaboard.
So why is it so warm? Did Mother Nature not get the memo that it's December? This Indian Summer, if you will, is caused by a couple factors. First, there is zonal flow in our jet stream. Those west-to-east upper winds keep the cold air locked up to the north and allow warmth to build and plateau across our region until some sort of cold front changes that up. Southerly winds for days on end have brought enough moisture our way to keep temperatures from dropping very much at night while enough sunshine during that day has allowed those readings to soar. Unusually mild temperatures in the mid-levels of the atmosphere have also played a role in keeping us dry and warm.
A cold front will move through tonight and bring us a limited chance of rain. However, the end of the above-normal temperatures is not at hand. While we won't likely be in record-breaking territory for the rest of the week, the upper-level pattern remains nearly the same with zonal flow. Without any Arctic air to plunge south, we simply can't get too cold.
That may ALL change by early next week. Winter weather lovers, be on stand-by because it will begin to feel a lot more like Christmas in just a week's time. Longer-term computer models are indicating a reversal to a strongly negative Arctic Oscillation (AO) and North American Oscillation (NAO) pattern while the Pacific North American oscillation (PNA) goes positive. This can get a bit technical, but what it means is that the jet stream will orient itself so it goes much deeper into the eastern U.S. and a trough forms to our west. This creates a conveyer-belt of cold air waves to come our way. It's no guarantee with some computer model discrepancies, but this could be the most significant pattern change for us in months.