Wednesday, October 10, 2012

From Heat To Cold In The Drought Belt

The cold snap that brought record setting early freezes to Oklahoma City and Tulsa, among other locations in the Plains, is easing a bit, with temperatures today expected to warm into the 70's and 80's across the center of the country while we in Philadelphia get a shot at the 70's ourselves by day's end.

The cold snap's impact was strongest in the Midwest and Plains -- the lion's share of the over 600 record lows set in the last week were from Minnesota south to Texas, with record cold highs in much greater supply and spread across a much larger swath of the country, due in large measure on Sunday and Monday to clouds, showers, and a chilled northeast wind from Georgia to Pennsylvania helping to drive temperatures down to very cool levels during the day.

Record distribution (map and chart) courtesy of

The cold snap here was also a bit significant  -- temperatures were ten degrees or more below average on Sunday and Monday and we threatened a century old record cold high on Sunday on Philadelphia when we missed the cold high mark by two degrees.  It does and can get pretty cool around these parts in can also snow (happy 33rd anniversary to our earliest snow on record).   However, compared to the Midwest and Plains, the cold snap's impacts locally were not as extreme on the night side of things.  To an  extent, Midwest and Plains drought helped contribute to the litany of record lows that impacted these regions.  Due to abnormally dry soils, "heat" was quickly able to radiate out at night on the clear nights in these regions and temperatures were able to drop at a more efficient clip than if there was moisture in the ground.  The cold airmass definitely had some bite to it on its own merit but the impact of the cold at night may not have been as record breaking across the Midwest and Plains had the soils in these areas been a bit more moist.

These areas two months ago were breaking records left and right on the warm side of the equation...and in the right atmospheric setup (ridge overhead), record highs would certainly be doable again in winter since dry soil has an easier time jumping or dropping in temperature.   In other words, this area could use a very good, very solid, very steady soaking rain for a day or two.

The bigger pattern picture (extreme trough/ridge) may itself be a foreshadow for the winter across the Northern Hemisphere.  The low Arctic sea ice/extreme blocking correlation has been mused here and elsewhere a few times.  The challenge for forecasters is if extreme blocking sets up shop over varying portions of North America or on the other side of the globe.  The next few weeks will (hopefully) offer the long range forecasting segment some clues on what will transpire for the coming winter.