The strong squall line vs. low-end derecho debate has been going on among meteorologists and weather geeks. The Storm Prediction Center released a graphic on Thursday displaying two “Severe Wind/Derecho” events, as it termed them, on Thursday. It’s an academic debate that won’t turn lights on or lift trees off houses, but important in the sense that it has become obvious that weather professionals are not reading off the same sheet of music, with entirely different definitions of the term, based on differences in longevity of severe winds, required peak winds, and the means of confirming wind reports. And that can affect not only post-storm analyses, but forecasts and media transmission of warnings ahead of time. Via Twitter, the SPC said to me: “Agree we need standard definition. Not sure whose to use.” As 6/29/12 was the impetus of “derecho” entering the public lexicon for many in the East, hopefully 6/13/13 and the frenetic forecasting days leading up to it will be the impetus for a standard definition of “derecho” being developed — and a re-examination of how severe weather potential is projected days in advance.
On to the future. We may not be done with squall lines/mesoscale convective systems/derechos with the weather pattern that appears to be setting up. Not this weekend, though. Saturday appears to be totally dry, while Sunday may have a few isolated showers/storms in the afternoon/early evening as moisture begins to build back, cooked by sunshine and lifted by the higher terrain. The next in what could be a long series of cold fronts arrives about Tuesday, with an increased chance of storms accompanying/ahead of it Monday and Tuesday. At this distance, atmospheric shear does not appear to be nearly as strong as with the last couple of severe weather threats, but a cold front pushing into hot, moist June air is often enough for clusters or a line of storms forming that could be locally severe. Something to keep an eye on. Long term, the pattern is looking to take on either a “Ring of Fire” or progressive look, either of which would bring periodic cold fronts and storm systems. The “Ring of Fire” concept involves a central core of hot/dry high pressure — signalled somewhat on the 6-10-day Climate Prediction Center temperature map by the red circle in Texas and Oklahoma — with storm systems circling the perimeter of the high to the north and east, diving toward our region. A progressive pattern would involve less of a stagnant high and more of a west to east movement of storm systems, mostly across the northern half of the U.S., as the jet stream winds continue lifting northward typical of the season. Either way, it will not allow a long-lasting hot/dry air mass to set up anytime soon over us. Continue to expect 2 or 3 days of mostly dry, gradually warming weather, followed by a chance of showers and storms, then somewhat cooler/drier weather.
I’ve been asked a bit about the summer as a whole. We’re already to mid-June and the pattern is unusually active for this time of year. The lean now would be to a near-normal temperature summer — averaging between periods of warmth and cooler weather — and wetter than normal, as storm systems continue to move across the northern U.S. and drag cold fronts through. I think a prolonged heat wave is going to have a hard time getting established in the East, both with the current prevailing pattern and the ample moisture, but wouldn’t rule out a few extremely hot days at some point. Just some thoughts.