Quincy

An ugly pattern coming up for the next week. Even next week's trough ejection may be muddled by continued troughing in the eastern U.S. It's not all that common for a lull in severe weather to start May, but still...

In the past, they only did 30%, so it's not completely unprecedented.

It's nice to see a stretch like this being modeled inside of 10 days. Of course details are subject to change, but this type of pattern should deliver at least one or two solid days:

April is seen as a transition month during the severe weather season, as the frequency of tornadoes typically picks up rather quickly through the month. Despite what the calendar has to say, tornado activity has been fairly lackluster so far this month. In fact, after moving well above the average to-date tornado count in late February, the U.S. has steadily been losing ground. As it stands now, through April 18, the U.S. is near average this year for tornadoes, but with a relatively quiet rest of the week forecast, it looks like the country will fall below average for the first time since February. (The 1986-2015 climate period of 30 years is used for this average) The month of April started with the “dreaded” trough of low pressure across the Northeast. Locally, it was cold and snowy after a winter that was relatively mild and snowless. Likewise, after an active winter season for tornadoes, severe activity has been sporadic over the past several weeks. With all of this said, a pattern change is finally on the not-to-distant horizon, with troughiness returning to the West and the welcomed return to ridging across the Southeast U.S. This pattern will broadly support a more active period of weather across the central states, including an uptick in tornado potential. If we’re keeping track, a pattern change was slated for mid-April a long time ago, back as early as mid-March. That pattern change has been delayed somewhat as pesky troughing across southeastern Canada hangs on and the models display a glaring ridge (positive height) bias. This past week saw a shuffling of the pattern, but an omega block led to a messy setup and only a few isolated tornado reports in parts of the High Plains. The models often have issues handling larger scale pattern changes, but now that such a change is effectively inside of a week, confidence is increasing and the models are getting into good agreement. By this weekend, the first in a series of troughs is likely to swing across the western half of the country with some modest ridging to the east. Watch for lee-side cyclogenesis in the central High Plains vicinity between Sunday and Monday. While this is encouraging, the setup is not without flaws. This first trough ejection and evolution of the system is kind of junky (for the lack of a better word) in terms of tornado potential. There’s some instability as early as Saturday progged in the north-central states, but shear is forecast to be lackluster. The similar is the case for Sunday and Monday from the Plains into the Upper Midwest – generally marginal overlays between modest shear and favorable instability as a frontal system slides east. This is subject to change, but the trends are not particularly impressive. It’s the middle and latter portion of next week that really bears watching, figuring that this first system may at least get the gears turning for building a warm, moist air-mass over the Plains. With the Euro and GFS in good agreement (including the ensembles), it’s fair to use the GEFS analogs as a baseline for what type of setup we could be looking at, somewhere in the Tuesday to Saturday (April 26-30th) time-frame. Even before looking at specific dates, the string of digging troughs in the West with increasing moisture return in the central states sets the stage for a classic period of near-peak/peak tornado season activity. This does not necessarily mean we will have a massive number of tornadoes or that there will be a high-end setup, but at the very least, it is probable that tornado activity will markedly pick up as the week wears on. Now speaking of those analogs, there are some big dates and periods that show up, in order from ranking: 5/10/1953: A couple of days removed from the day 6-10 analog, but this date featured a localized outbreak of strong tornadoes in the Upper Midwest. 4/25 – 4/29/1994: 124 tornadoes in five days, including an outbreak from the 25th into the 26th. 5/12 – 5/13/1980: Not an outbreak, but strong tornadoes in Missouri followed by a pair of EF-3 tornadoes in Michigan the next day. 4/17/1995: AR/OK/TX outbreak with 21 tornadoes. 4/26/1991: Plains outbreak with 53 tornadoes, including the Andover, KS EF-5 tornado. 5/2/1994: The only analog in this bunch that didn’t have notable tornado activity. 5/7 – 5/11/2008: 122 tornadoes in five days. (2008 has been an analog on the radar for a while, also one of the busiest spring seasons of this century) 5/8/1979: 21 tornadoes, though mostly in Florida, two were reported in Iowa, including an EF-3. 4/30/1978: 15 tornadoes in the southern Plains, including 6 strong tornadoes and a mile-wide EF-4 on the northwest side of Oklahoma City. 5/4 – 5/6/1960: 71 tornadoes in three days from the Plains into the Midwest, including a long-track EF-5 tornado in eastern Oklahoma. If the pattern unfolds closely to what is modeled, it would appear that April certainly has the potential to go out with a bang. Through some of the research I’ve done with a May tornado outlook for USTornadoes.com, I noticed that the analogs have things in common. Without giving away too many of the details, one of the common themes in the analog was for the potential for violent tornado events in May. It could be the case that we’re just getting warmed up next week…

High-end or not, at least the overall pattern signs are encouraging. Back in mid to late March, it looked like change was going to happen around mid-April and for a time, but then the models lost it, only to see it come back about a week to 10 days late of earlier indications. Now that it's on the horizon, the general pattern looks solid for next week and perhaps late this weekend out in the High Plains. (Weekend won't happen if the slowdown continues and we maintain neutral or rising heights) Moisture won't be an issue with much of the Plains drought knocked out this past week and Texas getting inundated once again with copious amounts of rain. As you mentioned, pesky troughing in southeast Canada/Northeast is probably the biggest issue. Either way, at least we should see severe activity steadily pick up for the last week or so of the month. Maybe with some luck April will only end up slightly below average for tornado counts. It's going to take a couple of big events or a very solid string of days to push the month to AOA average.

That's true. Aside from the potential for one of these cutoffs to locally produce, we could just as easily see a pattern flip (models can and have been wrong in the long-range) or a random event pop up. Even the worst spring seasons have their share of events. Climo says it's very difficult to get through the last 10 days of April without some notable uptick in severe activity, if that's one piece of optimism I can throw out there.

Weeklies essentially show CONUS riding from the last week of April, right through the end of the run. Bright side, maybe it will be wrong again, but on the realistic side, I am becoming increasingly skeptical about any significant pattern change for the better in terms of severe potential.

CFS has showed an overall dearth of potential for the same time-frame over the past few runs. This seems to line up with most medium-range guidance. Although the pattern isn't 0% supportive of severe, it's looking fairly likely that tornado activity will remain below average for the next 1-2 weeks. The weeklies will be out in a few hours, but the EPS/GEFS show little optimism through day 15.