WeatherMatrix (Jesse Ferrell)

Bomb cyclone or not, the April Plains storm was crazy

By Jesse Ferrell
4/12/2019, 4:35:51 PM

I was interviewed for this article by AccuWeather.com about whether not this week's storm in the Rockies and Plains was a "bomb cyclone." It didn't qualify (see my reasoning at the bottom of this blog entry) but it sure did have some crazy weather! First, a (unusually large and powerful) gustnado was caught on film in Pueblo West, New Mexico:


One of the NWS's spotter reports said that a 107-mph wind gust was measured at a weather station in the area -- quite likely the gustnado passed over this sensor, I'd wager. Although I couldn't find the 107-mph reading online, amateur weather stations in the area from the Weather Underground network showed winds as high as 70 mph. It's possible it was a station owned by WeatherBug (which often supplies weather stations to schools) but they no longer show their weather station data online, so I can't be sure.

Amateur Weather Stations Near 107 mph Gust


High winds from the storm also literally blew sand from the White Sands, New Mexico, monument into Minneapolis. Some dust made the trip all the way from Mexico to Canada!


The dust was lofted at least as high as 25,000 feet over Nebraska, according to 3D radar:

3D Radar Shows Dust Aloft Over Nebraska


That all took place on Wednesday. On Thursday, the storm system was so intense that it dropped two Severe Thunderstorm Warnings in areas where heavy snow was falling and it was 29 degrees. The warnings were issued for hail (confirmed by spotters) and there was also lightning with each storm.


In fact, the low pressure area dropped over 31,000 lightning strikes, many of which were in the cold sector of the storm (shaded blue below), where it was snowing or freezing rain. I don't think I've ever seen that many strikes in a winter storm.

Lightning strikes from 4/10-4/11 storm


But was it a bomb cyclone? The official definition is very simple: “Bombogenesis… occurs when a midlatitude cyclone rapidly intensifies, dropping at least 24 millibars over 24 hours.” This storm did not meet that definition according to the WPC surface maps, showing only a 20 millibar drop, at best.

Why did some people say that it did qualify? While it may be technically dependent on latitude, according to a research paper from 1980, latitude is not part of the official definition, and until it is, we can’t use other measures. I think the official definition may have left that nuance out because it makes labeling a storm a “bomb” more confusing. For example, what if the storm changes latitude during the intensification process?

The real problem, however, is that the official definition doesn’t specify how you determine the “central pressure” or lowest pressure of the storm.

I believe that using individual official weather station readings, as Dr. Roth suggested, is problematic because the airports that transmit can be widely spaced (the central pressure could occur in between them), and I don’t believe the observations are always accurate.

Pressure is dependent on elevation, but an equation is used to convert it to “sea-level pressure” which meteorologists use. Because pressure is the only meteorological variable that’s elevation dependent, it’s difficult to properly maintain pressure equipment calibration. It’s also more likely that stations go uncalibrated because the public doesn’t really care about pressure, compared to something like temperature, which is probably calibrated more often.

Because of all those potential errors, I choose to trust the NOAA WPC’s Surface Pressure Analysis map, which shows their estimated central pressure of the storm. I assume their analysis takes into account multiple stations and perhaps other data, and estimates pressure between stations.

WPC Surface Maps for April Storm


The WPC maps (shown above) analyzed three low pressure systems in the Rockies Tuesday morning, their central pressures measuring between 1005 and 1010 millibars. 24 hours later, the low pressures were between 990 and 994. While there is some question of which low pressure system Tuesday matched which one Wednesday, even the most extreme difference (1010-990) still fell short of the definition of 24 mb in 24 hours, and looking at maps before and after this time, the number is no higher.

In any case, this was a strong and interesting storm, at 983 mb pressure, even when compared to the 968 mb storm in March.

The views expressed are those of the author and not necessarily those of AccuWeather, Inc. or AccuWeather.com

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WeatherMatrix (Jesse Ferrell)