Having worked in Wichita for a year, I considered myself fortunate to have experienced only a few tornadoes during that time. After all, I was new in my profession and only just beginning to realize how little I knew about them at the time.
This spring has been extraordinary in the plains. Through Monday, Oklahoma has experienced zero tornadoes. That's a record tornado drought for one of the most tornado-prone locations on earth, but that record is about to be smashed.
This will be a very active, severe weather week, building in coverage and overall threat on Wednesday into Thursday. There can be a tendency even with a public far more experienced and knowledgeable about severe storms and tornadoes than Western New Yorkers to let their guard down. But since late last week, broadcast and National Weather Service meteorologists have been advising residents that all this relative tranquility will come crashing down this week.
Oklahomans and Kansans have experienced tornado droughts before. In 2010, Oklahoma had just three tornadoes up until May 10. This is what happened that fateful day:
What does a slow start to tornado season mean? The 2010 Oklahoma tornado season started off slow. As of 3:37pm on May 10, there had been only 3 tornadoes in the state. By 8:45pm, that total was up to 59. That's 56 tornadoes in a little over than five hours. #okwx pic.twitter.com/LTsZRNiptL
— NWS Norman (@NWSNorman) April 24, 2018
Some 56 confirmed tornadoes struck the state between 3:37 p.m. and 8:45 p.m. that day.
What’s been happening this year is the presence of a northerly storm track, in which the deep areas of low pressure have passed well north of the central plains. When this occurs, the lows are unable to bring distinct boundaries between subtropical warm, moist air masses and bone-dry cooler air masses across the central plains. Note, on the surface map at left, how the main “L,” or low, is way up on the Minnesota/Canada border.
Starting Tuesday of this week, though, those lows over northwest Kansas and southeast Colorado will begin to bring copious Gulf moisture into parts of the plains and Midwest first, and then a larger portion of the plains, with a trailing boundary you can see in faint orange “bubbled” front dropping from the low into western Oklahoma into Texas.
That boundary is known as a dry line. It separates the subtropical moisture ahead of it from the often desert-dry air behind it, and can be one of the most important features in setting up a severe storm and tornado day. We don’t get dry lines in our part of the country, but they are a common feature in the plains.
As I’m writing this, such a dry line has developed in the west central plains. Look at the tremendous contrast in dew points from the rich, green area of moisture compared to the air over Colorado and New Mexico in this analysis from 10 a.m. Tuesday.
When you combine that moisture content and low-level moist, warm flow ahead of the dryline out of the south or southeast, with very dry, strong winds aloft that have veered to the southwest, that speed and moisture differential in the winds from the surface to aloft can spawn intense, rotating thunderstorms and supercell . Those storms are more likely to become tornadic. Here is the orientation of the winds at 10 a.m. at the surface, and here is the wind orientation at about 18,000 feet up on this morning.
The difference in wind speed and direction with increased height is wind shear, which sets thunderstorms up to develop with more spin and rotation. With these and other factors in mind, the National Weather Service's Storm Prediction Center in Norman is indicating more favorable conditions for severe storms and possible tornadoes for Tuesday. (Here is Wednesday's outlook and Thursday's.)
You may notice that on Thursday, even Western New York is in a dark green area referring to “marginal” (or 5 percent) risk for severe thunderstorms with damaging gusts. Tornadoes would be quite unlikely in a marginal risk area, though not absolutely impossible.
No, Western New York is nowhere near the “tornado alley” regions such as the southern and central plains, nor the tornado-prone Gulf states, but it is time to begin paying more attention to the risks of severe weather in our region and what precautions need to be considered. This just happens to be Severe Weather Awareness Week in our region, and here is some extremely useful information from the National Weather Service Buffalo Forecast Office.