HASTINGS — The National Weather Service Hastings saw over 200 people participate in a three nights of virtual weather spotter training, after all in person events had been canceled due to the COVID-19 pandemic.
Warning Coordinator Mike Mortiz said 206 people participated throughout the three nights the training was held.
Mortiz said the turnout shows the virtual training is a viable option for future trainings. The NWS Hastings will continue their in person trainings in the future, but Mortiz said future virtual trainings could he held later in the year, when the peak of Nebraska’s severe weather season is close.
The peak of severe weather season in central Nebraska is June 17, Mortiz said during the training, with tornado season reaching a climax in early June. Other hazards such as large hail peak in mid-June and high wind in late June.
Nebraska sees an average of 50 tornadoes each year.
Mortiz said the next two to eight weeks will be the peak of the severe weather season in the area and people should have a safety plan in place.
So far 2020 has seen a majority of severe weather focused in the southern central Plains, with 81 severe weather watches issued across the nation. Tornado activity has been regulated mostly to the south-eastern states, with 94 watches being issued.
The severe weather season has gotten off to a noticeably slow start in Nebraska, the NWS Hastings did not issue a severe thunderstorms watch in the whole of April.
Certain severe weather hazards are often limited to a certain point in the day. For instance, Mortiz said the peak for tornadoes across the country is 7:45 p.m. with a majority of warnings being issued between 5 p.m. and 9 p.m. There are few to none in the overnight periods, from 3 a.m. to 9 a.m.
Flash flooding, which Nebraskans have experienced in 2019, tends to occur more in the overnight periods with most warnings being issues from 9 p.m. to 3 a.m., Mortiz said. The timing is down to rain falling in the evening periods and then overwhelming the system overnight.
In 2019, 66 percent of flood fatalities occurred due to driving, said Mortiz. Of this, 68 percent of the fatalities last year were men.
In a nearly 10 year period, 2010-2019, the NWS Hastings warning area has had only one flash flood fatality, Mortiz said.
This occurred on July 9, 2019 in Dawson County. A Eustis woman drove her car into flood waters covering a road south of Cozad, the vehicle was overturned and swept into a ditch, the woman later died of her injuries.
Mortiz advised people to know the difference between a weather watch and a weather warning. A watch means people should be ready to take action and seek shelter if necessary. A warning means people should take action immediately.
Especially in the case of tornado warnings, Mortiz said many people will seek shelter, but it seems an equal number of people go outside to look for a tornado and, “have to see it to believe it.” This can be dangerous and leave precious few moments to seek shelter if the worst comes to pass.
For those interested in weather outlooks, Mortiz said the Storm Prediction Center’s website, spc.noaa.gov, has a wealth of information. Mortiz said the SPC has now expanded their severe weather probabilities to the Day 2 period, which is 24-48 hours out from any given day.
When people hear of a 10 percent chance for tornadoes, issued by the SPC, this should not be correlated to a 10 percent chance of rain, Mortiz said, a 10 percent chance of a tornado means the area under threat will likely see a tornado.
Mortiz offered his own rules of thumb for these types of warnings. He said if there is a 10 percent chance of a tornado, people should be ready. If there is a 15 percent or higher chance of tornadoes, people should be, “really,” ready. The same goes for a 30 percent chance of wind and hail versus a 45 percent chance for wind and hail.
While the Doppler radar operated by NWS Hastings at Blue Hill is a powerful tool when forecasting weather, it has its limitations. The beam can only lower so far and cannot look into the lowest levels of the atmosphere in certain areas.
Over Dawson County it can only see 6,000 feet above the ground. For what is occurring at ground level, the NWS relies on the reports of trained spotters and the public.
Mortiz noted from 2010-2020, 5,428 weather reports had been made across the whole NWS Hastings warning area.
The type of thunderstorm which often produces the most damaging tornados, large hail and high winds is the supercell.
A supercell thunderstorm is characterized by a persistently rotating updraft of air, known formally as a mesocyclone.
This type of storm organization is due to the amount of wind shear in the atmosphere. Wind shear comes in two forms. Speed shear is when wind at different heights is moving faster than another and directional shear is when wind at different heights its moving at different directions. Both can be present in an area.
If wind shear is present in the lowest levels of the atmosphere near the ground, along with other key factors, tornadoes could be likely.
A supercell thunderstorm is made up of multiple components, but the two most important to tornado formation is the forward flank downdraft, FFD, and the rear flank downdraft, RFD.
The FFD is where the majority of the rain and large hail can be found. It is often located on the northwest side of the storm. Rain and hail is lofted high into the sky by the updraft, which is then pushed down stream by upper level winds and falls away from the updraft, allowing it to continue.
The FFD is a cooler region of the storm, made so by the rain cooling the air around it. This area often has a low cloud base. Sometimes the precipitation manifests itself in an inflow tail, which point towards the storm’s updraft, this is a key sign the storm is still taking in air and could strengthen.
The other part is the RFD, which is a complex process of wind momentum being pushed downward. This structure wraps around the updraft of of the storm and can even suck in precipitation into it, giving supercells and characteristic, “hook echo,” Mortiz said.
The RFD is mainly dry, with a higher cloud base, said Mortiz. Due to the dryness, when this feature wraps around, it can create a, “clear slot,” in the back of the storm. This is believed to be a component in the birth of a tornado; they often form on the northern edge of this slot.
For those out spotting in the field, Mortiz said to keep maintain their own, “social distance,” from the storm. Spotters should be close enough to see, but far enough to escape.
Landspouts and Lookalikes
There are different types of tornadoes than those produced by supercells and phenomena which look much like actual tornadoes and can fool spotters and the public.
A gustnado often forms in the outflow region of the storm, and due to wind shear, can begin a ground circulation which looks much like a tornado on the ground, but the giveaway is the feature is not connected to the rotation of the storm itself.
A landspout tornado is a true tornado, but one which is not being driven by the RFD of a supercell. Instead these can form when circulation on different boundaries is tilted into the vertical. These tornadoes often have a translucent tube look, while not as powerful as supercell tornadoes, they can still pose a danger, with some winds in excess of 100 mph.