1:15 PM | *Tornado season is off to a slow start thanks in large part to late season cold air outbreaks…Oklahoma is about to set a record for their latest first tornado ever*
As we know full well here in the Mid-Atlantic region, there have been an unusual frequency of late winter and early spring cold air outbreaks leading to consistently below-normal temperatures during March and April. This extended period of unusual cold has also impacted other parts of the nation including the Ohio Valley, Great Lakes, central and northern Plains, and parts of the Southeast US. The late season cold has also had an inhibiting effect on the tornado season so far across much of the US with overall numbers way down compared to normal. In fact, the state of Oklahoma – right in the heart of tornado alley – is about to set a record for their latest first tornado ever. There are signs, however, that it could get a lot more active in the central Plains later next week as atmospheric conditions for severe weather and tornadoes finally become more favorable.
There are numerous factors involved in the formation of tornadoes in the US including overall temperature and humidity patterns with a classic setup beginning with cold air dropping southeast across the middle of the country as very warm and humid air simultaneously rides northward from the Gulf of Mexico. The cold air outbreaks have been so widespread and persistent in recent weeks across much of the nation, the usual requirement for severe weather of an influx of warm, humid Gulf of Mexico air has simply not materialized in the tornado belt. Cold air masses have pushed far enough to the south and east in recent weeks from Canada and the northern US they have not allowed any consistent flow of air from the Gulf of Mexico into the Plains or south-central states.
The composite temperature and specific humidity anomaly maps for the period of March 1, 2018 to April 20, 2018 show widespread colder-than-normal conditions and overall moisture levels are actually below-normal in much of the country – not exactly conducive to severe weather and tornadoes. In Oklahoma, temperatures have been near normal throughout this period and it has been drier-than-normal in much of the state. The latest first tornado ever for the state of Oklahoma occurred on April 26th in 1962 – coincidentally, a year with a very cold March and April in much of the nation. \
The average date in Oklahoma for their first tornado is March 11. On average, Oklahoma has around 5 tornadoes reported during the month of March and 14 in April and zero have been reported year-to-date. The number of tornadoes (228) reported so far on a nation-wide basis in 2018 are about one hundred or so below-normal for this time of year and ranked in the 25th percentile.
The news on the lack of tornadoes may not stay this good for much longer in the central Plains including in the state of Oklahoma. A strong upper-level trough will slide eastward from the southwestern US into the central Plains later next week and this could very well set off a tornado outbreak in much of that region. At the same time, the eastern US will experience a major warm up with temperatures likely in the 80's for highs during the Wednesday-to-Friday time period.
Meteorologist Paul Dorian