Another Severe Weather Outbreak

Severe Weather Briefing

Discussion: Severe weather outbreaks in early March are not unusual. However, to the degree in intensity we’ve been observing such as the recent killer Alabama tornados the severe weather of early March 2019 will continue to be potentially unusually extreme and violent. The cause of the unusual violent character of U.S. severe storms during late calendar winter has been a persistent positive phase of global atmospheric angular momentum which means a stronger than normal jet stream in the middle latitudes. Research has shown this (AAM) pattern is common with El Nino and El Nino has been coming on strong the past few weeks. The jet stream speeds during the Alabama tornado outbreak were 170-180 mph, about 50% stronger than normal. For today the jet stream wind speeds are increasing into the 110-130 mph range which is (fortunately) closer to normal. Here’s what to expect this weekend.

At the moment, 3 severe thunderstorm watch areas are in effect from northeast Texas across Arkansas into Missouri. The severe weather episode is DEVELOPING. We haven’t seen any damage reports yet. By early afternoon the quall line is well organized stretching from eastern Texas to far southern Illinois (Fig. 1). Tornado risk is STARTING at this time. Strong low-level atmosphere wind can be brought to surface level east of the (blue) cold front and along and south of the (red) warm front. Strongest gusts to 65 mph are beginning at this time and damage reports begin to develop and increase rapidly.

Squall line peak intensity is 4-7PM EST crossing Louisiana, northern Mississippi, western Tennessee and through central Kentucky. The tornado risk area is southwest Kentucky, western Tennessee and northern Mississippi. At 7PM violent storms from Mississippi to Kentucky are present (Fig. 2). Wind gusts 55-70 mph are possible in heavy rain zones from far southern Indiana/Ohio to northern Mississippi/Alabama.

By 1AM EST Sunday the squall line is losing its punch stretching from Mississippi/Alabama to far southwest Virginia (Fig. 3). The high wind zone is less intense but stretches north to the eastern Ohio Valley. A new high wind zone is developing across the Midwest.

On Sunday the squall line is not as strong but will stretch southwest to northeast ahead of the cold front reaching central Georgia and the eastern Carolinas by 8PM EDT (Fig. 4).

The location greatest impact will be later this afternoon and into the evening from northeast Texas to the northern half of Mississippi to western Tennessee and much of Kentucky. Damaging wind gusts can reach the eastern Ohio Valley during the evening hours although more isolated.

Fig. 1: NOAA/SPC depiction of fronts and weather with Climate Impact annotations valid at 1PM EST Saturday.

Fig. 2: NOAA/SPC depiction of fronts and weather with Climate Impact annotations valid at 7PM EST Saturday.

Fig. 3: NOAA/SPC depiction of fronts and weather with Climate Impact annotations valid at 1AM EST Sunday.

Fig. 4: NOAA/SPC depiction of fronts and weather with Climate Impact annotations valid at 8PM EDT Sunday.