Major storm affecting much of the eastern U.S. (H. Michael Mogil, CCM, CBM, NWA-DS*)
With the arrival of Spring, major holiday celebrations arrive (e.g., Passover, Easter). With the arrival of spring, major, large-scale storminess often arrives, as well. While we may think that major storms are most likely in the middle of winter, it isn’t the cold weather that sets the stage for such storms. Rather, it is the contrast of different air masses – typically warm and humid nearby to cold and dry. With the arrival of Spring 2020, comes a major storm event that started late yesterday (April 11, 2020) across Texas and has since spread throughout the Deep South this Easter Sunday (April 12, 2020). Fig. 1 shows how widespread the storminess is and will be with, with watches, warning, and advisories for a potpourri of weather hazards for almost all of the U.S. east of the Continental Divide.
Thanks to a very dynamic upper-level wind pattern (winds at 30,000 – 35,000 feet above ground level – Fig. 2) will be blowing at speeds in excess of 150 knots (165 miles per hour). In addition, computer forecasts for the jet stream pattern across the Deep South have continued to show (for days) that the jet stream will be spreading apart, a feature often linked to very strong upward air motion, the kind that favors the formation of strong to severe thunderstorms, including wide, long-lived, strong tornadoes. Fig. 3 shows the upper-level cloud
pattern across the Deep South this Sunday afternoon, almost a perfect match to the computerized forecast of winds that spread apart.
Added to this has been the infusion of vast of amounts atmospheric moisture into the region on strong southerly low-level winds; the dew point at Jackson, MS, for example, has risen from the upper 30’s yesterday afternoon to the upper 60’s this afternoon.
NOAA’s Storm Prediction Center (NOAA = National Oceanic and Atmospheric Administration) has already posted tornado watches covering northeast Louisiana and much of northern and central Mississippi (Fig. 4). Due to the strength of the various severe storm parameters already in place, the watch has been classified as a Particularly Dangerous Situation (PDS). PDS’ mean the likelihood for deadly and destructive tornadoes is especially high.
Fig. 5, the early afternoon radar composite map, attests to these atmospheric interactions. Several lines of strong thunderstorms are already affecting the area from northeast Louisiana into northern Mississippi. Fig 6 shows a cluster of tornado and severe thunderstorm warnings across northeast Louisiana. In the past hour, a tornado reportedly damaged 20 homes near Monroe, LA.
Tornado and severe thunderstorms watches and warnings will continue to be issued eastward and northeastward through midday Monday as the weather system sweeps quickly to the east. Severe storms may even reach as far north as the Washington, DC area. Individual thunderstorms may be moving at speeds of 50 to 60 miles per hour or more, lessening the chances of early warnings for approaching severe weather.
The only good news is that even though thunderstorms may produce excessive rainfall, the fast storm movement will lessen the likelihood of widespread flash flooding. Still, some areas can receive far too much rain too quickly, especially in more vulnerable locations (small creeks in hillier terrain).
To the north of the storm system, the necessary cold air ingredient of this large-scale storm system has led to the development of a band of locally heavy snow. The heaviest snow should fall from northern Nebraska across extreme southern Minnesota and then northeastward to the Upper Peninsula of Michigan. Areas near Minneapolis, MN could receive half of a foot of snow, while areas near Marquette, MI may see as much as a foot and a half. High winds associated with the intensifying large-scale storm will lead to local ground blizzard conditions.
The storm will also generate a large-scale high wind event that will affect most of the northeast quarter of the Nation by later today into Monday evening. High wind watches (for winds gusting to 50 miles per hour) are already posted for many areas of Michigan, Pennsylvania, and New York. Gale and storm warnings have been hoisted for most of the Great Lakes.
This is a dangerous large-scale storm system with a large number of weather hazards. People in the path of the storm system (and especially in the path of fast-moving thunderstorms in the Deep South) should be monitoring the latest weather information and ensuring that they are prepared to take immediate safety actions, as warranted.
© 2020 H. Michael Mogil
Originally posted 4/12/20
* The National Weather Association Digital Seal (NWA-DS) is awarded to individuals who pass stringent meteorological testing and evaluation of written weather content. H. Michael Mogil was awarded the second such seal and is a strong advocate for its use by weather bloggers.