Above: GeoColor visible satellite image from 1:10 pm CDT Wednesday, March 18, 2020. The upper-level wave that will kick off severe weather and blizzard conditions on Thursday is reflected in the swirl of clouds off Baja California. (RAMMB/CIRA/CSU)
Nature has grabbed the March playbook off the shelf and gone for an American classic—a potent spring storm system with high-impact weather on both sides. Severe thunderstorms with a threat of tornadoes will erupt across the Southern Plains tonight and shift toward the Mississippi Valley on Thursday, while blizzard conditions are projected to develop Thursday on the central High Plains.
A compact but potent upper-level wave will be driving this week’s wild weather. The wave (see image above) is now rotating around the upper low centered in Nevada that’s brought welcome moisture to California and other parts of the West. This upper wave will pivot across the Plains on Wednesday and Thursday, fostering upward motion and strong vertical wind shear that will support severe weather. The wave will also strengthen a surface low in eastern Colorado that’s expected to accelerate toward the upper Midwest on Thursday, with snow and high wind on its northwest side.
Meanwhile, a push of notably warm, moist air for late March was surging into Texas on Wednesday afternoon, with temperatures into the upper 70s Fahrenheit and dew points as high as the upper 60s as far north as the Dallas–Fort Worth area. This unstable air will serve as fuel for severe thunderstorms.
The NOAA/NWS Storm Prediction Center placed parts of Texas and Oklahoma under an enhanced risk of severe weather into early Thursday, as scattered supercells are expected to form west and north of the DFW area on Wednesday evening. A tornado or two is possible, along with very large hail, before the storms congeal into several lines and clusters of severe weather late Wednesday night from western and central Texas into Oklahoma. The main threats will shift from tornadoes and hail to high winds and heavy rain as the night progresses.
The severe weather will likely split into two main regions on Thursday. Close to the deeper moisture, scattered severe storms may regenerate from Arkansas to Indiana. These storms are expected to become less likely to rotate and produce tornadoes over time, as the winds shift to southwesterly at all heights, reducing vertical wind shear. Strong downburst winds and heavy rain would still be a threat, though.
Further north, a small but notable tornado threat could emerge across southern Iowa, where the main surface low will be tracking. It’s unclear how much of the moist, unstable air will make it that far north. However, surface winds there will have enough of an easterly component to produce substantial vertical wind shear, so even modest instability could lead to a tornado concern.
Snow, cold, and wind—but how much?
The great uncertainty with the Plains snowstorm isn’t so much whether it’ll snow, but how much will fall. Amounts will generally be light across a broad belt from eastern Nebraska to Minnesota. However, there will be pockets of local enhancement based on small-scale bands that are difficult to predict more than a few hours in advance. Moreover, temperatures will be close to the rain-snow boundary in many areas, so some of those enhanced areas could be all rain, all snow, or a mix.
Toward the High Plains, where the elevation works in favor of temperatures cold enough for spring snow, the amounts will be heaviest and the winds will be strongest. A blizzard warning is in place for Thursday from southeast Wyoming and northeast Colorado (just east of the Denver area) into much of northwest Nebraska.
A winter storm warning is in effect for Denver and vicinity, which could see anywhere from 4 to 10 inches of snow—a big late-winter storm for most places, but par for the course in the Denver area, where March is the snowiest month of the year.
From central Nebraska and southeast South Dakota into Minnesota and Iowa, where snowfall amounts will be on the lighter side, high winds could still lead to a period of difficult travel conditions while the snow is falling and blowing.
See weather.com for frequently updated outlooks on the late-week severe weather and winter weather expected.
