The storm that Decoded Science forecast on Friday has materialized. Bad weather stretches from Texas to Iowa and Florida to New Jersey. And there’s more to come, thanks to conditional instability and the polar vortex.
Whom Will Waldo Impact?
The Weather Channel has finally gotten around to naming the storm that will dump a significant amount of snow on Washington, D.C. after pummeling Texas with five-inch hail.
Decoded Science named this storm Waldo last Friday, but The Weather Channel has chosen the unfortunate name Winter Storm Wiley. The storm is straightforward and not very tricky, though it will provide a variety of foul weather from the deep south to the Midwest to the northeast.
Waldo’s track has been a little south of the original Decoded forecast, with snow in Missouri as well as Iowa. The heaviest snow, up to a foot, is now scheduled to fall tonight and Monday in the mountains of Virginia and West Virginia. Further east, Washington is in the cross-hairs rather than Philadelphia as previously forecast.
In the deep south, the violent weather materialized a little further west than originally expected, but the tornado threat came right on target in Alabama and Mississippi. Thunderstorms and a slight tornado threat will move to the Carolinas and peninsular Florida tonight and Monday.
The cold air has made a deep intrusion into the southern states east of the Appalachians, thanks to the still-robust polar vortex. As a result, there could be a wedge of freezing rain in Virginia and North Carolina.
The Character of Storms is Changing With the Season
Waldo represents a transition from winter to summer – a spring storm that combines winter-storm aspects in the north and instability-caused heavy thunderstorms to the south. With every thrust of warm, humid air northward from the Gulf of Mexico, each wave in the jet stream which is accompanied by a dry, mid-level flow from the west, can create the conditional instability that produces severe weather, including tornadoes.
What is Conditional Instability?
Normally the profile of temperature with height shows a decrease of around three degrees per thousand feet. A dry parcel of air cools at five degrees per thousand feet, so normally the atmosphere is stable – if a parcel of air is lifted, it finds itself cooler than the surrounding and wants to sink back to its original position.
However, when the air is saturated, moisture condenses as it cools. This condensation releases heat, and a displaced parcel of air cools at less than five degrees per thousand feet. A rising column of air which is saturated at the bottom and dry at the top will experience an increase in the lapse rate, the rate of decrease of temperature with height.
If the process goes on long enough and the lapse rate becomes steep enough, any displacement of a parcel of air will result in a force causing it to continue to rise or fall. Violent overturning of the air mass ensues and thunderstorms and tornadoes form.
Will There Be More Storms?
Temporarily there is no change in the pattern of a strong polar vortex.
Another storm (Xenia is the name agreed on by Decoded Science and the Weather Channel) could form this week.
The long-range forecasts have recently hinted at a change in the pattern.
The latest computer runs, however, are a disappointment, showing high pressure returning to the Pole, which will keep the polar vortex displaced to the south.
Well, forecasts can be wrong, you know.
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