A snowstorm in Colorado is cranking out blankets of snow, and numerous states in the Great Plains — from Texas to Nebraska — are gearing up for massive flooding. Meanwhile, in the Tennessee Valley, we are enjoying the beginning of a stretch of warm and dry weather. Coincidence, right?
Not really. In fact, the two are related, as they are part of a weather pattern called the ‘omega block.’
— NWS Huntsville (@NWSHuntsville) April 15, 2016
The Colorado snowstorm as well as the Great Plains floodwaters are all a result of a strong low pressure system (denoted by a red L) that is parked over the Southwest. This low is blocked from moving east by a high pressure system (the blue H) located over the Southeast. However, that high is block from moving by a different low pressure system (a different red L) located off the coast of the Northeast. On a weather map, the resulting L/H/L pattern and the flow of air around them resemble this: Ω, which is the symbol for the Greek letter omega.
Stunning view of blocked pattern, including Kelvin-Helmholtz instability waves riding periphery of W-Atlantic low. pic.twitter.com/yAuDNbFiRY
— Anthony Sagliani (@anthonywx) April 17, 2016
Because each pressure system is blocking one another, it will take as many as four to five days for the “systems” to either weaken or finally move out of position. As a result, the weather associated with those “systems” will persist throughout the duration of the block. For example, heavy rain and major flooding is expected from central Texas to Kansas because warm, moist air will continue to stream into the region around the parent low over the Southwest. Here in the Tennessee Valley, high pressure dominating our region means we are in for a stretch of sunny and dry days; rain will only return when the high pressure system weakens and allows the Southwest low to move east, and that is not expected to happen until late Wednesday/early Thursday.