The intensity of the cold air damming event.The southern extent of where the wedge forms.While they will always have issues during small-scale events, they usually have a difficult time determining the following: Our weather models have improved significantly over the past ten years. Weather models sometimes have a difficult time with predicting temperatures in CAD events. The wet-bulb temperature is the temperature a parcel of air would have if it were cooled to saturation (100% relative humidity) by the evaporation of water into it. Sometimes the best way to gauge whether or not a location will drop at or below freezing is by monitoring the wet-bulb temperature. For this reason, meteorologists are always on guard for the potential of freezing rain when the airmass is extremely dry. The drier the airmass, the lower the temperature can drop. When rain falls into the shallow, dry layer of cold air at the surface, temperatures begin to drop via evaporative cooling. The warm air aloft and cool air at the surface enhances low level clouds. Moisture from the Gulf of Mexico “overrides” the shallow layer of cold air at the surface. For most cases, CAD events are notorious for creating ice storms in parts of the Southeast United States. CAD can affect precipitation types depending on the strength of the feature. CAD can result in freezing rain/ice events in the winter across eastern Alabama, Georgia, South Carolina, and North Carolina.ĬAD can be an extremely complicated feature in the winter months. If you look higher than about 925 mb, it typically becomes more difficult to detect since temperatures increase with height above the CAD layer. Usually when CAD events form, drier air filters across the region and results in higher barometric pressures. CAD is identified using observations of surface wind directions, temperatures, higher surface pressures, and dew points. This feature is very shallow, and only occurs at the surface to around 925 millibars (hPa). High pressure off the Northeast or near Nova Scotia brings a northeasterly surface wind that allows cooler (and drier) air to advect southwestward. Across the Appalachian Mountains, this shallow layer of cool air forms on the eastern side of the mountains and propagates to the southwest as ridging builds across the area. Image Credit: Matt DanielĬold-air damming occurs when cold air becomes entrenched against the windward side of a mountain range. Cold Air damming develops from high pressure to the northeast. Ultimately, accurate prediction of CAD comes down to a thorough understanding of the dynamics and physical processes that trigger them, climatology, and a working knowledge of how the numerical models operate. How does CAD form, and why is it a tricky meteorological feature to nail down for meteorologists? You will find out that human forecasters can forecast these events better than most atmospheric models. While CAD can occur in the Rockies, it is predominant east of the Appalachian Mountains. Topography plays a major role in CAD events, and you need a mountainous range for this feature to develop. Cold-air damming (CAD), often called “the wedge” in the Southeast, is an interesting meteorological feature that can result in tricky forecasts for meteorologists.
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