Summary of the Colorado Blizzard December 24, 1982

(a classic mid-continental lee-side cyclogenesis case)

1. A strong polar jet dug into a pre-existing long wave trough from Dec 21-24, creating a huge cutoff low in the upper air. The tilt was NOT negative so the storm moved on a typical panhandle hooker track. However, since the upper air trough was cut off, the surface storm moved slowly.

2. At the surface, cyclogenesis occurred to the lee of the Rockies and organized in the panhandle area of Oklahoma and Texas.

3. Strong warm air advection occurred over a large area in the eastern half of the U.S. with overrunning north of a stationary front in the northern U.S. This was accompanied by strong moisture advection, with dewpoints near 70˚F at the Gulf coast and near 50˚F near the stationary front. There were numerous thunderstorms in the warm sector, some of them severe. These storms helped inject water vapor high in the Troposphere.

4. The “warm conveyor belt” transported the water vapor north, over the stationary front, then west at mid-tropospheric levels and finally, back toward the southeast over Colorado. Precipitable water over Colorado was low, but water vapor advection was strong.

5. Cold air from Highs anchored over the Pacific Northwest streamed southward into Arizona, New Mexico, and Mexico itself. Temperatures in Colorado were in the upper 20’s and near 30˚F.

6. The 1000-500 mb thickness was around 541-542 dm. However, with the high elevation of the High Plains, the rain/snow line was well east of the Low.

7. Models of the time (LFM, Spectral) did a credible job predicting the storm, although the LFM forecast precipitation amounts were typically anemic.

8. Mesoscale factors enhanced the snowfall. Whereas most mid-continental storms produce snowfall in the 4-8” range, this storm snowed 24” at Denver’s airport with much higher amounts in the mountains and in the plains south of Denver. There was a mesoscale push of high dewpoints just north of the stationary front and a small scale wind intensification through the Denver area. This was possibly caused by northwest winds around the Low being compressed by the front range of the Rockies. It created a mesoscale convergence zone which enhanced vertical motion and precipitated out the higher water vapor from the mid-troposphere.