Dr. David M. Schultz

CURRENT RESEARCH INTERESTS:
Western United States Fronts and Cyclones

Although much research has examined the structure of midlatitude cyclones over the relatively flat eastern United States and the oceans, my interests are to understand the structure and evolution of cyclones and fronts as they pass from the eastern Pacific Ocean, across the Rocky Mountains, and redevelop in the central United States (for example, how Alberta Clippers are formed).

"It's so windy in Wyoming that you can watch your dog run away for two days if he's headed upwind. Downwind, he's in Nebraska in 3.7 seconds." Roaming Wyoming by James W. Ballard (1997).

This research raises two issues dealing with surface analysis over the western United States.

Chuck Doswell and I have written a manuscript for Weather and Forecasting entitled "Analyzing and Forecasting Rocky Mountain Lee Cyclogenesis Associated with Strong Winds." First, we start with a case study (12-14 December 1988) of an Alberta clipper that produced numerous Storm Data reports of winds 20-30 m/s over MT, ND, WY, and SD. The movement of the surface cyclone away from the lee slopes occurred abruptly (the center of the circulation jumped 300 km in one hour). We can relate the movement of the lee cyclone away from the mountains to a mobile sea level pressure minimum (pressure check) at upstream stations. An MM5 simulation shows that this pressure minimum is associated with the height falls from the shortwave trough aloft. Thus, examining the surface pressure checks upstream of the lee slopes will help in locating the effect of the shortwave trough aloft.

One of the techniques employed to analyze this case was to band-pass the observations of sea-level pressure, retaining features resolvable on the mesoscale. (View the filter characteristics.) Viewed in this manner, the low-pressure anomaly moves over the mountains in a discontinuous manner. [large animated gif, small animated gif, or javascript animation]. It is hoped that techniques such as band-pass filtering will help operational forecasters follow the movement of the forcing through regions of complex topography.

We also perform a climatology of Alberta clippers and show that the overwhelming majority of these events (about 75%) are associated with Storm Data reports, thus indicating their potential for generating hazardous winter weather. This came as a surprise to me, since I always considered Alberta clippers to be relatively innocuous storms (too dry to dump a lot of snow and too weak to produce strong winds). Obviously these storms create lots of wind and heavy snow reports in the mountains and on the lee slopes (MT, WY, ID, Dakotas) that I never really appreciated before.

Finally, we show that this mobile pressure minimum (which is commonly analyzed on surface maps as an occluded or cold front due to continuity) is not a front and should not be analyzed as such. This feature is more akin to the feature termed a baroclinic trough by Fred Sanders, although we prefer the term nonfrontal trough, since these features may or may not be associated with baroclinity.

MANUSCRIPTS

Schultz, D. M., and C. A. Doswell III, 2000: Analyzing and forecasting Rocky Mountain lee cyclogenesis often associated with strong winds. Weather and Forecasting, 15, 152-173.

My research on western United States weather has spawned other side projects such as conceptual models of upper-level frontogenesis, the Intermountain Precipitation Experiment, and lightning associated with lake-effect snowbands over the Great Salt Lake.

I have also lectured to the Storm Prediction Center on Selected Topics on the Synoptic and Mesoscale Weather of the Western United StatesSynoptic

If you have any further questions about the research discussed here, or desire a manuscript, please feel free to write to me: david.schultz@noaa.gov.

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