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Don Paul: Narrowing down lake-effect warnings

As I write in my office, a band of lake-effect rain has been hitting northern Erie and southern Niagara counties … liquid, lightweight and no warnings involved. One of these days (as Ralph Kramden used to say) the real deal will come along … frozen, heavyweight and requiring warnings.

Last year, the National Weather Service's Buffalo office was one of several that experimented with a more precise and timely method of warning the population of shifting lake-effect snow and its impacts. The experiment worked out rather well and drew good support from the public, emergency managers, transportation managers and school systems. The use of movable and adjustable polygons is superior to what had been used for a long time: full forecast zones. (A polygon is a closed plane shape with multiple sides.) And polygons are what we’ll be seeing from now on for moving lake effect bands.

Jon Hitchcock, lead forecaster for the National Weather Service Buffalo office, explains the limitations on the use of polygons: “The new snow squall warning product will not replace the county-based lake-effect snow warnings and will not be used for stationary or slowly moving lake-effect snow bands. This new warning is for fast-moving snow squalls, such as an arctic front that drops a quick inch or two and takes visibility to near zero. We will still have our experimental polygon lake-effect snow warnings available on our website this winter.”

Prior to polygons, which have been used successfully for severe thunderstorm and tornado warnings, an office like the Buffalo NWS would warn for a forecast zone whether a band was stationary or shifting. In the eight counties of Western New York, each county is a zone (ith the exception of Erie County, which is divided into two zones: northern Erie and southern Erie). Southern Erie County begins at Orchard Park and extends southward. That means other parts of the Southtowns, such as Hamburg, West Seneca and Lackawanna, are in the Northern Erie zone, along with Buffalo and the rest of the county northward.

Using the old forecast zone display, at left is a typical view of what warnings and advisories looked like in graphic form.

Now, with more detailed, higher-resolution computer models, it is possible to narrow down the coverage of the weather service warnings and cut back on “overwarning” parts of forecast zones less likely to see major impacts during movement of those bands. Here is an example of a model forecast for western Lower Michigan, narrated by a Grand Rapids National Weather Service meteorologist.

Western Michigan often gets multiple thinner bands off Lake Michigan, but this model output demonstrates how only parts of counties are likely to be hit at any given time. With this higher-resolution modeling – not only National Weather Service models, but most TV stations have in-house high resolution models as well – it is often possible to shrink heavy snowfall coverage with higher reliability.

With the old zone warning system, if heavy snow were expected from South Buffalo and Lancaster down into the southern Erie county zone, a warning had to be issued for northern Erie County, even if forecasters were expecting no major impact north of Buffalo to Tonawanda Creek. That’s the way the warning software worked until now. Even if wording were more specific to, say, exclude Amherst and Clarence, the map still looked like the first example above. It could be confusing to the public.

Now, with better tools and better software, the polygon has arrived for shifting bands.

(National Weather Service)

The polygons can also be adjusted during the course of the southward shift for location, size and intensity, just as polygons are adjusted during severe thunderstorm outbreaks. In short, greater detail is offered throughout the course of a lake-effect snow event before, and during, its development and passage.

Almost needless to say, I will add the caveat: most of the time.

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