The National Weather Service is among the best and most trusted forecasting outlets in the United States, but sometimes their limitations cause them to screw up. Today is one of those times. This afternoon's snowfall map is ridiculous and physically impossible, and they need to fix this issue in order to stay on top.

First, a little background. The National Weather Service is the official weather forecasting agency for the federal government. It devolves its forecasting duties down to 122 individual weather forecast offices (WFOs) across all fifty states, Puerto Rico, and Guam. Each WFO is responsible for forecasting the weather for a geographic area outlined by a boundary known as a County Warning Area (CWA), which, as the name suggests, is a group of geographically-linked counties that surround the WFO.

A few months ago, I proposed an idea that the National Weather Service should completely eliminate the concept of counties from weather forecasting. The "county" as it relates to boundaries drawn on a map is an artificial construct that has no respect for how nature works. We use counties in weather forecasting to make it easier for us to communicate and understand where certain features (like the rain/snow line or threat for tornadoes) are located in relation to where we are at that moment.

Operationally, it's easy to understand why the National Weather Service needs to run its offices on the concept of the county warning area. It allows the agency and its forecasters to cover the weather for a finite area, and provides each part of the country with experts who are well-versed in that area's meteorological quirks.

However, as I outlined in October, these county warning areas can wind up doing more harm than good when you look at the weather in the big picture. The discrepancies are hard to notice when you're looking at the point forecast for your neighborhood, but they're readily apparent when you click to the forecast three miles down the road and snowfall totals jump up by six inches. Unless you live along the Great Lakes, snowfall gradients usually aren't that extreme. The stark difference is even uglier when you use the agency's Enhanced Data Display, a stellar feature that combines forecasts from all 122 offices into one powerful, interactive map.

Many people are surprised when they find out that meteorologists are not just copying their answers from the weather models. Weather forecasting is an art that requires skill, knowledge, and experience complimented by guidance from weather models. Few forecasts are exactly the same—look at forecasts issued by each of your local news stations to see that. Each forecaster has his or her own bias towards certain data. These sometimes-subtle differences usually go unnoticed, but when such a large area is impacted by a robust storm like today's nor'easter, the differences come into light and can wind up harming the public's trust in such forecasts.

Look at central New York, for example.

Snowfall forecasts abruptly jump up from eight inches to more than fourteen inches once you cross the line that surrounds Adirondack Park. Snowfall totals aren't really going to double as you cross that line—the terrain at that point doesn't affect snowfall totals much if at all. The difference lies in forecasters at the NWS office in Albany disagreeing with those over in Buffalo. Buffalo expects less snow in that area than Albany does, so the forecast map reflects it.

This map is a monument to a quiet, professional nerd fight between forecasters. Weather geeks understand why it looks like that, but to the public, it sends a message of discontinuity and breeds distrust. As the agency and weather enthusiasts around the internet give more play to the Enhanced Data Display, more and more people are seeing these rough, discordant maps. Even though the agency is doing an excellent job forecasting the event on the whole, let's face it—at least one of these offices is going to be wrong. Neighboring forecast offices disagreeing with each other on forecasts at their borders looks awful at best, dangerous at worst.

Running a simple smoothing algorithm over the snowfall data is an easy fix for the public perception problem, but it doesn't address the underlying causes behind forecasts dramatically changing once one steps across an artificial county line. Today's nor'easter is yet another weather event that shows it's time to banish counties from meteorology. We have the technology. It's just a matter of getting it done.

[Images: NWS, author]

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