Earlier this year, the Storm Prediction Center announced that they're adding two new categories to their severe weather maps in an attempt to better convey the threat for severe weather to the public. They recently announced a date for the transition, sounding the death knell for ridiculous maps like we have today.
For years, the SPC has issued severe weather forecasts (called "convective outlooks," or just "outlooks" for short) using four basic categories:
- General thunderstorms (green)
- Slight (yellow)
- Moderate (red)
- High (magenta)
The green category — general thunderstorms — indicates the chance for run-of-the-mill storms that probably won't turn severe. Slight risk indicates a low risk for severe weather, with moderate and high significantly ramping-up the threat.
The problem is that these categories are terrible, and at 11:00AM EDT on October 22, they'll get a little less terrible.
Just a little, though.
The green shading that indicates "general thunderstorms" is misleading, which is why the SPC has to print a "see text" stamp over certain areas. The "see text" tells users that the threat for severe weather in this area isn't zero, but it's not high enough to warrant the issuance of a slight risk; users should see the scientific text written by the forecaster that explains the threats present in the "see text" areas.
Today's "see text" zones are mostly for the low chance of large hail or damaging winds. The probabilities (which I explained here a few months back) are sitting at 5% this afternoon — high enough to worth mentioning but lower than the 15% threshold for issuing a slight risk for severe weather.
Here's one of those blocks of text the SPC is telling the general public to refer to on its maps, this one valid for areas around and south of Chicago:
A NNE-SSW-ORIENTED BAND OF TSTMS MOVING THROUGH THE CHICAGOLAND AREA AS OF 16Z HAS EXHIBITED SOME FORWARD-PROPAGATING CHARACTERISTICS WITH ISOLATED WIND DAMAGE REPORTED ALONG ITS TRACK. BY AFTERNOON...A SUBSET OF THESE STORMS WILL LIKELY MERGE WITH A DOWNSHEAR CLUSTER OF SLOWER-MOVING TSTMS ONGOING OVER IND.
DAYTIME HEATING COUPLED WITH THE PRESENCE OF A VERY MOIST BOUNDARY LAYER WILL ONCE AGAIN YIELD A STRONGLY UNSTABLE AIR MASS AHEAD OF THESE STORM CLUSTERS WITH MLCAPE APPROACHING 3500-4500 J/KG. AND SIMILAR TO MONDAY...EXPECT STORM MOTIONS TO BECOME MORE SLY WITH TIME AS ACTIVITY IS DRAWN INTO THE BACKSIDE OF A MID-LEVEL ANTICYCLONE CENTERED OVER THE OZARKS. VERTICAL SHEAR WILL ONCE AGAIN REMAIN WEAK...BUT THE PRESENCE OF THE STRONG INSTABILITY AND HIGH MOISTURE CONTENT WILL FOSTER INTENSE WATER-LOADED DOWNDRAFTS CAPABLE OF DAMAGING SURFACE WINDS.
Unless you're a hardcore weather geek or degreed meteorologist, odds are you don't understand most of what they're talking about, and that's a big problem in a world where good communication skills are almost as important as good forecasting skills.
Starting on October 22, forecasts like this will go from making users "see text" to telling users there is a "marginal risk for severe weather."
Instead of looking like this:
Today's forecast would look like this instead:
It'll look better than a terrible map hastily made by a blogger, but you get the gist. The change will better convey the threat for severe weather on any given day, and even though there is a debate over the subjectivity of the terms "marginal," "slight," "enhanced," "moderate," and "high," almost everyone agrees that those terms are better than "see text."
[Professional maps by the SPC, crappy maps by the author]