Storm Prediction Center Archives - New York Metro Weather

Storm Prediction Center releases details on outlook changes

April 22, 2014/0 Comments/by John Homenuk

The Storm Prediction Center has used the same risk categories for a large part of most of our meteorological careers. Although they have adjusted the probabilities, percentages, and yes even the colors — the categorical risk areas have remained the same. In Spring 2014, that will change. The Storm Prediction Center currently uses a simple categorical risk system which highlights the potential for severe thunderstorms across the country. The risk areas of Slight, Moderate and High are triggered by percentage chance of a type of severe weather within 25 miles of any point. And while the newer outlooks also highlight the potential for general non-severe thunderstorms across the country, Spring 2014 will mark a dramatic change in the outlooks.

The main change will be the addition of two risk levels, both falling on opposite sides of the “Slight” risk of severe thunderstorms. “Marginal”, a new risk category, will highlight the potential for severe thunderstorms that includes a 5-10″ chance of wind and hail and a 2-5% chance of tornadoes — but does not trigger a slight risk. “Enhanced” falls on the other side of “Slight”; in other words the risk levels are enhanced (30-45% risk) but not organized or widespread enough to trigger a Moderate Risk. Below, the Storm Prediction Center has released an example of the changes in the outlooks using an example in the Northeast US from 2011. You can visualize the new outlook area with an “ENH” or Enhanced risk running throughout the majority of our forecast area. Previously, the outlooks would only show this area as “Slight”despite there being an enhanced percentage of severe weather within that slight risk.

An example of proposed changes to the Storm Prediction Center’s categorical outlook and graphics.

Spring Wx Awareness: Severe storms, and SPC

April 7, 2014/0 Comments/by John Homenuk

Each year, as the atmospheric pattern begins to undergo a transition and wavelengths begin to change, the threat for strong to severe thunderstorms becomes a focus of the meteorological community in New Jersey, New York and Connecticut. Spring, in fact, marks the beginning of “Severe Weather” season in our area — which generally has been known to begin on May 1st. There are obviously severe thunderstorm events outside of that date, but in general the most consistent potential for organized severe storms begins in May and ends in August or September.

Interestingly enough, severe thunderstorms feature some terminology and atmospheric interactions which can be very confusing not only to interpret as meteorologists, but to understand on the public level. Knowing the basics of how organized thunderstorm events develop, and how forecasters attempt to predict and quantify their potential, will help to make things a little less confusing when severe weather season comes around this year.

Thunderstorms can dump tremendous amounts of rain over small areas in a brief period of time.

SPC set to add two new risk categories in 2014

January 14, 2014/0 Comments/by John Homenuk

The Storm Prediction Center has used the same risk categories for a large part of most of our meteorological careers. Although they have adjusted the probabilities, percentages, and yes even the colors — the categorical risk areas have remained the same. In Spring 2014, that will change. The Storm Prediction Center currently uses a simple categorical risk system which highlights the potential for severe thunderstorms across the country. The risk areas of Slight, Moderate and High are triggered by percentage chance of a type of severe weather within 25 miles of any point. And while the newer outlooks also highlight the potential for general non-severe thunderstorms across the country, Spring 2014 will mark a dramatic change in the outlooks.

The main change will be the addition of two risk levels, both falling on opposite sides of the “Slight” risk of severe thunderstorms. “Marginal”, a new risk category, will highlight the potential for severe thunderstorms that includes a 5-10″ chance of wind and hail and a 2-5% chance of tornadoes — but does not trigger a slight risk. “Enhanced” falls on the other side of “Slight”; in other words the risk levels are enhanced (30-45% risk) but not organized or widespread enough to trigger a Moderate Risk. Below, the Storm Prediction Center has released a new probability to categorical description table to help understand the changes.

The new SPC risk categories expected to be implemented in 2014.

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