John Homenuk

Understanding the difference between potential and hype

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I think I personally hit a bit of a breaking point today. Around 6:00am this morning, we received an inquiry regarding the potential winter weather events next week.  This is nothing terribly unusual — our email inbox is normally filled with these and we do our best to try and answer them and keep people informed. The title of the email read “Information Regarding Blizzard Feb 8” and the contents essentially asked us for our snowfall forecast for the upcoming “Blizzard” which the mailer was under the assumption was going to arrive next week. In the email was a model image, produced by Weatherbell Analytics, which showed the snowfall totals from a ECMWF Ensemble Control run at 200+ hours. It was then that I realized we had a big problem on our hands.

This is nobody’s fault. Not the mailer, nor the company which produced the map. It isn’t our fault, your fault, or any meteorologists. In fact — nobody is to blame. But it is a problem, because the image went viral on social media and many in the general public took it as fact. And so, as meteorologists, it is our job to source back this issue and try to figure out how to avoid it happening again. Similar things have occurred during storms in the past, as recently as a month ago, and the end result is never pretty.

This snowfall total map, which went viral yesterday, is a snowfall forecast from an ensemble member of the ECMWF model.

This snowfall total map, which went viral yesterday, is a snowfall forecast from an ensemble member of the ECMWF model.

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John Homenuk

SPC set to add two new risk categories in 2014

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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.

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

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John Homenuk

Ice Jam along Delaware River raises major flood concerns

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Observations from this afternoon confirmed a major ice jam along the Delaware River near Trenton, and concern is rising for flooding potential along and near the river and its banks as the ice melts. Water levels have risen over 7 feet since last night. Latest reports suggest initial flooding occurred this afternoon near Market Street and Route 29. The National Weather Service has issued Flash Flood Warnings along the Delaware River from Trenton southward to Philadelphia for the potential of river flooding. The warnings continue through the morning hours on Thursday January 9th.

An ice jam occurs when pieces of floating ice, carried with the stream’s current, accumulate at an obstruction to the streams flow. The ice cams can develop near river bends, banks, mouths, or even points where the slope of the river decreases. The water held back can rise rapidly and cause significant flooding. Moreoever, if the obstruction breaks suddenly, flash flooding can rapidly occur downstream. This is the concern of forecasters this evening.

Ice jam on the Delaware River near Trenton as photographed on January 8, 2014.

Ice jam on the Delaware River near Trenton as photographed on January 8, 2014.

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John Homenuk

Heading into winter, 5 myths about forecast models

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As part of our winter forecasting feature this autumn, we’re releasing a few posts with information and tounge-in-cheek opinions about winter and meteorology. The first in the set comes this afternoon, where our forecasters sat down to compile a list of the 5 biggest forecast model myths as we head into winter. You can check them out below, to get a quick primer on what to expect over the next several months.

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