Ask Tom Why / Weather / Weather Blog

How low does the pressure have to drop for a storm to officially be a bomb cyclone?

Posted On: Oct 18, 2019   |   Posted By: WGN TV

Dear Tom,
How low does the pressure have to drop for a storm to officially be a bomb cyclone?
Liz Houser Oak Park
Dear Liz,
It's not how low the barometric pressure falls, but how rapidly. Bombogenesis is a term applied to a rapidly intensifying low-pressure system in which the central pressure drops at the rate of one millibar an hour for 24 hours. In terms of inches of mercury, that would equate to pressure falling at least .03 inches an hour for 24 hours. This type of rapid intensification often occurs with cold-season storm systems off the Atlantic Seaboard dubbed nor'easters, which produce many of the region's major snowstorms. While not as common, these storms do occur in the Midwest. On Dec. 14-15, 1987, low pressure moving northeast from the southern Plains “bombed out,” bringing 8-12 inches of heavy, wet thundersnow to the Chicago area.

Continue reading ...

 








In virus talks, Pelosi holds firm; Mnuchin wants a deal

In virus talks, Pelosi holds firm; Mnuchin wants a deal

Monday brought no new talks between Trump's team and negotiators on Capitol Hill as the president tries a go-it-alone strategy meant to circumvent the legislative standoff. Read more ...

White House on lockdown, Trump press conference interrupted after reports of...

White House on lockdown, Trump press conference interrupted after reports of shots fired

US President Donald Trump's press conference was interrupted after just a couple of minutes by the Secret Service, which ushered him out of the briefing room amid reports of... Read more ...

McDonald's is suing its ousted CEO for lying about sexual relationships with...

McDonald's is suing its ousted CEO for lying about sexual relationships with employees

The fast food chain is suing Steve Easterbrook for the amount of his exit package: about $40 million. Read more ...

Amazon may take over old JCPenneys and Sears to try and speed up deliveries

Amazon may take over old JCPenneys and Sears to try and speed up deliveries

Amazon may replace closed department stores at struggling malls. Read more ...

Derecho with 100 mph winds moving across the Midwest

Derecho with 100 mph winds moving across the Midwest

A derecho is a widespread, long-lived wind storm associated with a band of rapidly moving showers or thunderstorms. Read more ...

Disney World to reduce theme park hours in September

Disney World to reduce theme park hours in September

Operating hours at all Central Florida parks are changing. Read more ...

Kuzma's 3-pointer lifts Lakers to 124-121 win over Nuggets

Kuzma's 3-pointer lifts Lakers to 124-121 win over Nuggets

LAKE BUENA VISTA, Fla. - Kyle Kuzma hit a 3-pointer with .4 seconds left and the Los Angeles Lakers beat the Denver Nuggets 124-121 Monday night to snap a three-game losing streak. Read more ...

Trump says he will deliver nomination speech from either the White House or...

Trump says he will deliver nomination speech from either the White House or Gettysburg

President Donald Trump said Monday he's narrowed down the location where he will deliver his Republican National Convention speech to two locations: either the White House or... Read more ...

Red Sox blow early 3-run lead, come up short against Rays

Red Sox blow early 3-run lead, come up short against Rays

On a positive note, J.D. Martinez hit a solo shot for his first home run of the season, while Jonathan Araúz collected his first major league hit. Read more ...

Trout homers twice, helps Angels rally to 10-9 win over A's

Trout homers twice, helps Angels rally to 10-9 win over A's

ANAHEIM, Calif. - Mike Trout hit two home runs, including a tiebreaking shot in the eighth inning, and the Los Angeles Angels rallied from an early five-run deficit to snap... Read more ...