The stratospheric temperature pattern as of Thursday, March 20th, featured a relatively “warm” blob of air directly over the North Pole (center) and a weakened and “split” polar vortex (shown in blue). Temperatures at the 10-millibar level over the North Pole are now about 40 degrees warmer than those observed in the surrounding stratospheric polar vortex regions. Map courtesy NOAA
Overview
An on-going stratospheric warming event that began in late February increases the chance for additional cold air outbreaks across much of the nation as we wind down the month of March. In fact, the typical lag time between a stratospheric warming event over the polar region and its impact on US temperature patterns suggests there may very well be cold air outbreaks to deal with at least until the middle of April. As it turns out, big-league baseball gets underway in earnest on Thursday, March 27th, and the early part of the season may feature plenty of cold weather games thanks in large part to the on-going big-league stratospheric warming event and low “Home Run Forecast Index” values.
There have been six stratospheric warming events in recent history that took place during the month of March and the average 10-millibar temperature pattern in those years (left plot) is very similar to the current situation. The impact on US temperatures in each of those six years during the subsequent month of April was quite dramatic. In fact, the average temperature in those six years for the month April was below-normal across virtually the entire nation (right plot). Maps courtesy Weather Bell Analytics (Meteorologist Joe Bastardi, X), NOAA
Details
While there were a couple of regular season games played already in Tokyo, Japan (roofed stadium) between the Cubs and Dodgers, the main start to the 2025 big-league season comes on Thursday, March 27th with 14 games on the schedule. At least half of the games are to be played in southern states from Florida-to-Arizona where the weather is likely to be quite favorable for baseball or are scheduled for the “relatively-safe” southern California cities of Los Angeles and San Diego. There are a handful of games, however, that are scheduled for next Thursday in the Midwest (Chicago, Cincinnati) and Mid-Atlantic/Northeast US (New York City, Washington, D.C.) where cold weather is always a possibility this time of year and appears to be quite likely in a week’s time. In fact, the first few weeks of the 2025 baseball season are likely to feature plenty of cold weather games thanks in large part to an on-going stratospheric warming event the likes of which have often been followed by several weeks of cold air outbreaks into the US.
These chilly games would also likely feature low Home Run Forecast Index values indicative of weather conditions that would not be favorable for the hitting of home runs. The Home Run Forecast Index is displayed on a scale of 1-10 where 10 represents the most favorable weather conditions for a baseball to travel (i.e., for hitting home runs) and a 1 the least favorable. The index is updated on an hourly basis and is calculated using stadium-specific weather conditions.
Stratospheric warming is a naturally occurring phenomenon that can take place in any given winter in the northern hemisphere and perhaps even on more than one occasion. Typically, temperatures are very cold in the stratosphere over the polar region during the northern hemisphere winter, but periodically, significant warming takes place which can disrupt the polar vortex. In some cases, the polar vortex is displaced from its usual location near or over the pole, but it remains fully intact. In other cases, however, the polar vortex can break apart into multiple pieces and is considerably weakened…indeed, this is the pattern we are experiencing right now in the northern hemisphere polar region.
When the polar vortex is disrupted during the northern hemispheric winter, it can set off a chain of events in the atmosphere that ultimately results in cold air masses being unleashed from the high latitudes onto the middle latitudes such as here in the US. History has shown that there tends to be a lag of several weeks from the beginning of the stratospheric warming event over the polar region to its eventual impact on US temperatures. In this particular case, the stratospheric warming event began during late February which increases the chance for colder-than-normal weather across much of the nation from late March to at least the middle of April…and this will make for many chilly baseball games during the early part of the 2025 baseball season.
The early part of the 1982 baseball season was marred by plenty of cold and snow and the stretch of winter-like weather that April followed a stratospheric warming event in March that was pretty similar to the one we are currently experiencing over the polar region. The home openers for the Mets and Yankees were postponed several days due to a snowstorm on the 6th that generated a foot of snow in the New York City metro region. Newspaper article courtesy New York Times (top) and snow scene at Yankee Stadium (bottom) courtesy WABC (NYC, Channel 7).
In recent history, there have been six stratospheric warming events that took place during the month of March and each one of these years (1975, 1982, 1984, 1993, 2007, 2018) featured a colder-than-normal month of April across a huge part of the nation…the kind of scenario that is on the table for this April. One of these stratospheric warming events marred the early part of the b-league baseball season in April 1982. In fact, a snowstorm in April of caused postponements of both the Mets and Yankees home openers when a foot of snow fell on New York City. Other home openers that year had to be postponed as well including those in Chicago and Milwaukee.
Meteorologist Paul Dorian