The likelihood of El Nino is increasing, with onset of the climate phenomenon known for snowy winters in these parts expected by fall. 

There is "increased confidence" in a weak to moderate El Nino, according to the Climate Prediction Center. Forecasters included the information in an update to the hurricane season outlook issued last week, saying it could impact those storms by late in the season.

They expect onset of El Nino by the end of September, though there could be a weeks-long delay in its effects reaching the Atlantic. But it could strengthen in time for winter.

It isn't just the presence of El Nino that might have you stockpiling the shovels and salt. The strength of an El Nino has the heaviest bearing on Baltimore winter weather. A weak to moderate El Nino, in particular.

The presence of an El Nino is associated with heavier than normal snowfall, in general, according to this handy guide in which the National Weather Service's Sterling, Va., office looks back at 18 El Nino winters since 1950. Of course, not every El Nino year sees heavy snowfall -- it's just an average. Snowfall was about 11 inches in Baltimore in winter 2006-2007 despite a weak El Nino, most recently, for example.

Average snowfall in Baltimore from 1971 to 2000, according to the guide's charts, was about 18 inches. (Overall, Baltimore's average is 20.8 inches.) El Nino winters, meanwhile, averaged closer to 27 inches of snow.

In a weak El Nino, temperatures have been coldest, at 33.4 degrees, 1.5 degrees below normal, while snowfall was an average 24 inches.

In a moderate El Nino, snowfall has been even higher, at about 31 inches, and temperatures also cold, slightly below normal at 34.2 degrees.

Strong El Nino years are typically warmer than normal but still with plenty of snow, about 27 inches on average.

El Nino is difficult to predict, so it's hard to say what sort of intensity could arrive by winter. The phenomenon is based on surface water temperature anomalies in the Pacific Ocean along the equator.

But El Nino winters have produced some of the most memorable snowstorms in the region -- "Snowmageddon" of February 2010 at the top of the list. El Nino was considered at moderate strength during that storm.

About half of the biggest snowstorms on record for Baltimore occurred in El Nino years, according to this chart, which isn't up to date enough to include the 2010 storm that dropped nearly 25 inches of snow at BWI Marshall Airport.

Have a weather question? E-mail me at sdance@baltsun.com or tweet to @MdWeather.