The Fall Line: The Difference Between All rain and mostly snow for the I-95 Big Cities

Above is a picture of the major cities of the East Coast. The very fine white area is called the “Fall Line”.   Can weather really straddle a line? Does one or two degrees west or east of the line make a difference? The two answers are: Yes, Yes. If you look to the west of the “Fall Line” you will see that the land rises-elevation. Temperatures are impacted by that small difference. In Philadelphia, it could be 34 degrees as a storm approaches. Fifteen miles west of Philadelphia in Montgomery County it could be 32 degrees and falling as a storm approaches.  You could have snow in Lower Merion, and rain in Center City-cold rain at that. In that case, if it’s 34 degrees in Philadelphia you can rest assured it’s 35 in Wilmington, DE almost a certain rain event as you can see Wilmington, DE almost is sinking in the sediment of the Delaware River.  Yet, at the same time, it could be 35 in Wilmington, DE and further north and west of Wilmington, DE in Chadds Ford just a mere 6-8 miles from Wilmington to its south could be startling the freezing line and could either bet wet snow or even just snow.

So, the weather follows I-95 because of I-95 changes in elevation. It’s the strangest, but the most fascinating piece of geography that no other part of the country has.


Snowstorm along the I-95. Arctic cold air is the solution if you want big snows in the megalopolis cities of Washington, D.C. to New York City.




I know. We have just experienced two Nor’easters in two weeks and you are probably crying UNCLE at this point. Yet, it’s getting increasingly likely we might have to go through this one more time this coming weekend Sunday into Monday. And this one, if all the elements come together right this one could end the winter season with quite the bang.

And I don’t want to hype anything, but as you can see in the graphic above this one takes a scary track. A shortwave drops from the Pacific NW into the plains.  It dives down to the Gulf, picks up moisture and then heads right for the coast. And there is still a block to the north although it isn’t super strong is strong enough to pool some cold air into the East Coast region. There is a noticeable ridge in the Pacific. In the graphic, you can clearly see the bulge.  This helps the trough dig into the Gulf states where it picks up moisture. Now, the day to day runs of the EURO has been showing it sliding it off the East Coast to the south with no harm, no foul. Yet, the ensembles of both the GFS and EURO have been showing a big storm around the March 12th-13th time period. The GFS has been showing something more consistent day to day and on their ensembles as well. Again, a suspicion that if the EURO picks up on the radar in the coming days we could be dealing with our THIRD Nor’easter in as many weeks and the potential for an end of winter event that would certainly cap a wild, willy, and wacky Winter 2017-2018.

To be continued!


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500 Millibar chart showing a shortwave diving into the Gulf states then shooting right off the coast. This would create big snows just about for everyone, or it could be a non-event that ends the Winter 2017-18 Season. Yikes!