Tuesday 10 a.m.
From Chicago to Syracuse and from Cincinnati to Philadelphia, yesterday was among the very hottest Memorial Days ever. Records were set in Chicago Sunday and again yesterday with highs of 97 and 95. The 97-degree high on Sunday represented the earliest date it had ever been so hot, and came within 1 degree of tying the all-time record for May. In contrast, temperatures may drop to the middle 40s in Chicago tomorrow night. That's still about 10 degrees above record lows, but more than 50 degrees lower than it was during the holiday weekend days.
Temperatures also reached the 90s in Buffalo, Syracuse and New York City. Philadelphia has had its warmest spring ever (where spring means March through May), and it has now been warmer than average for 16 consecutive months, one short of the record (thanks PhillyWeather.net). Meanwhile, cooling breezes from the east held temperatures in the 60s most of yesterday in Portland and Boston. A cool front that was on a line from Lake Erie to Kentucky will take the edge off the heat as it advances. The westerly flow will also bring a reduction in humidity. One exception: the New England coastal area that remained cool will actually have high temperatures tomorrow and Thursday as west winds arrive.
The video shows how things should play out for the rest of the week. Once the heat is broken, it will not return til at least some time next week. Keep in mind that violent thunderstorms are possible ahead of today's cold front... and there may be more nasty storms with the system approaching as we go into the weekend. This map below the video outlines where the greatest chance of severe thunderstorms will be today.
One concern: the chance of cold frontal snow squalls that could move all the way to the East Coast tomorrow night. Sudden snow squalls have been implicated in chain reaction collisions that turn deadly and damaging.
These two maps show the change from the very, very cold flow likely this Saturday to the much milder Pacific-origin westerly flow later next week.
When we look more closely, we see a variety of disturbances embedded in the main current, each capable of temporarily increasing or cutting off the chance of snow. This map shows the setup:
This map shows the circulation around the offshore storm and a larger but less intense storm moving into the Great Lakes. With this sprawling storm likely to be in the region for several days, the weather can vary widely.
...speculation about a snowstorm Monday or Tuesday, and one is still possible. However, timing and placement remain elusive. This map shows the GFS ensemble mean "solution" for Tuesday morning showing snow just off the New England coast. Watch this story evolve on accuweather.com all weekend.