Spring in Rochester has a tendency to be, let’s say, fickle. This year has certainly been no exception to that rule. If you live up near Lake Ontario, you know how that works. Note the lake water temperatures from late Wednesday afternoon:
We are almost half way through the month of May and still seeing temperatures overnight flirting with the freezing mark. Parts of the Southern Tier are still seeing lows into the 20s! And, for the second Mother’s Day in a row, parts of Western New York saw wet snowflakes fall. Parts of Pennsylvania saw enough snow to actually cover the ground and even accumulate on cars in a few spots!
As of this writing, the month of May in Rochester is averaging 5.8 degrees below normal per day. That’s a significant departure for the cooler, but pales in comparison to the cool start we had May of last year! Through today’s date, the month was averaging nearly 12 degrees below normal per day!
However, if you consider temperatures for the entire meteorological spring, as defined by the three months of March, April, and May, the picture is a little different. March was warmer than normal by more than four degrees, while April was just a fraction of a degree warmer. When you combine those departures with the departure for May so far, spring as a whole basically ends up just slightly cooler than normal to date.
So what’s behind the change?
Note the Climate Prediction Center’s depiction of a region of well above normal projected warmth centered over Minnesota and South Dakota. That’s part of an expanding ridge of High pressure in the upper levels of the atmosphere.
You can also see that in the 500 millibar chart above. The contour lines here represent the height of the 500 millibar level in the atmosphere. The higher the values of height, the warmer the air. You’ll note the height of the 500 millibar level is approximately 579 decameters over the same region that’s been highlighted by the Climate Prediction Center to see the strongest likelihood of above normal temperatures. The expansion of the upper level ridge from west to east allows warmer air to also work its way east. This should mean the return of 70 degree air by early next week and the potential for temperatures to soar well into the 70s mid-week .
How long can we plan on this pattern staying? Well, at this point I would say that the warmth should be with us at least until the latter part of next week. As I had indicated earlier, sometimes this season is a fickle one. One of the proverbial flies in the ointment that make it a bit fickle is the backdoor cold front. The term implies that the cold air comes in through the “backdoor,” moving in from northeast to southwest vs. the usual movement of northwest to southeast.
The above depiction shows a pool of very chilly polar air spreading east from Hudson Bay into Atlantic Canada. Note how the isotherms (lines of equal temperature) just to the north of Rochester appear to sag south. This indicates to this meteorologist the potential of a cool down, especially closer to Lake Ontario by the time we get to the end of next week.
So, enjoy the warmth while its here. Spring really is busting out all over!
~Meteorologist Josh Nichols