Busy, busy day in the Gothamist weather center. First, yesterday's temperatures were exactly normal. Our high of 38 and low of 26 were precisely equal to the average high and low for January 11th. Thus Central Park's streak of above normal temperatures ends at 32 days. However, our streak of no below normal temperatures continues into its 34th day today. That streak is likely to end next week as major changes are taking place in the atmosphere.
Yes, it is becoming clearer and clearer that winter weather is soon to arrive. Let's get geeky and look at the maps. Shown in green lines on the map at left above is the atmosphere's normal circulation pattern for today. Note how it dips down over the eastern U.S. and ridges up over the west coast. The yellow lines, with the reddish and bluish fringes, show the observed circulation pattern. Dipping out west and ridging in the east, the actual pattern is the opposite of what normally happens. This is why our winter has been so mild.
Now take a look at the forecast map on the right. The green lines haven't changed much, but the yellow lines now take a big plunge over the eastern part of the country. That's the forecast for twelve days from now. With that eastern plunge, cold arctic air will be free to flow southward over us. The scattered red and blue lines indicate the uncertainty in the ensemble forecast –the more scattered, the more uncertain. You can better see the changeover in the animated version.
There are still a few warm days before the cold arrives. Or not. Weather.com says highs will be around 50 through Monday. The Weather Service has us cooling into the 40s by Sunday. However many warm days we have left, today will be the most enjoyable of them. All three days of the holiday weekend will be rainy. The cold weather will arrive once the rain moves out late Monday.
Ensemble forecast "spaghetti plots" from the NOAA Earth System Research Laboratory.