A strong frontal system that’s currently pushing its way into the Central Plains will be arriving in our area Friday, bringing showers, potential thunderstorms, and much warmer temps. Currently, the storm system is impacting a wide swath of terrain. Blizzard warnings up for most of the state of Iowa, and heavy snow is expected across Wisconsin and Minnesota.

Though this storm will weaken somewhat before it hits our area, it should nonetheless bring widespread rain showers with the possibility for a strong thunderstorm and wind gusts up to 50mph. Temps tomorrow will range in the mid 50s with a warm front passing over tonight and southwest winds pumping in warmer air ahead of the cold front tomorrow. Timing of the cold front passage looks to be in the late morning/early afternoon. Rain showers/thundershowers could band together and form a continuous line with some embedded stronger thunderstorms. Chances of  strong thunderstorms are slim, though. As you can see below, the Storm Prediction Center in Norman, OK, placed the far reaches of southern New Jersey in its outlook for severe weather.

Once the cold front passes, temps will regress back to average over the weekend, with temps on Saturday expected to top out around 50 under mostly sunny skies, and highs on Sunday in the mid 40s. Our reprieve from the cold will be short, however, as a reinforcing cold front will pass on Sunday, opening the door to a longer term trend of colder and below average temperatures.

You might be wondering why this has been such a cold winter for the Northeast. Well, something called the Arctic Oscillation (AO) is a contributing factor. The AO is a measure of the strength of the arctic jet stream. When the AO is positive, it means the arctic jet is strengthening. When negative, the AO signals a weakening in the arctic jet. Negative readings on the AO index generally correspond with colder surface temperatures. Why? When the arctic jet is speeding up and growing stronger, it keeps the coldest air trapped around the polar regions. When the arctic jet slows down, it allows this colder air mass to move southward, shifting the jet along with it. In extreme cases, it can even allow polar vortexes to take unusual orientations.

If you take a look at the AO Index bar graph below, you can note that the AO index was indeed negative during the latest outbreaks of bitter cold temperatures in our region.

I bring this up because the forecast for the next 7 days indicates a return to a negative AO regime, which should lead to colder temperatures through the week. This won’t be as bad as other cold spells, since the angle of the sun is about what it would be for early October, and the days are getting longer, allowing for more daytime heating. Currently forecast highs in the Monday-Wednesday timeframe are all just under freezing for NYC.

There are some slight chances for precipitation Tuesday, but the next significant storm system looks like it will impact the area around Wednesday. Given the temperature trend, this storm should fall as mostly snow, so we’ll see how subsequent forecasts turn out on storm track and available precipitable water.