Late afternoon temperature surge today, 90s tomorrow, thunderstorms Thursday

Good afternoon! As I write this article, most of the region is under mostly cloudy skies with humid conditions, as dewpoints have surged to around 70 degrees. Temperatures are primarily in the upper 70s to around 80. However, over the next few hours, temperatures should rapidly surge into the mid and upper 80s. An isolated hot spot could even hit 90.

Currently, there are showers moving through Connecticut, associated with a warm front that surged to our north. This warm frontal passage is what has brought us warmer temperatures with increasing humidity. As that system moves off the coast, skies will begin to clear from southwest to northeast. Considering how warm our 850mb temperatures are, the sunshine will allow for mixing through the surface, which leads to compression and warmth.

850mb temperatures are expected to spike to between 16-18 Celsius later this afternoon. This could yield surface temperatures in the upper 80s.

Above is a map of the projected 850mb temperatures, valid for 4 p.m. this afternoon. The warm front helped to spike them up to between 16-18 Celsius. On a sunny day, it is typical to add between 13 and 15 Celsius during the summer months to the 850mb temperature, to predict the high temperature at the surface. For example, if the current 850mb temperature is 17 Celsius, and enough sunshine has occurred, or is expected to occur, then adding 15 Celsius to that yields 32 Celsius — translating to 89.6 degrees Fahrenheit at the surface. The basic explanation for doing this is that if you have enough sunshine, an air parcel at 850mb can be mixed with the surface, and compress and warm dry adiabatically — through “sinking” to the surface. Without sunshine and mixing, these parcels cannot “sink” to the surface, and thus will not warm via compression. But with sunshine later this afternoon, many areas can expect mid to upper 80s, with perhaps an isolated spot hitting 90 degrees!

As far as tomorrow is concerned, it’s going to get down-right hot. The humid conditions tonight will prevent temperatures from dropping much, so we’ll already be in the low 70s tomorrow morning. Additionally, 850mb temperatures are projected to spike to around 20 Celsius. Tomorrow will also feature plenty of sunshine, with continually high humidity.

Projected 850mb temperatures for 3 p.m. tomorrow afternoon from the NAM. This could easily result in 90s at the surface for high temperatures.

Taking an 850mb temperature of 20 Celsius, adding 15 Celsius to that (35 Celsius), and converting to Fahrenheit yields a surface temperature of 95 degrees! It is certainly possible that urban areas, such as Newark, will hit this mark tomorrow afternoon, especially if we can get enough sunshine. The rest of the area can expect temperatures around 90 or in the lower 90s, except for most of Suffolk County and immediate shores, where upper 80s can be expected.

It may not be prudent to add a full 15 Celsius everywhere for tomorrow, considering the wind direction at 850mb is a bit south of west — which is a moist win. When there is more moisture, air parcels do not compress dry adiabatically as efficiently, since more moist air will have a tendency to rise. This is what is preventing us from forecasting widespread mid 90s everywhere. That being said, many 90 degree or higher readings can be expected tomorrow. It will really feel like summer!

For Thursday, the cold front to the west will sweep through, leading to a chance of thunderstorms in the afternoon. Early sunshine will still yield warm and muggy temperatures, and the degree of sun will determine whether we hit 90. Some storms in the afternoon could provide a decent punch — with gusty winds and heavy rain. We will be sure to keep you posted on the thunderstorm potential.

After the cold front sweeps through, we return to autumn-like weather for Friday and Saturday — we might not get out of the 60s on Saturday!

But for now, summer has returned.