vis

Potential week-long heatwave begins today

In what has generally been a summer lacking heatwaves, this week looks likely to be an exception. While not everyone in our area will reach or exceed 90 degrees every day, many locations in New Jersey probably will — possibly for five days straight.

Every summer, a feature affectionally known as the “death ridge” sets up in the Southern Plains. It’s a persistent area of strong heat ridging where a trough crashes into the western half of the US, and a consistent source of heat is pumped out ahead of it. Depending on other aspects of the weather pattern, this ridge can expand and/or head northeastward. If upper level winds are slow, and there is another trough to its east to “sandwich” it, then it can stall over an area for a prolonged period of time.

While record heat is unlikely, a stretch of 90+ degree weather is likely over the next seven days.

In fact, Central Park has already reached 92 degrees as of 1:00pm EDT. This is only the 5th time Central Park has reached 90 degrees this summer, well below its average of 15. However, Newark has already reached 91 degrees today, which is its 14th 90-degree day.

Today's NAM Model valid for 5:00pm shows the heat ridge in the Southern Plains expanding northeastward, in between a large trough in Montana and north of NewFoundland.

Today’s NAM Model valid for 5:00pm shows the heat ridge in the Southern Plains expanding northeastward, in between a large trough in Montana and north of NewFoundland.

The current weather pattern, as shown above, fits the illustration for a sustained heat ridge very well. A large ridge in the Southern Plains  is sandwiched between a trough in Montana and a trough near Newfoundland, while the ridge itself expands. The mid and upper level winds are also pretty slow, which means that this pattern will generally be stagnant.

While the overall weather pattern looks pretty similar over the next week, there are some individual nuances to each day. For the most part, the strong ridging will provide enough of a capping inversion in the atmosphere to limit any showers and thunderstorms from developing. However, Thursday could see a weak shortwave disturbance riding over the top of the ridge, which may be enough to trigger some isolated showers and thunderstorms during the afternoon.

Today and tomorrow will be similar in that both days will initially have westerly winds, which is a warm wind for all locations, including the coast. These winds will be pretty light, though, which will not be able to stop a seabreeze from developing in the afternoon. By the time the seabreeze develops, most areas will have still reached the low to mid 90s in the early-afternoon.

Today's NAM Model valid for Wednesday afternoon shows low to mid 90s in most areas away from the immediate coast, but a wind shift to the south keeping the immediate coastal areas a bit cooler.

Today’s NAM Model valid for Wednesday afternoon shows low to mid 90s in most areas away from the immediate coast, but a wind shift to the south keeping the immediate coastal areas a bit cooler.

The above model image for tomorrow afternoon illustrates it well. Areas away from the immediate coast will easily be in the mid 90s, and a few areas in urban NE NJ could warm into the upper 90s. But a wind shift to the south will make the immediate coastal regions settle back into the upper 80s after initially touching 90 or the low 90s before the seabreeze hit. In fact, much of Long Island may not reach 90 degrees at all until Friday.

Since the heat ridge is partially sourced from the Gulf of Mexico, the humidity will also be high, though not necessarily soupy. Dewpoints in the upper 60s to around 70 will make heat indexes range anywhere from 95 to 100 degrees, which while very hot, isn’t nearly as hot as it could be given the actual air temperatures. In the locally hottest areas, the dewpoints may fall just a tad as temperatures rise, which mean that heat indexes will generally be uniform everywhere despite some differences in the actual air temperature.

The humid conditions will also mean warm nights. In the NYC area, low temperatures may hold in the mid to upper 70s; though most areas will be in the low to mid 70s.

Out ahead of the shortwave trough on Thursday, southerly winds will accelerate with the seabreeze, causing southerly winds to dominate earlier in the day. Additionally, a few more clouds and some showers and thunderstorms will be around in the afternoon and evening. This may mean that most areas east of I-95, rather than just the immediate coast, will hold in the 80s, while most of New Jersey will still be in the 90s, but a few degrees cooler than on Wednesday.

Today's NAM Model valid for Friday afternoon shows temperatures hitting the low 90s along the coast.

Today’s NAM Model valid for Friday afternoon shows temperatures hitting the low 90s along the coast.

Moving forward to Friday and the weekend, the heat will be generated a bit differently. The shortwave trough will have generated a weakening cold front which will have crossed the region. As the trough near Newfoundland slowly moved eastward, it will have pumped up the Bermuda High. So while the airmass will be a tad cooler behind the cold front, there will be a deeper westerly flow aloft, but also warmth pumping in from the Bermuda High and the leftovers from the original “death ridge.” Deeper westerly flow tends to promote more warmth along the coast as it halters the seabreezes and leads to downsloping. Fortunately, it will not be as humid as earlier in the week, but another three or four 90-degree days in a row is possible from Friday through Monday, though there is a chance that not all four of those days hits 90 degrees. As the Bermuda High gets more established, humidity will gradually be increasing again on Sunday through Tuesday.

Comments

comments