Big heat on hold for the foreseeable future

We finally saw a nice break today from the high humidity values, as dewpoints dropped into the low 60s this afternoon, making it feel quite comfortable outside this afternoon. With the lower humidity, this means that temperatures have more room to drop tonight — mid 50s in colder, inland areas to mid 60s in more coastal sections. This is quite the stark contrast from the constant stream of 70s for lows that we have had all month.

European Ensemble Mean Valid for tomorrow evening shows a frontal boundary being stalled as it runs into the stubborn Western Atlantic Ridge. Image courtesy of the WSI Model Lab.

European Ensemble Mean Valid for tomorrow evening shows a frontal boundary being stalled as it runs into the stubborn Western Atlantic Ridge. Image courtesy of the WSI Model Lab.

As far as what is going on with the synoptic weather pattern, the heat wave has broken as that huge ridge has finally dissipated and split into two ridges — one in the southwest, and one in the NW Atlantic. The NW Atlantic ridge is the same one that has been plaguing us all summer with humidity, showers, thunderstorms — and at times, heat. Although it has fluctuated in position at times, it has generally remained in the western Atlantic.

This 500mb image valid for tomorrow evening gives a good general summary as to what is going on now and what we can expect over the next few days. There is a trough in the northeast, as a cold front made its way through the area yesterday, giving us drier conditions. However, there are still clouds around as the front has stalled just to our east. Because of the tremendously strong western Atlantic ridge of 600 decameters  (!), the front was forced to stall, as it ran into a “wall”, instead of clearing the coast. This leads to a tight 500mb height gradient along the eastern seaboard (which in this case is pretty much a frontal boundary). This leads to the potential for waves of low pressure to develop along this front.

Since the front is just to our east, the biggest rainfall threat would be east of NYC, with NYC itself being on the gradient. For now, we will mention the relatively high chance of showers, with periods of moderate rain at times — especially in eastern sections of the region (such as Long Island) — in an otherwise relatively mostly cloudy regime for tomorrow. With surface winds more northerly, instability should be too low for much in the way of thunderstorm activity, as temperatures may not get out of the 70s tomorrow.  A stark change from last week, considering our lows were often in the mid to upper 70s!

For Friday, the exact track of this same storm system will determine the rain chances for our area — but most guidance turns the low a bit too far north and east for the rain to linger much longer. Perhaps partly sunny to mostly cloudy skies in western sections and mostly cloudy skies to overcast skies in eastern sections with the chance of a few scattered light showers. Skies should slowly clear as the day progresses

pattern overview

The European Ensemble Mean valid for Sunday shows a strong mid-level disturbance with a tight height gradient along the east coast. This leads to more showers and thunderstorms, before a cold front clears the area sometime next Monday. Image courtesy of the WSI Model Lab.

For the weekend, another cold front should slowly work its way eastward. Given the past storm system departing, Saturday should start of sunny, before increasing clouds with the slight chance of showers and thunderstorms later in the day with increased instability. Humidity will be on the increase again as winds turn more southerly — though it won’t be as oppressive as it was recently. Overall, though, Saturday should be a decent day and perhaps a good beach day as well.

Once again, the image on the right shows a strong western Atlantic ridge on Sunday, which will slow down the front’s progress as it slides eastward. See a general theme yet? Sunday and Sunday night will have a higher chance of showers and thunderstorms than on Saturday given the cold front’s closer proximity. The front may still linger a bit on Monday with slightly improved weather conditions before finally clearing the area sometime on Monday afternoon, evening, or night. This will allow more tranquil conditions to build in for next Tuesday — similar to what we had this afternoon.

pattern overview 2

The European Ensemble Mean valid for the middle of next week shows a period of tranquil conditions. Image courtesy of the WSI Model Lab.

Moving forward to the middle of next week, the western Atlantic ridge is still a feature, but seems a bit weaker and further east than we have seen recently, which could give a few day’s worth of sunny skies with temperatures near average for this time of year. The decent height gradient to the north, however, does lead to the potential for another front to sweep through later next week with the chance of showers and thunderstorms. But generally speaking, there are no heat domes building into the area at all in the foreseeable future. It is a relatively repetitive pattern of a front slowly clearing the area with some showers, then a brief break, then another front slowly approaching the area, and then another break, but perhaps each break being a bit longer in duration each time. Given the troughs and fronts, heat domes are not able to build into the area. Any warmth will be due to briefly being on the warm side of a cold front, as southerly winds ahead of the front increase heat and humidity levels, with the chance of a shower or thunderstorm from time to time.

We will also keep an eye on Tropical Storm Dorian, but considering lots of uncertainly in forecast strength and the fact that it won’t even be near Puerto Rico until Monday, we will keep any mention of it out of this discussion. Once things become a bit more certain, we will let you know.