Wednesday - Thursday Outlook:
A surge of heat currently located over the Great Lakes and Midwest regions is moving east towards the area, bringing a 3 day heat wave containing some of the hottest temperatures of the entire summer, which is shaping up to be a chilly one. The main difference with the expected set up is a developing low pressure in the north central US; some models, especially the NAM/GFS, noticeably mishandled the development of this low pressure even as late as this morning, which is resulting in a trend towards a storm slower to develop, and thus a slight delay in the warm air mass. This may point to very slightly cooler temperatures for tomorrow, although the heat is still expected away from the immediate coast, with temperatures rising into the lower to mid 90s inland, upper 80s to mid 90s in Long Island/S CT, and mid to upper 90s in the immediate NYC area, locally reaching 100 degrees just west of the city. Heat index values in the immediate NYC area are expected to reach the 100-105 degree range and are expected to approach 100 degrees further inland.
Thursday will still be the hottest day, with temperatures approaching or reaching 100 degrees near NYC. Temperatures will be quick to rise, already reaching the mid-upper 80s near NYC by 8 AM and the mid 90s by 11 AM. Highs are expected to reach the mid 90s inland, upper 90s in the immediate NYC area except for the coastal areas, and lower to mid 90s in Long Island/S CT with areas closer to NYC reaching the upper 90s. Temperatures in parts of NE NJ may reach and/or slightly pass 100 degrees. As with Wednesday, heat index values will reach 100-105 degrees in the immediate NYC area while approaching 100 degrees further inland.
The change in the expected set up mentioned earlier results in a delayed cold front, which is now likely to move through during the day on Friday. As a result, the first part of Friday may once again start out hot and humid, with temperatures quickly rising again in the morning; depending on cloud cover and rain, temperatures may reach 90 degrees in the immediate NYC area as early as 11 AM. Afterwards, scattered showers and thunderstorms are expected during the afternoon, and depending on the exact timing, which could still be a bit slower than currently expected, temperatures are likely to reach the lower to mid 90s in the immediate NYC area, with upper 80s to lower 90s inland and further east.
Longer Range: Chilly Pattern Returns
As yesterday's discussion mentioned, the current heat surge is only an interruption in the chilly pattern observed since the start of the month, with blocking and Greenland/Canada ridging once again expected to set up in the medium to long range. With the blocking pattern returning, a strong upper level low for this time of the year will drop into the region, bringing below average temperatures and the potential for rain during early-mid next week. The models are in disagreement with the development of any low pressure and the intensity of the trough, with the CMC model the weakest and the ECM model the most extreme. The ECM solution is likely exaggerated, although cooler temperatures, returning into the 70s for highs, with more cloud cover and the potential for some rain is expected for early-mid next week.