Behind yesterday’s string cold front, a cooler air mass entered the region again, with lows falling into the 40s inland this morning. A persistent northeast flow will set up over the region this week as a coastal low develops to the south, with steady light to moderate rain mostly to the south but possibly reaching the area on Thursday and Friday, with otherwise near or slightly below average temperatures and a NE wind continuing through early next week.
Monday, October 7 Observations:
A strong cold front moved through the region on Monday, bringing an end to the unseasonable warmth. A strong low level jet set up, quickly pushing the frontal boundary north with highs surging into the mid 70s to near 80 degrees; the highest temperature was 82 degrees in Teterboro, NJ, and the lowest high temperature was 73 degrees in Port Jervis, NY and Danbury, CT.
Scattered showers affected northern NJ and NYC around 11 AM, with a line of heavy rain, strong wind and thunderstorms entering western areas around 2 PM, NYC around 3:30-4 PM, and Long Island/CT around 4-6 PM. The heaviest rain fell in north central NJ, with 1/2 to 1 inch; the strongest storms shifted north of NYC, but with storms producing scattered wind damage in northern NJ and SE NY, especially in Paramus, NJ where an EF1 tornado was confirmed. Otherwise, windy conditions were present across the area with sustained winds around 15-30 mph and gusts up to/locally over 40 mph. The rain quickly ended by the evening with temperatures steadily falling.
This Week – Weekend: Coastal Low Persists Offshore
As the strong shortwave trough exited the region last night, quickly phasing with a Canadian trough and lifting north, ridging began to amplify in the central and eastern US ahead of a trough digging into the western US. Normally, this would result in a significant warm up; in this case, however, the ridging will be displaced to the north of the region due to energy left behind from the trough over the southeastern US, which will gradually lift north towards the region. The ridging to the north, along with a building surface high pressure into New England, will keep the upper level low trapped near the region, with a surface low pressure expected to form near the Mid Atlantic coast. With the jet stream kept well to the west of the region as the western US trough gets picked back up into Canada with another trough entering the same region by the weekend, this setup is expected to continue through the rest of the week.
This setup will result in a persistent area of light to moderate rain, possibly heavy at times, focusing over the Mid Atlantic into southern PA and NJ, primarily on Wednesday further south and Thursday-Friday further north, with the potential for 1 to 3 inches of rain in that region, locally higher. Additionally, a persistent northeast wind up to 10-25 mph will be directed onshore towards the Mid Atlantic coast. The main uncertainty at this time is regarding how much rain reaches the NYC area, as the high pressure in New England will mostly keep the rain suppressed to the south, but with some possibly entering the area. At this time, I added a 50% chance of showers for most with a 30% inland, which is subject to change over the next 1-2 days as confidence increases on the northern extent of showers. This will also determine the high temperatures; due to the northeast flow, temperatures on Wednesday before the arrival of rain will peak in the low to mid 60s from NYC and further east and the mid to possibly upper 60s west of NYC. Should the rain stay to the south, similar temperatures are likely to continue on Thursday and Friday. If the rain enters the area, however, high temperatures will struggle to rise above the mid to upper 50s, with the possibility of at least 1/2 inch of rain, possibly higher near and east/south of NYC.
By Saturday, as a strong low pressure in the western US tracks north into Canada and a strong upper level low settles over SE Canada due to developing blocking east of Greenland, a strong high pressure from Canada will slide southeast into the region, which is likely to suppress the coastal low temporarily. As such, the latest 7-day forecast reflects drier conditions for the weekend with slightly higher temperatures, in the mid to upper 60s, possibly near/slightly over 70 degrees for some, but with temperatures struggling to significantly warm up as a northeast flow persists.