We have had a pattern of a ridge in te west trough in the east alignment, leading to an early invasion of fall weather over the Northeast US and I don’t see that changing any time soon
We will modify tomorrow(Saturday) to slightly above normal temperatures however it will only last 1 day, the last 2 week overall have been dominantly average to below average and that overall pattern will continue through the next 7-10 days.
We have a cold front over the Midwest and that will come east tomorrow afternoon and evening, this will introduce a strong push of polar air from Sunday through Tuesday of course after giving us showers and thunderstorms tomorrow evening
Most of the day Saturday should be dry for the whole area, with a mix of clouds and sunshine, highs will be in the mid 70s to around 80 with some modest humidity as winds change southerly ahead of the front, it’s not until 5-6 pm when we introduce the chance for isolated thunderstorms over east PA then becoming more widespread by 7-9 pm as the cold front comes east pretty slowly, the line will slowly progress east and cross the rest of the area between 9 pm and 2 am again SLOWLY from west to east
5-7 PM Saturday
8-10 PM Saturday
10pm Saturday to 12 am Sunday
And it finally exits by 3-4 am Sunday
There will be a SLIGHT threat for severe weather, especially over Eastern PA and western NJ as frontal passage time will be more favorable in these areas. There will be marginal to modest instability over the whole area, but the front will pass through too late east of western NJ so the line should slowly weaken coming east.
Still , especially west of NYC a line of showers and thunderstorms, some strong will come through late tomorrow evening with heavy rain and gusty winds the biggest threats anda widespread 0.25-0.75, locally higher in thunderstorms.
By the time you wake up Sunday morning, the sun will be shining and a cooler drier air mass will be in control with gusty Northwest winds 10-20 mph with higher gusts , highs on Sunday will be in the low to mid 60s NE PA to around 70 in the coastal/urban areas, lows tomorrow night are expected to be the coldest of th season, with upper 30s over NE PA , to mid to upper 40s along the coast, upper 40s in those warm urban locations.
Monday will be the coolest day so far with highs in the upper 50s to around 60 over NE PA to mid 60s along the coast, some upper 60s in urban locations, lows will be similar to Sunday, upper 30s over NE PA to mid to upper 40s along the coast and urban locations which will be below average
Tuesday and Wednesday a similar air mass will remain in place but begin to modify slightly, still slightly below average levels with highs in the low to mid 6os NE PA to 70-73 over coastal and urban locations with sunny skies and low humidity, although some increasing humidity Wednesday.
Wednesday night into Thursday another cold front will come through, with the chance for showers and thunderstorms , , this cold front will keep the cool fall air mass in place through next weekend with highs Thursday through Sunday in the lower to mid 60s NE PA to 67-73 coastal and urban locations which is at or slightly below average, lows in the mid 40s NE PA to lower 50s along the coast
Long Range Thoughts (October)
Looking longer range as we head into early October, I see this pattern relaxing a bit, not anything to significant but as blocking relaxes a bit and the NAO comes from deeply negative to more neutral to maybe slightly positive.
However, ridging is expected to remain dominant in the west, and that will lead to overall a WNW to NW flow in the 500 MB pattern and so I don’t see any real big or significant warm ups
What I see happening , is overall WEAKER troughs dominating the east instead of modest to strong ones, so I expect that going into October, we will be around average temperature wise , going slightly above at times ahead of weak to modest cold fronts, when the flow turns zonal at times.
I believe as we head beyond day 10 in October and especially the 2nd half of the month, a similar pattern to now will develop and take hold again with ridging remaining in the west , I expect blocking to re-establish itself and thus stronger troughs should begin to remain dominant again.