While September generally ended up being a below average month temperature wise, as soon as the calendar hit October the pattern took a pretty big turn (or perhaps a pattern relaxation) , and lets face it the last 15-16 days or so have been very mild for not only our area but for the whole eastern half of the country generally speaking with just a few days in the mix that were near average. We will continue to see these mild conditions over the next 48 hours, but big changes are on the way beyond the 48 hour mark for much of the country.
We go out towards the Pacific because this is where the driving forces of this pattern change are occurring , the dominant pattern since early October has featured a deep trough over Alaska and at times the western US , (which lead to a record snowstorm over the northern Rockies last week) and it leads to a progressive flow across the country and floods it with Pacific air, especially east of the Rockies and helps to build a ridge over the eastern US which we have clearly seen.
For a “cold” pattern to take hold over the eastern half of the nation you want a trough over the Aleutian islands and a ridge over Alaska and into the western US , we can see on the satellite above that clearly a powerful trough is about to take hold of the Aleutian Islands and in response a ridge is beginning to build into Alaska , this is mostly thanks to Cyclone Philian that hit India last week with some help from some convection trying to fire over the dateline in the Pacific (MJO going weakly into phases 7-8), in response to these changes a cold front is sweeping through the eastern US.
Our cold front is currently located around Ohio, this will take its time moving east as the front itself has lost a lot of its punch , the main impact of this front will be the start of a pattern change more than anything else, with a much colder air mass taking hold of the Midwest and Central US , currently we have a warm front over the Mid Atlantic which will lead to cloudy/overcast skies through today (maybe an isolated shower and spotty drizzle as well) which will keep high temperatures down in the mid to upper 60s for most, but with cloudy skies and a developing southerly flow lows tonight will be mild and well above average in the 50s.
The warm front will move over or north of the area tomorrow which will lead to at least partial clearing and a very mild day in the low to mid 70s for most of the region, upper 60s NE PA , but as the cold front comes east some isolated showers will start to move in from west to east during the afternoon hours and increase in coverage tomorrow night as a bit of a low pressure currently over the southern Plains rides the front over the area and enhances rain somewhat , this low will move through quickly and just lead to a period of widespread showers/brief steady rain tomorrow night into Friday morning, tomorrow night will be very mild for lows in the mid 50s to low 60s but the marked change for our begins on Friday as temperatures will not rise much from morning lows, with highs in the mid to upper 60s under clearing skies and lows Friday night will drop into the upper 30s NE PA to upper 40s along the coast, Friday is more of a transition day
By Saturday a trough is establishing itself over the Central US/ Northeast and Mid Atlantic, for the weekend into early next week it is likely that the bulk of the trough/cold air will remain to our west as the ridge building over Alaska and the western US will be a bit to far west but regardless our temperatures will fall to slightly below average levels this weekend with highs in the upper 50s to mid 60s and lows in the mid 30s to mid 40s
Early next week we will see continuous reinforcing cold shots and cold fronts coming through the Central/Eastern US which will gradually allow the trough to shift/expand east ward brining well below average temperatures by mid to late week it is likely that most of the area will see their first widespread frost/freeze of the season sometime next week (some parts of NE PA/NW NJ could see it this weekend) which could become quite continuous as this trough really establishes itself and remains in place with constant reinforcing cold shots
We see by mid week as the ridge in the west slowly moves east, the bulk of the trough also moves east
And by weeks end we have the eastern US engulfed in a big trough, it is likely that the models are over doing this trough a bit but the general theme is likely correct here , by mid to late week we could be struggling in the 40s to low 50s for highs and lows in the upper 20s to mid 30s interior to upper 30s to lower along the coast. As the fall forecast https://northeasternnjwx.wordpress.com/autumn-2013-forecast/ stated we would likely see the change to a very chilly 2nd half of October after a volatile start to the autumn season, so far the forecast is on track.
Above are expected temperature anomalies for the next 15 days, you can see the first 2 days are above normal but then a shift to average around days 3-4 then it just tanks down gradually to well below average after that.