Northeast weather about to become active

The region has stayed sunny and dry under a strong high pressure ridge in the past 10 days. In fact, the entire CONUS has stayed relatively dry and inactive for the last week. This trend should continue through the next 4 days as the high slides to the south and east and 2m temperatures could edge above average, which is in line with the GWO approaching phase 1.

By day 4, the main story is tropical wave invest 93L that is currently near Puerto Rico. At this time it being subject to strong shear, and also interaction with land. However, its environment will be improving over the next 24 hours, and it will likely be named a tropical depression by tomorrow. Meanwhile, an upper level low is projected to be sitting off the Carolina coast by day 3, with the strong high pressure to our east. This would force 93L, by then likely TS Kyle, to move north and bend northwest as it interacts with the high. Regardless of its tropical rank, it could phase with the upper level low and become a formidable hybrid nor'easter. The latest ECMWF, HWRF, and GFDL are in good agreement with 93L bending to the NW around days 4 -5 and approaching the southern New Jersey coastline, however the GFS ensembles have a large spread, so there is still a lot of uncertainty in the forecast around Friday to Saturday. If the senario pans out with the low moving further west, we could be dealing with widespread wind and flooding impacts from Philadelphia, north.

Beyond day 7, forecast ensembles have a strong consensus in a +PNA continuing through the next 10 days. Negative mountain torques will send the GWO into octant 1 of phase space, which will begin to favor closed lows approaching the SW. This is supported by the latest operational GFS runs which shows a sub 570dm mid level low nearing central California. Meanwhile, the GFS is showing the first polar vortex of the season dropping down into Minnesota by day 8, and over northern Michigan by day 9 as a sub 540dm low. With the 850mb 0C isotherm passing through central Illinois and Indiana, some first of the season snows are possible in the Great Lakes region during this period. The GFS forecasts the low to remain over the northern Great Lakes before pulling northward around day 11-12. So here in New England, expect below normal temperatures to reach us by day 10, but the trough axis will remain to our west the entire time. The ECMWF 8 to 10 day composite is less robust in below normal heights over the Great Lakes. Using 5 different roll-forward analogs for the current pattern, the first half of October could feature continued below normal temperatures in the northeast.