Storm missing to the south; unusually little temperature variation again this week with a few scattered showers through late Monday, then more sunshine through Thursday; possible big storm next weekend; then warmer?

Plain-language summary:

 

A storm that missed to the south yesterday will strengthen and then stall east of us, providing a few showers through late Monday. It gradually clears out afterward through Thursday, with warmer days but cooler nights and little wind. Rain is likely next weekend, but it remains to be seen if it is a major storm with heavy rain and strong winds or just a shorter period of light to moderate rain. Day-to-day temperature variations will be unusually small for the 2^nd week in a row, but a more changeable but mostly warm pattern could resume afterward. Many areas could set a record for the latest first freeze, though any modest cold shot would provide the first freeze outside urban areas and near bodies of water.

 

Meteorological discussion:

 

The storm I mentioned in last Sunday’s blog post missed to the south yesterday. It is finally turning north, but is already too far out to sea to directly affect our region, instead hitting Atlantic Canada before occluding and stalling for a couple of days. However, the broad cyclonic flow around the storm is still wrapping around some Atlantic moisture into our area, leading to a few showers and plenty of clouds. A weak high pressure gradually builds in by Tuesday, ending any showers by then, and winds will lighten. That should also allow for more clearing, though at this time of year, it is always possible for low-level moisture and clouds to be trapped underneath a subsidence inversion even with high pressure in control. Assuming it is not too cloudy, daytime highs will warm up with the ridging, but nighttime lows will actually be cooler due to the clearer skies. Still, with the low-level moisture and lack of a true cold air mass, it will be hard to get any frost outside the coldest hollows. With an unusually weak temperature gradient, high pressure in control, and associated weak temperature advections, day-to-day temperature variations will be unusually small for the 2^nd week in a row.

 

Source: TropicalTidbits

 

By next Friday, high pressure will be moving offshore, with a low pressure moving into northwestern Quebec and its associated cold front draping across the Great Lakes. At the same time, a southern disturbance will be plowing eastward across the U.S. Deep South and gradually pick up more Gulf of Mexico moisture. These moisture-laden southern disturbances are likely to become more and more common due to the moderate to strong El Niño. If the southern disturbance is fast enough to get just ahead of the northern disturbance, the two disturbances would phase to form a quickly strengthening storm along the U.S. East Coast, essentially an early-season Nor’easter, with widespread heavy rain and strong winds across the region. However, this is far from certain at this point; it could also very well be a much weaker, disorganized system with just a period of light to moderate rain.

 

Source: TropicalTidbits

 

Source: TropicalTidbits

The following week, we may finally see a somewhat stronger temperature gradient more typical of October, though models have shown that before, only for that to not happen. The -NAO is expected to weaken somewhat, though there is considerable uncertainty. and the +PNA crashes to near neutral or even slightly negative, which should promote a more changeable pattern with no sustained warmth or chill, but perhaps biased on the warm side unlike the past several days. We are already running unusually late for the first freeze almost everywhere outside the coldest hollows, and a warm pattern could lead to a record late first freeze for many. However, at this time of year, any modest cold shot with clear skies will lead to a freeze outside urban areas and near bodies of water.

 

Source: TropicalTidbits

 

Source: Climate Prediction Center