Major pattern changes are occurring over the Northern Hemisphere right now and they will have major implications on the weather pattern to end the month of November.
First and foremost: A storm tracked just close enough to the Mid Atlantic coastline to throw moisture into a cold air mass, and stayed far enough off the coast to allow a colder, offshore flow to dominate, resulting in major snows for Philly, NYC and much of adjacent NJ and Southern New England today, November 7th. This deep trough however is going to be short lived for a couple of reasons:
- Troughing now extending into Greenland. NAO is quickly rising with just a bit of a thumb ridge extending towards Iceland. This is speeding up the flow over the N. Atlantic and is not a true –NAO anymore.
- High amplitude ridging extending well into Alaska has sent a very strong piece of energy crashing towards the northwest US and western Canada. This energy is quickly breaking down western ridging and will replace it with a trough, resulting in rising heights and “ridging” over the eastern US.
As this trough in the west interacts with the ridging over the Northeast US next week, the middle of the country will be in line for stormier than normal conditions:
The first likely storm to come out of this setup will mainly impact the central and northern Plains and western and northern Great Lakes Saturday into Sunday as a potent piece of energy rounds the base of the western US trough and allows it to briefly take on a negative tilt over the northern Rockies this weekend, as shown above on the European model. Gulf moisture will be somewhat limited, however the depth of the trough combined with the temperature differential, seen in the bottom right image, the storm will be tapping should result in a moderately strong storm with some potential for accumulating snows in parts of the upper Midwest Saturday into Sunday. Severe thunderstorm prospects don’t seem too significant closer to the Mississippi and farther south due to warm temperatures aloft, but may be something to watch as well. The strong low level wind fields ahead of this system may support a squall line with strong winds, even if convection doesn’t become too intense.
As the trough continues to move east and runs into an upper level ridge over the Northeast US, it may take on enough of a negative tilt near the Mississippi River on Tuesday, as shown above, before shearing out to causing another way of low pressure to ride up the cold front, this time farther east.
Due to the very positive AO and NAO, noted by much lower heights than normal from northern Canada to Iceland, any storm will likely track up the west side of the Appalachian mountains. The whole trough will gradually be shearing out as it treks east towards the Great Lakes and Ohio Valley, however, this low pressure system may be enough to enhance the severe threat Monday-Tuesday over parts of the Ohio Valley, and bring a snow threat to areas from Missouri northeast towards parts of the Great Lakes.
When looking at some individual GFS ensemble members valid Tuesday morning, it is apparent that much uncertainty exists, with several members bringing a very weak area of low pressure up the front near the Appalachians, while other members track a low pressure near Chicago.
Given the shearing out of the trough as it moves east which supports a weaker storm…and the strong +AO/NAO which support a storm cutting into the Great Lakes…I think a balanced approach at this point is the best option, with my forecast currently calling for a weak wave of low pressure to develop over the deep south and ride northeast to near Cleveland, with some potential for snow from Missouri into the Great Lakes. However, this is a low confidence solution and I will be watching for trends one way or another over the coming days.
Rolling forward, the next storm threat will come from the piece of energy poised to move out of the Southwest US in the above image off the European Ensembles, valid next Wednesday morning.
This piece of energy will likely have minimal impacts as one heads east of the Rockies however:
-In the above image, note the extremely strong +AO
-Note the Gulf of Alaska vortex re-emerging.
-Note how the geopotential height lines are beginning to tighten from south of AK to Greenland.
This all points to the polar branch of the jet stream tending to stay farther north than normal near the end of next week, meaning any storm coming out of the southwest will have little cold air to tap into. However, this possible weather maker will be watched over the next several days.
As we look towards the latter half of November, it appears as though a more zonal flow with less stormy and warmer than average temperatures will take hold over the eastern half to two thirds of the nation…With the PNA remaining negative and the NAO and AO both expected to remain positive through at least the third week of the month, cold air will keep dumping into the western US and there will be little to force the cold air east, meaning warmer conditions will prevail over the east.
How long will this warm tranquil pattern last? All indications are the pattern will begin taking hold towards the end of next week, with the only potential blip being the possible “storm” moving out of the southwest towards the end of next week and heading northeast. It then appears that the telleconnections, shown above, will not favor significant cold or storminess east of the Plains through at least November 20th.
With the MJO diving into the “circle of death” currently and expected to remain there for at least the next two weeks, there is no indication of the western US troughing breaking much before Thanksgiving.
Thus, it appears reasonable at this time to say that after next week, a period of warm and somewhat dry weather will take hold over the eastern US for the foreseeable future.