Welcome to 2016. In last week's Mo Mo I discussed how the new year will bring a new pattern. The biggest difference between December's pattern and the one we're currently in is the western U.S. is no longer seeing the core of the cold.
December 2015 was the warmest December ever for Central Park, NY and neighboring suburbs.
The difference between December and January at 500mb that will bring the biggest influence to our sensible weather is the circled area of Alaska and the western Arctic. In December, this region saw negative height anomalies which extended all the way into the western U.S. (-PNA).
This month is showing positive heights over this area which signals the EPO to be negative. The EURO projection of the EPO does indeed take it from positive in December to negative in January. What this does is help weaken the Tropospheric Polar Vortex and bring it into the lower latitudes of Canada. In turn, colder air is forced into the CONUS.
The higher heights along western NA and from the Kara Sea into the Arctic promote a negative AO. The EURO projection above also shows an AO going from a positive mean state in December to a negative phase in January. I have already seen some people argue "what pattern change" as they see what their sensible weather will be like the first week of January, but I urge them not to focus strictly what the weather in their backyard will be like. It is important to see what is happening over the Continent. The Globe for that matter. These higher heights over the EPO and AO domains should definitely be characterized as a pattern change compared to December's H5 pattern.
That said, is this the type of pattern change that will bring extreme cold and numerous snowstorms to the northeast? No it is not. I stated in last week's Mo Mo this is a pattern TRANSITION that will lead to a full-scale pattern change probably by week 4 of January. And even a full-scale pattern change, which should involve a Sudden Stratospheric Warming Event, will not bring the type of cold we have seen the previous two winters. Under a strong El Nino regime, it will be difficult to suppress the Sub-Tropical Jet Stream over an extended period of time.
There are two storm systems that will effect the area this weekend and next week. The first one is for January 8th-9th and the second one - at this juncture - is for January 10th-11th. The second system has a higher probability of bringing our first accumulating snowfall event of the season.
If we look at the EURO valid the morning of January 6th using 500mb vort, we can see all the players are on the field for both of the aforementioned systems. Storm #1 is located over Texas and Storm #2 is in southern California. Storm #1 will cut into Chicago as a weak surface low. This means rain will move into our area late Friday into early Saturday this weekend. With Storm #1 cutting, this will sweep a cold front through our area which will lower heights and bring colder air. Is the cold air that follows behind the cold front from Storm #1 cold enough to support wintry weather for Storm #2? This is a tricky question and one that may not be answered over the next couple days.
Fast forward to Saturday morning, Storm #2 is already in the southeast ready to come into the northeast. Notice how close both storm systems are to each other. Storm #1 effects us Saturday morning which is the same time frame Storm #2 is in the southeast. If this is the case, Storm #1 is not going to have a lot of time to act as a potential 50/50 block to help keep cold air entrenched over the northeast. Also, northern stream energy could essentially get cut-off from phasing in with Storm #2 (southern stream energy). The more wave spacing between these two systems, the better. So far, operational models are NOT showing that. Storm #2 is likely to take two possible tracks:
Blue track is up the east coast but it does not guarantee snow for coastal sections since we're not sure if there will be a phase with northern stream energy. It will be up to how quickly Storm #1 gets out of the way and whether or not northern stream energy can dig into the CONUS as a result of the Pacific Ridge amplifying. Right now, Pacific and Polar energy are phasing together to keep the PV too far west, thus keeping the cold we need for it to snow too far away.
Purple track is what the 12z EURO OP from yesterday showed. There was no phasing with northern stream energy and the surface low cut to our west since the PV is in western Canada and there is no 50/50 block from Storm #1.
There is also a chance Storm #2 goes out to sea. If the Pacific Ridge collapses the flow will turn progressive and all the energy is shunned east.
Noteworthy is how different the Ensemble suites are from their OP counterparts. For example, the 18z GEFS and the 12z EPS Means look nothing like the Operational Runs in regards to Storm #2. The GEFS, shown above, depict a PV over the Hudson with northern stream energy digging into the eastern CONUS. The southern vort is not able to cut because of the NW flow so it has no choice but to take a track off the coast. Like I mentioned, just because the storm takes a track up the coast does NOT mean it will be cold enough to snow. Ideally we like to see a phase with northern energy occur around the Mid-Atlantic so the storm deepens and pulls in cold air. The GEFS were close but no cigar in that regard.
The 12z EPS Mean were much closer with the phase. They showed an amplified western ridge which allowed northern stream energy to dig sooner toward the coast and ultimately phase with southern stream energy. Notice how neither Ensemble Suite cuts Storm #2. It is either a track off the coast or out to sea.
My initial thought's are Storm #2 will end up being a coastal system or one that heads out to sea. I stress, a coastal system may not have enough cold air to promote snowfall. If models trend differently with how the handle the northern stream energy, specifically not trying to phase it with Pacific energy, then I think we can get a nicely timed phase which could result in a widespread snowstorm for the area. There is still a lot of time to see how this plays out. Once models put Storm #1 behind them, we should have a better idea of where and what Storm #2 will do.
Layman's Terms
The first two days of this week will feature cold temperatures. High's in the 20's to low 30's and low's in the single digits N&W to teens around NYC. Expect rain to move in late Friday into early Saturday. Less than half an inch of rain is expected. Once the cold front comes through, colder temps will move into our area Sunday into early next week with another storm system possible Monday-Tuesday. This storm has the potential to bring accumulating snow to the area, but it largely depends what happens with Storm #1 and the behavior of northern stream energy. I am still expecting a full-scale pattern change to occur by the end of January which should bring sustained cold and better snow chances for our area.
I may have another blog update in the middle of the week.
Have a nice day.
Best,
Francesco Paparatto
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