January 2014: Pattern Change & Possible Storm Threats

A Merry Christmas and Happy Holidays to all on this brisk Wednesday morning. The focus of this blog will be to analyze the upper level pattern for around New Years time and into the first week of January. December has been eventful for the northeast U.S. thus far, but we have hit a relaxation period and the pattern is getting ready to re-load for 2014.

The global models that show what the weather COULD be like 1, 2, and even 3 weeks from now, are honing in on a couple of storm threats that I think need to be looked at more closely. The notable dates are:

December 28th - December 29th
December 31st - January 1st
January 3rd - January 6th

Our weather pattern has been driven by the presence of Pacific blocking, also known as the WPO (west-Pacific oscillation) or EPO (east-Pacific oscillation) which have been in predominately negative phases dating back all the way to the fall. This has allowed ridging, or positive heights, to extend into Alaska and at times the western Arctic region, which in turn forces the arctic air southward into the CONUS. This has created a cross-polar flow effect which takes cold air from the west U.S. to the east U.S. Another element to note from our pattern up to this point is the lack of blocking (+NAO) has allowed the southeast ridge to amplify and draw warm temperatures up the eastern seaboard at times, which is evident by the couple of ice storms we have seen already since extremes usually occur when polar air collides with tropical air.

However, the pattern is changing and the concentration of this blog will be on the PNA, AO, and NAO. I have already mentioned the NAO has been positive so far this Meteorological winter. The AO has also been positive despite the impressive cold shots we have seen at times this month. The PNA has been negative, which supports trough's in the western U.S. (but I have already disclosed the -EPO has helped us offset warmer temperatures from getting into the northeast).

There is evidence that all those signals do a flip once we approach the New Year. The AO is heading negative, the PNA positive, and the NAO negative. I'm more confident on the first 2 panning out than the latter, but we'll look at things more closely and you can draw some of your own conclusions as well.

The above image from the GFS shows the AO going from a positive stage to a negative one. Once we look at the h5 maps, you will be able to see why this is the case with not just the AO, but all the signals. 

Also from the GFS, the PNA is rising into positive territory. 

Lastly, the NAO on the GFS is shown to all be going negative. In case you did not know already, a              -NAO/-AO/+PNA strongly supports colder than normal and stormier than normal weather in the eastern U.S. 

The following 500 mb maps are taken from the 00z EURO run from last night. 

 

The first storm threat we have to deal with is the one for this weekend. You can see from the broader pressures around Texas that energy is building and a low pressure system is trying to form. Since the cold air has retreated north, positive heights off the Atlantic are getting into the northeast. At this time, the PNA is still trying to get positive (shown to be neutral on this image), the tanking of the AO is still in its early stages, and the NAO is positive. So, if a storm does run up the coast this weekend, it supports a rain storm. There is a slight chance the energy in the south holds back a bit, allowing cold air get into the northeast first, but this does not seem likely at this time.

The next time period I mentioned is December 31st to January 1st. This will not be a big storm if it materializes, but at this time the pattern is setting itself up for a potential bigger storm around the 4th. Some models are showing a clipper rotating around the Polar Vortex and potentially amplifying once it reaches the coast. This is similar to the clipper storm in mid-December that bombed out off our coast and brought decent snow to parts of the area and southern New England. 

These type of systems favor New England the most, but there is still time for a south trend just like the other system. I do feel someone could see a measurable snowfall out of this storm. Plenty of cold air around at this time as well, with a nice High Pressure system to the north. Another thing to note from the 500 mb map I posted for this time period is the AO is now negative and the NAO is as well, evident by the positive height anomalies into Greenland. Look at what is happening in the north Pacific, the -EPO ridge is connecting with another ridge in the western Arctic, forming a mega-block. The formation of that block coupled with the        -NAO, is forcing the Polar Vortex south to the Hudson Bay area and calling for the -AO regime to form. 

The last time period I wanted to briefly talk about is the January 3rd-6th time period. The above 500 mb image from the 00z EURO is as extreme as it gets (*pay attention to the general idea, not the extreme-like solution*). The general idea from the long range EURO shows the north Pac ridge shifting into the western U.S. (+PNA) with crazy blocking consisting of positive heights still present in the Arctic region. The NAO is even more negative and the Polar Vortex is still situated around the Hudson Bay. It is unlikely the PV gets as far south as the EURO is showing here, which actually phases the PV with the sub-tropical jet stream and forms a massive storm system. Again, unlikely to happen. 

To me, what is more likely to happen is the PV remains north around the Hudson and the +PNA ridge in the west comes to fruition. I think the blocking is modeled to be too extreme right now, which is usually the case, and it is causing the models to spit out extreme storm solutions. The general idea though is for a -NAO/-AO couplet to develop in conjunction with the +PNA. This should lead to interesting times down the road after we get by the next 2 storm systems I talked about earlier. 

This type of pattern has support from most models, it is not just from the EURO. The ensembles agree as does the GFS OP. 

One reason why we have seen moisture-laden storms this year is due to the active STJ, or sub-tropical jet stream. The STJ around the 3rd-6th time period is also projected to amplify with knots in excess of 150 along the eastern CONUS. Put together a signal package I mentioned above along with the STJ, and the pieces are all there for a big storm to potentially come together. Whether it does or not remains to be seen, but the pattern is turning ripe and the time period needs to be monitored. 

Have a great Christmas and a safe and happy New Years. 

Francesco Paparatto 

Storm Briefing for Saturday, December 14th

Another storm is brewing for the Mid-Atlantic and Northeast states, and this time, it could pack quite a punch compared to our last couple storm systems. Although the pattern is not optimal for one that would condone a major snow-maker in the Northeast since the NAO / AO continue to remain positive and the PNA is negative, we are still on track as of tonight for parts of the northeast to receive a significant snowfall. Another component I am also concerned about is the possibility of ice accretion for areas along the immediate coast of the Northeast. 

Here are a couple images of the current water vapor loop. The bottom picture is simply a zoomed in version of the SW Conus from the top image. Both pieces of energy that will work in conjunction to bring a storm system together for this Saturday are on land and beginning to advance east. There are a couple things that should be noted:

1. The STJ, or sub-tropical jet stream, is much more active than it was this time last year. This is helping the southern vorts, or upper level low's, to strengthen before they even reach the eastern U.S. and there is a feed of energy from the eastern Pacific flowing through the jet and into the vort. 

2. The Gulf of Mexico's warm sea surface temperatures were not hindered much this past summer due to the  inactive hurricane season. It is open for business and providing additional energy to the storm that develop in the southeastern U.S. There has already been a few examples of moisture-laden storms this fall that have brought high rainfall amounts to parts of the southeast. 

3. Our northern branch energy is likely NOT to phase with the southern branch energy with this upcoming storm system. Much of this is due to the lack of "real" blocking, or -NAO, and the zonal flow in the western U.S. (-PNA). I say "real" blocking because, although the NAO is positive, there is a PV (Polar Vortex) over Greenland helping to provide confluence over eastern Canada which is one of the reasons why cold air will remain in place (for some locations) when this storm arrives. 

The 2 biggest factors that will ultimately determine who sees rain, snow, ice or a mixture of all three is the positioning of the upper level High Pressure system(s) and the strength of the southern vort. There will be partial phasing with the northern branch which will help develop a broad LLC (low-level center) and bring ample precipitation amounts to PA, MD, NJ, NY and eventually New England, but how strong it gets is significant. A stronger system brings up warm air from the south and could potentially initialize a dangerous ice situation (specifically for NJ), while a weaker system keeps cold air intact and keeps most of the precipitation in the form of snow. 

Once the next set of tonight's model runs come out, I plan to release a 1st call snowfall map so everyone can see what my initial thought's are. Given the active STJ and presence of GOM energy filtering into the storm system once it develops, I am favoring a more warmer solution (plus ice) at this time for the Mid-Atlantic and Northeast up to NYC. But we'll see what happens...stay tuned!

Francesco Paparatto  

What's To Come: Minor Snowstorm to Arctic Blast to Possible Major Coastal Storm?

Most important information from this blog is bolded and/or in font color red

So, it has begun.

Meteorological winter began 9 days ago and it only took those few days to get our fist significant snowstorm of the season around the Philadelphia Metro and southern New Jersey areas. Snow amounts ranged anywhere from 4 to as much as 12 inches in isolated towns in southern NJ.

Today, more snow, ice, and rain is expected in those same areas that got the surprise snow yesterday and some of it could even get as far north as NYC. Not much in the way of additional accumulations should be expected, however.

Once this system moves out, another one will quickly follow its heals and bring the threat of more widespread accumulating snowfall amounts. Granted, this would be a quick moving system, but it has the potential to drop an additional 1-3 / 2-4 inches of snow. If the surface low strengthens some, isolated areas around the Tri-State could see 6 inches of snow.

Here is the stripe of snow being shown on the 00z GFS extending from CT into northern VA:

If things still look impressive after the 12z runs later this afternoon, I will release a snowfall map and hold a chat at 9:00 pm EST so we can have discussions on the 00z NAM and 00z GFS runs as they come in. 

The next thing that should be addressed are the cold temperatures set to move into the Northeast and Mid-Atlantic states later in the week. Here is a look at the temperature anomalies map by Friday morning:

-10 to as low as -25 degrees below normal throughout the Eastern U.S. 

Here is a zoomed in look at our area:

COLD ! 

2-meter temperatures (temperatures 2 meters from the surface) are only shown to be in the teens and single digits...

And it's not even the heart of winter! Thus far, we have seen some very impressive arctic air masses that do not seem to be moderating at all as they make their descendant from Canada into our region. 

Temperatures will try to moderate by to normal by the weekend, but we should still stay on the below normal side of things. 

The last thing I wanted to briefly mention without going overboard is the threat of a possible coastal storm next week for the Mid-Atlantic to New England states. 

Some models such as the EURO have been close in showing a potent coastal storm early next week. There is a high chance one does not happen, but there is still an interesting set-up in the pattern that causes me to raise my eyebrow a bit. 

Two pieces of energy will be diving into the eastern U.S. next weekend. Piece #2 like I have labeled on the image above broke off Piece #1 and is digging into the southeastern U.S. These two pieces of energy are going to make an attempt to phase somewhere along the coast. And if they do, you can expect a coastal storm. 

Although there is not a -NAO at this time, there is a strong Upper Level Low that may act as a blocking mechanism to help get these two pieces of energy to phase. 

That, to me, is the key. If that ULL can stay on the models through this week and not try and escape northeast, it could force a phase with those two pieces of energy. There are other factors as well, but we are still too far out to even worry about them right now. Some may say this blog has been written too early,  but I'm not calling for a coastal storm. I am just trying to say the set-up is interesting at the 500 mb level and I could see how one forms. 

Have a great day 

Francesco Paparatto 

Notes:

1. Check out the NJ Strong Weather Forum at www.njstrongweatherforum.com to participate in daily discussions involving the weather, including scheduled chats.