First and foremost, Happy New Years to everyone. If 2014 was a good year for you, do not take it for granted. Try to make 2015 an even better one.
This winter has not gone as planned for long range forecasters who predicted below normal temperatures and above normal snowfall for the eastern U.S. While it may only be January 2nd, long range outlooks from latest guidance for this month are uninspiring. We'll take a look at how December turned out and what is expected in January later on in the blog.
When I put together my Winter Outlook for this season the main variables I focused on were the ENSO, Stratosphere (QBO), NH Snow Cover, Sunspots, then came up with some analogs to reflect past years that matched projections based on those variables. I do not believe 1 specific variable should hold more weight than the others, but I do feel if one is too extreme, specifically an oscillation such as the QBO, it will be the main pilot in the overall weather pattern while the others act as co-pilots.
As explained in the Winter Outlook, the QBO measures the easterly and westerly wind regimes in the equatorial Stratosphere. Once zonal winds reverse from westerly to easterly, that is indicative of a SSWE (Sudden Stratospheric Warming Event) which most likely leads to the development of high latitudinal blocking (-NAO). Exactly where the blocking develops determines whether or not it would benefit our Atlantic pattern.
The SON (September - October - November) QBO values were -21.64, -23.24, and -23.65, respectively. The extremely negative state of the QBO indicate that zonal westerly winds have been dominating the equatorial Stratosphere. We need them to reverse to easterly to get our SSWE and eventually help change the 500mb pattern to promote higher heights in the AO and NAO regions of the Arctic. The December QBO value is not in yet, but observations show that it is still in a highly negative state which is not what we want to see if you're looking for a developing -NAO/-AO couplet.
Lets bring back the rising QBO table to refresh our memories on how this works. A QBO in an extremely negative state, such as what we're in now, that collapses toward a neutral/positive territory brings about an above normal chance of a -NAO developing. History shows that most Meteorological Fall's that had an extremely -QBO ended up seeing a SSWE that brought the QBO index rising toward neutral (-8 to +8) in December or January. Historical trends say that if the QBO has been in an extreme state for 5-6 consecutive months, whether it be positive or negative, it usually always reverses in the subsequent 1-3 months. However, that has not yet happened to our QBO this season and January makes the 7th month. A possible reason why higher heights have struggled to form over the Arctic or Greenland.
That said, July-December (6 months) the QBO has been highly negative and we still have not seen a reversal with the zonal winds. This is something that many long range forecasters, including myself, did not expect to happen since it is not common. What ends up happening is the +ENSO/MJO act uncharacteristically and the Pacific Jet turns very active, a big reason why the PNA has been mainly negative.
This image represents the H25 wind speeds and is a useful tool in analyzing jet streams. Study shows that there is a direct correlation with the strength of wind and the strength of storms. As you can see, the jet streak over China at the 250 mb level is very strong and fast, around 215 kts. Recall that there have been several powerful Typhoons this past summer and fall, notably Typhoon Nuri. There has also been a train of potent cyclones that have tracked the northern tier of the Pacific these last couple of months. The strong Pacific Jet is a likely cause of these strong storms, as well as a culprit why our weak El Nino has not behaved as it's supposed to. According to NOAA, ENSO-Neutral conditions continue despite the SST's along the Equatorial Pacific suggesting otherwise. Additionally, positive OLR (Outgoing Longwave Radiation) has persisted over the Dateline which means convection is weak and precipitation is running below normal in areas that usually see above normal precip. during +ENSO events. In other words, the atmosphere is not behaving like it should during an El Nino regime and is a reason why NOAA has not declared it one...yet at least. This may be a reason why the MJO has been in mainly unfavorable phases, since negative OLR has been constrained near the Philippines. The strong Pacific Jet in conjunction with our neutral ENSO are the main reasons why our PNA has struggled to remain positive, though fortunately the EPO has been steadily negative which is a reason why we're currently in this cold spell.
Getting back to the QBO, I went back and researched years that had highly negative consecutive QBO values from July-December and you have to go all the way back to the 60's and 70's to find a few. These years include 1965, 1970, 1972, 1974, and 1979.
Here is what their December 500mb pattern looked like:
Not very pretty. The glaring commonality between all of them is the +NAO/+AO state with a mean ridge pushed back near the Aleutians, resulting in a -PNA. This is pretty much how our December transpired.
December 2014 500mb:
A distinct difference is our recent December had a much more robust -EPO signal compared to those other years. The Aleutians have experienced below normal heights thanks to a pattern retrogression that occurred around mid-December which has helped our -EPO, whereas the other strongly -QBO years and their December H5 experienced a neutral or +EPO.
Keep in mind the above maps are upper air maps, not surface maps. This is the temp. departure from normal image you get when putting together that analog package for their Decembers.
December 2014 temp. departure was flat out warm for the entire country:
Central Park, NY total snowfall (December - March) in those years:
1965-66: 21.4 inches
1970-71: 15.5 inches
1972-73: 2.8 inches
1974-75: 13.1 inches
1979-80: 12.8 inches
CPK, NY for 2014 is currently at 1.0 inch with December through and January's 1st half not looking so promising either.
In case you were wondering, the ENSO forecast for those winters were all mixed. A couple moderate Nino's, a couple moderate Nina's, and one ENSO-Neutral. Hence why I do not think the ENSO was a big driver in those winter seasons.
As bad as those years were snowfall-wise, they all had a fairly cold February (shown below). It is important to know most of these years, besides 1965-1966, saw their -QBO's begin to crash by December. It was not until February of 1966 that the QBO rose to -17.14 (still fairly negative).
If we take a look at the GEFS & EPS we'll see what they are predicting for the period after January 10th. Between now and January 10th we should be in a mainly below normal temp. regime thanks to the -EPO. If we can sneak in a storm or two while the cold is around would be great. After that period, the -EPO could break down while the +NAO/+AO regime persists.
12z/01 Euro Ensembles:
You see that we lost the above normal heights in the northeast Pac. and Alaksa while the PV is bottled up in the Arctic.
Continuing out into mid-January and you'll see the +EPO signal grows stronger, the PV is nowhere to be seen, and there is a zonal flow in eastern Canada and the U.S. There is a +PNA signal though, so that could be a good thing as long as we have a semblance of cold air to help bring us a light to moderate event.
12z/01 GEFS:
GEFS also have the PV up in the arctic resulting in a +AO, but notice they still keep in tact the -EPO in conjunction with a -EPO. If this is true it would help keep a mean trough in the eastern U.S. even after the January 10th period.
And that pattern continues into mid-January according to the GEFS. But the main issue still exists: there is no semblance of a -NAO/-AO and consistent +PNA on either models. If the Pacific Jet is going to be a problem, it would greatly help us if we could get help from the Atlantic but that is not happening any time soon.
Updated Winter Forecast
Taking all of this data into consideration, I have decided to scratch my original winter outlook of below normal temps. and above normal snowfall. My new forecast (January-February 2015) consists of temps at average to slightly below with below to average snowfall for the area. I think if the Stratosphere can gets its act together, and there are signs heading in that direction, we could still possibly salvage a winter season of at least average snowfall for CPK. If not, expect a below average season in the snowfall category with mean storm tracks either to our north or west.
I felt this update was necessary instead of waiting until the end of the winter to see what happened. Rather, lets see what has already went wrong and examine what needs to go right in order to salvage at least an average season.
We'll see what happens! Enjoy your day.
-Francesco Paparatto
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www.njstrongweatherforum.com
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