After our 2nd consecutive above normal snowfall winter, we now look forward to the growing season, the return of the warmer temperatures, and coming out of hibernation from a long winter to engage in outdoor activities. Much like last year, this Spring will start off on the colder side we think, but we look for an abrupt flip during the month of April 2015. We will still have a few more amplifications to the pattern in the near term that will allow the end of March to be colder than average. The Madden-Julian Oscillation in phases 8 and 1 consecutively shows this well (below)
This does play a role in our April forecast since we do still have a tremendous amount of cold air and snow cover around us and to our north in Canada, and a collapse into the MJO circle of death once again. Any amplification to the pattern in early April could bring with it enough cold air for a minor wintry event. Most likely time frame to see wintry potentials would be in the late March to early April. After that, it will take an absolute perfect set-up on many different fronts to get more snow past Easter weekend. Not impossible, but unlikely. We explain in a few factors below:
El niño will be a factor as we enter the Spring with the western basins remaining warm. Latest 30 day anomaly trends and the charts above show the weakening of the warmer waters over the eastern basins.
Quasi-Biennial Oscillation (QBO)
Once again the 1958-1959 analog is coming up a close match. We are in rare territory here with the QBO values coming in so low for this long of a duration heading into Spring. But most analogs show a easterly QBO heading towards westerly. The only exception would be the 2004-05 analog. Considering the QBO values are as low as they can possibly go in that easterly component, it can only go up from here trending toward westerly.
1959 Analog: 1959 is our closest matched analog, and is closest to the state of the QBO. Many the past winter dismissed the QBO as not having that much of a factor on our sensible weather – or downplayed its significance. As we have seen during this past winter, it most certain did have an effect on the zonal stratospheric easterlies, which had a direct correlation to a very fast Pacific jet and northern stream.
The Analogs chosen do show a few things nicely. The 1959 analog matches up fairly well with the current SST anomalies, but the main problem with this year was the cold March – which does not match up to the near average look to March in 1959. The QBO also increased from March to April which may have supported the near average look to temperatures. A breakdown of how our 1959 Spring looked, see the graphics below:
1980 Analog: 1980 is probably 2nd closest given similar reasons mentioned above for 1959. What’s keeping this analog year 2nd is a return to well below normal temperatures in June after a well above normal month in May. Long term, it doesn’t look that will occur. But the farther you look into the future of a seasonal outlook, the more room for error you have to allow for. Recurving typhoons in the Pacific may become an issue again this summer given the state of El Nino and Sea Surface Temperature (SST) orientation in the Pacific. This was a major reason that summer ended up very cool at times relative to normal last year – and for long stretches at a time. Since we are in March, we will allow for the possibility again, but will re-address this with the summer outlook in a few months.
EPAWA official temperature and precipitation forecast by month:
April is expected to start off below normal for the first 10 days, but we will begin to see the pattern change to a milder one but slowly. The signal is pretty strong for May to be our first warm month in a while. With the transition comes the increasing potential for severe weather, especially with a cold pool remaining in close proximity to our north.
May and June will feature near normal precipitation for the coverage area as a whole.
As stated above, June can go two different ways depending on how things unfold. The 1959 and 1980 analogs went two different routes, 1980 was more cool/wet while the 1959 analog went with slightly warmer and drier conditions. The main difference between the analogs is the handling of the QBO values. A strong negative QBO was already ongoing with the 1959 analog and continued negative through June. The 1980 analog had the QBO rising to positive levels in April already. We also have to watch for the potential for the Pacific to get active with typhoons again, which could affect our sensible weather this summer if they recurve in the Pacific much like last year.
Next update expected just before the start of summer in mid-June 2015.