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- The NAO is tanking
- The PNA is strongly negative
- The EPO is strongly negative
- The Pacific jet has weakened greatly
- The MJO is in phase 2
With a major block setting up, the NAO should soon go very negative. This will help to displace part of the Polar Vortex into SE Canada, putting a very cold/dry/surpressed type pattern in the NE through the rest of February. Everyone seems to be on the same page regarding that. The big question mark arises in early March. That is, how fast does the block collapse, and will another block set up behind this one? Also, will there be a big storm as the NAO rises back to neutral?
If the CDC forecasts are correct, the NAO will drop below -3.0 in the next couple of days. As seen below, that is as low as the chart goes.
As many have mentioned, when the NAO rises from an extreme negative state back to neutral is when we are mostly likely to see our "historic" storms occur. Because of this, there is an attitude of "MECS likely" on this board. I would just like to be a reality check, and remind everyone that more often then not, historic storms DONT occur given this pattern. This is because everything has to be perfect for one to develop, and rarely does that happen. I would elaborate further on this whole situation, but several mets have done a wonderful job at explaining it. See Vawxman's pinned thread for a great explanation on possible scenarios with this storm.
As we end meteorological winter and head into March, the suns angle, and the tilt of the earth becomes more of a factor. Because of this change, indexes that were once a major player have less of an impact on our weather. The PNA and EPO still play a role in our overall weather pattern, but a lesser role then what they did in the hear of winter (DJF). The NAO now becomes our most powerful index. The state of this index will dictate a lot about the month of March.
With a weakened Pacific Jet, and the NAO our primary index, I am going to put quite a bit of weight into a method that is still fairly new to me... The MJO. We are now in phase 2 which does historically favor a -NAO. With it starting to move along, we should be in phase 3 soon.. As seen below, MJO phases 3-4 favor cooling over Greenland, and a rise in the NAO, but in this case, our block will be so strong that the MJO might not have enough power to completely do that.
Im sure you have seen this before, but here is a map which gives a good representation of what phase 3 should like in terms of temps on a global scale...
Does the world always look like that when the MJO is in phase 3? Of course not, but it moving into regions unfavorable for a sustained negative NAO makes me think that the negative NAO is gone no later then March 8th. From there, a positive NAO should develop and hold strong till the end of the month. However, a positive NAO doesnt exactly mean warmth for the NE. The displaced PV could very well become a 50/50 low as it remains cutoff from the main cold. From there, all the the cold to the SW of this 50/50 should sit over the NE until it eventually becomes "stale", but it is likely that the cooler then average temps should stay in place in the east through mid-march despite the +NAO that will be in place. This will make it really hard for the month of March to produce above average temps in the NE.
Since it is likely that the NAO will most likely average out being positive for the month of March, lets take a look at what a positive NAO means in terms of temps throughout the nation. For the map below, I took the 10 most NAO positive March's (since 1958) to accurately show what this index can do to our temps when in that state during the month of March. Notice that above average temperatures are located just about everywhere but the NE. I expect this to be the case once again this March.
Lets now talk about the EPO... This has arguably been our most dominant index so far this winter. The recent turn to negative has allowed for very cold air to filter into the US over the past few weeks. In the month of March, the EPO looses a lot of its value, but it is still very important (especially in Canada). Im still looking for a way to accurately predict the EPO without having to rely models, but for now, this is all we have...
Several ensembles back up the CDC in the claim that the EPO will make a return to positive in the beginning of March. That will really help to warm up Canada in early to mid March putting the main Polar Vortex back on the other side of globe (where it was in January). Today's 12z 8-10 day Euro does a good job at showing this...
From there, the trend this season has been for the EPO to run positive, and when it switches phases, it stays in that state for at least 3 weeks at a time. Because of this, I expect the EPO to be positive for most of the month of March although where it goes at the end of the month is very unclear right now (but it wont matter much). To get an idea of what a positive EPO does to the temps across the country in the month of March, here is a composite of the 10 most EPO positive March's since 1950...
As expected, Canada is the warmest place on the globe during the positive EPO. The problem with a warm Canada this late in the winter is that it takes a while to get out of this pattern. We saw this in late Jan/early Feb, as indexes became favorable for cold to come back into the US, but there was just no cold air in Canada to work with. Eventually when the PV came back to our side of the globe, and Canada cooled is when we saw our cool down in mid-Feb. By the time all that happens again, Im afraid it will be a to late. Winter may very well end early March in the Midwest, and mid March in the NE.
The PNA is currently negative. Climo says that the month of March actually favors a negative PNA over a positive one. Since 1950, 39/55 (71%) of March's have seen a negative PNA. Although the PDO is positive, and the PDO and PNA correlate, the relationship becomes less stable as we get late in the season. In March's where the PDO was positive (the PDO will most likely be positive this March)...
7/17 (41%) of the time the PNA is positive for the month
6/17 (35%) of the time the PNA is neutral for the month
4/17 (24%) of the time the PNA is negative for the month
As seen by the stats posted above, there is still some correlation with the PDO/PNA in March, but not as much as previous months. Since the odds do favor a +PNA with a +PDO, I am going to forecast the PNA to rise and become positive for the second half of March. With a negative first half, and a positive 2nd half, the PNA should end March as neutral, allowing it to not have a major impact on our pattern.
Overall, here are my key points...
- Possible big winter storm early March
- NAO negative early March to positive for mid-late March
- Cutoff cold in the NE through the middle of the month
- EPO becomes positive and stays that way for most of the month
- Canada will warm up making it hard for us to get another cold shot before April
- PNA negative to positive... No major implication on our pattern
- Winter is pretty much done as of March 15th
Here is my temperature map for the month of MARCH-
BLUE = Below Average
WHITE = Average
RED = Above average
DARK RED = Way above average
