8:07 AM

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The pattern for February has certainly delivered as advertised, producing near record if not surpassing record snowfalls throughout the region.  However, like any other pattern, this pattern will come to an end and the clues to the pattern ending are already showing up.

10:05 AM

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Over the past three weeks, the 500 MB pattern has been generally unfavorable for any significant winter storms for a variety of reasons.  At first, the overwhelming strength of the negative NAO suppressed any potential for Sub Tropical disturbances to interact with the cold air at place, leading to a cold and dry pattern for the start of January with only a few minor snow threats producing an inch or two.  Then the past two weeks as the rapidly cooling stratosphere caused high latitude blocking to collapse and the MJO went into a more supportive La Nina phase, moderation or a January thaw has taken hold with the result leading to more rain threats than anything else and even some days with highs in the 50′s.  However, as I’ve been alluding over the last several days, all of the support for a warm pattern is coming to a crashing end.

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9:15 AM

As discussed yesterday, the rapid cooling of the Stratosphere the past few weeks lead to the collapse of the high latitude blocking that supported the strongly negative Arctic Oscillation and the negative North Atlantic Oscillation.  Over the next ten days, the Sub Tropical jet stream will be the dominant influence on the pattern, which is an important factor considering the trends the MJO is moving towards.  As a result, a Pacific air mass will become the dominant air mass across much of the United States.

After a strong trend to falling temperatures from 10 MB to 70 MB over the past several weeks, there is now a reversal in the trends of temperatures and the stratospheric winds are starting to revert back to what was seen in late November and early December.  This is an important observation and if these trends continue, then the high latitude blocking observed for much of December and early January will become reestablished over North America.  For now, the important observation I’m keying on is the fact that the influence of the warming at 10 MB is starting to be felt at the lower levels of the stratosphere as well.  This ability for the warming, which is even more impressive at 5 MB tells me that there is potential for a significant shift towards a warmer stratosphere, which can lead to the crashing of the negative Arctic Oscillation and the trend of a more negative North Atlantic Oscillation seen on the ensemble model guidance after January 16th.

I envision the Polar jet stream to remain in a positive EPO state for another 7 days before moving back into a negative EPO state by around January 21 or the end of next week.  The change in the EPO index will be the lead indicator to a cold pattern returning with the heart of the cold air likely directed towards the Plains at first.  As the stratosphere continues to warm and the negative Arctic Oscillation continues to become established, the negative NAO pattern will not be far behind.

In the mean time, a Pacific influence to the pattern will be strongly felt over the next several days with even a hint of the upper 40′s for highs by the middle of next week.  I don’t buy into the GFS solution of a rapid return of cold conditions as this is based on the storm for this Sunday phasing with the Polar branch.  Yes, if that happened, then the negative AO/NAO pattern will return rather rapidly to coincide with the trending MJO wave into stage 6.  However, with little support from any other model guidance, I’m staying away from the GFS solution unless there is a defined change in the guidance from the ECMWF, CANADIAN, and UKMET.

9:04 AM

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There can be no doubt that change is in the air as the Arctic Oscillation relaxes and the Sub Tropical jet stream gets some breathing room to flex its muscles now.  The result of which is a pattern that by next week leads to a ridge moving through the East and a deep trough extending from the Gulf of Alaska to the West coast.  This pattern will bring a significant amount of rain into California and a threat of severe weather for the Plains, but is this the end of winter?  Is it time for those in the northern Mid Atlantic to throw their hands up in despair as another winter exits without everyone getting into the “party” of snow and cold?

Well, while it is true that the pattern is trending towards a return to warmer temperatures for the Philadelphia and New York City metropolitan area, I don’t think this pattern has much legs beyond a few days and I’m going to explain why.

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9:33 AM

The MJO has gone into the circle of death, which basically means the wave has fallen apart.  What does this mean for the pattern going forward?  Also, what do I expect for the storm next week?