MJO High Amplitude P7-8 Analogs for Mid to Late March: Pattern Implications

[Isotherm]

With the latest MJO forecasts indicating a very amplified phase 7-8 wave, I thought it would be interesting to analyze prior years that featured a similar MJO progression at this time of year.

 

The current model consensus is for an eastward propagation of the MJO wave into phase 6 in the coming week, followed by phase 7, and eventually phase 8 around March 20th +/- a couple days. Due to the high amplitude of this wave, it's likely that there will be a fairly significant response in the mid latitudes. That response is precisely what the post here will focus on.

 

Below is a list of years [6 cases] that featured MJO propagation into P 7-8 in March, at varying magnitudes.

 

1977

1980

1981

1992

1997

2004

 

The 500mb patterns of those periods were as follows.

 

A common denominator appears to be the development of mid level troughiness in the Northeastern US, and a tendency for higher than normal heights either over AK, the Arctic Circle, or the NAO domain. In other words, high latitude blocking tended to develop in response to the MJO 7-8 propagation, particularly in the years with highly amplified waves.

 

1977

 

 

1980

 

 

1981

 

 

1992

 

 

 

1997

 

 

 

2004:

 

 

 

 

Most of these cases responded w/ the initiation of either an east based or west based -NAO blocking episode as a result of the tropical forcing. High latitude blocking of some type was a common element in the years.

 

In terms of sensible weather, of course, the development of blocking doesn't guarantee wintry weather, but the probability will be elevated for late season snowfall in the Northeast if the forecasted pattern comes to fruition. 1981 had several inches of snow in early April in New Brunswick, 1997 had the April 1st significant snow event, and 2004 had a couple moderate snowfalls in the third week of March. If you were wondering about the 500mb patterns of 1956 and 1958 (two years with historic snowfalls around March 20th), there was also significant blocking in the NAO domain.

 

The key to late season snowfall is achieving a -NAO block to some degree. A -EPO / +NAO isn't as effective late season as it is during the winter months in terms of producing coastal Northeast snowfall. For the I-95 to have a chance at another accumulating snow event, the +PNA signal must couple with a -NAO (either east or west based) to hold the confluence in SE Canada. Blocking connection from W Canada-Greenland would also be effective in locking / closing off a mid level trough in the East, which tends to be more common in the spring due to shorter wavelengths, and the seasonal weakening of the mid latitude jet stream.

 

What appears to be fairly certain is that the coming 5-7 days will feature near normal temperatures in the Northeast, followed by a resumption of colder than normal weather for March 18th-31st as the -EPO / +PNA resumes. The questionable NAO signal will be the potential deciding factor for increasing our snow chances in late March. For the reasons mentioned, I do believe the -NAO signal is legitimate (given the strong tropical forcing, seasonal feedback / shorter wavelenths, and historical precedent for the -NAO response following amplified P-7-8 March MJO).

 

[Guest Pamela]

Very excellent analysis & writeup...you touched on a topic I don't have a great deal of familiarity with but am anxious to learn about. 

[yhbrooklyn]

Interesting stuff.

What do the differences in the Euro and GFS forecasts mean in terms of sensible weather? GFS seems to be forecasting a much bigger wave than Euro, at least in Phase 8.

[marsplex]

And when does this end? the 1 week of April or are we going to be locking to a year with cold on gloom right in to May or worse? Or does this just fall apart and things get back to "normal"

[Isotherm]

Very excellent analysis & writeup...you touched on a topic I don't have a great deal of familiarity with but am anxious to learn about. 

 

 

Thanks!

 

Interesting stuff.

What do the differences in the Euro and GFS forecasts mean in terms of sensible weather? GFS seems to be forecasting a much bigger wave than Euro, at least in Phase 8.

 

That could be the reason why the GEFS was initially more amplified w/ the -NAO development, while the ECMWF had more of an east based block. But overnight ECMWF ensembles seem a bit more bullish now on the development of the -NAO signal. Often times I've seen the ECMWF attempt to weaken the MJO wave too quickly, while the GFS has a bias for maintaining the wave for too long.

[Isotherm]

And when does this end? the 1 week of April or are we going to be locking to a year with cold on gloom right in to May or worse? Or does this just fall apart and things get back to "normal"

 

 

Doubtful. These regimes once initiated tend to run in cycles of possibly 2-4 weeks. We could be looking at overall cooler than normal weather from March 20th through mid April. My guess right now is we don't break for prolonged warmth relative to normal until the second half of April.

[PB GFI]

Doubtful. These regimes once initiated tend to run in cycles of possibly 2-4 weeks. We could be looking at overall cooler than normal weather from March 20th through mid April. My guess right now is we don't break for prolonged warmth relative to normal until the second half of April.

 

It was very rare for both the Euro and GFS ensembles see the - EPO - AO -NAO + PNA  that far away .

You already see days 9 -thru 15 at 500 look to great .

When you trap the vortex under that type of blocking , you should invite a cut off cyclone at your latitude sooner or later . 

I like March 20 thru the 31st  period to be safe , but if it went for15 days it would not shock me . 

 

Rare late March snowstorms tend to respond to those looks at 500 

[donsutherland1]

And when does this end? the 1 week of April or are we going to be locking to a year with cold on gloom right in to May or worse? Or does this just fall apart and things get back to "normal"

It's difficult to say. A number of cases that featured an extreme AO+ in early March (1990 saw the MJO progress into Phases 7 and 8 at high amplitude for the 3/17-3/28 period) featured a cool start to April, a short period of much above normal temperatures near the end of April, and then a cool May in the Northeast. April 1990 saw the temperature peak at 91° in NYC on April 27. 1956 featured an extreme AO+ in early March, too, but the MJO was not measured at the time. 1956 saw a cold start to April and then a temperature of 84° in NYC on April 28. May 1956 was cool in the Northeast.  But May is so far into the future, I don't think one can draw conclusions with much confidence other than to note that there might be some possibility of a cool May.

 

It does appear that the closing 10 days of March into at least the first week of April will likely be colder than normal with at least some possibility of accumulating snow in parts of the Middle Atlantic region and New England given the ongoing pattern evolution and ensemble forecasts. After that, we'll see what happens.

[Isotherm]

[Isotherm]

[PB GFI]

Unreal look aloft . It is this look at 500 that all the honking has been about.

Those are big ticket set ups. We will need the surface to respond .

You may wake up one day and there is a monster cut off modeled at your latitude.

That's the potential here. Now let's see of it happens.

[Isotherm]

Unreal look aloft . It is this look at 500 that all the honking has been about.

Those are big ticket set ups. We will need the surface to respond .

You may wake up one day and there is a monster cut off modeled at your latitude.

That's the potential here. Now let's see of it happens.

 

 

The potential is certainly through the roof in the 18th-25th period. Whether it is realized or not is yet to be determined. rRelative to normal, a very cold period should occur which may persist through at least early April.

 

Strong tropical convection propagating eastward toward the dateline and the stratospheric PV displacement into Siberia supports the notion of mid level height rises in the AO / NAO domains over the coming two weeks.

[Wxoutlooksblog]

The potential is certainly through the roof in the 18th-25th period. Whether it is realized or not is yet to be determined. rRelative to normal, a very cold period should occur which may persist through at least early April.

 

Strong tropical convection propagating eastward toward the dateline and the stratospheric PV displacement into Siberia supports the notion of mid level height rises in the AO / NAO domains over the coming two weeks.

Beautiful upstairs, the question is does this transfer to anything exciting at the surface. Sometimes it does, sometimes it doesn't. I've seen us waste great potential many times before. Only time will tell.

WX/PT

[marsplex]

[Isotherm]

Still liking the 21st-23rd period for a storm threat. MJO phase 8 strong amplitude during the 18th-23rd period.

 

Forecasted 500mb pattern late next week:

 

 

 

MJO >1 amplitude phase 8 500mb composite fits nicely w/ the progged regime:

 

 

 

 

 

Tropical forcing near the dateline has been very impressive this week. We will see the mid latitude reaction begin over the next several days.

 

 

 

 

Today's Euro ensembles indicate numerous members with storm threats for the 21st-23rd. As the -NAO reaches a peak around the 20th-21st and the mid level block retrogrades westward, the PNA simultaneously spikes around the 20th, shortly thereafter is the time to watch. The operational run looked good overall, we just need to see some more amplification of the short wave, but the surrounding pattern is very conducive.