It’s the battery that keeps recharging — an energizer bunny type pattern with regards to the warmth. In the Northeastern part of the United States, the 2010-2012 period has been the warmest on record for many cities. For the NYC local area, this past cold season, November through March, was the mildest on record. April will finish slightly warmer than normal as expected (probably +1 to +2 range in NYC), and not as anomalously mild as the previous months. The past several days have seen the longest stretch of negative departures since mid January, and before that, since October. However, it’s not saying much as this current stretch of moderately below normal temperatures should end by early next week. Prior to that time, late season frosts and freezes are likely in the suburbs of I-95 cities tonight and again late this weekend into Monday/Tuesday mornings.

Looking ahead to May, it doesn’t appear that we’ll break the seemingly eternal stretch of consecutive warmer than normal months. The weak-moderate La Nina event of 2011-2012 is slowly fading away, although SOI daily values have been positive in recent weeks, suggesting that we’re unlikely to see a rapid onset of an El Nino regime. Latest SSTA in ENSO region 3.4 indicates a reading of -0.17c, which is cold-neutral, and thus we’re not receiving any strong influence from ENSO right now. MJO tropical forcing patterns tend to be more noticable in times of weaker ENSO, and that will be spiraling toward phase 8 over the next couple weeks, a warm signal for much of the United States at this time of year.

NCEP model guidance projects a phase 8 MJO, while ECMWF based guidance essentially remains in the circle of death over the coming weeks. Either way, if the MJO does attain low amplitude phase 8, the signal produced for the eastern US will be a warm one.

Both the NAO and AO have remained fairly stable over the past several months, with predominately positive modalities for both indices. Although the AO has briefly turned negative this week (and we see the cool weather in response over the Northeast), models are in strong consensus that the AO will shoot slightly positive in early May. Meanwhile PNA forecast guidance suggests a slightly negative to near neutral look in the medium range.

When we combine the above factors, we get a May with near neutral ENSO conditions, a slightly positive NAO, AO, and near neutral PNA. MJO signalling will be weak, possibly low amplitude phase 8 in a couple weeks if anything.

The resultant analog package is as follows: Not many changes from the list of years that comprised the April forecast (and those years worked very well by the way with both temperature and precipitation departures in the US):

1951

1976

1986

2001

2009

The analog forecast May 500mb pattern:

Predicted May temperature anomalies:

Projected May precipitation anomalies:

Canadian temperature anomalies over the next 10 days — near to slightly above normal for the most part:

Conclusion:

1.) May should feature slightly warmer than normal temperature departures in the Northeast US, with above normal temps stretching westward into the Great Lakes and Mid-west.
2.) Precipitation should increase over the southern Plains and Southeastern US
3.) Precipitation anomalies in the Northeast should be near normal (maybe slightly below avg), which is a step in the right direction after a very dry Jan-April period around here.
4.) May will start cool in the Northeast but trend milder. Bursts of 80s and summery weather is likely on a number of occasions.
5.) Summer outlook will be posted in late May. Early indications are that May “may” be the last month of the consecutive warmer than normal month stretch here in the Northeast. Our first “cooler than normal” temp month in awhile is likely to occur in either June or July.