Sure-Fire El Nino Next Winter? Not So Fast.

Many climate models are predicting an El Nino following the double dip La Nina this year and last year. While a neutral to weak El Nino (possibly moderate) is likely, the forecasts for a super El Nino will most likely not verify, and here's why.

Here is the past analysis for the Pacific Decadal Oscillation, or PDO. It is recognized by either a warm or cold temperature anomaly in the northern Pacific. Likewise, there are warm and cold phases, respectively. Right now, based on the above image, we are, and have been, in a cold phase. This means an increased likelihood for La Ninas. However, as observed in 2009, that is not always the case, hence the 'increased likelihood' part.

This is the PDO forecast out to 12 months off the ESRL's LIM long range model. As you can see above, we are projected to remain in a deep negative phase from now until at least March 2013. But let's not get ahead of ourselves. Long range forecasts can be ticking time bombs of failure, or fairly spot on. There is barely, if any, room for forecast success 12 months out.
I ran over some verification scores for 3, 6, 9, and 12 month forecasts off this LIM model. I got 81%, 67%, 55%, and 41% verification for those respective forecasting periods. Now, don't get me wrong here- 44% is a very high verification rate for a full year out. However, it does not ensure confidence.

All I am saying here is that those going for a super El Nino for the upcoming winter (I haven't heard any of those forecasts, but I'm bound to run across a couple sooner or later) should take a look at how strong the negative PDO will be and how it could very well tamper the possible El Nino down to a neutral or weak Nino year.

Andrew

South Wisconsin May Get Crushed with Late Season Snow

Sorry everyone, the automatic publisher didn't work! Sorry!

The latest GFS is showing over a foot of snow for southern Wisconsin and far eastern Iowa. This comes as a fast moving storm system appears to absorb additional moisture to provoke additional snow amounts.

Before I go any further: This image may be produced with 10:1 ratios, which would be higher than what is being shown here. The keyword is 'MAY', because a comparison to other 10:1 ratio images yielded different results. That said, I am treating this image as a 10:1 ratio image in order to not get everyone's hopes up too high.

Anyhow, I would expect a realistic scenario to be 1-4 inches in southern Wisconsin, with another 2-4 in Pennsylvania. I really don't know with the difference in images using the exact same data, which should yield the same results.

Possible Weekend Snow Update at 4:00 PM CDT

Southwestern Low May Ignite Severe Weather in Plains

The ECMWF is projecting that a large low pressure system will swing into the Southwest and likely ignite some showers and storms if it should progress eastward into the Plains.
There isn't too much I can say about this storm system, but the jet stream appears to be latched onto the system, which would increase tornadic shearing and the overall intensity of the system.

Snow Event Potential This Weekend

A storm system is expected to bring a snow event to the Lower Great Lakes and lower part of the New England region. This image portrays 500mb relative vorticity values. For a refresher, positive vorticity values indicate low pressure systems. So, as you can see, there is an area of higher vorticity values in lower Iowa, which is the system we are watching for possible snow.
The system should quickly shift eastward and weaken in the process. Despite this, expect snow values to quickly increase in the North Ohio and New England regions, as the Atlantic Ocean enhances the moisture content of the system.

Here is a snow map valid for April 29 off the 12z GFS model. It has been showing snow in the area for a while. As you can see, a good 6 inches of snow is being forecasted in Pennsylvania off this system, with 2-4 inches in north Ohio and around the 6 inch swath.
Just for kicks, let's imagine that this snow is going to have a 10:1 ratio (10 inches of snow = 1 inch of liquid). Now, 10:1 ratios are uncommon in early and late season snowfalls, so take a look below.

This is a 5 day accumulation map.

Andrew