Sunday, March 18, 2018

Spring outlook 2018

Well it's March which is the beginning of Meteorological Spring. I've been dropping a lot of hints on how this spring will go during my Facebook post. I wanted to get this out a couple of weeks ago. But one thing or another prevented me from doing that.

This outlook will cover March through May. It will also touch on the spring severe season and my first thoughts on how this year's Atlantic Hurricane season go.

First a look back:

Winter 2017-2018 turned out much different than many thought it would. Many outlets winter outlooks, talked about warmth and a lack of snow.  But through pattern analysis a few like myself were able to come up with a forecast that worked and worked well. 

My 2017-2018 winter outlook and be found here.

But December into the first week of January saw temperatures that were well below average. Temperatures became extremely cold around Christmas into the first week of January.  January had two big thaws that ended up taking most of our snowpack. Pass the first week or so of February my outlook called for the cold to return for the rest of winter. But for the last 20 days of February the Madden Julian Oscillation (MJO) stayed in the cold phase 7. So the East Coast had to deal with that big ridge.  I said our winter was going to be a bookend style winter with cold on both ends. Even though February didn't go as expected. My ideas did become reality as we got into March. I had said March was going to see below average temperatures with several chances for snowstorms.  That turned out to be quite true. As of this writing we've had three March nor'easters with the possibility of another around the spring equinox. Most of New York State and New England has seen above too well above snowfall for the winter of 2017-2018.  And we still have time left to add even more snow to the seasonal totals. Parts of Pennsylvania and the Mid Atlantic didn't see much snow until March, so these areas are at average to below average snowfall amounts. Here are some reanalysis images that show how the temperature anomalies worked out. Why talk about a winter outlook, before I post one for Spring 2018? It is to show, that long range forecasting is possible, using a blend of the new and old way of doing meteorological forecasting approaches using analog and pattern analysis.

The Eastern Pacific Oscillation (EPO) was habitually negative this winter. This was one of the main reason winter 2017-2018 was as cold as it was.

The Pacific Decadal Oscillation (PDO) was mostly positive this winter. This helped to keep an active southern storm track.

Anyway enough about the winter. Let's take a look at Spring 2018.

Spring is harder to forecast than winter. But we can still use many of the same techniques to arrive at a general conclusion.

The El Nino-Southern Oscillation (ENSO), NOAA is still saying the La Nina conditions are still present in the equatorial Pacific. But, from the data I've seen, I think the weak La Nina has shifted into neutral, this is ahead of what NOAA had forecasted. ENSO neutral is called La Nada. The surface water temperatures (SST) in ENSO region 3.4 will continue to warm over the next few months. These warm SSTs  and subsurface temperatures will work east.  The other teleconnections are borderline, with some split one way, others are split the other way. The tropospheric (lowest level of the atmosphere) circumpolar vortex (polar vortex or PV) is weaker than normal for this time of year.


Because the PV is weak, a lot of the late spring into early summer heat will be in the South especially in the Southeast US. The weak PV will still allow some of the cold air to our north to enter the northern contiguous United States (CONUS) from time to time over the next few months.


The current pattern will make the rest of March colder than average. We even could see a few days where temperatures are similar to what we would expect for the end of December.

This march has been cold depending on the state you live in, this march has been the 5th-8th coldest on record so far this month.

The MJO isn't going to rotate into the warm phases anytime soon. With all that cold rebuilding in Canada. I think the pattern is going to stay widespread cold in the Great Lakes, Northeast,  and Middle Atlantic Right into the first weekend of April.

We've had a lot of snow this March, so we have a snowpack. The cool temperatures will lead to chances to add to the snowpack. The buildup of ice in the Great Lakes and the replenished snowpack will make it easier to hang on to the colder temperatures longer.  This will have implications as we move into April and even May.


April will see a slow transition to spring like temperatures. But we will see some mild to warm days especially during the second half of April. But, because the large scale pattern is neutral. I am thinking that temperatures will end up being below average overall.  But by the last week of April Spring should be firmly in place.


The same setup that leads to the coolness for March and April, will also be in play for May.  We will see several days where temperatures are seasonal to warm. But, with no real driving factors in play; the slide into Summer will be a slow process.  Overall I think May will be slightly below average to seasonal in temperatures.  


I still expect to see an active storm track.  This should allow for above average precipitation for the Great Lakes into parts of the Northeast for the three month period. This should help keep any drought issues to a minimum into the early Summer. But we do run the risk for flooding; with the Gulf of Mexico (GOM) and Atlantic much warmer than average any storm systems that can tap into that moisture could bring heavy rainfall to the region.  

Severe (tornado) season:

There was a large severe weather outbreak on February 24th. But since then the United States in running below average in the number of tornadoes.  Active severe weather seasons typically occur when colder air hangs on across the northern tier of the CONUS. This is because we have the cool dry air to the north and the warm moist air to the south. When these two air masses interact results can be explosive.  Sometimes this setup can lead to major tornado outbreaks.

There is a coloration between ENSO phases and severe weather. During El Nino we normally see the Jet stream shifted to the south. This blocks moisture from the Gulf of Mexico from moving north. This cuts down on the number of severe weather outbreaks. During La Nina we tend to see more variation and a shift northward of the jet stream. Because the jet is to the north the moisture from the GOM is free to come north allowing for a better chance of a clash between the cold dry air and the warm moist air.  It appears that Spring years that followed a La Nina are at added risk of seeing severe tornado outbreaks; The super outbreaks of 1974, 2008, and 2011 occurred following a La Nina the previous winter. 1953 was a very deadly spring tornado season. 1953 followed a weak El Nino winter. So La Nada could be the culprit, because of the wild shifts in the jet we get during a La Nada phase of the ENSO. Since this Spring follows a weak La Nina we very well could see an uptick in severe weather events contributing to tornado outbreaks.  The PDO could help keep the 2018 severe season from being to explosive. The PDO was negative in 2008, which allowed the storms to dig into the southwest close to that Gulf moisture. If the PDO can stay mostly positive this Spring it would help counter the idea of being in a La Nada. But if it goes negative it would increase the odd that this Spring severe season could be like 2008 or 2011.


Above, Spatial impact of El Nino (left) and La Nina (right) conditions of subsequent March, April, May MAM tornado and hail. Units are number of tornadoes (top row) and number of hail events (bottom row; events as defined in Allen et al,2015) per 1x1 box.

For 2018, I think southern Pennsylvania and the Mid Atlantic will see above average severe weather activity, with the northern Pennsylvania and New York seeing slightly above average severe weather activity.  New England would see average to slightly below average severe weather activity.   

My first thoughts on the 2018 Atlantic Hurricane season:

This year will be active. But, not quite as active as 2017. Because we're in a La Nada, there is a better chance for hurricanes to stay east of the eastern CONUS. So the risk of US land falling tropical cyclones will be less than last season. This hurricane season should end up being slightly above average in the number of Atlantic hurricanes.  10-14 named storms look to be on the table based on what I'm seeing now.