Posted: 7:03 am Friday, March 30th, 2018
By Kirk Mellish
For months on Twitter and here in this blog I’ve been covering how warm spells would come but with periods of below-normal temperatures in-between.
So far most signals support this pattern continuing through at least the first week or two of April.
However, the signals are starting to become more mixed beyond that.
Its been a see-saw past 90 days:
This time of year the negative North Atlantic Oscillation (-NAO) is a primary driver for temperatures. It does not show signs of going positive anytime soon:
In the Spring a negative NAO will often allow for cool snaps even in the face of warm signals from other less dominant teleconnections.
In fact the European model Ensemble wants to keep the pattern of up and down into the start of May, with warmth to hold to follow that.
The American CFS2 model has trended cooler for April from what it showed at the start of March:
But as in all things weather, there is never just one factor at work influencing trends.
The Madden Julian Oscillation (MJO) in the South Pacific Ocean impacts the Jet Stream patterns and thus temperatures and moisture. It’s expected to move around from phases 7 to 2 through April 11th:
The precipitation correlation varies with the temperature it goes wet, dry, wet, dry between now and April 11th or so.
The swings will bring above normal precipitation back to the region by the second week of April, while temperatures continue to bounce around.
That’s fine with me as I don’t want severe weather and I hate it when we jump right from winter to mid-summer level heat as we do so often in these parts.
I disagree with the ECMWF and GFS Ensembles on a snow dusting in Atlanta as of now.
As the MJO gets to Phase 2 by the 10th or so the jet stream starts to extend from the Pacific trying to fight off the -NAO resulting in a trough out west:
That would favor warmer after that, and IF it holds and the -NAO fades would be the death knell for any remaining winter.
10% ( twice as much as normal) of the Phase 2 MJO in March-May have tornado outbreaks, especially to our North and West but to some extent in the Southeast.
However, the pattern looks transient and past attempts by models to change the regime to full-on spring warmth have failed, so grain of salt for now.
16-day temperature anomalies GFS Ensemble:
Meanwhile MARCH has been normally wet in North Georgia but dry in most of the state, with cooler than normal temperatures:
Moderate to severe drought South of Metro Atlanta:
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