The Calendar Says Spring...

Good evening everyone!  The calendar says Spring, and in fact the new season got underway this morning.  However, this post will attempt to explain why we are not seeing spring like weather as winter still has a firm grip on a large part of the country. 

The main cause for the winter like weather is due to the AO and the NAO both being severely negative.  The AO is the most negative that we have seen in a long time and for late March, it is the most negative that we have seen since record keeping began!  The index value from yesterday came in at a whopping -5 and it could bottom out at -6!  The AO when in a negative phase causes the polar vortex to be displaced to the south, along cold, arctic air to invade the Lower 48.  With the NAO also being very negative, the cold pattern has been able to stick around for a while.

Here is the forecast for the AO for the next two weeks as predicted by the GFS Ensemble Model from this afternoon's 12Z run.  *Image courtesy of Allan Huffman*

As you can see, the model shows the AO finally rising to positive values by the time we get into April so we could see a bit of relaxation in the cold weather by then.  Next, let's take a look at the NAO.  It has also been very negative but the various computer models do show a tendency for it to rise as well from this afternoons 12Z run.

*Image courtesy of Allan Huffman*

Based on these two teleconnection indices, we should see a little warmer weather ahead.  I do think, however, that we won't see significant changes until we get into April a little bit as far as above normal temperatures go.  But once we do see some warmer air move in, severe weather will become a concern and I will have more information down the road for you on that, once we get closer.

The 12Z GFS Ensemble Mean shows the cold pattern nicely through the end of March as you can see in the image below.

As you saw earlier in this post, that when the AO and NAO rise I mentioned that the pattern should turn a little bit warmer.  Well, let's take a look at the GFS Ensemble Mean for the 11-15 day period.

The pattern does not look at cold as it has been.  You can see the blocking as weakened and the large, cold trough has lifted out of Ohio.  This will be a slow warming trend once we get into April and the GFS Ensemble Mean clearly shows this. 

In conclusion, look for the winter like pattern to continue through the end of March with a slow moderating trend as we get into April.  Severe weather season is coming and I will alert you to that threat as conditions warrant.

Lester Rhoads
Ohio Weather Blog
Long Range Forecaster