I hate to be the bearer of bad news, but if you’re a warm weather lover in the Eastern US longing to slide right into that summertime feeling as we enter the month of May, you’re out of luck. It almost seems like we used up all of our warm days during the winter/early spring and are paying for it now with a continued chilly, rainy pattern.
As we discussed last week, high latitude blocking (-NAO), continued western ridging (+PNA), and a still-negative AO are working together to keep the Eastern US cooler and stormy.
This pattern remains firmly in place into next week. Further, it will deliver yet another shot of unseasonably cold air to start the new week.
Ugly, isn’t it?
Meanwhile, lingering ridging over the Western US will allow temps to soar significantly above average for many. After the winter they’ve had though, they kind of deserve some warmth.
If you’ll glance back at the 500 mb heights anomaly map at the beginning of the blog, you’ll notice that as the week wears on, the pattern begins to change some.
- Ridging over the West (+PNA) begins to break down and is replaced by troughing.
- High latitude blocking west of Greenland persists (-NAO), but then strengthens while moving further westward.
This leaves us with troughing in the West, strong ridging centered over Northern Canada, and troughing in the East.
This pattern is known as an Omega Block (due to the way it resembles the Greek letter Omega). It consists of an area of high pressure flanked by an area of low pressure on both sides.
What does a pattern such as this produce in terms of sensible weather?
- Those under the ridge generally experience sunny skies and warmer-than-average temperatures.
- Those under either of the lows generally experience prolonged periods of cooler, unsettled weather.
Unfortunately for those under the influence of the lows, this type of blocking can be stubborn and slow to clear out.
That seems to be the case for this particular forecasted block. Using temperature anomalies, we can see the signal I mentioned develop and linger before moderating some toward the middle of May. Yes – the middle of May. A whole two weeks away.
Both the EPS and GEFS have similar solutions at the moment. But can the block clear out faster? It’s possible. It could also linger a bit a longer. Right now though, based on ensemble guidance, mid-month seems like a good guess at when we’ll see our next big pattern change.