I’m amazed at the repetitive nature of the subseasonal forecast as of late. Since early March, it seems we’ve been on a regular cadence between warm and cold across the Lower 48. Granted, the timing hasn’t been exact, as there are some transition days between the swap, but given the fact that there is no definitive forcing from a strong El Nino or La Nina, the pattern is allowed to oscillate with somewhat reliable predictability.
Shown above is the animation of the latest sea surface temperature (SST) anomalies. Note that initially the Eastern Pacific was trending toward an El Nino state. However, just over the last two months, it scaled back, and SSTs are now favoring a neutral state – what some commonly refer to as La Nada.
Forcing is coming from the tropics, but not from ENSO (El Nino Southern Oscillation). It’s driven by the MJO, which is cast on a background of the repetitive pattern that we are highlighting. Thing is, the MJO is in a weak phase right now:
with magnitudes on the order of -1, as its remains bogged down in the Indian Ocean.
So if we allow the simple warm/cool pattern to continue, the East will be warming in the short term, while the West (Washington and Oregon specifically) cool down. Carrying that a few steps further, the East will see another brief cool down just before the middle of July, before it heats back up after the middle of the month.
The west is an entirely different beast. The models keep suggesting searing heat will return just after the middle of the month, but the period leading up to that isn’t suggestive of a huge warm up:
My concern is that cool blob of blue (air) in Alaska. Given the progressive nature of the warm/cool pattern, it would seem that would be poised to drop into the West and foil the warm up after mid month. This fits our warm East scenario nicely as well, since in order for the East to warm, the West typically cools down.