Tuesday, February 21, 2017

Will Cold Air Return After the Late February Warmth?

The stubborn southeast ridge threw a wrench in our winter temperature and snow outlook for Cleveland and the Ohio Valley (more on that next week). We anticipated it to stay further east It has remained very strong throughout winter driving many panhandle low type storms along with temperatures recently to levels only reached a few times since record keeping began in 1871.

The stretch of warmth in Cleveland will more than likely end up being the warmest 11 day winter stretch ever!  This February stretch is similar to a warm February stretch back in 1976 and 2000. Notice the widespread nature of the warmth back in those years.

Looks similar to this stretch...

Yet California keeps getting pounded with heavy rain/snow as the very strong Pacific jet stream continues. Reanalysis of vector wind anomalies at 300 mB since December 1st (3 day running average). Pacific jet is through the roof strong. No sign of the ominous western ridge which was dominant over the last several winters.

The MJO strength increased significantly since early February to very high amplitudes into Phase 6,7 and 8 territory.

Phase 7 and phase 8 in February with high amplitudes tend to favor warmth east. Yet look at Phase 8. It tends to favor cooler temperatures east (middle chart below). So even with a very strong MJO the temperatures can be highly variable. What I find interesting is that the Phase 1 temperature composite (far right map below) looks very similar to the overall pattern since this current warm up began.
The chances of this February finishing out as the warmest ever in Cleveland is climbing fast.

Will colder air return?  If so, how strong?

To answer this we look at the Pacific teleconnections to start March. I reference my quick cheat sheet so that I can visualize the pressure regions in question.

PNA is heading sharply negative
EPO is heading positive/neutral
WPO is heading negative (strongly negative)

Strongly negative WPO during the first week of March
What do these teleconnection levels mean for our sensible weather?  Historic temperature composites for each of these indices (PNA,WPO,EPO) in March mean below normal temperatures across the northern states centered over the Corn Belt and High Plains. The Computer models are also depicting colder air (see graphic below, lower left) centered across the upper midwest/west to start March with above normal temperatures across the eastern US and deep south.

While we should anticipate short-lived cool intrusions across the Great Lakes, temperatures overall will average out near the 30 year average (see lower right graphic) for the first week of March.  For Cleveland, daytime average high temperatures for March are in the lower 40s. 

Long range teleconnections for the middle of March show some colder signs centered central US and west. Something to watch over the next week.

The South Oscillation Index (SOI)--changes in the pressure patterns in the tropical Pacific Ocean (click here for more on the SOI and here)--shows rising pressure in the central US March 10-13th after the central US trough slides east March 7-9th.

Will the weak trough be a more permanent feature over the Great Lakes or will a warmer ridge develop by the 3rd week of March?  The answer will be apparent in both the SOI changes. The teleconnections will reflect the changes by the end of next week.

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