Sunday, April 6, 2014

Long Range Outlook for April 2014

Today's post will look at the expected weather pattern for the month of April, 2014.

We currently see tropical forcing located over the Indian Ocean, specifically southeast of the subcontinent of India. This forcing is associated with a convectively-coupled Kelvin Wave (CCKW), which will begin progressing east in future days. Currently, the placement of the CCKW supports cooler than normal weather, which we have been seeing recently, and should continue to see in the next few days, probably into about April 9th or 10th.

Specialized maps from the Australian Bureau of Meteorology indicate we will see this CCKW push east in coming days, taking the tropical forcing with it into a pattern that should bring more seasonal, possibly even above normal temperatures to the United States.

Typically, when we see enhanced tropical convection entering the western Oceania region, we tend to see the weather pattern favoring warmer than normal weather in the United States. On the Madden-Julian Oscillation scale, this would mean movement into Phases 5 and 6.

500mb height anomalies for Phase 5 MJO events in April (left)
500mb height anomalies for Phase 6 MJO events in April (right)

Temperatures for March-April-May for all eight MJO phases
If we take a look at mid-level height anomalies for MJO Phases 5 and 6, as well as temperature anomalies for phases 5 and 6, we see that the pattern decisively supports seasonal to slightly above normal temperatures. Even though it won't be a Madden-Julian Oscillation wave going into western Oceania, the tropical forcing from the CCKW should suffice to bring about these seasonal temperatures.

Despite this, a recent spike in East Asian mountain torque anomalies means we're likely to see those warm temperatures dampened a bit. In the winter, positive East Asian mountain torque values indicate the perturbation of the upper Arctic, and these +MT events can bring about sudden stratospheric warmings. In this specific case, though, we can just expect those warmer temperatures to be tempered some by this positive mountain torque event in East Asia. These warm CCKW-induced temperatures should come about in the general mid-April timeframe, but again, watch for cold shots in response to the positive East Asian mountain torque in the not-too-distant future.

Moving along, we can look ahead into late April by examining outgoing longwave radiation (OLR) plots from Paul Roundy at Albany. Looking specifically at the bottom plot, valid for April 20th to 27th, we see strong negative OLR anomalies (enhanced tropical convection) present in western Oceania, the same place where the CCKW is expected to travel in just a couple days. If this chart is to be believed, we may expect seasonal to warmer than normal temperatures for the end of April, as these negative OLR anomalies are in the typical Phase 5 and 6 MJO phases, which, as we looked at above, bring about warmer than normal weather in the US.

To sum up, here is a graphical representation of expected temperature anomalies across the month of April.


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