Was record March “Warm Wave” predictable?

90+ cities set records for the warmest March ever in 2012

“We will also demonstrate, using seasonal climate forecast models, that the circulation pattern and the associated heatwave was remarkably predictable at long lead times, from initial atmospheric conditions at about 1 February 2012. This fact also gives important further clues on the leading processes responsible for the heatwave. Importantly, the meteorological conditions associated with the heatwave had an appreciable, and perhaps unusual, long-lead predictive element.”

-NOAA’s Environmental Systems Research Laboratory on the predictability of the record March 2012 heat wave.

NOAA’s CPC called for above average temps in March 2012 in the Upper Midwest. But how well could we have predicted the magnitude and coverage of the record March 2012 heat wave?

An eye opening report from NOAA’s Earth Systems Research Laboratory says there were signs that could have better predicted our “off the charts” March this year.

Here are some excerpts from NOAA’s report.

1. What were the meteorological conditions associated with the heatwave?

“It is first useful to place the heatwave into a Northern Hemisphere context (Fig. 1). The heatwave was clearly regional in scope and was not part of a pervasive hemisphere-wide warm regime. Rather, widespread cold conditions at the same time occurred over the western U.S., western Canada, Alaska, eastern Asia, and southeast Europe.”

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Figure 1: Map of Northern Hemisphere temperature anomalies averaged over the period. Anomalies are calculated relative to the period 1981-2010.

[Data Source: NCEP/NCAR Reanalysis]

“The very warm air first pushed northward west of the Great Lakes region, and subsequently spread eastward. This synoptic view is consistent with structural aspects of the atmospheric circulation, shown in the Physical Processes section, that reveal intense poleward air mass movement propelled by an unusually intense low level southerly jet that stretched from Louisiana to western Wisconsin. Once this warm surge inundated the area, a remarkably prolonged period of record setting temperatures ensued. These time series thus identify a core period of the maximum heatwave intensity that spanned roughly 12 March thru 23 March, a period for which we will perform various time averaged analyses.”

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One interesting finding in the report is that it appears that the warm air surge drove the erosion of snow cover from the Upper Midwest in March…not the other way around.

In other words, the lack of snow did not cause the warm up…the warm air surge from the south caused the snow to disappear!

15 warm surge.gif

15 March sc anim.jpg

Climate Change signal?

Did climate change and greenhouse gasses play a role? According to the report, GHG may have increased the likelihood of a record event by anywhere from 5% to 10% over the “background” warming trends already in place at the time.

3. Was this extreme March 2012 U.S. heatwave event anticipated?

“Here we explore the evidence for a substantial human influence on the March 2012 heatwave, both on its magnitude and on the probability of such an extreme event occurrence. There is no doubt that there exists an influence of human-produced greenhouse gases on evolving weather and climate conditions, as the IPCC reports have clearly enumerated. Yet, while acknowledging that climate change plays a role in every weather event begs the issue of the direction of that impact and the magnitude of its effect. Unfortunately, when claims are made that a event “would not have happened without human produced greenhouse gases”, the incorrect conclusion is all too often drawn by the public and media that an event was caused, in some de novo manner, by human climate change. The pitfall of such framings is apparent from the well-known nature of chaotic weather and climate systems. In that paradigm of a nonlinear system, no event today or tomorrow would have happened owing to the smallest flap of a butterfly’s wings. But is there any predictability, and in particular, could the March 2012 heatwave have been anticipated?”

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“The sudden change in location and in magnitude of warming, as anticipated by February initialized forecasts ,reveals the role of an emerging state of internal atmospheric variability. This change is irreconcilable with changes in GHG forcing whose time scale is far too long, and whose influence would have been very similar in the prior initialized forecasts. What is also striking is that the 40-run ensemble mean magnitudes were on the order of +4°C for the monthly March average, which equates to about 2 standardized departures in the forecasts. One can repeat the analysis of how such a magnitude signal (in this case, the signal of the climate prediction rather than the projection) altered the odds for a 2 standardized (i.e. ~4°C) March heatwave. Such a major shift of the distribution in the CFS implies a roughly 10-fold increase in the probability of such a heatwave occurring.

In sum, the initialized forecasts possess many of the essential attributes of what crime scene investigators would look for in pinning a crime (the heatwave, in this case) to an individual (a physical cause, in this case). The forecast models give probable cause, namely that a particular atmospheric initial condition – emergent sometime in early February – led to a high probability outcome in the form of a large magnitude March heatwave. The sequence of forecasts allows one to largely reject other probable and immeditate causes for such a large magnitude event. For example, the GHG conditions that were known to be operative in prior months, had failed to predict or project an outcome of the magnitiude that was eventually observed. The forecasts further identify this particular culprit because those evolving internal atmospheric initial conditions yielded the precise location of the heatwave, at precisely the particular time of its occurrence, and with a high confidence of exceeding prior record heatwave magnitudes.

Epilogue

A black swan most probably was observed in March 2012 (lest we forget 1910). Gifted thereby to a wonderful late winter of unprecedented balmy weather, we also now know that all swans are not white. The event reminds us that there is no reason to believe that the hottest, “meteorological maddest” March observed in a mere century of observations is the hottest possible. But this isn’t to push all the blame upon randomness. Our current estimate of the impact of GHG forcing is that it likely contributed on the order of 5% to 10% of the magnitude of the heat wave during 12-23 March. And the probability of heatwaves is growing as GHG-induced warming continues to progress. But there is always the randomness.”

The bottom line?

Greenhouse gas “loading” of our atmosphere makes it more likely that more record heat waves will occur. Initial conditions leading into March suggested that a heat wave was more likely, but even the most extreme forecasts did not predict the magnitude of last month’s record event.

This paper strikes me as important because if we can latch on to those signals that caused the March heat wave…we may be better able to predict future extreme weather events.

PH

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