By now you likely know that El Nino and La Nina weather patterns help guide forecasters to make seasonal outlooks. El Nino, a warming of equatorial waters in the eastern Pacific can lead to warm and some what dry winters for the Pacific Northwest. Cooler ocean temperatures known as La Nina can bring wet, cold and active winter seasons to Oregon and Washington.
New research looking at data since 1979 may have found a pre-winter clue that will make forecasting winter weather during an El Nino year a little more certain. For years the rule of thumb has been, the stronger the El Nino, (meaning warmer water temperatures), the higher the forecast confidence for who gets wet and which parts of the country stay dry. New research found a clue amongst the tops of deep convective clouds before winter begins!
Research scientists Ed Harrison, Ph.D. of the NOAA Pacific Marine Environmental Laboratory in Seattle and Andrew Chiodi, Ph.D. of the NOAA Joint Institute for the Study of the Atmosphere and Ocean at the University of Washington looked at El Nino events since 1979 and found a subset of events showing a sharp dip in heat radiating from the tops of deep convective clouds, an indicator known as outgoing long-wave radiation or OLR. When comparing the El Nino events to historical weather records, the scientists found that the El Nino events with drops in OLR were the ones most likely to play havoc with winter weather. The dip in heat from deep convective clouds usually occurred before winter, which means the timing of the signal could help forecasters improve winter outlooks.
During El Nino years, seasonal forecasters will have one more clue to check before making the call for a long rough winter or a short mild season.
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KGW Meteorologist Rod Hill