Meteorological spring is only hours away.
The scientific community considers March 1st through May as the spring season. The National Weather Service is calling for cool -- meaning below normal temperatures -- and gives little confidence of projected precipitation.
The national map would suggest increased confidence toward normal to slightly below rainfall averages over the next three months. The "EC" areas represented on the maps, refers to equal chance of above or below normal trends.
"A" stands for above normal and "B" blue shades areas are below normal. Note that the precipitation outlook map has much of the West and Southwest in a dry pattern. The temperature map above shows a hot spring for Texas and much of the East.
Portland is coming off of three consecutive wet springs with all three years featuring at least one top 5 wet record month, including the wettest March on record at PDX in 2012 when 7.89 inches of rain fell. 2011 featured the 3rd wettest April at PDX and 2010 recorded the 3rd wettest May and a new record wet for June with 4.27 inches of precipitation.
I think it is safe to say, many of us are hoping for a somewhat normal or even dry spring. The last spring to see March, April and May all have below normal rainfall was 2007.
The so called "Enso" state of the atmosphere, which is the tracking of La Nina and El Nino conditions shows a neutral to very weak La Nina holding into early summer.
Developing El Nino conditions may begin to take hold early next fall. I looked at the last 10 years of data for Portland and found a strong correlation between temperatures and El Nino and La Nina episodes. Nine of the last ten years show a positive correlation when looking at temperature.
Nearly all warm Enso springs showed above normal temperatures and nearly all cool Enso patterns show below normal temperatures.
The findings would support a somewhat cooler than average spring this year. However, when looking at rainfall totals, the data is split nearly 50-50 percent, meaning zero confidence for projecting spring rainfall.
The conclusion for our March through May spring outlook is the following: Expect temperatures to average slightly cooler than normal. Rainfall will likely be near normal with a greater chance of averaging dry than wet over the three months.
Current forecast charts show below-normal rainfall through the first half of March.
No sharp transitions of weather pattern due to a change of equatorial water temperatures that drive El Nino and La Nina are expected through this summer. If true, we should expect somewhat normal and pleasant Northwest weather in the months ahead.
KGW Meteorologist Rod Hill
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