Got shorts? Seattle crushes record for warmest December day

It seems a bit weird -- normally when you think of setting all time heat records, the sun is shining, clouds are sparse to non-existent, Alki Beach is full of people and Frappuccinos are a top seller.

Not so in Seattle in December

With a downright tropical pattern in place this week already providing some warmth and a mega warm front pushing through the region Wednesday, temperatures got an added boost to levels never before seen in December, despite a thick overcast, drenching rains, and wind gusts reaching 45-50 mph!

Seattle reached a temperature of 66 degrees late Wednesday morning, smashing the all-time record for warmest December day, which was 64 degrees set in 1993. Bellingham also hit 66, breaking their all-time record of 63. Some spots got even a little warmer, with Renton reporting 67 degrees and Seattle's Boeing Field reaching all the way to 68 degrees!

For Seattle, the 66 degree reading means December 10 will go down in 2014 as warmer than six days we had in June.

How do we get so warm without a streak of sunshine or even peek of blue sky? Blame Hawaii.

A very strong and consistent pattern this week has the jet stream steering a plume of tropical moisture from near Hawaii all the way across the Pacific Ocean and into the Pacific Coast. We colloquially call this a "Pineapple Express" due to its Hawaiian origins but the more technical term is called an "atmospheric river".

You can see in the image above that shows the current moisture plume -- note the reds and purples showing high moisture values pushing right up against the Northwest.

So that not only brings the rain, but much warmer air. On Wednesday morning as a storm riding the wave moved into our region, the storm's warm front brought up a surge of even warmer air from the south, pushing temperatures well into the 60s -- no sun required.

In fact, the all-time December record we just broke -- also coincidentally on December 10th, just in 1993, also didn't require any sun -- the record was set at 3 a.m.! It too was a warm front/Pineapple Express but a cold front then came through and by the time people woke up around 8 a.m., it was already back in the 40s.

Making this year's warmth extra special was the strong winds that came along for the ride, helping to usher in that warmer air. Seattle hit a gust of 46 mph while Gig Harbor hit 56!

Here is a chart showing the zany heat/wind combo Wednesday morning. The peak gusts may have been offset from the max temperature reached:

** All time December high temperature

The record warmth will also clinch 2014 going down as the warmest year on record by overall average temperature and by average low temperature at Sea-Tac Airport. Still an outside chance at record by average high temperature if this warmth keeps up!

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