March 19, 2019

The Warmest Winter Day in Sea-Tac History, But a Tie for Seattle

Yesterday reached an amazing high of 76F at Seattle-Tacoma Airport, an extraordinary contrast to the frigid temperatures of only a month ago.

But there is more:   That 76F was the warmest winter (Dec. 21-March 21) temperature ever observed at the airport, in a record that goes back to the late 1940s.

But before we get too puffed up with thermal pride (or worry), it should be noted that the same winter high (76F) was observed on March 19, 1928.  So we only tied the record.

Today we might beat it.

A plot of the temperature at Sea-Tac versus normal highs and lows for the entire winter (below) illustrates the amazing thermal surge.  Through Feb 1, our temperatures were a bit on the warm side, but then the bottom dropped out as we entered the freezer.   Below-normal temperatures reigned through early March, and then the thermostat was suddenly turned up.
Another plot shows Sea-Tac daily high (purple) and low (cyan) temperatures against the daily RECORD high (purple dashes) and lows (cyan dashes).  Yes...we clearly beat the all-time winter record at Sea-Tac.
Why are we so warm? 

Everything had to be just right to do this.  We start with a very strong upper level high centered over southern BC and a trough offshore of California (see upper-level (500-hPa) map for 2 PM Monday).  This configuration is associated with warm air over the region and easterly (offshore) flow.  An unusual pattern.

The easterly flow is very important, since it produces downslope flow on the western side of the Cascades that warms the air by compression (as the air moves from low pressures aloft to higher pressures at low levels).   Just like your bicycle pump.

A plot of winds and temperatures  with height above Sea-Tac for the past day shows powerful easterly flow, reaching 30 knots.   That is strong.  Every major heat wave in late winter and early spring I can remember is associated with strong easterly flow...and this one is no different. (time increases to the left and is in UTC, heights are in pressure--850 is roughly 5000 ft)

With warm air and easterly flow just above the surface, expect a surge in temperatures today, as surface heating and associated mixing taps the warm air aloft.  Some locations near the Cascade foothills will get very near 80F.


  1. Actually,yesterday's reading of 76 at Sea-Tac tied for second place with 1928.It was 81 on March 11,1892 at the original weather station on First and Yesler in Downtown Seattle.

  2. Interesting 71 degree reading at Sea-Tac at 11am.Normally,during the warmer months of the year,the daily max temp ends up at least 11-13 degrees higher than the 11am DST reading.Low 80's today? Unlikely,but the all time March record max of 78 may be equalled or surpassed today.

  3. Here is what I think about this warm weather. I feel good . . .

  4. 80 degrees at seatac according to the times. My understanding is that this is all because polar amplification is causing the jet stream to weaken and wobble, causing wild temperature swings. Is that right, or is this all normal and not because of climate change?

  5. 69.6F this afternoon in NW Bellingham after a morning low of 31.9. 37.7 degree diurnal range!

  6. It was 82 degrees F in N Seattle and Shoreline along Aurora Ave N (Hwy 99) today, during ~1505-1520 PDT, according to my govt agency Prius car thermometer. The temperature dropped to 81 degrees F in S Snohomish Co during ~ 1520-1528 PDT. I observed evidence of ~ E winds (moderate).

  7. If the 59 degree minimum at Sea-Tac holds up,today will be the first time a cooling degree day(temp avg 66 or higher)has occurted in winter or the month of March.Also,it should be noted that today's average temp will be 22 degrees above normal.This may be the,or one of the, greatest departures from normal on any given day( for above normal temps) in The history of Sea-Tac.

  8. For a post about local trends since the 1940s, why are graphs featured that only go back to 2018? I'd love to see some longer-term temperature plots for Sea-Tac, for more perspective. Anyone care to share a link to your favorite Seattle area, long-term temperature plot graph?

  9. I wonder if there will ever be a posting here without at least one comment regarding whether or not it's due to AGW. Doesn't matter if it happens to be cold or warm, there must be a correlation, somehow, some way. Freud said that sometimes a cigar is just a cigar.

  10. @Eric Blair - with increasing global temperatures affecting atmospheric circulation and increasing extreme events, why would you want to have posts to a weather blog not reference a major forcing factor for weather events. That seems like a strange thing to wish.
    And search on "polar vortex" and "cooling" if you want to understand how global and arctic warming can cause lower latitude cold.

    It does matter "if it happens to be cold or warm" and record high (warm) temps are now far more common than record lows. You, and other readers of this blog, might find the content at this link educational

  11. John Franklin - by all means it's a subject worthy of discussion, but every freaking day? It borders on a compulsion with some folks. If Dr. Mass brings it up (as he often does, in case you haven't noticed), then of course.

  12. @ John Franklin

    Yes, Cliff has blogged about the trend of increasing number of record highs versus record lows but questions like "is this all normal and not because of climate change" imply that the current weather pattern over a short period of time (a few days) can be identified as "normal weather" or "a result of climate change". Climate change can be forecast as a future issue or looked as a past trend but current weather can't be lumped into an either/or category (it can be both though).

    With and without climate change, there will always be records; someday we may never see another record low as the trend continues up.

  13. Eric Blair - you could always just blow on by those comments but noooo - you have to protest and thus bring attention to them. You make me laugh!
    “We are what we are because we have been what we have been.”
    ― Sigmund Freud


Please make sure your comments are civil. Name calling and personal attacks are not appropriate.

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