Wednesday, July 17, 2019

JAWS2 Hits--And The Atmosphere is Not Ready to Return to Normal

JAWS2 hit today and precipitation was quite substantial for July.  (Remember JAWS stands for July Abnormally Wet System).  The total accumulation for the last 24 h is found below (click to expand).  Over an inch on the western side of the Olympics and similar values at some locations on the western slopes of the northern Cascades.  Just where we needed the rain.


And the precipitation is not over.   We are in a moist northwesterly flow and over the next 48-h the European Center model shows more rain in the Cascades and lots in British Columbia.  Closer to

Seattle, conditions are right for a Puget Sound convergence zone, that will produce a band of rain from Seattle to Everett on Thursday and Friday.  To illustrate, here is the 24 hour rainfall ending  5 PM on Friday.  Lots in the north Cascades and in the convergence zone band.


Although the worst should be over by late Friday, the atmosphere seems to be stuck in an unusual configuration, with an upper level trough in our vicinity.  To demonstrate this, let me show you the height anomaly from normal at 500 hPa, about 18,000 ft.  Blue indicates lower heights than normal (associated with troughing).  The heights are in the solid lines.

At 11 PM tonight, heights are lower than normal over us and to our north.   To our south, heights are higher than normal.  As a result of this configuration, there is a large change of height with latitude over the region, resulting in much stronger than normal winds from the west.  Not typical July!

 Now there are major changes over the weekend and by Tuesday morning a big ridge builds to our east.  But a very strong and unusual close low is to our west, resulting in strong southwesterly flow over us.  That means no heat wave and a chance for some showers.


In short, next week should bring upper 70s, relatively dry conditions, and nothing that will obviously be a wildfire issue.  British Columbia is soaked--so don't expect a fire outbreak there.   Typical temperatures and no smoke.  Don't feel guilty or worried about the weather--this is when we get pay back for December.

6 comments:

  1. Hi Cliff ! Your chart / map of rainfall in the last 24 hours shows what looks like - .03" of rain here on Whidbey Island. I JUST went out to check my "official" COCORAHS/NWS rain gauge - annnd ... my 24 hr. total for here in Downtown Greenbank is .14" ! LONNNNNNG LIVE JAWS2 !!!

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  2. Very disappointed to have this wet and gloomy July.

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  3. The amount of rain that fell in both Jaws 1 and Jaws 2 was very modest. While this July is experiencing above average amounts of precipitation, it makes little difference in the shortfall since January 1, which remains in the 5" to 15" less than normal for Western Washington. In terms of reduced fire risk, it is a short-term benefit given the general dryness in the Northwest. Any sustained heat and dryness will quickly return us to high fire risk.

    Probably what has influenced people's perception of the weather has been the above average amount of cloud cover for this month, which is considerably above average:

    https://twitter.com/NWSSeattle/status/1151722051868213250

    But even more unusual are nighttime minimums for July in Seattle. While 9 out of 17 days for July have had daytime maximums at or above normal, 17 out of 17 nights have had nighttime minimums above normal, often by fairly large amounts:

    https://www.wrh.noaa.gov/climate/monthdisp.php?stn=KSEA&year=2019&mon=7&wfo=sew&p=temperature

    This pattern is pretty much the same for all of Western Washington, so this is not a Seattle heat island effect.

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