Rain Shadow Winds

During the past times twenty-four sixty minutes catamenia or 2 in that place possess got been moderately rigid southerly winds over the fundamental together with southern Sound.    We possess got been cloudy, merely amongst really petty rain. In fact, this is approximately of most cloudy weather condition together with the lowest solar radiations nosotros possess got e'er experienced inward March when it was non raining.

 In contrast, winds on the coast possess got been westerly together with its been much wetter there, equally has been the illustration inward the Cascades.

What is going on?   The answer:  H5N1 profound pelting shadow over Puget Sound, together with what I telephone holler upwards rain shadow winds.  H5N1 novel term to add together to the western Washington weather condition lexicon.

Let's starting fourth dimension past times looking at the winds inward Seattle (at the UW) for the terminal 3 days (ending noon today).  The 2d panel is current of air direction.  We possess got been stuck inward southerly flow.  And for over a twenty-four sixty minutes catamenia the current of air speeds possess got been nearly unchanged... gusting to 10-15 knots. Virtually no pelting for the period  (.01 inches)

The winds aloft along the coast possess got been persistently from the westward (westerly) to southwest inward the lower atmosphere, something indicated past times the radiosonde soundings at Quillayute on the Washington coast.  H5N1 sounding at five PM yesterday shows this (below). The current of air barbs are inward bluish together with heights are inward damage of line per unit of measurement area 850 is nigh 5000 ft.  The winds were westerly at 10,000 ft (700) together with southwesterly below.

With westerly together with southwesterly current inward the lower atmosphere, the air rose on the western sides of the Olympics together with coastal mountains, producing precipitation.  But thus it sank over the eastern side, producing warming together with a pelting shadow over fundamental together with western Puget Sound.   And thus it rose i time to a greater extent than on the western side of the Cascades producing to a greater extent than precipitation.  

The NOAA atmospheric precipitation full for the 24h ending five AM this morn shows this atmospheric precipitation pattern.

And the sinking air together with pelting shadow were fifty-fifty evident inward the visible satellite imagery this morn (see below).  Small rain/cloud shadow to the due east of the Olympics, big i to the due east of the Cascades.

How does this all explicate the relatively steady southerly winds from roughly Lynnwood to the S Sound?

With rigid southwesterly/westerly current approaching the Olympics, in that place was substantial sinking on the eastern together with northeast sides of the barrier.  Such sinking causes warming past times compression together with warm air is less dense than mutual coldness air.  Less dense air results inward lower line per unit of measurement area to the lee of the barrier. 

H5N1 forecast of body of body of water score line per unit of measurement area (solid lines) together with winds from the WRF model, valid 2AM this morn shows this pattern--with a lee depression or trough of depression line per unit of measurement area due east of the Olympics.  South together with southeast of the depression in that place is a relatively rigid north-south line per unit of measurement area slope because of the lee low, together with that divergence inward line per unit of measurement area drove moderate southerly winds.

The bottom line:  in that place is a straight connectedness betwixt the pelting shadow together with the rigid southerly winds, amongst both forced past times sinking on the lee (eastern) side of the Olympics.

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Announcement:  The Northwest Weather Workshop is on Apr 27-28

The NW Weather Workshop is the principal annual coming together for those interested inward Northwest meteorology.  This yr nosotros volition possess got a major session on the meteorology of NW wildfires together with others on other aspects of our regional weather.  The gathering takes house at the NOAA facility inward Seattle.  To stance the agenda together with to register, larn to the meeting website.  The workshop is opened upwards to everyone, merely registration is required.
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