October 10, 2009

Tomatoes Beware! and the Importance of 2 meters


There was more clouds last night then originally predicted and they should hold in much of the area today. With the clouds intercepting and radiating infrared radiation back to the surface, temperatures held up overnight in the 40s over much of the area.

Tonight (Sunday AM) should be different with clearing skies and unusually cool temperatures aloft there will be good radiational cooling. Working against that will be the significant offshore pressure difference, which can keep some wind going in exposed areas. Wind causes mixing which helps stir up cool air near the surface. But sheltered valleys away from water could drop into the 20s tonight...and tomatoes don't like it. Below are two maps showing the low temps tomorrow morning. The first from probcast (www.probcast.com), the UW probabilistic prediction system and the other a straight forecast from our high-resolution WRF numerical forecast model. Cool away from the water, over the SW Washington interior and eastern WA.

Another pulse of cool air hit E. WA tomorrow..and that is when they will get some dust if they get any. This is really a marginal dust event.

Finally, keep in mind that surface air measurements shown on the web and TV are NOT at the surface, but at 2 meters (roughly 6 ft). On cold, calm nights it can be much cooler at the surface than 2 meters...perhaps 2-5F cooler. So keep that in mind while driving. And your car thermometer has the same issue (although it is measuring more like .5-1 meter above the surface).

6 comments:

  1. This seems like a pattern we get later on in the winter with high pressure offshore resulting in cloudy conditions east of the mtns and sunnier on the west side of the cascades with a east wind at locations like Troutdale. Off to Hood River on Monday to ride the track speeders on the MT Hood RR.

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  2. A couple of the vintners I spoke to in the Yakima Valley today have been up all night getting the grapes in before they freeze.

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  3. Cliff,

    Can you give us any information on the potential for a strong windstorm on Tuesday? I know it will be determined by the storm track, what does the current track look like? NOAA says 975mb, which would be a pretty deep low. Interesting that it would come just a day after Columbus day and would also be strengthened by the remnants of a typhoon.

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  4. From East Bellevue 1:10 am

    2 meter temp (Oregon Scientific pro weather station) 44.1F
    Cheap thermometer hanging from a bush 3" from the ground 38F

    So still well above frosty here. Thank goodness, I didn't get to attend to the garden today like I wanted to!!

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  5. Made it up to Spray Park in Mt. Rainier on Sunday. Cold, but not unpleasant, in the 20s though. At times it felt warm, especially when the sun was out, which was most of the time. We could see Mt. Baker and Glacier Pk, clear as a bell.

    Absolutely NO wind, even up at 6400ft which was our high point. The silence was awesome. Glad I got that hike in before this week!

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  6. Pressure at the house hit 20.199 in. which is just 0.01" shy of the record for the year (29.187, March 15).

    ~250 ft elev

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