A Warm Ridge

January 14, 2009

Snapshot  The weather may be boring, but for those temperature freaks, lots to talk about!  A very strong valley inversion has developed across the Pacific Northwest.  As you can see from the image, some spots in the 2,000-4,000' range made it close to 70 degrees today while the valleys sat in the 40s.  The layer of cold air is pretty shallow and has become a bit shallower this evening.  I see the temp on our tower at 1,800' has jumped to 60 degrees at 10:45pm. 

     This is all being driven by a strong upper-level ridge centered over SW Oregon.  Nothing changes the next few days except the center of the upper-level high moves north over Washington by Saturday afternoon.  850mb temps are astounding for mid-January.  They peak out in the +16 to +18 deg C. range.  For kicks, I pulled out the warm season "magic charts" for May and March.  For one, there are no temps that warm for the month of March.  For May, those temps plus easterly wind would get us up to about 90 degrees here in Portland!  So then you might think "we're going to get east wind the next few days, how come the warm air doesn't mix down?".  Well, between now and late February, the east wind is coming in through the Gorge BELOW the inversion top.  It's just bringing in cool air from east of the Cascades, not mixing down warm air from above.  This generally makes forecasting high temps at PDX simple in east wind events in the dead of winter (now).  Except for maybe the 1st day the wind arrives, you can add about 10 degrees from the DLS high to get the number.  Better to remember that in January you're not going to get much above 50 degrees on a good east wind day (except for maybe that 1st day).  45-50 is most common unless/until a good cold pool develops eastside.  I don't see that this time around, so I kept high temps at/above 45 degrees through early next week.

Looks like the surface high is now strengthening quickly in the Intermountain region.  The PDX-DLS gradient has gone from around 2 millibars late this afternoon to about 6 millibars now.  The wind hasn't made it to the Troutdale airport yet, but I would guess it's started blowing a bit up above in "upper" Troutdale and Gresham.  If not, it'll arrive soon.  6 millibars is enough to push wind all the way to downtown Portland by tomorrow afternoon.  With lower dewpoints spreading across the metro area, I have a feeling that tonght's patchy areas of fog will be the last until sometime early next week.  Lots of sunrises and sunsets will be seen from the Portland Metro area through the weekend!  Mark Nelsen


A Warm Ridge

January 14, 2009

Snapshot  The weather may be boring, but for those temperature freaks, lots to talk about!  A very strong valley inversion has developed across the Pacific Northwest.  As you can see from the image, some spots in the 2,000-4,000' range made it close to 70 degrees today while the valleys sat in the 40s.  The layer of cold air is pretty shallow and has become a bit shallower this evening.  I see the temp on our tower at 1,800' has jumped to 60 degrees at 10:45pm. 

     This is all being driven by a strong upper-level ridge centered over SW Oregon.  Nothing changes the next few days except the center of the upper-level high moves north over Washington by Saturday afternoon.  850mb temps are astounding for mid-January.  They peak out in the +16 to +18 deg C. range.  For kicks, I pulled out the warm season "magic charts" for May and March.  For one, there are no temps that warm for the month of March.  For May, those temps plus easterly wind would get us up to about 90 degrees here in Portland!  So then you might think "we're going to get east wind the next few days, how come the warm air doesn't mix down?".  Well, between now and late February, the east wind is coming in through the Gorge BELOW the inversion top.  It's just bringing in cool air from east of the Cascades, not mixing down warm air from above.  This generally makes forecasting high temps at PDX simple in east wind events in the dead of winter (now).  Except for maybe the 1st day the wind arrives, you can add about 10 degrees from the DLS high to get the number.  Better to remember that in January you're not going to get much above 50 degrees on a good east wind day (except for maybe that 1st day).  45-50 is most common unless/until a good cold pool develops eastside.  I don't see that this time around, so I kept high temps at/above 45 degrees through early next week.

Looks like the surface high is now strengthening quickly in the Intermountain region.  The PDX-DLS gradient has gone from around 2 millibars late this afternoon to about 6 millibars now.  The wind hasn't made it to the Troutdale airport yet, but I would guess it's started blowing a bit up above in "upper" Troutdale and Gresham.  If not, it'll arrive soon.  6 millibars is enough to push wind all the way to downtown Portland by tomorrow afternoon.  With lower dewpoints spreading across the metro area, I have a feeling that tonght's patchy areas of fog will be the last until sometime early next week.  Lots of sunrises and sunsets will be seen from the Portland Metro area through the weekend!  Mark Nelsen