Surprise Snow!

January 31, 2006

Sticking snow fell around 2-3pm down to at least 1,100′ in the metro area this afternoon.  A classic example of "evaporative cooling".  A dry and cool airmass from the last storm leftover, then moisture from today’s system begins falling into that dry air.  The rain drops evaporate, which takes heat out of the air.  So the temperature falls.  Notice at PDX the temp fell from 47 to 40 from noon to 2pm.  Then as the atmosphere gets saturated we "bottom out".  So as of 4:30pm temps are beginning to rise again.  Snow threat is over and now it’s on to the heavy rain and strong south wind this evening.  Gusts to 40 mph are likely with or just ahead of the cold front passing through around midnight.

Another weak system Thursday, then a rainy one later Friday-Saturday.  What I’m really excited about is a big ridge forecast now by all models beginning Sunday-Monday and continuing through next week.  I can’t wait for the dry and sunny weather!