Day 3 of Olympia, WA (KOLM)

Winds calmed down last night as expected (just in time for a 30F low for day 1) and even down to 21F this morning! That is pretty much the coldest spot in the whole area – this site really has strong radiational cooling. However, the nocturnal inversion is quite shallow, and with full sunshine for most of the day, it quickly warmed up. But despite little wind and no more cold advection, it still only reached 45F. I guess that the sun angle is low enough at this time of year that full sunshine does not automatically mean good boundary layer mixing.

Tonight’s forecast is trickier since while calm winds will continue, to some low clouds entering after 06z, when it would be the coldest. Actually, a shallow stratus cloud layer already came in unexpectedly this afternoon, but that will likely clear out by early tonight before the next batches of clouds arrive. It is not expected to be cloudy all the time though, which will allow for brief dips during clearer periods. But just how cloudy it gets is somewhat uncertain and will dictate how cold it gets. The low clouds will break by tomorrow afternoon while a more uniform veil of high clouds arrives, limiting sunshine slightly and perhaps lowering the high by 1F or so, offset by a slightly warmer air mass. Winds will be rather light again, perhaps switching to southerly.

 

Source: NWS

Source: Aviation Weather Center

Source: PivotalWeather