The pressure different across the mountains has grown to roughly 9 mb and downslope winds along the western Cascade slopes have increased. Gust of 70 mph reported at Enumclaw. Very strong winds (also gusting to 70 mph) on the western side of the Columbia Gorge.
Northwest Weather Workshop. This is major local meeting for weather professionals and enthusiasts. March 2-3 in Seattle. Info here.
A heroic meteorological conflict has been taking place between two implacable foes: (1) easterly winds passing over the Cascades and moving down its western slopes, and (2) a low-level inversion or cold stable air layer near the surface. When (1) wins, the temperatures stay warm at night or surge upwards. If (2) prevails, the location stays cool and sometimes foggy.
This morning many of us woke to find the same weather pattern of the past few days: high pressure inland, low pressure offshore, a strong pressure gradient over the region (particularly near the Cascade crest), and general easterlies over the region (see graphic)
Plotted are the seven vertical soundings beginning 4 AM (12 GMT) and ending 10 AM this morning (18 GMT-black color). Big inversion in the early AM (temps warm by roughly 6 C in the bottom 200 meters). The inversion weakens as the ground warms.
Inversions develop overnight as the ground emits infrared radiation to space...cooling the ground more than the air above. Inversions are very stable---meaning they work against vertical mixing. So we have a battle going on--easterlies moving down the mountains, trying to scour out the cool air versus stable air not wanting to be moved out of the way. Sort of like an easterly Godzilla versus Inversion King Kong.
|Easterly Godzilla versus Inversion King Kong|
This morning at 6 AM, before the sun rose, here were the weather conditions at the surface:
During the day, with solar heating destroying the inversion, conditions were more uniform. Here are the conditions at 2 PM: temperatures ranging from the mid 50s to LOWER 60s. Yes, these temperatures are more typical of April than February. You notice a lot more easterlies on this map?...that is because they were able to mix down to surface with the solar heating during the day.
During the summer, the sun is strong enough to destroy any inversions quickly. Midwinter, particularly December and early January, the inversions often win. Tuesday will be another fine day. But Wednesday will see some degradation--chance of light showers and cooler temps.