Thurs 29 Sept 2011

First image is of the winds aloft at 850 mb (approx 5000 ft). Winds are light and variable with an easterly bias.  A new low pressure system is building in the Pacific off of Vancouver Island.  You can see the SSW winds associated with the advancing front building to 50 – 60 knots which is not good for our feathered friends that are still lingering in the arctic.

Second image is of the surface winds and pressure. How long the cold front will stay off shore will depend on the interaction between it and the high pressure ridge centered off the coast of northern California.

Third image is a snapshot of the base velocity showing north to SSE directionality at a peak of 20 to 25 knots.  The easterly winds are pushing the birds in this trajectory so whatever birds are on the move they are probably going to end up on the west side of the valley.

Fourth image is the animated gif with snapshots every half hour of the base reflectivity above radar station RTX.  The density was not as heavy as last night and it was spotty.   The main movement was from an hour after sunset to about midnight and quickly tapering off after that. Animation runs from around 8:00 pm pdst yesterday evening through 5:00 am pdst this morning. (Click on the thumbnails to view the full-sized images and animation.)

Sunset last night was at 6:57 pm pdst.

Below is a snapshot of the national radar composite.   Look back at the winds aloft and note how they effect migration.  A large low pressure system centered over the Great Lakes is pushing a front into the SE states.  The high pressure system over Montana has some strong northerly winds funneling birds down the plains.  So, birds are on the move in the Central, Mississippi and southern half of the Eastern flyways, but not in the mid-Atlantic northward because of the strong southerly winds in the area.