Friday, October 19, 2012

Big Change Ahead

500 millibar map (about 20,000 ft) for 7:00 p.m. CDT October 18
This weekend will mark the start of a significant change in the weather pattern across the U.S
Right now the eastern half of the country is chilly as a large upper low spins over the area. Out west, it has been very warm recently under an upper level ridge. Temperatures, for example, in northern California have been in the upper 80s and low 90s. Yesterday new high temperature records were set in San Francisco and Oakland.


 SAN FRANCISCO AIRPORT     86           85         1988
 OAKLAND DOWNTOWN          87           84         1974
 OAKLAND AIRPORT           87           83         1974
 MOUNTAIN VIEW             89           87         1995

A number of daily temperature records have been set in southern California as well. On Wednesday El Cajon reached 102°F, breaking the old record of 96°F set in 1996.

As this weekend progresses, the pattern will shift as the upper low lifts out of the Midwest, and a strong trough develops off the west coast.

Forecast 500 millibar map for 7:00 a.m. CDT Sunday, October 21.

What's this mean? Well, the central and eastern U.S. will enjoy a period of mild fall weather. October so far has been cooler than normal from the Rockies eastward, and near to above normal west of the Rockies.

The west coast, from Washington south through northern California, will be in for a period of stormy, cool weather.

Do you have a question you would like answered or suggestions on topics you would like to see in future blog posts?  Feel free to email me your questions and suggestions at


  1. Although the coming of the rains began in northwest Washington on October 12, the temperatures so far have remained near normal.

  2. True about the rain, George. For October, temps are actually running about 2 degrees above normal in the Seattle area, for example. Say goodbye to those highs in the 60s for awhile.

  3. I am just happy that you are here, Steve. Interested in all of your topics. Thanks.

  4. Thanks, Kay - appreciate the comment!

  5. Very warm, out West, hasn't applied to the PNW as often, and even less since the high pressure over the Pacific gave way recently.

  6. Sorry if this is a dup, 1st comment seemed to be lost. What observers W of the Cascades note is often not representative of what the rest of the PNW is experiencing. Large swaths of the Columbia Plateau have not been warmer this year. Thankfully a below average stretch of moisture ended with the breaking of the pressure off the coast recently.

    OR-GL-2, and NWS spotter.