Thursday, October 26, 2006

Chilly Still on the Menu

A strong ridge of high pressure extending from northern Hudson Bay across eastern North America to Cuba continued pumping cold air into the Mid Atlantic region on Wednesday. A northwesterly breeze again gusting over 30 mph at times kept temperatures well below seasonal averages in the Washington metro area. High temperatures were 55° at National and Dulles, 54° at BWI.

Despite diminishing winds, temperatures will remain well below average today as a low pressure area becoming organized in the central Rockies and incorporating leftover moisture from what was eastern Pacific Huricane Paul brings the threat of rain late Friday into part of the weekend.

Surface weather map at 11pm last night from HPC/NCEP/NWS

Today and Tonight

Continued cold, less windy. Under mostly sunny skies, today's highs will be in the mid 50s. Overnight, clouds will increase toward morning with lows near 40° in the city, low to mid 30s in the cooler 'burbs.

For the outlook through the weekend, scroll down to Dan's post below.

Fun with Numbers

Larson's Long-Range is off today, but we can take the opportunity to look at the connection, if any, between fall and winter temperatures. With both September and October running cooler than average, the question arises whether or not this indicates anything about the upcoming winter. As Matt has already noted, the relationship is quite complex.

The chart shows the September and October (SO) average temperature on the x-axis, and the following December, January, and February (DJF) average on the y-axis. The data points include the 135 years of Washington observations through last year. The solid regression line represents the best fit to the data, with the equation of the line shown in the upper left. The upward slope of the line shows that there is a positive relationship, but the correlation is very weak. The value 0.09 for R2 means that only 9% of the variability in winter average temperatures is explained by the September-October average. Note that out of the 5 coolest SO averages, there was one year with the coolest DJF average, but there was also one with the second warmest DJF. (For more on regression analysis, see the discussion of the December-January relationship posted last year.)

For more Washington DC data, see:
Washington DC Weather Records chart from NWS data, photo © Kevin Ambrose

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Seasonal Outlook

Latest seasonal forecast: Click here.

Latest 3-month temperature outlook from Climate Prediction Center/NWS/NOAA.