WeatherWatcher: Weekly Report

Saturday, November 29, 2014

Forecast
Second Cold Snap
Monthly Temperature Graph
Last Week's Data

Forecast: We are in the grip of our second cold snap of the season, after only a short warm weather reprieve. As talked about in my previous report about the coming snow and cold, we are now well underway with the temperatures already down to 22°F tonight (Saturday 11-29-14). Sunday will be cold with a light north wind, temperatures will struggle to make it to 30°F. Skies will be clear with lows Sunday night dipping back into the upper teens to around the low 20's mark. Monday some moisture is expected to make its way up into the area for a slight chance of what is now called rain. However models are inconsistent with daytime temperatures, with most forecasts pointing to a low 30's for a high. If the temperatures are cold enough any precipitation will likely fall as snow or a wintery mix. Tuesday the cold will continue with highs in the low-mid 30's, lows in the 20's.

Wednesday - Friday temperatures may start to moderate a little bit as a new Pacific storm moves in bringing more precipitation. Again, a lot of forecasts are inconsistent with the temperatures, so right now I'm going to say that a rain/snow mix or snow is possible with this renewed surge of precipitation. I will do a special update if any significant winter storm threats become apparent.

Second Cold Snap: Friday and Saturday early morning we got a nice one-two punch of cold fronts that pushed through. First cold front was with the heavy rainfall Friday afternoon that brought us a daily rainfall total of 1.23 inches. The temperature Friday morning started at 53.6°F and dropped throughout the day dramatically to 34.7°F, a solid 19°F drop. As the edge of the cold front passed, as expected the rain started mixing with snow, at times and depending on location had brief periods of snow, with no accumulations. 

Saturday morning a second cold front pushed down, this one being the arctic cold front. As this cold front pushed through it developed a convergence zone band, which stayed up in the North Lynnwood - South Everett area until about 1am. After 1am the convergence band started moving south, bringing us our trace accumulation of snow. Temperatures Saturday continued to decline even after the sun came up. Temperatures went from 34.7°F at Midnight, down to 29°F by 10AM, by 3PM the temperature had dropped to 27°F.

Winds on Saturday were another big story with this cold front. Most stations recorded wind gusts to 25-30MPH, some of the strongest I was able to find within Shoreline or Lake Forest Park were 34 MPH.

The reason for such tree damage and widespread power outages? The winds were out of the North-Northwest. Our trees are adapted and accustomed to the typical south-southwest winds we normally get, but a strong northerly wind has been rare over the past 5 years. We also have very wet ground from the heavy rainfall on Friday. On top of that there was a significant amount of snow and ice weight built up on the tree branches that was just enough pressure on those trees and tree limbs to bring them down under those 35MPH gusts. The snow on the trees its self wasn't much of a weight load, but there was a lot of water on the trees from the rain we had yesterday that froze overnight long before the trees could dry off.

Below is the last 24 hours graphed on the weather station. You can see the winds spiking during the afternoon from about 10AM - 3PM. You can also see the pressure rising, and the temperature falling as the day progressed.

24 Hour Graph for Saturday November 29, 2014.
www.shorelineweather.com

Monthly Temperature Graph: I'm just going to show the daily high and low temperature graph this time around, it shows a significant swing through Friday. Saturday has not been counted yet because the day is not over yet.
November 2014 Graph by Carl Dinse
Last week's data:
High temperature: 57.9°F (Wednesday)
Low temperature: 34.7°F (Friday Night)
Rainiest Day: 1.23 inches (Friday)
Total rainfall: 2.29 inches
Warmest day: 56.3°F (Wednesday)
Coldest day: 43.2°F (Friday)
Average temperature: 48.5°F
Station average: 40.2°F

For current weather conditions and winter storm updates, see http://www.shorelineweather.com
Stay safe out there!



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