SO FAR, A NOTHINGBURGER WINTER
Despite the fact we've had a couple light snows, there's nothing on the ground to show for it with December a third of the way through. So far, winter has been a nothingburger, much like last year and the one before that. You may not be aware of it, but there is a scale to measure a winter's strength. It's called the Accumulated Winter Season Severity Index (AWSSI) and its developmental goal was to objectively quantify and describe the relative severity of the winter season.
Goals of the AWSSI
Use max/min temperature, snowfall, and snow depth to objectively index winter weather conditions.
Create a historical database of AWSSI for locations with available temperature, snowfall and snow depth.
Compare season to season AWSSI for a particular location in climatological context.
Allow users access to objective data to make winter-informed decisions, especially pertaining to snow removal, commerce, and transportation.
Defining the AWSSI Season
The AWSSI is not limited to meteorological winter (December ‐ February) but is intended to capture winter weather from its earliest occurrence to its last.
The winter season begins with the first occurrence of any one of the following:
First measurable snowfall greater than or equal to 0.1 inch.
Maximum temperature less than or equal to 32°F.
Winter season begins on December 1 if conditions above have not been observed.
The winter season ends with the last occurrence of any one of the following:
Last measurable snowfall greater than or equal to 0.1 inch.
Last day with 1 inch of snow on the ground.
Last day with max temperature less than or equal to 32°F.
Winter season ends February 28/29 if the above conditions have occurred.
How the AWSSI Accumulates
Daily scores are calculated based on scores assigned to temperature, snowfall, and snow depth thresholds. Daily scores are accumulated through the winter season, allowing a running total of winter severity in the midst of a season, as well as a final, cumulative value characterizing the full season. Accumulations of the temperature and snow components of the index are computed separately and then added together for the total index. This allows comparison of the relative contribution of each to the total score.
The AWSSI has been processed for 365 locations across the continental U.S. to provide a variety of locations in different climate regimes for analysis. The AWSSI is calculated for each season from 1950‐1951 to the current winter season. The seasonal data is then subject to quality control, and seasons missing data that would contribute 5% or more of the seasons AWSSI are removed. Averages and standard deviations are calculated for running accumulations of daily temperature and snow scores, as well as the total AWSSI.
Quintiles of AWSSI scores were determined for each location. Descriptive categories were assigned to each quintile as follows:
See an Example
Does not include wind (e.g. wind chill, blowing snow).
Does not include mixed precipitation or freezing rain explicitly.
Thresholds have been set with impacts in mind and are subject to adjustment in the future.
Available AWSSI Features
Monitor current winter season AWSSI scores.
Download current and historical daily AWSSI scores.
Analyze end of season summaries through maps and tabular data downloads.
Access the 1980-2020 AWSSI climatology map.
SO FAR THIS WINTER IS A NOTHINGBURGER...
Now that you know what the AWSSI is and how it's determined, here's the winter rating so far in the Quad Cities. It's a whopping 29 as indicated by the red X. That means this year is currently in the lowest 20 percent of all winters for severity since 1950. The all-time low at this point was 6 and the highest ever 206.
Below you can see, (based on analogs of similar winters to date), this year is projected to end up at 345, just above the all-time low score of 300. That would put it in the lowest 10 percent of all winters since 1950 in terms of severity. In other words, if the projected index is correct, we should have it very easy this winter with minimal snow and sustained cold.
By the way, here's the current ratings for a number of locations around the eastern half of the nation. There's a lot of moderate to mild categories showing up.
A COOL CHANGE...
Some obvious changes have taken place in our weather overnight, thanks to the passage of low pressure and its associated cold front. Showers which sprouted late Friday evening are in the process of ending from SW to NE as the storm center tracks toward Milwaukee. While this has been primarily a rain event, a few wet snowflakes may show up in the far NW before precipitation ends Saturday morning. Otherwise, lots of clouds and steady or falling temperatures in the upper 30s to low 40s are expected in the afternoon. Sunday should be even colder, with readings remaining in the low to mid 30s. At least the clouds will break as high pressure builds in from the NW.
We are now getting into the range where guidance is showing temperature and precipitation trends up to Christmas Eve. The screaming message is that the period December 14th-24th remains mild. These are the 10-day temperature departures during that stretch on the EURO.
Over that same period of time (December 14-24th), the EURO shows this for snowfall. Not much optimism for Midwest snow that's for sure. At the very best, chances for a white Christmas in my area are less than 30 percent and falling. We need to see major changes in the long wave pattern soon if we hope to turn that around.
On that less than upbeat note, I am calling it a post. Have a terrific weekend and roll weather...TS
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