A quick look at the National Weather Service’s web page this evening shows most of Colorado under some sort of weather-related advisory or warning. The big news over the past several days has been the potential for blizzard conditions over the Colorado Eastern Plains. The computer models used by weather prognosticators have been remarkably consistent in showing a storm system rapidly intensifying over eastern Colorado Tuesday night into a storm of record breaking strength over southeastern Colorado on Wednesday morning.
How do meteorologists measure the strength of a storm? The benchmark generally used is the central pressure of the storm. In the atmosphere, storms represent areas of lower atmospheric – or air – pressure. Depending on your system of measurement of preference, air pressure is either measured in inches of mercury (English) or millibars (mb) (Metric). Meteorologists, of course, use millibars. Average atmospheric pressure is around 1013 mb or 29.92 inches of mercury at sea level. While wind strength is also used to categorize tropical storms such as hurricanes and tornados, there is a direct correlation between the minimum pressure of a storm and the wind speeds associated with it. Because of this, central pressure is often used to measure the strength of a storm.
Areas of low pressure generally correspond to unsettled weather while areas of high pressure correspond to fair weather. If you are old enough to remember the TV news weather casts back in the 70s and 80s, then you will remember the low-tech (by today’s standards) weather maps with the red ‘L’s indicating the positions of storms, the blue ‘H’s showing areas of high pressure, and the myriad of blue and red lines indicating cold and warm fronts, respectively.
So what is the big deal with this storm? For a few days now, the models have been forecasting the central pressure of this system to drop down to somewhere between 970 and 974 mb. The Colorado State climatologist reports that the lowest recorded surface corrected air pressure measured in Colorado is around 975 mb. If the models are correct, then this will be the strongest storm – as measured by its central pressure – in Colorado weather history. And you are talking about data that goes back well over 100 years.
Also notable is how quickly this storm intensifies. You’ve probably heard the term “meteorological bomb” over the past few days. By definition, any storm which deepens 24 mb over a time period of 24 hours or less qualifies as bombogenesis. This term sounds really cool, and it is exactly a word that a geeky meteorologist would dream up. However, it does signify a rapidly intensifying storm and quickly deteriorating weather. Wednesday’s storm comes close to being a “bomb” (not to be confused with a bomb shell which is usually blonde with high heels).
Obviously, Wednesday’s storm will be really cool from a historical perspective, but what does it mean for our weather? Nederland and the Front Range foothills generally do not get much precipitation with deep storms over the plains. The winds typically blow from the north or northwest which actually act to inhibit precipitation in Nederland because of downsloping. The exception to this rule is if the storm tracks very close to the Front Range mountains. The weather models have been struggling with the exact position of this storm, and a difference of 50 miles in the track of the low can spell the difference between heavy snow in Nederland and hardly anything at all.
In this case, the models have been vacillating between 0.25 and 1.00 inches of liquid for us, and that would translate to a snow forecast ranging anywhere from 3 to 12 inches. My confidence is low that we will see a significant snowfall. However, my confidence is high that the plains will experience blizzard conditions as winds with this storm approach 70 mph in some places east of Denver. Remember, it does not take a lot of snow to produce blizzard conditions. It is the combination of strong winds and snow that can lead to whiteout conditions that can close highways and produce life threatening circumstances.
Enjoy this record-breaking weather. Even if we miss out on the snow, Colorado will still be making weather history!