No long post tonight; just the “Question of the Week”.

Since 1950, how many (official) tornadoes have occurred in January? Leave your answers in the comments. I’ll post the answer on Friday.

With apologies to Mr. Samuel Taylor Coleridge, the title above accurately captures my sentiment this morning. The 11:40 AM CST US Watch, Warning, and Advisory graphic above depicts two large regions of the country blanketed in winter weather headlines of various sorts.

In the southeast, Winter Storm Warnings have been hoisted in response to a strong short-wave trough and surface low pressure that are, and anticipated to, bring heavy snow to areas unaccustomed to such weather. Forecasts for southern Arkansas, northern Louisiana, central and northern Mississippi call for up to 8″ of snow in the next 24-36 hours. Furthermore, in portions of southern Arkansas, there is an outside chance for upwards of 12″!

In the plains, an assortment of winter weather headlines are in effect. This is in response to a developing cyclone that is anticipated to bring a fresh bout of cold air southward, but not nearly as cold as was previously advertised by the GFS model. Snow totals in the plains will range from a couple of inches in northern Oklahoma to upwards of a foot in portions of Nebraska.

So, as a winter weather aficionado, guess where I am? You probably guessed it. I’m located in the little swath of no winter weather headlines located along and just south of the Interstate 44 corridor in Oklahoma. So, central Oklahoma will miss out on the enjoyment of a fresh snowfall but experience the misery of several days of below normal conditions. Joy.

It’s been very dry across much of Oklahoma this winter. In fact, according to the Oklahoma Mesonet, in the last 30 days, Norman, OK has only received 0.13″ of rain. Over the last 60 or even 90 days the situation isn’t much better. Thus, it wasn’t much of a surprise this evening when I looked out my office window at the National Weather Center and saw the following:

Contrary to what a few people initially thought, this is not a pretty sunset highlighting a low stratus cloud. This is actually the smoke from what I initially thought was an out-of-control grass fire in extreme eastern Moore, OK. (Turns out this was apparently a controlled burn, which is surprising given the relatively high fire danger and other wildfires burning in the vicinity.)

Have you ever wondered why oftentimes smoke plumes tend to look like this? Namely, it initially rises and then appears to flatter out along some constant altitude? Turns out the answer lies in the vertical temperature structure of the atmosphere and to illustrate it, we’ll take a look at an atmospheric sounding from Norman, OK (taken approximately the time of this photograph) displayed on a Skew-T/Log-P Diagram, or Skew-T for short.

Above (and below) are tonight’s 00 UTC 08 January 2011 (6 PM CST 07 January 2011)) for Norman, OK. Even though the sounding is dated 00 UTC, it was actually launched approximately 45-60 minutes prior to 00 UTC. In this sounding, notice that the temperature decreases rapidly with height from the surface to around 800-millibars. In fact, it cools at around 10C over the first kilometer above the ground. This cooling rate is known as the dry adiabatic lapse rate. This is the rate of cooling expected if we were to lift any parcel of dry air vertically. Through the concepts of buoyancy and convective instability, any parcel that is warmer than ambient air will accelerate upward on it’s own, any parcel that is cooler than the ambient air will accelerate downward on it’s own, and any parcel the same temperature as the ambient air will continue to do whatever it is doing.

At around 800-millibars the temperature stops cooling as we increase height. In fact, it remains the same or even warms slightly! This warming with height is known as a temperature inversion, or inversion for short. I’ve circled this temperature inversion below.

So what does this have to do with the smoke plume? Well, the smoke from the fire acts like a parcel of dry air. This means that for every one kilometer above the ground, the temperature of the smoke would be expected to cool 10C. (In reality the temperature of the smoke would most likely cool at a slightly faster rate due to processes such as turbulent mixing.) If we were to assume that the temperature of the smoke was approximately the same temperature as the ambient temperature, or slightly warmer, we would expect the smoke to accelerate upward. However, as the smoke accelerates upward it begins to cool, as we previously mentioned. It continues to rise because it is approximately the same temperature as the air surrounding it, so it will remain doing what it had been doing (which was rising).

Eventually the smoke will reach the height of the temperature inversion and become colder than the air surrounding it. At this point the smoke will begin to descend until it reaches an altitude where it is in equilibrium with the ambient air temperature, typically at or slightly below the height of the temperature inversion. At this point the smoke will begin to spread out horizontally instead of vertically, frequently being blow in a specific direction by the wind, as was the case yesterday evening.

So, by seeing smoke plumes spread horizontally, instead of vertically, one is actually visualizing the altitude of a temperature inversions.

This answers to this week’s “Question(s) of the Week” are:

1. When was the last time Little Rock (KLIT) or Memphis (KMEM) recorded a daily minimum temperature below 0F?
   • The last time either site recorded a daily minimum temperature below 0F was 23 December 1989. KLIT recorded a minimum temperature of -1F and KMEM recorded a minimum temperature of -3F.
2. When was the last time they recorded a daily maximum temperature less than 10F?
   • *** Since 1950, KLIT has not recorded a day where the the temperature failed to rise above 10F. During this time period, KLIT has recorded only 1 day where the maximum temperature was 10F, which was 24 December 1989. KMEM, however, has recorded two days since 1950 where the temperature failed to reach 10F: 10 January 1962 (6F) and 22 December 1989 (8F).***
3. Since 1950, has either site recorded a day where the temperature failed to warm to greater than 0F?
   • Since 1950, neither KLIT nor KMEM has failed to warm to greater than 0F.

Congratulations to Tim for his correct answers!

Below are the data for these two sites. If you are interested in the full climatological data (that I have available), let me know and I’ll post it somewhere.

Every year the Storm Prediction Center (SPC) issues hundreds of severe thunderstorm watches and tornado watches throughout the entire contiguous United States. SPC Warning Coordination Meteorologist, Greg Carbin, has compiled a graphic that depicts the number of different type of watches by county for 2010. He went a step further to also calculate the deviation (anomaly) from the 1999 – 2008 normal. A couple of things stand out:

• Much of Oklahoma experienced at or below normal numbers of tornado watches, even though the state (unofficially) recorded the 3rd most number of tornadoes on record. (This is because of two large tornado outbreaks in May!)
• Portions of southern California and central Arizona experienced tornado watches this year (in October), even though the 10-year average is for less than 1 per year
• The central plains experienced an above normal number of severe thunderstorm watches
• Parts of western Louisiana and northern Florida did not record a single severe thunderstorm watch

What is the most interesting result to you?