Ramblings of a Graduate Student

Today marks the end of what is often referred to as “meteorological winter”.  Typically seasons begin and end on the solstices and equinoxes, but meteorologists tend to break our seasons based on calendar months.  Below are the months contained in each “meteorological season”.

• Winter: December, January, and February
• Spring: March, April, and May
• Summer: June, July, and August
• Autumn: September, October, and November

The United States will end a very active meteorological winter that saw numerous blizzards, at least one ice storm (in Oklahoma), and snow in all 50 states.  Two mid-level lows (shortwave troughs) are moving through the southern plains (yellow x’s) as well as a strong mid-to-upper-level jet stream (cyan color to the southwest of the southernmost x).  Also, the strong nor’easter that has affected New England for the past few days is slowly moving east, out to sea.

These mid-level lows are aiding in the development of precipitation in the central plains and western Texas as indicated by the radar images below.  There is a chance that portions of western and central Oklahoma will see some snow mix in with the rain, but little-to-no accumulation is expected.

I know the above image is not a “meteorological image”, but it was too rare of an event not to use it as today’s blog post.

Overnight a magnitude 8.8 earthquake decimated parts of Chile.  Shortly after the earthquake, a tsunami began affecting portions of the South American coast along with several islands off the coast of Chile.  The Pacific Tsunami Warning Center issued a basin-wide tsunami warning.  (There have been reports of tsunami damage along the coast of California.)

I spent a good deal of the afternoon watching live streaming video from television stations in Hawaii in anticipation of the tsunami’s arrival.  While watching Hilo Bay, HI empty and refill during the tsunami, my chair lurched forward as if someone or something hit me coincident with a distant thud sound.  I was stunned.  I then started to ask my friend, Kiel Ortega, if he felt the shake at his house, but before I could ask him if he felt it, he asked if I felt something.  I then went and asked Sarah if she felt something (which she had).  I quickly learned, via Facebook and Twitter, that it was not an isolated incident and people all around me (and not so nearby) had felt it.  It was a little after that when I learned it had been a 4.4 magnitude earthquake northeast of Oklahoma City.

I’ve always wanted to experience an earthquake.  Now, I can check that off my to-do list…

Educational Note: Just so everyone is aware, the Richter Scale, which is used to gauge the intensity of an earthquake, is a logarithmic scale – not a linear one.  I have heard several news outlets report that the 8.8 magnitude earthquake in Chile today was 1.8 times stronger than the 7.0 earthquake that hit Haiti recently. This is flat wrong.  The Chilean earthquake is actually 10^1.8= ~63 times stronger than the Hatian earthquake.  The Chilean earthquake was 10^4.4=~25,118.8 times stronger than the central Oklahoma earthquake

Above is this morning (12 UTC; 6 AM CST) surface pressure chart, as analyzed the by the Storm Prediction Center’s surface objective analysis dataset. (Essentially, what this means is that this is a model generated field that is “tugged” back toward truth through the use of observations.)  A couple of things stand out 1) the very strong low pressure centered over the New York City, NY area and 2) the strong high pressure located over the central Rocky Mountains.  The brown dashed lines indicate “troughs” or low pressure, or areas of lower pressure that are not completely closed off.  You’ll notice a trough to the northwest of the strong northeast surface low (this is indicative of strong warm aid advection aloft).  There is also a trough in the southern plains.  This trough is associated with a small, but potent, mid-level shortwave trough / closed low that brought rain (and some snow) to central Oklahoma over night.

A very active upper-air pattern persists across the United States with several speed maximums inferred in tonight’s water vapor imagery.  A powerful (fast) upper-level jet stream, with embedded jet streaks, is evident across the Gulf of Mexico into the far western Atlantic Ocean.  This jet streak is aiding the development of the northeast “snowicane”, as I’ve heard it referred to by some in the media.  A mid-level jet streak is propagating southeast out desert southwest into central Texas.  This mid-level jet streak is aiding the development of a mid-level low over the northern Texas Panhandle.  This mid-level low will slowly move southeast tonight, bringing with it the chance of a cold rain and even some snow (although, I’m not nearly as optimistic tonight about seeing much in the way of accumulations in central Oklahoma).

Below, I’ve annotated the mid-level lows (yellow X) and jet streams/jet streaks in thick cyan arrows.  The thing cyan arrow is not necessarily a jet stream, but more of an indication of the flow pattern over the northeastern United States.

Lastly, I thought I’d show a graphic that helps explain why I’m not so gung-ho about central Oklahoma’s snow chances tonight/Friday morning.  Below shows the northern hemispheric 500 hPa heights (color filled with lower heights in cool colors and higher heights in warmer colors) and surface pressure (solid black contours).  The Day 50 post discussed how it appears a surge of arctic air was preparing to plunge southward out of Canada into the southern plains.  Well, tonight’s northern hemispheric chart (below) clearly shows that the cold air did not plunge south into the southern plains.  Thus, without a true source region of cold air needed for heavy snow, central Oklahoma should stay a tad too warm for much in the way of accumulating snow.

Now, central Oklahoma might see snow overnight, and here is how it would happen.  As the upper-low and corresponding surface reflection move southeast across far eastern Texas panhandle and southwest Oklahoma into north central Texas, a lot of dry air from the east will become entrained into the storm.  This dry air will allow evaporational cooling to occur, allowing surface temperatures to cool sufficiently for snow to reach the ground.  However, whenever dry air is being continually advected into an area, this tends to decrease precipitation intensity…which would cut-back on any snow accumulations that might otherwise occur.

After several blog posts about Texas snow, it’s now Oklahoma’s turn.  The image below is from the National Weather Service’s Hydrometeorological Prediction Center (HPC) and displays the probability of a point receiving at least 4″ of snow between 00 UTC Friday 26 February (6 PM CST Thursday 25 February) and 00 UTC Saturday 27 February (6 PM CST Friday 26 February). Notice how a significant swath of Oklahoma has a chance of seeing 4″ of snow Thursday into Friday!

And if you don’t trust the HPC, here is the National Weather Service Forecast Office in Norman, OK’s take on the matter.

I will be holding a map discussion tomorrow for scientists in the National Weather Center (particularly National Severe Storms Laboratory and Storm Prediction Center) so I’ll hopefully have more to say on this tomorrow.  As for tonight, my attention was focused on the USA-Switzerland and Russia-Canada hockey games and so I didn’t have much time to prepare an in-depth discussion!

Today, areas south of the Dallas-Fort Worth metropolitan area received a significant snowfall by their standards.  As of this writing (9 PM CST), the National Weather Service Forecast Office in Fort Worth, TX has a graphic indicating that Waco, TX had received 3″ of snow (light snow was still occurring).  I thought tonight’s blog post would focus on what was the source of the lift associated with this precipitation.

As my former students should remember, when precipitation develops north of the surface warm front, typically one of two (or a combination of these two) mechanisms are responsible for the sustained lift necessary for precipitation to develop.  These two mechanisms are isentropic lift or frontogenetical forcing associated in the 850-700 hPa layer.  It just so happens that the heaviest precipitation across central Texas today coincided with the 850-700 hPa frontal zone.  This is illustrated in the sequence of images below.

In the images below, the Petterssen Frontogenetical equation values are contoured in purple (essentially, the larger the number the stronger the front in the layer) as analyzed by the Rapid Update Cycle (RUC) numerical model.  The corresponding radar reflectivity is underlayed in blue, green, and yellow.  Notice how the precipitation and the 850-700 hPa frontal zone are juxtaposed very nicely throughout the day.

1200 UTC 23 February 2010 (6 AM CST23 Feburary 2010)

1500 UTC 23 February 2010 (9 AM CST23 Feburary 2010)

1800 UTC 23 February 2010 (12 PM CST23 Feburary 2010)

21 UTC 23 February 2010 (3 PM CST23 Feburary 2010)

00 UTC 24 February 2010 (6 PM CST 23 Feburary 2010)

Above is the precipitation forecast for the next 5 days from the National Weather Service’s Hydrometeorological Prediction Center.  Several areas of the United States will experience a wet 5 days.

1. The northeast will experience a very strong storm system during the next 5 days.  A strong cyclone will park itself over New England and continue to draw in warm, moist air into a cold airmass at the surface.  Although along the coast will see a lot of rain, a lot of snow will fall farther inland.  This could be the first real big snow for upstate New York this winter.
2. Central Texas and areas along the Gulf Coast will experience several mid-level shortwave troughs moving through the area.  Each of these troughs will result in a new round of precipitation – some of it falling as snow tomorrow!
3. Oklahoma and Arkansas will experience precipitation late week as more mid-level shortwave troughs move through the southern branch of the jet stream.  It is too early to tell, but this may fall as snow across the northern portions of the states.
4. The west coast will continue to be battered by numerous storms over the next five days.  Each one will bring more precipitation to central and northern California.

With all of this, my attention will be focused on the northeast for the next few days.  The storm that is forecast in this area could be one for the record books.  The potential exists for a lot of snow in the inland areas, a lot of coastal rain, and beach erosion along the coast of Maine.