Can't We Get Rid of This Persistently Nice Weather?

Am I going crazy?  Why would anyone want to get rid of such nice weather?  Surely I must be joking, right?  Well, yes and no.  While I do enjoy nice sunny days, I very much long this time of year for the excitement of the spring storm season.  The clean, dry air of high pressure days, while pretty, just doesn't do it for someone who always is looking at the clouds.  A quick view of our extended forecast for North Texas puts daytime highs in the 60s and 70s - with only a few days mixed in with very low precipitation chances.  Boo!  (Can you feel the sarcasm dripping from this post??)

As it turns out, I actually can blame this weather on something:  a Rex Block

Who is Rex Block?  Well, a Rex Block isn't a who, but a what.  This is a meteorological term for a specific type of blocking pattern.  Blocking patterns are relatively stationary weather patterns that block other systems from coming through.  The Rex Block is a special type of blocking pattern in which an upper level center of low pressure is situated directly southward of an upper level high pressure center.  It was named after Dr. Daniel F. Rex who named this pattern in 1950.  Here is an idealized diagram:

Winds from the west encounter the high pressure area and begin to flow clockwise around it, then start to flow counter-clockwise around the low pressure area.  In other words, the winds blow in a backwards S pattern from north to south.  As there little west-east flow, this pattern can persist for days.

Here's what our current weather pattern looks like.  This image is taken from the NAM weather model.  It shows the 500mb weather patterns (winds at around 18,000 ft. above the ground).

 

There's a few features that I need to point out so that all of this makes some sense.  I've added a large, blue H over northern Mexico.  This (as I'm sure you've seen countless times on other weather maps) is an area of high pressure.  High pressure generally gives clear skies and dry air - exactly what we have today. Also, take a look at the solid black lines.  See how they make patterns that look like a large right-side up and upside down U?  Now look at how Texas is west of one of these U-shaped features.  Generally speaking, the western side of the U tends to have sinking air (i.e. high pressure) and fair skies, while the eastern side of these U shapes generally have rising air (low pressure) and cloudy skies.  

 

The large, red L is of course a low pressure area - responsible for clouds and rain - exactly what is happening in Washington and Oregon today.

 

As the NAM continues over its 84-hour forecast period, it shows the low swooping down from the Pacific Northwest, but then starts to retrograde (or move westward) and finally positions itself on the north end of the Baja Peninsula, directly southward of another high pressure ridge.  This pattern now forms the classic Rex Block.  Here's the 84-hour forecast NAM view.

 

 

You'll notice how Texas continues to be generally westward of one of those U shapes.  Again, this region generally has sinking air and fair skies.  When you add the effects of the Rex Block, it's going to ensure that we have clear sailing for a long time to come.  The GFS weather model also shows a Rex Block for the same time period (roughly 84-hours out).  However, because the GFS forecasts out to 240 hours, it also shows that we could be in for a nice change (and by that I mean RAIN) by early next week. 

 

Until then - enjoy the weather!