Snow and Cold Returns to the Northwest and California

The atmospheric flow pattern is changing in a big way, developing a deep trough over the eastern Pacific, and driving much colder air south...and I mean south.  The Cascades will get its first real snowfall starting this weekend and then the white stuff will push southward towards the Sierras.  The snow level will drop sufficiently that even our lower passes could get covered with a few inches of the white stuff.   Get your snowball arm warmed up, grease that sled for the kids....the first taste of winter will soon hit the higher elevations.

 By Saturday, deepening upper level troughing will develop over the Gulf of Alaska.  This trough is associated with cold air, and the tight packing of the height lines suggest strong jet stream winds.

During the next few days (Tuesday AM),  the trough plummets southwards, bring much colder air over the NW (see graphic below)

The Climate Prediction Center's 6-10 day forecast shows the result of this pattern:  a high probability of below normal temperatures (dark blue colors) over the NW and California.   This air will be cool and unstable, and the result will be snow in the mountains. How much?   Lets check the model forecast!

 First, for the 24-h ending 5 PM on Saturday.  Up to 8 inches in the north Cascades and mountains of southern British Columbia, with lighter amount spreading down into norther Oregon.

 The next 24 hrs (ending Sunday at 5 PM), the same thing.

One more day later, snow starts spreading into southern Oregon, and lightens up in Washington.

 Then early next week the snow picks up again in the Cascades and extends over the Sierras.

 The snow level by the end of the weekend will drop to around 3000 ft, so even Snoqualmie should see some white stuff.  Stevens is a sure thing.   This is good news for the Ski folks...they are going to get a good start to a base on their higher runs.  El Nino has weakened and in any case the first part of the autumn is not influenced by it much anyway.

This is all great impetus for us to get our application Seattle SNOWWATCH ready for this winter, with new capabilities that I will describe in a later blog.

How high do weather balloons rise?

This week we were all thrilled by the jump of Felix Baumgartner from a balloon that ascended to 128,000 ft.  At that height he was above the vast majority of the atmosphere (99% of the atmosphere was below him!), the sky was nearly as black as space, and the curvature of the earth was obvious (see picture).  Simply amazing.

But what about weather balloons...also know as radiosondes...how high do they fly?

Radiosondes are launched twice a day at 92 locations around the U.S. (see map and picture).

As shown by the picture, these units include a balloon, a parachute, and an instrument package that radios back temperature, humidity, pressure, and sometimes position (for units with GPS).    Winds can be computed by tracking the radio signal and some trigonometry.  Radiosondes originated in the late 1920s and have been an important part of the weather observing network ever since.  The biggest problem with them is that they are mainly limited to land stations.

The pressure near sea level averages around 1013 hPa (hPa is unit of pressure and is the same as a millibar).  Most radiosondes rise to 5-15 hPa before the balloons burst (the balloon expands as the pressure decreases around it...finally the balloon gets so large it breaks up).  Then the parachute brings the unit back down to earth in an controlled way.

What heights are these balloons reaching?  Roughly 100,000 ft or 20 miles.  A few of the balloons ascend to 5 hPa, reaching around 115,000 ft---not quite as high as Felix Baumgartner.

Pressure tells you about the amount of atmosphere above you, so if you go from roughly 1000 hPa to 10 hPa, you are rising above 99% of the atmosphere.    Felix was virtually in space--without his space suit he would not have survived.

Many people wonder...how many of the radiosonde are recovered and reused?  According to the National Weather Service less than 20% of the 75,000 radiosonde launched by the U.S. are recovered.  Considering that they cost several hundred dollar each, this is not a trivial cost (plus gas, parachutes, labor costs).

A funny story...several years ago I gave a lecture on radiosondes to my 101 class. The next day a grinning student walks in with one.  Where did you get it, I asked?  Turns out he was playing basketball with his friends when the sonde drifted down into their game.  The radiosonde had been launched at McChord and then drifted north under southerly winds.    His friends were mighty impressed with his knowledge of the device!

Here is the plot of the latest radiosonde data from a nearby launch location:  Quillayute (or Forks) on the Washington coast.  This unit got to 10 hPa.  The black line to the right is temperature, left line is dewpoint, and the y axis is pressure.  The bottom (x axis) is temperature.  Temperatures dropped off with height until the radiosonde reached the stratosphere, after which they increased.  The winds were weaker up there too.

One of my favorite type of videos are made by folks launching a camcorder on a weather balloon--essentially doing remotely what Felix did this week.  Here is a good one (click on image)

http://www.youtube.com/watch?feature=endscreen&NR=1&v=1h0ptpimm04