June 30, 2025

Warming and Then Much Cooler for July 4

Time for the July 4th forecast, and we are close enough that skill should be good.  

The bottom line:  current warming (caused by high pressure aloft) will be followed by a cool-down as an upper-level trough approaches.

This morning, the Northwest was clear except for the typical June low clouds along the coast:


During the next 48 hours, a transient upper-level ridge will be positioned over southwest Canada, allowing temperatures to rise into the 80s in western Washington and mid to upper 90s over eastern Washington (see upper level map, 500 hPa, around 18,000 ft today).


The high temperatures as of 4 PM today (Monday) are shown below.  50s and 60s on the coast, 80s over the Puget Sound lowland, and 90s in the Willamette Valley. Toasty east of the Cascades.


Tomorrow will be similar.   But then the situation will change significantly as a complex collection of low-pressure troughs approaches the region (see the upper level map at 11 PM Thursday) as the ridge of high pressure moves eastward.


Consider the forecast temperatures for Seattle (below).   Lower 80s on Tuesday, followed by a decline into the mid to lower 70s.


In the Tri-Cities, temperatures near 100F will decline into the "cool" upper 80s.


The normal high for Seattle right now is about 74F and for the Tri-Cities about 88F.   So a return to near normal conditions by the end of the week...nearly perfect weather.

What about precipitation?

The predicted ten-day total is shown below.  Precipitation over northern BC, Idaho, and Montanta.  Eastern Oregon gets a few showers.  But nothing really over Washington.


Strangly enough, this has a silver lining:  no forecasts of thunderstorms over WA state, which means fewer fire starts.

Which is a reminder to be careful with fireworks...or avoid them completely.








June 28, 2025

Will Fewer Balloon Weather Observations Mean Reduced Forecast Skill?

 Due to retirements and hiring suspensions, the number of launches of balloon-launched weather balloons (called radiosondes) has been reduced by about 10% in the U.S.  

Specifically, of the 92 U.S. radiosonde locations, about ten have reduced launches either totally or partially.


Several media sources have suggested this reduction could seriously degrade U.S. weather prediction (see samples below).   


But is this true?   As discussed below, there are several reasons to expect that the impacts will be very small, not the least because balloon-launched weather observations now play a much, much smaller role in the modern observing network.

Why upper air data matters

The atmosphere is fully three-dimensional, and predicting the weather requires understanding the 3D distribution of temperature, wind, and humidity.

Such three-dimensional data is the starting point of the key technology of weather forecasting: numerical weather prediction (NWP), in which meteorologists simulate the evolution of the atmosphere by solving the equations describing atmospheric physics on the largest computers available.

Such forecasts start with a three-dimensional description of the atmosphere, called the initialization.

During the early years of NWP (1950-1970), radiosondes were the only source of weather information above the surface.  Absolutely critical.

The number of radiosondes has declined modestly over the years, with the current global network shown below.  

Lots over the U.S., Europe, and Southeast Asia.  You will notice a major issue with the radiosonde distribution:  there are few over the oceans and the polar regions, which encompass about 70% of the planet!


The current U.S. radiosonde network is displayed below, with red circles indicating radiosonde sites that are either suspended or only launched once per day.  Keep in mind that at most sites, these observations are only made twice per day.

Is there any objective evidence that forecasts have declined with fewer U.S. radiosonde observations?

As far as I can tell, the answer is no.  

I have gone through all the objective verification scores and could not find any degradation in National Weather Service forecast skill.  For example, the 5-day precipitation scores over the U.S. in March 2025 are better than March 2024.


I could show you a dozen more like this.  

But we have to be careful here.  Perhaps 2025 was an easier year to forecast.  

To do this right, we need to do OSSEs...observing system simulation experiments... in which we run identical periods we different amounts of radiosonde data.

However, there are powerful arguments about why the radiosondes are no longer as important to weather prediction, and particularly whether the temporary loss of a few of them would make much of a difference.

Today, three-dimensional satellite observations are dominant--in fact, approximately 99% of the weather data used today in numerical weather prediction is from satellites.    For example, we can determine the winds by tracking features in the infrared part of the spectrum.


 Or we can use satellites to measure how humidity varies with height.


Other satellites measure temperature and humidity with height by noting how GPS signals are bent by the Earth's atmosphere.


I have hardly warmed up.  There are dozens of other examples of how satellites provide detailed, three-dimensional weather data over the entire planet...over most of which there are no radiosondes.

But there is more.   Many aircraft take continuous observations in flight and provide vertical profiles of the atmosphere (called soundings) are they take off and land at airports (see below).   Such soundings are very much like the radiosonde data, but are taken at more locations and at more times.


The bottom line of all this is that balloon-launched weather instruments (radiosondes) are now only a very, very small proportion of the atmospheric weather data used by meteorologists for weather prediction.   

As a result, a loss of a few observations over a portion of one country probably has very little impact.

Thus, the headlines of gloom and doom are probably wrong.    

Let me be clear....I think we should restore the U.S. radiosonde network and then complete careful experiments to determine how many of them are really needed for calibrating the satellite data and other uses.  From what I have learned, restoration of the missing radiosondes will occur over the next few months, with the National Weather Service now hiring again.






Warming and Then Much Cooler for July 4

Time for the July 4th forecast, and we are close enough that skill should be good.   The bottom line:  current warming (caused by high press...