On the origin of the thunderstorm symbol (R)

This blog post has a special significance to me, as it is the result of wondering about this for years now and finally getting around to digging in and figuring out the story here.  It has to do with the symbol that meteorologists use on weather maps to represent thunderstorms.  You may be familiar with this symbol--a stylized "R" shape with an arrow:

The symbol has acquired quite a following among meteorologists and it is widely used as a "cool" weather emblem.  The University of Oklahoma School of Meteorology even uses it as a part of their logo:

However, I have long wondered---where did this symbol come from?  Who developed it?  What is it actually trying to represent?  The story, as I found it, is as colorful as I had hoped it might be.

The symbol traces its initial origin back to the 1870s.  The late 1800s were a blossoming time for meteorology as a science.  The advent of the telegraph made it possible for weather observations to be rapidly disseminated across countries and continents and made observations of the large-scale structure of the atmosphere (the synoptic scale) possible for the first time.  In 1870, the War Department created a branch of the US Army Signal Corps to collect and publish weather information, and the precursor to our weather service was born.  They started issuing 2-3 times daily weather maps that summarized the temperature, pressure wind direction and sky cover reported in from major telegraph stations across the US.  Our weather mapping was born.  Several other countries also had developed weather services and each country developed their own way of displaying weather information on the maps.  Each country also had different priorities for what sorts of weather they wanted to show on the maps.

It became apparent quickly that given the large scale of synoptic weather features, international cooperation would be needed to get the full picture of the weather.  As such, a series of international conferences were held in Europe to help set international standards for how weather should be observed and recorded. The narrative that follows here is adapted from a report on one of these conferences (the 1973 International Meteoroloical Conference in Vienna) given to the Royal Meteorological Society by Robert H. Scott.  A digital copy is available through Google Books at this link.

Our attention here first turns to the 1872 International Meteorological Conference in Leipzig.  At this conference, a sub-committee was formed to address guidelines for "Hail, Thunderstorm and Cloud".  One of the questions put before this sub-committee was:

"Is it desirable to introduce for Clouds, Hydrometeors and for other extraordinary phenomena, symbols which shall be independent of the language of particular countries and therefore universally intelligible?"

The sub-committee, formed by E. Ebermayer (Bavaria), H. Schoder (German Empire) and C. Sohncke (German Empire) [along with support from H. Wild (Russia), J. Lorenz (Austria) and E. Plantamour (Switzerland)] addressed this question in an interim year and presented their report on the question at the 1873 International Meteorological Conference at Vienna.

 Their procedure for developing symbols was to poll all the nations that had organized weather reporting and mapping and learn how each of them annotated various weather phenomena.  Most nations simply used the first letter of the word that described the phenomenon in their own language.  For instance, in the US we put "R" for rain and "S" for snow (and that was about it).  Since it was expressly noted in the question for the sub-committee that these symbols should be "independent of the language of particular countries and...universally intelligible", the committee sought out more "iconographic" representations of the weather.  In their report, they present the following two tables, which show all of the different nations' weather symbols and the symbols that the sub-committee proposes to be used (click the image to get a bigger view).

There, at the bottom, we see what I believe is the first publication of the thunderstorm "R".  So where did it come from?  Examining each nation's symbols shows us a likely scenario.  If we look at the column for "thunderstorm", most nations don't bother annotating it.  Of those that do, three (Prussia/Saxony, Wurtemburg and Switzerland) all use the letter "G" (or "Gew") which is the first letter of the German word Gewitter, meaning "thunderstorm".  This doesn't match well with the requirement that the symbols be "independent" of the local language.  Austria uses a double-ended arrow for thunderstorm with a single-ended arrow for lightning. But it's the Russian symbol that is the most intriguing.  It is comprised of two components--a zig-zag line for lightning, which makes a lot of intuitive sense, and then the Cyrillic character г on the left.  If you look up the Russian word for "thunderstorm," it's гроза or "groza".  So I believe that again we have a nation just using the first letter of its native word for "thunderstorm" for the symbol.  I'd hypothesize that the sub-committee decided to take the most stylistic of the symbols (the lightning zig-zag is a really nice, intuitive touch) and merge them together to make our thunderstorm symbol  (Even if it included part of a Russian word). The addition of the arrow looks to come from the Austrians who used the arrow to indicate "lightning".  And, voila! Our thunderstorm symbol is born.

While my focus is on the thunderstorm symbol here, you'll note that many of our other symbols we use were also proposed here.  The filled circle for rain was used by France and Russia (and Austria for mist) as was the asterisk/star for snow.  The filled triangle for hail seems to be a hybrid of the open triangle from the Austrians and the filled squares from France and Russia.  Grauple is an extension of that with an open triangle.  But as to mist, hoar frost and dew?  Those aren't so clear...

Regardless, these symbols were proposed at the meeting, but the total number of categories of how many symbols were needed was debated.  The sub-committee later published a more extensive list of proposed symbols for a wide variety of weather categories.

But there was still debate on how many of these symbols to officially adopt, so the conference as a whole postponed the approval to a later meeting.  It wasn't until the 1891 International Meteorological Conference in Munich that the symbols were finally adopted by the committee.

The US seemed to approve of these standards and responded accordingly.  In 1893, amidst a flurry of reports about the climates of a variety of cities and how to observe thunderstorms and whatnot, the US Weather Bureau (having moved to the US Department of Agriculture in 1890) re-published the list of symbols approved by the International Conference, showing that these are the symbols they would start using.

In the meantime, in 1892 the Weather Bureau launched a project to investigate the possibility of forecasting thunderstorms using rapid telegraph messages.  They tried having local telegraph operators telegraph stations to their east if they were experiencing a thunderstorm with the idea that the stations further east could then warn the local population that the thunderstorm was approaching (we're talking thunderstorm warnings in the 1890s here...which I think is amazing...).  They tried it in three regions--the northeast, the upper midwest, and Ohio--and got reports back on the effectiveness.  The findings are summarized in Bulletin 9 of the Weather Bureau (which also is digitalized on Google Books, though you have to scroll way down to get to Bulletin 9 toward the end of the document).  While some of the reporters felt that these warnings were not practical and didn't give enough lead time (things we still work on to this day), the results were generally encouraging.  (As a side note, it probably helped that they focused on June-July-August across the northeastern quadrant of the country, where linear and quasi-linear MCS storms are the dominant mode of convection.  These lines of storms are pretty coherent and can last a long time--even overnight.  This makes them a bit easier to predict in this way.)  The Weather Bureau seems to have realized after this experiment that it could be useful to include thunderstorm information on their weather maps.

Finally, the US Weather Bureau (which was still issuing daily weather maps) upgraded their map printer from a 'milliograph' stencil-duplicator to a faster and more efficient "chalk-plate" process in 1896 (as described in this interesting paper).  All the maps from that time are archived through the NOAA Central Library Data Imaging Project.  There is a clear change in the style of the maps on June 15, 1896.  Here is the title bar and legend before the change:

No mention of thunderstorms--just sky cover, rain or snow, and by "storm track" they mean the path of the low pressure center over the previous few days.  "Storm Signals" indicate if a station reported storm-force winds.  Here's the title bar and legend after the map change:

It appears they hadn't switched over to the new "Rain" and "Snow" symbols (probably because there remained a conflict with the filled dot for "cloudy".  But we see the addition of a "C.W." annotation for "cold wave" (they didn't have the Norwegian cyclone model yet, so the concept of a "cold front" did not exist yet).  And, in the second line from the bottom, we see our R for thunderstorms reported during the previous 12 hours.  Here's a snapshot of the map on June 15, 1896 showing the reports from the central US, including the first thunderstorm symbols on a Weather Bureau map.

Looks like they had thunderstorms in Dodge City, Kansas, Des Moines and Keokuk, IA and Springfield and St. Louis, MO.  Another batch of storms impacted Milwaukee, WI and Grand Rapids, MI.  And so our thunderstorm reporting began.

I had a lot of fun researching this topic.  There's more to come for sure.  A lot of the other symbols we use were defined at a later time.  For instance, when did the extra "kink" in the thunderstorm symbol get added for "heavy thunderstorm"? And what of all the different symbols for each type of cloud?  There's a history there to be sure.

Strong winds and rain in the east; snow in the northwest?

In my last blog post I talked about the blast of arctic air that was forecast to move across the country last weekend and into this week in association with a cut-off low that would slowly creep across the southern US.  Here we are on Monday and today's 500mb pattern from the ECMWF still shows that cut-off low over Texas and New Mexico.

The colder air and lift that are accompanying this storm have already contributed to snow and ice throughout New Mexico, Texas and Oklahoma.  In fact, the weather map from the Oklahoma Mesonet today shows several sites that are not able to report the wind speed or direction (the red dots on the map below) because the anemometers and wind vanes are frozen!

This storm is expected to  slowly chug eastward over the next few days before ramping things up along the east coast.  Look again at the 500mb chart above.  See that other trough in the northern Great Lakes / northwestern Ontario?  That trough is forecast to merge with the cut-off low sometime during the next few days.  One one hand, this means that the cut-off low will no longer be cut-off---back in the normal flow, it will accelerate and move on out of here.  Before it does, though, the cold air it's bringing behind it is going to run into the warm Atlantic Ocean, and that means rain--heavy rain--for the eastern US.  Here's the ECMWF forecast rainfall around 15Z Wednesday morning:

Heavy rain up and down the east coast on a day when lots and lots of people will be travelling.  Not good.  Fortunately by Thanksgiving day itself, it appears that the precipitation will be on its way out (as this storm accelerates off the coast).  Here's the ECMWF precipitation forecast for Thursday morning at 15Z:

Only light precipitation for parts of the northeast.  A lot of this near the lakes may be lake effect snow as strong northwesterly winds will occur behind this storm.  See the tight gradient in the blue contours on the above map?  Those are the surface pressure contours, and the tighter the pressure gradient the stronger the winds.

This brings up another question that I know many people are dying to hear the answer to--will the Macy's Thanksgiving Day parade balloons be able to float with this weather?  I'm told that if the winds gust higher than 35 mph then the balloons are a no-go for the parade.  So what are the models saying?

It's probably going to be close.  Our models mostly forecast sustained winds, that is, the average wind speed over a certain amount of time (usually a few minutes).  Wind gusts are instantaneous wind speeds, and the wind gusts can be significantly higher than the sustained winds.  Here is the ECMWF sustained wind forecast over New York City for 15Z on Thursday while the parade is going on:

You can see the winds really pick up speed off the coast.  But over the city itself, the bluish-greenish colors indicate winds of 15-18 knots or 17-21 mph.  Again, those are the sustained winds--gusts will be higher.  The GFS and NAM have slightly stronger sustained winds, getting up to more like 25-28 mph--again, with higher gusts.  So, as of right now, it's going to be borderline.  We'll have to watch the model runs as we get closer to get a better idea of how strong the winds are going to be.

And finally, just as a teaser for everyone out here in the Pacific Northwest, the really long range models for next Sunday-Monday have a strong cold front coming through in association with a sharp trough coming down the Pacific coast from Alaska.  Here's the ECMWF 156 hour forecast (!) of 850mb heights and temperatures for next Sunday.

A blast of cold air headed our way.  The ECMWF has some low-level instability following this cold front and is throwing out some convective snow showers in its wake.  Though we should never, ever believe models this far out into the future, for fun here is the ECMWF snowfall accumulation forecast for next Monday morning:

Two inches of snow in the lowlands east of Everett?  Eh...maybe.  Don't take my word for it yet.  But it's definitely something to keep an eye on...

From calm to cold with cut-off lows

Looks like we're in for a major synoptic pattern change over the next week or so.  This morning's 12Z analysis from the ECMWF model at 500mb finds us with a nice zonal (east-west) pattern.  There are a few minor shortwave troughs but nothing very large in scale.

By tomorrow morning (Thursday), that is forecast to change.  The weak troughing over the eastern Pacific and western US is forecast to deepen rapidly into a strong trough.

And by Friday morning, the trough has deepened to become cutoff low--completely separated from the main jet stream winds (shown by the enhanced colors on the map) that are blowing to the north.

It's pretty amazing how over the course of 48 hours the upper-level pattern can change so quickly.  As I noted in previous blog posts, cut-off lows like this tend to stick around for a while.  Because they are separated from the main jet stream winds, there's nothing to really force them to move along from west to east.  So they usually just sit there.  This low will hover around for just a few days though, before transitioning back to an open-wave trough by next Monday as seen here:

But then, yet another cut-off low is forecast to re-develop off the west coast by next Wednesday!

I should also note that this particular upper-air pattern forecast for next Wednesday is bad news for the east coast--you have a deep trough covering the northeastern quarter of the country and then another shortwave trough racing through the southeast US and about to emerge over the Gulf Stream.  Nor'easter type storms are often born with this sort of setup as cyclogenesis occurs off the Carolinas.  This is still a long way out in the forecasts (168 hours), but it's something to watch...

Another aspect of this cut-off low moving across the US this week into next is that it will open the door for colder air currently over Canada to sneak down into the US.  Compare this morning's 12Z surface temperature analysis from the GFS:

With the forecast for Friday morning's low temperatures:

Much colder air moving in.  Pretty strong front at the leading edge of it too.  There are chances for some severe weather tomorrow as the front crashes through the plains, followed by a round of wintry precipitation. We're going from tornadoes this past Sunday to winter weather by the end of the week.  Such is autumn...

Severe, tornadic storms and upper-level forcing

Just thought I'd quickly share this one screen capture I grabbed yesterday during the unusual November tornado outbreak over the Midwest.  I find myself more and more often using Weather Underground's "Wundermap" tool to overlay weather model output on current observations, satellite and radar to try and both see how well the model is doing and make connections between model features and what's actually happening.  Here we see the composite radar image over the continental US overlaid on top of the ECMWF 300mb forecast for around 1 PM CST on Sunday.  The 300mb wind speeds are shown in color with the 300mb height lines shown as the white contour lines.

You can really see how these lines of convection in the radar imagery formed along the exit region of the upper-level jet streak.  This is a favorable location for divergence aloft, particularly when the jet streak has cyclonic curvature as it does here.  Furthermore, the surface cold front associated with this storm was actually back over central Illinois at this time.  It was upper-level support out ahead of the cold front---this strong jet streak coming around the base of the trough---that provided a lot of the forcing to get this convection going.  Of course, once these storms organize into line segments they can be self-reinforcing in generating enough lift to keep themselves going.  But once again, this emphasizes how understanding what's going on in the upper-levels (something our models forecast fairly well) can be both useful and important for understanding when and where convection is going to develop (something our models don't do nearly as well).