Climate News - September 2020

Hope everyone has been doing as well as possible! For this newsletter, we will begin with the usual summary of regional climate features over the past few months. That will be followed by a look at abnormally warm ocean waters, also known as a “marine heat wave”, which have set up across the North Pacific. Finally, we’ll throw in a few words about climate averages from The National Centers for Environmental Information which are due to be updated by the middle of next year.

Note: If you have any questions or would like clarification on what is presented in this newsletter, feel free to message us on Facebook (https://www.facebook.com/NWSReno/) or email w-rev.webmaster@noaa.gov

________________________________________________________________________________



So, what’s been happening from a climatological perspective across northeast California, the Sierra, and western Nevada? Summer high temperatures ran considerably above average when compared with the averages from 1981-2010 (the last climate period used for comparison). By examining the summer highs (June-August), you can see that most spots were well above average (1.5 to 3 degrees over a season is notable).


As f

Low temperatures this summer, they were around average (not shown) for areas around Fernley, Fallon, and Lovelock, with most of eastern California, western/northwestern Nevada, and Mineral and southern Lyon counties around 1 and 3 degrees above average. One might think that the above average lows could be due to the urban heat island effect; while this is likely a factor in places like Reno-Sparks, most areas outside of urbanized areas also saw the bump.

 

Precipitation over the summer was, as you can see from the image below, mostly below average for many locations across the southwestern CONUS. There were pockets of close to average precipitation in eastern CA and western NV...at least partially due to periodic thunderstorm formation. Note that from June-August the region typically receives less than 2 inches of precipitation as it is reliant mostly on hit-and-miss thunderstorms or the occasional late spring system.




What is the EDDI?

Finally,  let’s take a look at a measure of the evaporative demand or thirst of the atmosphere over the summer. It is called “EDDI” for evaporative drought demand index and it looks at temperature, humidity, windspeed, and solar radiation to determine how much ground moisture has been lost to (or gained from) the atmosphere over a given period. It then compares the gain or loss to the 1979-2016 climatology to find out if evaporation loss to the atmosphere has been more or less than is typical. It can be used to see where excessive ground moisture loss to the atmosphere is exacerbating drought conditions.


Directly below is a look at the EDDI between mid-June and mid-September versus the 37-year average for the same 3 month period. Breaking down this period further, the two 1-month images for mid-August (below left) and mid-September (below right) show the progression of the evaporative loss, with the mid-September image indicating that much of the increased ground moisture loss has occurred towards the tail end of summer. In fact, only 2% of the past mid-August to mid-Septembers between 1979 and 2016 indicated as much loss as 2020. 



Note: Images provided by the NOAA/ESRL Physical Sciences Laboratory, Boulder, Colorado, at: https://psl.noaa.gov/.


Yet Another Marine Heat Wave For the North Pacific


A “marine heat wave” (MHW) occurs when ocean temperatures are much warmer than usual for an extended period of time. MHWs are of concern as researchers have documented many ecological effects including harmful algal blooms, shifting distributions of marine life, and changes in the marine food web. Several MHWs of note have occurred since 2014. MHWs in the 2014-2016 (aka “The Blob”), 2019, and 2020 time periods are the three largest in size since monitoring began in 1982. This year’s MHW has just recently increased in size to become the largest since 1982. Below is an image showing sea surface temperature anomalies with the area surrounded by the black line corresponding to the marine heat wave. 


Below’s chart shows the relative size of MHWs since 1982. You can clearly see that the events since 2014 are by far the largest.  



Note that we at the NWS in Reno are no experts on MHWs and their effects. For more information on MHWs from researchers, see the sources below or visit http://www.marineheatwaves.org. 



 


________________________________________________________________________________




Updated Climate Normals From NCEI Coming in 2021


The National Centers for Environmental Information (NCEI) is responsible for collecting vast amounts of data in order to create 30-year normals with which to compare to current weather and climate events. New 30-year normals are created every 10 years, with the 1991-2020 period expected to be revealed no later than May 1, 2021. To keep up with the pace of climate change, there is talk of providing 15-year normals every few years if NCEI resources allow.  


If you would like to check out various climate information for stations around northeast California, the Sierra, and western Nevada, go to our NOWData page. Note that NOWData is available for all National Weather Service offices...just go to weather.gov and pick your area of choice!







NOWData page image:





Well, that wraps it up for this climate newsletter. Stay safe and we’ll catch you all next time (probably early 2021)! 


  • Your NWS Reno Climate Team

Popular posts from this blog

NWS Wind Forecasts: AKA What's the Deal With Friction?

Image
We have had a number of comments on social media which mention much lower observed wind speeds locally than are in the forecast. Well, you are unlikely to know this (it is not exactly advertised!) but National Weather Service wind forecasts are for 10 meters, or almost 33 ft, above the ground. As we are about to explain, that makes all the difference in the wind between eye-level (~5-6 feet) and ~33 feet.  It is natural to wonder the purpose of a wind height forecast well above where you and I typically reside. The main reason for this is the complication in forecasting wind as one nears the ground due to frictional influence caused by the surface. Here is a diagram showing the concept of wind speeds change as one gets away from the ground.  As you can see above, there is a rapid speed reduction (gray dashed line) near the ground with a lesser change away from the surface. Note that the above diagram is generalized. How much reduction is realized depends on the nature of the s...
Read more

What is the Rain Shadow and What's Wind Gotta do With It?

Image
The dreaded rain shadow - something that those of us who live east of the Sierra crest are more than familiar with and hate to hear. So what is this rain shadow and why does it even exist? Lets start with the topography just to our west... The Sierra Nevada mountain range runs 400 miles from north-to-south and is approximately 70 miles wide. It includes the highest peak in the lower 48, Mt Whitney at 14,505 feet, and rises above 10,000 feet in many locations. Left: The Sierra Nevada Mountains highlighted in blue. Right: A relief map showing elevation (in meters) of the Sierra. The Sierra are a significant barrier for Pacific storms which typically move from west to east. The movement of air masses and associated weather cannot go through the mountains and is forced up and over the mountain range. As Pacific moisture is driven eastward by the wind, the air mass is lifted up and over the Sierra. Rising air will cool and once it reaches the point of saturation, condense into...
Read more

Forecasting "Dry Microburst" Potential From Soundings and Observations

Image
Summer afternoons in the valleys of eastern California and western Nevada usually feature dry low level relative humidity. In certain cases where low levels are very dry (single digit relative humidities) and enough instability for showers and/or thunderstorms exists, there is the heightened possibility for severe (over 60 mph) outflow winds. Now, severe winds are possible from strong thunderstorms in many cases, even without very dry surface relative humidity. However, what makes very dry surface or low level conditions special is that severe outflow winds are possible even with w eak  convection such as light showers...or even just cumulus clouds! When severe winds are produced by convection with little or no rainfall reaching the ground, it is referred to as a "dry microburst". Microbursts can be of significant danger to aviation and, if they are strong enough, life and property. Before we move onto what conditions we look for to determine the threat for dry microbursts,...
Read more