Climate Newsletter January 2021


Image source: Westwide Drought Tracker... https://wrcc.dri.edu/wwdt/

Red X = approximate location of Reno-Sparks.

Percentile: 100th percentile (darker green) would mean an area had their wettest precipitation period as compared with past October-December or December periods in the climate record. 0th percentile (dark brown) would be the driest. Therefore, for the October - December period, most areas in eastern CA and western NV received precipitation in the lowest 1/3rd of other October-December periods in the climate record.



Image source: climatetoolbox.org 


Percentile: 100th percentile (darker red) would mean an area was ranked the warmest when compared to past October-December periods in the climate record...with the 0th percentile (darker blue) the coldest.

So, for high temperatures between October and December, most areas, with the exception of the valleys out in west-central/northern NV, were warmer than 2/3rds of past October-December periods in the climate record...with much of the Sierra warmer than 9/10ths of past October-December periods.

For lows, higher terrain ranked warmer than 2/3rds of past October-December periods with a fair amount above 9/10ths; however, for valleys most areas were closer to or even below the median value (white and blue areas).

Note that the last 30 days (not shown) were even colder for valley lows...perhaps due to a fairly low frequency of storms/clouds along with dry air which allowed for better overall radiational cooling at night for the early November to early December period.




Source: nrcs.usda.gov

Black line:  Snow water equivalent (snowpack) for Lake Tahoe Basin for 2020-2021 water year.

Green line:  Median snowpack 1981-2010.






Source: https://cnap.ucsd.edu/storage_in_sierra_ucrb/  


Additional charts breaking down the water storage in the northern, central, and southern Sierra as well as some specific reservoirs are at the website above.




Source:  http://nrcs.usda.gov

Red line in chart = driest soil moisture in the (30-yr) climatology.

Green line in chart = average soil moisture in climatology.

Blue line in chart = wettest soil moisture in climatology.

Black line/red X in chart = 2020-2021 so far.


Highest soil moisture usually between May and mid-June around the heaviest snow melt season.


 

Only going yellow (some interest) for low snowpack into early February as there is still time to make up much of the losses so far if a wet late winter sets up...too early to be sure right now.

La Niña persisting is of some interest as the stronger variety (moderate-strong intensity) often puts higher precipitation amounts north and west of the Sierra and western NV.



Source: https://cw3e.ucsd.edu/

Water Year = October 1 - September 30. Covers the main period of precipitation accumulation and snowmelt in spring/summer better than a calendar year in most of the West.


Note: There is less than a 20% chance of reaching 125% of normal precipitation.




Source: https://www.cpc.ncep.noaa.gov/ Reno/Tahoe area indicated by X. 


As you can see, our region is stuck between the two more certain areas that are the Pacific Northwest and southern tier of the U.S. This increases uncertainty for temperatures/precipitation in our region as we aren’t too far from the “EC” area which indicates equal chances for above, below, or near normal conditions. Oftentimes, “EC” can mean the Climate Prediction Center simply doesn’t have enough information to confidently say what a region’s most likely outcome is (which is more certain in the darkly shaded areas). 








Info source: Combination of buoy reports, NWS Anchorage posts, and a summary from the Capital Weather Gang (Washington Post).  Land pressure reading taken at Eareckson air station on Shemya Island (yellow arrow). 

BONUS: Note the “cloud streets” over the Sea of Japan (red arrows) due to instability when cold air from the Asian continent moves out over the much warmer ocean. This produces ”sea effect snow”  which enhances further when the clouds hit the Japanese Alps (Honshu) and are forced to rise and squeeze out their moisture. It is similar to lake effect snow...but on a VERY big lake! As this happens frequently in winter, seasonal snowfalls can reach between 700-1500 inches per year on average in the Japanese Alps!


Location: NWS Reno

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