Wednesday, January 13, 2021

2020 Annual Climate Report for Memphis, TN

2020 Annual Summary

Overall, the year 2020 featured temperatures that averaged 0.4 degrees above average, identical to 2019. However it came about with fewer extremes than the previous year. Six months averaged above normal temperatures and six below, though the warm months had greater departures from normal than the cool months, thus resulting in an above average year. 

The map above shows the departure from normal temperatures for 2020. (WeatherBell)

Precipitation-wise, the year started wet, but spring and early summer drought reversed the early excess. By December 29, precipitation was just slightly below normal, however three inches of rain to end the year resulted in a departure of +2 inches.

A NOAA map of landfalling tropical cyclones in the U.S. Three of these brought rainfall to the Mid-South - Hurricanes Laura, Delta, and Zeta.

Month-by-month recap

The year started warm and wet with temperatures that averaged over five degrees above normal and precipitation totaling almost 2.5 inches above normal. The patter favored severe weather in the pre-dawn hours on the 11th as a squall line moved through, dropping six tornadoes in the Memphis metro, the strongest an EF-2 that passed between Hernando and Olive Branch, MS. About 40,000 MLGW customers lost power due to strong wind. There were also a few snowflakes around the area on the 20th, but none recorded at Memphis International Airport. February continued the wet trend, finishing nearly 2 inches above average, but temperatures were closer to normal. There was one snow event, with up to an inch of snow falling on the night of the 6th-7th and flurries again on the 20th. Thunderstorms also occurred on five days, but there was no severe weather. 

The first quarter of 2020 ended in March the way it began - warm and wet. Temperatures averaged 4.5 degrees above normal and precipitation was more than 4 inches above normal as spring set in. From the 9th to the 24th, measurable rain occurred on 14 of the 16 days, and 20 days for the month reported rain, tying the record set in 1897. Severe weather occurred on the 28th with trees down in multiple locations across Shelby County. For the first three months of 2020, rain fell on 51 days, just missing the record of 52 set way back in 1882.

Heading into April, the weather turned cooler with temperatures averaging over 2.5 degrees below normal. It was still wet, but very near the average of 5.5 inches of rain. However, almost half of that occurred on a single day - Easter Sunday, April 12 - when severe wind damaged some trees and power lines. Severe weather also occurred on the 8th and 28th/29th, all of which were wind related. Only two April days reached 80 degrees, one less than March! May typically sees much warmer temperatures as summer approaches, and though it did warm up, Memphis still averaged more than 2 degrees below normal, with only one day that eclipsed 90 degrees. In fact, there were some late-season lows in the 40s during the second week of the month! While severe weather was limited, a destructive event on the 22nd produced widespread damaging wind in Crittenden and Shelby Counties with over 52,000 MLGW customers without power as Memorial Day weekend started.

Meteorological summer began in June with cooler than average temperatures for the third consecutive month, though not be a lot. It was also a bit drier than average, though severe weather occurred a couple of times in the first week of the month. The main event was a straight line wind system that resulted in the highest wind of the year at Memphis International - 58 mph - on the 5th. There was also some flash flooding on the 9th from slow moving storms. July was the hottest month of the year, with temperatures that averaged about 1.5 degrees above normal, in the mid 80s. In fact, the heat was persistent with only two days that failed to reach 90 degrees and low temperatures that never left the 70s the entire month. Precipitation was well below average, less than two inches for the month. Severe weather was limited. 

Finally, summer wrapped up with a break from persistent heat in August as the first week of the month averaged five degrees below normal and the month ending 1.3 degrees below average with several mornings in the 60s. Precipitation ended well above normal (12th wettest on record) with remnants of Major Hurricane Laura contributing both heavy rain and strong wind, as well as a few weak tornadoes in northeast AR on the 28th. Overall, to have two of the three summer months with below average heat was not too bad. Memphis did not reach 100 degrees in 2020.

The cooler than average trend in August was reversed for the first half of September as summer hung around, but was countered by autumn's arrival in the second half of the month. October saw multiple fronts and large temperatures swings but also ended below normal. September precipitation was hard to come by with just over an inch and a half total, though October made up for the previous month with well over four inches recorded. However, most of that fell on either the 10th, as remnants of Hurricane Delta passed through north MS, or the 28th, with remnants of Hurricane Zeta combining with a front to drop heavy rain. There was one severe weather event, on September 2nd, when scattered strong storms downed some trees and a Tornado Warning was issued as one briefly rotated on approach to the Bluff City.

The winter season began warm and dry in November. In fact, the average high temperature for the month ended up 7th warmest on record, while the average temperature for the month was in the top 10% of all Novembers on record, despite a cold snap to end the month that included snow flurries. There were only four rain days and precipitation ended up only 32% of normal with no severe weather. To end the year, December ended slightly warmer than average as a whole, but featured one of the coldest Christmas Days on record with a high of only 33 degrees. Precipitation was below average until the last two days of the year when three inches of rain fell, yielding an annual total that was two inches above average.

A month-by-month summary of average temperatures and precipitation can be found below.

Severe weather

In 2020, the Memphis office of the National Weather Service issued 286 combined Severe Thunderstorm and Tornado Warnings in their service area (221 Severe Thunderstorm and 65 Tornado). The combined number of severe weather warnings is well below the average for the past 25 years of 406. Also in 2020, there were 19 Tornado Watches and 9 Severe Thunderstorm Watches issued by the Storm Prediction Center that included some portion of the Memphis service area. The Tornado Watch count was well above the 25-year average of 11, while the Severe Thunderstorm Watch count was just below the average of 10.

The Mid-South (defined by the National Weather Service Memphis service area of eastern AR, the MO Bootheel, west TN, and north MS) recorded 33 tornadoes during 2020. There were four EF-2 tornadoes, including one in DeSoto County, and one EF-3 in Craighead County, AR, while the rest were rated EF-0 or EF-1. 

Within the eight-county Memphis metropolitan area, there were five tornado touchdowns rated EF-0 to EF-2. All five occurred in the pre-dawn hours on January 11. All but one occurred in northwest MS, including the EF-2 in DeSoto County mentioned above, and one touched down in southwest TN (Fayette County). For the year, the NWS-Memphis office received 577 severe (convective) weather reports within their service area. Below is a listing of all tornadoes that occurred in the state of TN in 2020 and severe weather reports in the greater Memphis metro.



Severe weather reports in the Memphis area in 2020

The following represents a statistical recap of the weather for 2020 in Memphis.

Memphis International Airport, Memphis, TN


Temperature
Average temperature: 63.5 degrees (0.4 degrees above average)
Average high temperature: 72.5 degrees (0.0 degrees below average)
Average low temperature: 54.5 degrees (0.9 degrees above average)
Warmest temperature: 97 degrees (August 9, 10, and 11)
Coolest temperature: 21 degrees (December 25)

Heating degree days: 2599 (366 below average)
Cooling degree days: 2167 (91 below average)
Days at or above 90 degrees: 63 (1.3 days below average)
Days at or below 32 degrees: 25 (17.8 days below average)
Last freeze/first freeze: February 27-November 30 (277 day growing season)

Records set or tied: There were no monthly average temperatures that placed in the top ten warmest or coldest on record in 2020. There were also no daily warm weather records for the year, but there were three daily cold weather records set in 2020. These included:
  • January 15 (59°, record high minimum)
  • May 9 (43°, record low)
  • May 12 (57°, record low maximum)

Comments: 2020 had the exact same average temperature for the year as in 2019, which ranks both in the top 17% warmest (tied for 24th) in the 147-year historical record at Memphis. However there were fewer extremes in 2020 than the previous year. The number of days with high temperatures at or above 90 degrees was very near normal at 63. There were 25 days that fell to or below freezing, which was well below average.

Temperatures for 2020 (lows/highs) are plotted in dark blue against the normals (brown), record highs (red) and record lows (light blue).  Where the dark blue extends above or below the brown indicates temperatures above or below normal, respectively.


Precipitation
Annual total: 55.69" (2.01" above average)
Days with measurable precipitation: 134 (26.3 days above average)
Days with 1"+ precipitation: 17 (0.4 days below average)
Wettest day: 2.68" (October 28)

Total Snowfall: 0.6" (3.2" below average)
Days with a trace or more snowfall: 6 (3.2 above average)
Days with 1" or more snowfall: 0 (1.2 below average)
Greatest snow depth (6am CST): Trace (February 7)

Records set or tied: There were no monthly precipitation totals that placed in the top ten wettest or driest on record in 2020.  Daily records included:
  • March rain days (20, record tied)
  • October 28 (2.68" rainfall)
  • November 30 (Trace, tied snowfall)
Comments: 17 days recorded an inch or more of liquid precipitation; two days had more than 2".


Precipitation accumulation for 2020 is plotted as the dark green line, compared with a normal year in brown. 


Miscellaneous

Peak wind gust: North / 58 mph (June 5)
Average wind: 7.9 mph
Average relative humidity: 69%
Average sky cover: 55%

Click here for monthly/daily statistical recaps for Memphis International Airport.

Cirrus Weather Solutions / MemphisWeather.net, Bartlett, TN

Temperature 
Average temperature: 61.8 degrees 
Average high temperature: 72.4 degrees 
Average low temperature: 52.4 degrees 
Warmest high temperature: 99.2 degrees (July 20th)
Warmest low temperature: 77.5 degrees (June 28)
Coolest high temperature: 28.4 degrees (January 20)
Coolest low temperature: 20.2 degrees (December 25)
Comments: None

Precipitation 
Annual total: 55.68" (automated rain gauge), 59.16"(manual CoCoRaHS rain gauge) 
Days with measurable precipitation: 141
Wettest date: 2.69" (April 12) (via automated gauge) 
Snowfall: 1.0 inch
Comments: One inch of snow fell on February 6-7. Traces occurred on January 20, February 20, November 30, and December 15.

Miscellaneous 
Peak wind: Northwest/52 mph (May 22)
Average relative humidity: 78% 
Average barometric pressure: 30.03 in. Hg
Comments: None

Click here for a daily statistical recap for Bartlett, TN.

MWN Forecast Accuracy

Number of MWN forecasts produced and verified in 2020: 514
MWN average temperature error: 2.11 degrees
MWN forecast temperatures within 2 degrees of actual: 67%
MWN average dewpoint error: 2.20 degrees
MWN forecast dewpoints within 2 degrees of actual: 67%

MWN's forecasts extend out five periods (2.5 days, or roughly 60 hours) and the numbers above represent the error/accuracy of the entire 2.5 day period. Historical accuracy statistics can be found here.

Erik Proseus
MWN Meteorologist

----
Follow MWN on Facebook and Twitter for routine updates and the latest info!
Complete MWN Forecast: MemphisWeather.net on the mobile web or via the MWN mobile app
Download our iPhone or Android apps, featuring StormWatch+ severe weather alerts!
MWN is a NOAA Weather Ready Nation Ambassador Meteorologist Erik Proseus is an NWA Digital Seal Holder

Saturday, January 9, 2021

Saturday thoughts on Monday's snow chances (deep dive)

I've been keeping a close eye on Monday, January 11, for several days as the calls for "more than snow flurries" increase (yep, I hear you even if there's nothing I can do about it!). The overall pattern is somewhat intriguing given a generally favorable track for low pressure across the southern Gulf Coast states and cold air in place. 



Let's start with a recap of the "more than flurries" snowfalls over the past 5 years, which lends credence to the desires for a "good snow" (all totals are from Memphis International Airport):

January 22, 2016 - 0.3"
January 6, 2017 - 2.0"
January 12, 2018 - 0.7"
January 16, 2018 - 1.8"
November 14, 2018 - 0.6"
January 19, 2019 - 0.2"
February 6-7, 2020 - 0.6"

That's all of them. One to two events per year on average, and only two dropping more than an inch.

Nuts and bolts: the winter forecast ingredients

So with that backdrop, let's look at Monday in more depth. (Apologies to those who don't care about details. You can skip ahead to The Bottom Line below.) 

A couple of ingredients are present for the potential for snow: high pressure to our north providing cold air and low pressure tracking by to our south. However, if we look at this morning's GFS model showing the surface features (below), two issues are evident: the responsible low pressure system is A) relatively weak and  B) too far south, for ideal snow-making in our area. If you look at the blue "blob" that moves across the northern Gulf of Mexico (Sunday through Tuesday morning in this loop), it is fairly subtle and it would be positioned moving across LA into southern MS and AL.


The other main ingredient is, of course, available moisture. A favorable setup of cold air and a surface low is all for naught if there is no moisture to fall! Therein lies the other conundrum... seems we could use some more of it. The loop below shows this morning's 3km NAM model precipitable water anomaly, or the departure from normal of total atmospheric moisture, from Sunday evening to Monday evening. We need more moisture than a typical January day (when the atmosphere is pretty dry) to produce a decent snowfall. You'll notice the greens (above average moisture) stay to our south. This model actually has a bit more moisture than the GFS and European models do. In other words, not ideal.


So given the track of the weak low being too far south and the available moisture also shunted to our south, you might deduce that the best chances for decent precipitation (snow if it is cold enough) are to our south. And in that case, you would be right. But that doesn't necessarily mean we are left high and dry. What does the model guidance say about actual precipitation?

Nuts and bolts: forecast model precipitation

So let's get into what the various guidance actually depicts as far as snow is concerned. I'll start with a caveat: any precipitation that falls is likely to be snow from onset (early morning Monday) through most of the event, which appears to be mid-day or early afternoon, based on temperature profiles. The temperatures support snow over rain until at least mid-day. We could see some very light rain in the afternoon if there is still precipitation falling.

Starting with the 3km NAM model, which is the "wettest" and most bullish, it drops anywhere from half inch to a little over an inch and a half across the metro (red star on each image, which are all courtesy of WeatherBell). Also worth noting that much of that falls in the afternoon, which I believe is not likely. (Note though, the swath of snow that this system produces as that low moves off the TX/LA coastline, even if totals are exaggerated!)
 

Next, the Saturday morning run of the American-made GFS model. Again note the swath to our south, closer to the low and where there is more moisture. For the metro, a dusting to *maybe* half an inch.


Next up, the overnight run of the European model. It's pretty bullish to our south, but not much more than a dusting in the metro.


We also look at the NWS official forecast, the NDFD data, which shows roughly half an inch for the metro (a little less to the north and a little more to the south).


And finally, from the NWS Weather Prediction Center, the probability of an inch or more of snow falling between 6pm Sunday and 6pm Monday, which covers our event. It says our chance is less than 1 in 20 of that occurring.


The Bottom Line

Unfortunately, if you are wanting a snow day, you may be disappointed. If you want "more than flurries," it's still possible. Our best guess right now looks like this:

When: Pre-dawn to early afternoon Monday
What: Light snow, possibly changing to light rain after lunch

How much: Likely 1/2" or less
Boom forecast: An inch (1/10 chance of occurring)
Bust forecast: Flurries

Impacts to travel: Minimal
Bread/milk/TP scale: 1 of 5 (don't bother)


With temperatures starting near 30 degrees and not much wind, minor issues are possible Monday morning if the snow starts quick enough or in an initial "burst" to lightly coat elevated roadways. By mid to late morning I expect no issues as temperatures creep above freezing. In the afternoon we should reach the upper 30s, perhaps with a little late day sun. There is a small chance of any leftover water Monday night to re-freeze in the typical areas, but we're not talking about much water falling from the sky in our area. Currently, I'd be surprised if there are any issues. 

The NWS Winter Storm Severity Index (WSSI) provides a look at potential impacts from winter weather given the forecast conditions and the geography impacted (i.e., 1" of snow in Memphis is more impactful than 1" in Chicago). Areas south of I-40 currently are forecast for potential "Minor Impacts."

After this passes, we'll warm up into the 50s by midweek with intervals of sunshine and some clouds. Another round of cold air arrives to end the week but it looks to be dry when it does. Follow our social media channels, particularly Twitter, over the next couple of days for additional forecast information and guidance, as well as routine updates Monday.

Erik Proseus
MWN Meteorologist

----
Follow MWN on Facebook and Twitter for routine updates and the latest info!
Complete MWN Forecast: MemphisWeather.net on the mobile web or via the MWN mobile app
Download our iPhone or Android apps, featuring StormWatch+ severe weather alerts!
MWN is a NOAA Weather Ready Nation Ambassador Meteorologist Erik Proseus is an NWA Digital Seal Holder

Wednesday, January 6, 2021

December 2020 Climate Report for Memphis, TN

December Climate Recap

The month of December ended warmer than average for the most part, but there were swings in temperatures throughout the month, including a cold mid part of the month, and of course one of the coldest Christmas Days in the past couple of decades. Below average precipitation in November was made up for in December with over six inches of rain at the airport and nearly 7.5 inches in Bartlett. During the mid-month cold spell, a trace of snow was recorded on both the 15th and 16th. Despite a wet month and large temperature swings, no records were set. Thunderstorms with strong wind occurred on the 23rd, leading to the Christmas Day cold snap, but wind gusts did not reach severe criteria. There were no severe weather watches or warnings issued.

Temperature departure from average for December 2020. (WeatherModels.com)


Memphis International Airport, Memphis, TN

Temperature 
Average temperature: 44.3 degrees (0.7 degrees above average) 
Average high temperature: 53.5 degrees (1.4 degrees above average) 
Average low temperature: 35.0 degrees (0.1 degrees below average) 
Warmest temperature: 73 degrees (10th) 
Coolest temperature: 21 degrees (25th) 
Heating Degrees Days: 634 (31 below average)
Cooling Degree Days: 0 (2 below average) 
Records set or tied: None
Comments: Nine dates recorded low temperatures at or below freezing versus an average of 12.4.

Precipitation 
Monthly total: 6.39" (0.65" above average) 
Days with measurable precipitation: 9 (0.7 days below average) 
Wettest 24-hour period: 2.66" (30th-31st) 
Snowfall: Trace 
Records set or tied: None
Comments: None

Miscellaneous 
Peak wind: West/38 mph (23rd) 
Average wind: 8.0 mph 
Average relative humidity: 68% 
Average sky cover: 51% 

 Click here for a daily statistical recap for Memphis International Airport.
 

Cirrus Weather Solutions / MemphisWeather.net, Bartlett, TN

Temperature 
Average temperature: 42.9 degrees 
Average high temperature: 53.1 degrees 
Average low temperature: 33.1 degrees 
Warmest temperature: 73.3 degrees (10th) 
Coolest temperature: 20.2 degrees (25th) 
Comments: None 

Precipitation 
Monthly total: 6.83" (automated rain gauge), 7.48"(manual CoCoRaHS rain gauge) 
Days with measurable precipitation: 9
Wettest date: 2.14" (31st) (via automated gauge) 
Snowfall: Trace 
Comments: Snow flurries were recorded on the evening of December 15

Miscellaneous 
Peak wind: West/50 mph (23rd)
Average relative humidity: 77% 
Average barometric pressure: 30.10 in. Hg
Comments: None

Click here for a daily statistical recap for Bartlett, TN.
 

MWN Forecast Accuracy

MWN average temperature error: 2.61 degrees 
MWN forecast temperatures within 2 degrees of actual: 56% 
MWN average dewpoint error: 2.34 degrees 
MWN forecast dewpoints within 2 degrees of actual: 64% 

MWN's forecasts extend out five periods (2.5 days, or roughly 60 hours). Historical accuracy statistics can be found here.
 

Climate Outlook - January 2021

The January climate outlook for the United States from the Climate Prediction Center is shown below. Above average temperatures are forecast for much of the United States, with highest probabilities in the Great Lakes and northeast. Odds favor above average temperatures for Memphis, with a 44% chance of this occurring, against a 23% chance of below normal temperatures. The average temperature for December is 41.2 degrees, a couple degrees cooler than December.



Precipitation is expected to be above normal across much of the eastern U.S. and well above average along the Pacific coast in January. Near average precipitation is forecast for the Rocky Mountains and interior western U.S. For Memphis, odds favor above average rainfall (a 47% chance) versus only an 20% chance of above average rainfall. Precipitation historically averages 3.98 inches.

--- 
Follow MWN on Facebook and Twitter for routine updates and the latest info! 
Complete MWN Forecast: MemphisWeather.net on the mobile web or via the MWN mobile app 
Download our iPhone or Android apps, featuring StormWatch+ severe weather alerts!
MWN is a NOAA Weather Ready Nation Ambassador Meteorologist Erik Proseus is an NWA Digital Seal Holder