Sunday, June 13, 2021

Relief from falling water - from the sky and our brows!

Last weekend on this blog, we correctly forecast a wet pattern for this past week, though we didn't expect to see 10-15" of rain across sections of southeast AR into northern MS! Meanwhile, those of us north of I-40 (or so) enjoyed tolerable rain amounts most days that helped green up our Bermuda lawns! 

Departure from average rainfall amounts for this past week show nearly a foot of rain above average across north MS and southeast AR. In west TN, near average in the metro but below average just to our north. (WxBell) 

We also correctly identified our first 90-degree temperature of the year occurring in the past couple of days. However, one thing we missed on last weekend was this statement regarding this (current) weekend's weather: "...a push of drier air into the region that will bring relief from high dewpoints and a breath of fresh air from the north." Oops! While the temperature and scattered thunderstorm prediction we also made was correct, the front that has passed through has done nothing for the humidity (yet)!

The week ahead - sunshine and low humidity

About that "(yet)" mentioned above... perhaps the week-ahead models were just off a couple days. Starting tomorrow, we will finally feel the effects of drier air that is pushing south behind this weekend's cold front. Dewpoints, which are a direct measure of the amount of moisture in the air, will fall from the mid 70s to near 80 in some spots this weekend (oppressive!), to the 60s Monday and then maybe the 50s by mid-week (very pleasant!).

The Muggy Meter for Tuesday afternoon shows dewpoints 10-15 degrees cooler than this weekend!

In addition, a dry pattern sets up as high pressure at the surface builds in from the north and aloft from the west, while a trough of low pressure settles into the eastern U.S. This pattern results in slightly cooler temperatures (mainly 80s during the days and 60s at night), lower humidity, and abundant sunshine. I believe the farmers and others flooded out to our south this past week will gladly take that forecast!

The mid-level pressure pattern and departures from normal for this week from the European ensemble shows a massive ridge of high pressure over the western U.S. extending east to the Mississippi Valley, while a trough of low pressure sits over the eastern seaboard. (WxBell)

The surface weather pattern on Wednesday morning, according to the European ensemble, shows high pressure over the Great Lakes extending well south with drier and cooler than average flow around it. (WxBell)

Next weekend - tropics get the attention

By next weekend, eyes will be turning south as a tropical disturbance could be moving towards the western or central Gulf coast. While it's still early, indications are that an area of showers and storms will remain fairly disorganized well south in the Bay of Campeche, off the Mexican coast south of the TX coastline, into mid-week. After that, it could start to move north and perhaps organize a bit. It's entirely too early to make any predictions, but the western to central Gulf coast (TX, LA, MS, AL) could see a fair amount of rain from this system next weekend into early the following week and it's conceivable that a tropical storm could bring gusty wind to the coast in that timeframe as well. 

The National Hurricane Center (NHC) is keeping a close eye on a disturbance in the Bay Of Campeche. It currently poses no threat to the U.S., but by mid-week could start moving north bringing rain to the western Gulf coast. (NOAA/NHC)

For now, it looks to have little to no impact on the Mid-South for the next 7 days, though another frontal system is more likely to bring precipitation chances back to the Mid-South next weekend with humidity increasing as well. Stay tuned!



Erik Proseus
MWN Meteorologist

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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
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MWN is a NOAA Weather Ready Nation Ambassador Meteorologist Erik Proseus is an NWA Digital Seal Holder

Sunday, June 6, 2021

Pesky upper low brings a wet & muggy pattern this week

The average first occurrence of 90 degrees in Memphis is May 24. This afternoon as I type this, on June 6, the temperature is 76 under cloudy skies with scattered showers over the region. We hit 89 twice near the end of May and really have not threatened it so far in June. And as you'll see from the forecast below, it's not likely to happen this work week either. Three cheers for less A/C (if you can tolerate the humidity that has arrived in its place)!

Atmospheric Overview

A large upper level low pressure system over the Southern Plains the past few days will lift slowly northeast into Missouri on Monday, then into the Ohio Valley mid-week as it weakens. A trough will extend south from the low into the Mid-South early this week before shifting east as high pressure aloft builds into the area from the southwest behind the weakened and departing low. 

This pattern has pushed summer heat well to our north - into the Northern Plains and east into the Northeast U.S. where highs are reaching the 90s to near 100 degrees in spots! Meanwhile, scattered to widespread showers and embedded heating-of-the-day thunderstorms cover the south-central portion of the country with rain chances having spread east into the southeaster U.S. this weekend. As the upper low shifts east, so do the higher rain chances, before diminishing later this week as high pressure overhead starts to regain control. Let's walk through the week day-by-day...

The upper level pressure pattern from the European model ensemble through Friday evening shows an upper level low weakening and lifting northeast this week, replaced by higher pressure. The blue colors indicate anomalously low pressure, while the orange anomalously high. (WeatherBell) 


Monday

Rain has been relatively hit and miss this weekend and I expect that trend to continue into Monday with scattered showers and thunderstorms during the warmer part of the day and lingering showers into the evening. You may or may not get wet - it's impossible to predict where and when the rain falls. However, we can be sure that southerly wind keeps the dewpoints elevated at or above 70, which is high enough to ruin your hair-do and considered very muggy. After a morning low near 70, afternoon highs reach the low 80s.



Tuesday-Wednesday

With the weakening upper low passing by to our north and the trough passing through our area, rain chances are a bit higher (in the 60-70% range) and may include more of the overnight hours as well, though any thunderstorms that occur are more likely to be in the afternoon/evening hours when peak heating occurs. Humidity remains gross as southerly wind continues to fetch Gulf moisture and throw it over the region. Lows remain at or above 70 (which honestly isn't that low) and highs top out in the low to mid 80s. 


Thursday-Friday

As the low starts to move away to our east, high pressure aloft takes its place. However, lingering humidity and a bit more heating thanks to some sunshine breaking through means scattered shower and thunderstorm chances continue, though at lower probabilities (50% Thursday and about 30% Friday, as of now). Precipitation totals through Friday morning could reach the 2-3" range after multiple days of elevated rain chances, though the scattered nature on at least a couple of days could mean wide variances from place to place.

Forecast rainfall through Friday morning from the NWS Weather Prediction Center. 2-3" will be common across the Mid-South. (PivotalWx)

High temps will likely reach near average values in the upper 80s by Friday. With dewpoints remaining uncomfortably high, you should make sure your deodorant supply is in good shape to start the week. 



Next weekend

Early signs point to a bit of relief Saturday in the form of a cool front. If models are correct (that may be a 50/50 proposition six days out, but there is at least some agreement amongst them), then we'll see one more day of scattered thunderstorms. But we'd also receive a push of drier air into the region that will bring relief from high dewpoints and a breath of fresh air from the north, leading to a dry Sunday. 

One thing to consider though is that it won't necessarily be cooler behind the front. In fact, high pressure aloft looks like it might continue to build, so there's a decent chance that by next Sunday afternoon we will be looking the first 90-degree temperature of the year squarely in the eyes. And by mid-June, it's not only almost 3 weeks behind, but also perfectly normal to see 90 every day for a couple of months. Summer is on the horizon!



Erik Proseus
MWN Meteorologist

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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
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MWN is a NOAA Weather Ready Nation Ambassador Meteorologist Erik Proseus is an NWA Digital Seal Holder

Saturday, June 5, 2021

May 2021 Climate Report for Memphis, TN

May Climate Recap

May continued the cooler and drier pattern compared to normal that began in April. Temperatures averaged about two and one-half degrees below normal with no 90 degree readings for the month, though the high temperature did reach 89 a couple of times at the end of the month. (The average first date of 90 degrees is May 24.) There were 12 days with daily average temperatures above average, most of those in the latter third of the month, but none well above average. On the other hand, the high temperature on the 29th of 61 degrees tied the record for coolest on that date. 

Precipitation ended below average (76% of normal), even though the number of rain days and number of one-inch-plus rain days for the month was very nearly average.  In fact, 83% of the total May rainfall fell in the first 11 days of the month. Following a very quite severe weather month in April, severe weather in May was also almost non-existent with only one day in which severe weather reports were received. On the late afternoon of the 9th, a broken line of strong to severe storms affected the metro with a few wind damage reports in Tunica and Tate County and a brief tornado touchdown in Tipton County near Drummonds that caused EF-1 (95 mph) damage along a roughly five-mile path. Fortunately there were no injuries or casualties.

Radar imagery as the Tipton County tornado moved just east of Drummonds, TN on May 9.




Memphis International Airport, Memphis, TN

Temperature 
Average temperature: 69.5 degrees (2.6 degrees below average) 
Average high temperature: 78.6 degrees (3.1 degrees below average) 
Average low temperature: 60.4 degrees (2.0 degrees below average) 
Warmest temperature: 89 degrees (24th, 25th, 27th) 
Coolest temperature: 49 degrees (7th) 
Heating Degrees Days: 30 (9 above average)
Cooling Degree Days: 175 (65 below average) 
Records set or tied: May 29 - daily record low maximum (61 degrees)
Comments: There were no days with high temperatures above 90, nor any days with low temperatures below freezing. The average first 90 degree day is May 24.

Precipitation 
Monthly total: 4.01" (1.26" below average) 
Days with measurable precipitation: 10 (0.6 days below average) 
Wettest 24-hour period: 1.53" (2nd-3rd) 
Snowfall: 0.0"
Records set or tied: None
Comments: Two days recorded precipitation of more than an inch, right at average for May.

Miscellaneous 
Peak wind: North/38 mph (6th) and Southwest/38 mph (9th) 
Average wind: 8.7 mph 
Average relative humidity: 64% 
Average sky cover: 62% 

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

Cirrus Weather Solutions / MemphisWeather.net, Bartlett, TN

Temperature 
Average temperature: 68.0 degrees 
Average high temperature: 79.2 degrees 
Average low temperature: 57.6 degrees 
Warmest temperature: 92.0 degrees (27th) 
Coolest temperature: 44.6 degrees (14th) 
Comments: None 

Precipitation 
Monthly total: 3.62" (automated rain gauge), 4.04"(manual CoCoRaHS rain gauge) 
Days with measurable precipitation: 11
Wettest date: 1.16" (4th) (via automated gauge) 
Snowfall: 0.0"
Comments: None

Miscellaneous 
Peak wind: South/27 mph (9th)
Average relative humidity: 74% 
Average barometric pressure: 30.04 in. Hg
Comments: None

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

MWN Forecast Accuracy

MWN average temperature error: 1.96 degrees 
MWN forecast temperatures within 2 degrees of actual: 73% 
MWN average dewpoint error: 2.11 degrees 
MWN forecast dewpoints within 2 degrees of actual: 68% 

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

Climate Outlook - June 2021

The June climate outlook for the United States from the Climate Prediction Center is shown below. Above average temperatures are forecast for much of the northern and western U.S. Below average temperatures are forecast in the Southern Plains to Lower Mississippi Valley. Odds favor near average temperatures for Memphis (34%) versus a 33% chance of above or below normal temperatures. The average temperature for June is 79.9 degrees.




Precipitation is expected to be above normal for the Southern Plains and southeast U.S., stretching into the Mid-Atlantic, with highest odds in eastern TX into LA. Below average precipitation is forecast for the northwestern U.S. For Memphis, odds favor above average precipitation (51%) versus only 16% chance of below average precipitation. Rainfall historically averages 3.99 inches.

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Complete MWN Forecast: MemphisWeather.net on the mobile web or via the MWN mobile app 
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MWN is a NOAA Weather Ready Nation Ambassador Meteorologist Erik Proseus is an NWA Digital Seal Holder

Tuesday, June 1, 2021

Cool and wet for the first week of June, and Atlantic hurricane season begins!

Summer weather has held off for about as long as possible across the Mid-South. May temperatures finished off below average, coming on the heels of a cooler than average April. Overall, it was quite a nice spring across the Memphis area and for most of the Southeast! Rainfall was also a bit below normal, due to frequent cold fronts pushing Gulf moisture out of the area. We still have yet to hit 90 degrees this year, and are now almost a week behind the average first 90° reading of the year! 

Temperature departure from average for the month of May. Much of the country experienced cooler than typical weather. (WeatherBell)

Forecast overview - wet and cool

Now as we enter the month of June, another pattern shift will bring tropical moisture back into the region and set the stage for daily chances of showers and thunderstorms. Persistent lower pressure in the upper atmosphere over the central and eastern U.S., along with increased cloud cover from daily rain and storms will keep temperatures below average over the next week. We should finally be back in the 80s by Thursday, but temperatures will only slowly climb to the mid 80s as we enter this weekend and next week. Not an above average day in sight! 

We were a bit below average for rainfall in the month of May, but that trend looks to quickly be reversed as we enter the month of June. The Mid-South will be positioned between a ridge of high pressure to our east over the Atlantic and another large ridge over the western U.S., which is bringing very hot temperatures all the way into the Pacific Northwest. This pattern allows moisture to be pumped off the Gulf. When combined with a trough of low pressure over the area and repeated disturbances moving through the trough, we'll see daily chances of scattered to numerous showers and thunderstorms. 

The upcoming pattern (as depicted by this upper level forecast chart for Wednesday night) features a trough of low pressure in the middle of the country and ridges of high pressure to the east and west. This pattern is very favorable for showers and storms, as well as cooler than normal temperatures. (WeatherBell)

Rain chances and amounts

Tonight and Wednesday look to have an almost guaranteed chance of rain across the area as a disturbance moves through the Mid-South. Rain chances diminish a bit Thursday through Saturday, but there will still be a chance for widely scattered to scattered afternoon showers and storms. By the latter half of the weekend and into the beginning of next week, another disturbance is poised to move through the area, once again bringing more widespread coverage of showers and thunderstorms. 

Over the next week, models are showing most of us picking up a healthy dose of rain - around 1.5 to 2.5 inches by next Tuesday. However, it is important to note that this time of year, storms can be fairly random, and it can rain 2 inches on one side of town but be completely dry on the other. Forecasting exactly where and who will get a storm is nearly impossible with pop-up storms, but just know there will be at least  a chance nearly every day. Severe weather doesn’t look to be a threat, but any storm could have lightning, torrential rain, and gusty wind. Just because it isn’t warned doesn’t mean you shouldn’t be careful, especially if lightning is present.

The European model forecast of rainfall over the Mid-South through next Tuesday morning. Due to the random nature of storms, a wide range of rainfall accumulation is likely across the area. (WeatherBell)

Atlantic hurricane season begins

Something else of note as we enter the month of June - today is the first day of the 2021 Atlantic hurricane season! While we may be a few hundred miles away from the coast, tropical cyclones can still have a significant impact in Memphis, with flooding rains and the potential for spin-up tornadoes. Nothing is on the radar in the Atlantic at the moment, but just something to keep in the back of your mind, especially if you are planning on a beach vacation later in the summer.  NOAA's prediction for this year is a 60% chance of above normal activity with 13-20 named storms. (We've already had Tropical Storm Ana - another early-bird that formed in May - that affected Bermuda!)

NOAA's prediction for the 2021 hurricane season.


Overall, as long as you don’t mind some rain and humidity, the pattern is not looking bad for us. We have really lucked out on missing any big-time heat so far this season, and that trend looks to continue for at least the next week. However we know our luck can’t last forever, and 90 degree days are probably lurking just around the corner. Stay tuned, and enjoy this first week of meteorological summer! 


Christian Bridges
MWN Social Media Intern

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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

Thursday, May 27, 2021

Stormy lead-in to a fabulous holiday weekend

The heat and humidity has built this week with spotty precipitation over the past couple of days. High temperatures have generally been near 90 degrees, though as of early Thursday afternoon we had yet to actually reach 90 degrees yet this year. Looking ahead to the Memorial Day holiday weekend, fabulous weather is on tap - low humidity, cool mornings, pleasant afternoons and sunshine! However, we'll first need to deal with a late spring cold front...

Storm chances the next 24 hours

With unstable and humid air in place ahead of a cold front that arrives on Friday, the ingredients are in place for thunderstorms, and those will affect us over the next 24 hours. There are multiple small-scale (or "mesoscale") atmospheric features that are affecting thunderstorm development well to our northwest today - chiefly over the central plains. The development and propagation of those storms will determine when we see storms in the Mid-South, which makes pinpointing the timing somewhat complex. In addition, the timing of the arrival of those storms will also factor into the risk of severe weather. 

Our best educated guess at what to expect is that an initial wave of thunderstorms will move into the area late this evening, most likely after 8-9pm. Models hint at these mainly affecting northern AR and western TN. The Memphis area may be on the tail end of this cluster or line. After what should be a lull of perhaps a few hours, a more substantial threat of storms arrives in the wee hours of Friday morning. The exact timing is again in some doubt, but most model sets suggest that they will roll through at some point between 2-3am and morning rush hour. These storms, due to their timing in the "coolest" part of the day (though it will still be relatively warm and muggy) will likely be weaker when they arrive than when they are moving across AR during the overnight hours and should mostly fall apart as they shift east of the metro. Below is the HRRR model's opinion of how the scenario unfolds, with caveats that it's timing and/or intensity could vary, perhaps quite a bit.

The mid-day Thursday HRRR model showing forecast radar through noon Friday. Model output does not equal gospel. (WeatherBell)

Storm threats and preparation

Our main threats with any severe weather would be strong wind gusts due to the expected linear nature of the storms - in other words a squall line, though weakening. Minor flash flooding or small hail are also possible. The tornado threat appears minimal. Below is our latest impact graphic. Best ways to prepare include tying down anything that might blow away in strong wind and garaging vehicles if able. After a fairly long dry spell, the ground should readily accept most water than falls with little issue as rainfall will average under an inch.



A Memorial Day weekend to remember!

Speaking of the weekend ahead, we'll have quite a nice few days to spend outdoors without too much sweat! Overnight lows behind the cold front are expected to dip into the mid 50s with highs Saturday and Sunday in the 70s! We'll warm up some Monday, but still should feel very pleasant for holiday cookouts. Look for more humidity to build into the middle of next week with daily rain chances by Wednesday.


Erik Proseus
MWN Meteorologist

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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

Tuesday, May 18, 2021

Farewell spring, it's been fun...

It has been a wonderful spring so far across the Mid-South, and for many in the Southeast. April was a below average month for temperatures, and that trend has continued into May. In fact, we are 5-7 degrees below average so far for the month of May! With average high temperatures now rising into the 80s, this has given us several weeks of beautiful, pleasant spring weather overall. However, after today, rain chances and cloud cover will decrease, allowing temperatures to quickly rise through the 80s and approach 90 degrees by Saturday. Farewell spring!

This month-to-date (May) high temperature anomaly map for the U.S. shows much of the eastern two-thirds of the country has experienced well below average temperatures for the first half of May. (WeatherBell)


We knew it couldn’t last forever, and sure enough a major pattern shift is coming for us here in the Memphis area. The cool weather was caused by a persistent trough of low pressure over the Mid-South and eastern U.S., which helped to continually funnel cool air down into the south from the northern US and Canada over the last month and a half. The hot weather has been confined to western portions of the country, as a large ridge of high pressure with sinking, hot air has refused to budge for the month of April and into the first half of the month of May. Now, that pattern is finally changing. A trough will dig into the western US, bringing the West Coast and Rocky Mountain region some much needed rain, cooler air, and wildfire relief. 

Unfortunately for us, a large ridge of high pressure looks to build in over the next few days and intensify, ending our very nice spring weather and setting the stage for the arrival of more summer-like weather. With this high pressure center sitting to our south and east, the clockwise flow around the high will pump Gulf moisture directly into the Mid-South, quickly warming our temperatures. Due to the sinking air of the high pressure, rain chances will also diminish, leaving us with lots of hot sunshine and humidity. 

As we go into the latter part of this week, an upper level pattern known as an ‘omega block,’ because the pressure pattern resembles the Greek letter omega, will set up across the United States. This will keep the ridge of high pressure parked over the central and eastern US for at least the next week, if not longer. This is a classic pattern for hot temperatures under the high - a “heat dome” is not a bad way to describe it.

The upper air pattern setting up for this weekend and early next week features an 'omega block' across the country, with high pressure covering most of the eastern half of the nation. (European model, WeatherBell)


The ridge sitting over us for so long will allow temperatures to quickly climb each day, and our first 90 degree days of 2021 are in the forecast for this weekend. In fact, almost every day next week has the potential to reach the 90 degree mark. Luckily, many area pools are beginning to open for the season, and next week is looking like prime time to inaugurate the neighborhood pool for the summer. The center of the high pressure will be to our east, so we should escape the more extreme heat expected for areas like southern GA and northern FL. Some of those areas could approach 100° next week! 

These kind of patterns are notoriously hard to break, and we could be looking at a couple weeks of hot, dry weather. Dry as in lack of precipitation, not in lack of moisture, as there will be continuous southerly flow off the Gulf, keeping our dewpoints high and making for a pretty unpleasant feel outside. Feels-like temperatures will be several degrees higher than actual temps, so find a way to stay cool. Summer weather lovers, your time is coming! 

Another concern for this pattern is the persistent lack of precipitation. With temperatures well above normal and very little cloud cover, evaporation rates will be high, and the nearly 3 inch rainfall surplus for the year could quickly be erased. Models are showing very little in the way of precipitation for the couple weeks. Looking at the European model through next Thursday, only a quarter inch of rain is forecast to fall, with most of that coming today. The GFS model is a little more optimistic on rain chances returning late next week, but that could change as we get a closer in time - definitely something to watch, especially for those with interests in agriculture. 

The European model forecast precipitation from today through the next 10 days. (WeatherBell)


As the heat of summer approaches, it’s a good time to revisit some heat safety tips. Wear sunscreen, especially during the afternoon hours, as UV indexes will be maxed out across the area next week. Stay hydrated, especially if you are planning on being outside in the peak heating of the day, and take plenty of breaks.



If you are planning on working out outside, it would be best to do it in the morning or evening hours. Heat is not something to mess around with, it kills more people each year than hurricanes, floods, earthquakes and tornadoes combined! Stay cool and stay safe Memphis, and get ready - summer is well on the way! 



Christian Bridges
MWN Social Media Intern

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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, May 15, 2021

Meet the "new normal" in Memphis weather - NWS releases updated data

Most of you are familiar with the weather data referred to as "normals" - the normal high and low temperature for the date, normal precipitation for the month, etc. You see them every night on the TV meteorologist's weathercast and we post a climate summary graphic each evening on social media as well that shows the day's data and our normals for the day. 

[ Personally, though the term normal is generally accepted in the meteorological community, I actually prefer the term "average." However, the statistical calculations made are not precisely the simple mean, or average, of the previous 30 years of data, though they are very close. ]

So what defines "normal" in the meteorological context? The National Weather Service (NWS), as well as the World Meteorological Organization (WMO), use a 30-year average. Why 30 years? Here's how the NWS explains it:
Normals serve two purposes: a reference period for monitoring current weather and climate, and a good description of the expected climate at a location over the seasons. They provide a basis for determining whether today’s weather is warmer or colder, wetter or drier. They also can be used to plan for conditions beyond the time span of reliable weather forecasts. A 30-year time period was chosen by the governing body of international meteorology in the 1930s, so the first normals were for 1901-1930, the longest period for which most countries had reliable climate records. International normals were called for in 1931-1960 and 1961-1990, but many countries updated normals more frequently, every 10 years, so as to keep them up to date. In 2015 this was made the WMO standard, so all countries will be creating normals for 1991-2020. - "1991-2020 U.S. Climate Normals: An Update"
Up until just recently, our daily weather conditions have been compared to the climate normals from 1981-2010. However, as they do every 10 years, NOAA and the NWS has released updated climate normals for 1991-2020, which means we have a new set of normals to compare the day's weather to. It's always an interesting exercise to see how the normals change when a new set of data becomes available. Even though 20 years of data overlap between the two sets of data, in the case of the 1991-2020 data, the 1980s are dropped off and the 2010's are added. 

These two side-by-side maps of the contiguous United States depict the change in U.S. annual mean temperatures (in degrees; left map) and precipitation totals (% change; right map) between the new set of Climate Normals, 1991-2020 (most recent last 3 decades) and the previous set of Normals, 1981-2010. (NOAA NCEI)


Temperature

So how do the 1991-2020 normals compare to the period from 1981-2010? Glad you asked! I've created a few charts to show temperature and precipitation comparisons. Let's start with monthly mean temperature and mean maximum and minimum temperatures (in other words, average highs and lows).

Comparison of new climate normals vs. previous normals for average, maximum and minimum temperatures at Memphis International Airport. Positive values indicate warmer temperatures in the most recent period.

The most obvious take from this chart is that, in general, temperatures are warmer in the 1991-2020 period versus the 1981-2010 period. The largest change in temperatures are in the cool season, while the summer did not warm as much. The notable values that are cooler are the overnight low temperatures in the heart of the summer (July and August) and in the month of November. The latter skewed the overall November temperature average cooler than the previous normals dataset as the average high temperature did not change. In fact, November was the only month that, on average, was cooler in the new dataset, while December had the largest positive (warmer) change. For the year, the average high temperature rose 0.4 degrees to 63.4 degrees. The average high temperature rose 0.6 degrees and the average low temperature rose 0.2 degrees.

Precipitation

So temperature has  generally warmed in the most recent data for Memphis. What about rainfall? Turning our attention to precipitation data, below are the changes in monthly precipitation from 1981-2010 to 1991-2020.

Comparison of new climate normals vs. previous normals for total precipitation by month at Memphis International Airport. Positive values indicate wetter conditions in the most recent period

The main takeaway of the new data from a precipitation perspective is we're generally receiving more water from the sky. In fact, for the year, average rainfall for the year increased 1.26" to just shy of 55" per year (or a bit more than 2%). The increase can be attributed to positive change from early spring through late summer. There was almost no change in September and October, while November and December saw rainfall totals fall, particularly November. This results in the wettest month of the year shifting from December to April. The driest month of the year moved later by a month, from August to September. 

Snowfall

Let's look into more precipitation data, specifically of the frozen variety. (Snow and sleet are lumped into "snowfall" data by the National Weather Service.)

Comparison of new climate normals vs. previous normals for monthly snowfall at Memphis International Airport. Negative values indicate less snow in the most recent period

The snow season for Memphis ranges from late November through early March with the highest totals typically in January and February. With the warmer temperatures discussed above (and to the surprise of no one who has lived in the Mid-South for an extended period of time!), average annual snowfall continues to decline. In the new data, the annual average has dropped from 3.8" to 2.7", or about 30%. The largest change has occurred in January, falling by an inch in the new normals. February's total also fell a bit. Interestingly enough, though the amounts are very small, average snow for November and March increased just slightly. The takeaway here seems to be that, although snowfall totals have fallen, the "winter season" seems to have expanded just a bit. In fact, the cooler month of November described above may have contributed to the slight increase in average snowfall in that month.

Recapping the 1991-2020 Normals

So, to wrap it up, our daily and monthly weather data will now be compared to a more recent set of average, or "normal" data. Overall, that data indicates a trend towards warmer and wetter conditions in the Memphis area, though there are exceptions such as a cooler and drier November. The largest positive change in temperatures occurred in the cool season, while precipitation increases were spread over many months, with the exception of late autumn to early winter. Snow lovers may want to look further north!

Erik Proseus
MWN Meteorologist

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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, May 8, 2021

April 2021 Climate Report for Memphis, TN

April Climate Recap

While March was much warmer than average, April cooled down a fair bit relative to average, ending almost two degrees below normal. While there were several days of above average warmth, only a couple were excessively so. On the other hand, there were several days were it was abnormally cool, including a few days with morning lows in the 30s to start the month, and another particularly cold shot centered around the 21st, when frost occurred again and high temperatures were quite cool. A daily record low was set on the 22nd with a minimum temperature of 37 degrees. As usual though, a wide range of temperatures occurred, from a few lows in the mid 30s to a few days with highs in the mid 80s.

Precipitation ended well below average (56% of normal), even though there were several days with rain, as only one day recorded more than an inch of rain. In fact, two-thirds of the total April rainfall fell in the last week of the month. Surprisingly, in what historically is one of the busiest months of the year for severe weather, no severe weather reports were received and only a couple of weather warnings were issued in the metro during the month, on the evenings of the 7th and 9th.


Memphis International Airport, Memphis, TN

Temperature 
Average temperature: 61.0 degrees (1.9 degrees below average) 
Average high temperature: 71.3 degrees (1.7 degrees below average) 
Average low temperature: 50.6 degrees (2.3 degrees below average) 
Warmest temperature: 84 degrees (12th) 
Coolest temperature: 35 degrees (2nd, 21st) 
Heating Degrees Days: 166 (29 above average)
Cooling Degree Days: 51 (24 below average) 
Records set or tied: April 22 - daily record low minimum (37 degrees)
Comments: There were no days with high temperatures above 90, nor any days with low temperatures below freezing.

Precipitation 
Monthly total: 3.10" (2.40" below average) 
Days with measurable precipitation: 7 (2.6 days below average) 
Wettest 24-hour period: 1.17" (29th) 
Snowfall: 0.0"
Records set or tied: None
Comments: One day recorded precipitation of more than an inch, 1.0 day below average for April.

Miscellaneous 
Peak wind: Southwest/40 mph (22nd) 
Average wind: 8.1 mph 
Average relative humidity: 61% 
Average sky cover: 48% 

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

Cirrus Weather Solutions / MemphisWeather.net, Bartlett, TN

Temperature 
Average temperature: 60.7 degrees 
Average high temperature: 72.8 degrees 
Average low temperature: 49.1 degrees 
Warmest temperature: 85.9 degrees (9th) 
Coolest temperature: 29.2 degrees (2nd) 
Comments: None 

Precipitation 
Monthly total: 3.72" (automated rain gauge), 3.90"(manual CoCoRaHS rain gauge) 
Days with measurable precipitation: 8
Wettest date: 1.69" (29th) (via automated gauge) 
Snowfall: 0.0"
Comments: None

Miscellaneous 
Peak wind: Southwest/29 mph (8th)
Average relative humidity: 68% 
Average barometric pressure: 29.98 in. Hg
Comments: None

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

MWN Forecast Accuracy

MWN average temperature error: 2.36 degrees 
MWN forecast temperatures within 2 degrees of actual: 64% 
MWN average dewpoint error: 2.90 degrees 
MWN forecast dewpoints within 2 degrees of actual: 55% 

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

Climate Outlook - May 2021

The May climate outlook for the United States from the Climate Prediction Center is shown below. Above average temperatures are forecast for all of the southern US., with highest probabilities from the southern Plains to Desert Southwest. A low probability of below average temperatures is forecast in the upper Great Lakes. Odds favor above average temperatures for Memphis (41%) versus only 26% chance of below average temperatures. The average temperature for April is 71.7 degrees.




Precipitation is expected to be below normal southwestern U.S. in May. Above average precipitation is forecast for much of the Mississippi River Valley east to the Appalachians. For Memphis, odds favor above average precipitation (41%) versus only 26% chance of below average precipitation. Rainfall historically averages 5.25 inches.

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MWN is a NOAA Weather Ready Nation Ambassador Meteorologist Erik Proseus is an NWA Digital Seal Holder