"Destructive" severe thunderstorms to trigger wireless alerts

You are probably familiar with Wireless Emergency Alerts (WEA), the push notification-based alert you receive on your smartphone when a Tornado or Flash Flood Warning has been issued in your area. These alerts are defaulted on from the cell phone companies, but can be disabled in your phone's alert settings if you wish. They are triggered from cell towers to those within their broadcast area whenever the tower's coverage area (roughly) overlaps the weather-warned area. Thus, they are a little more precise than county-based alerts (like those from NOAA Weather Radio), but not quite as precise as a well-designed weather alert app that pinpoints your specific location. 

A sample WEA for a "destructive" Severe Thunderstorm Warning.

Beginning Monday, August 2, the National Weather Service will make a nationwide change to "tag" Severe Thunderstorm Warnings into one of three categories based on expected impact. The highest of these alert levels will also be sent to smartphones via the WEA system. All three categories will continue to be called "Severe Thunderstorm Warnings," but there will be additional information in the warning as to their degree of severity. The three categories are:

1. Base (or baseline) - These warnings follow the existing criteria for a severe thunderstorm: 1.00 inch (quarter-sized) hail and/or 58 mph thunderstorm winds are expected. These are the lowest level of severe thunderstorm and are a threat to those not properly sheltered and will not trigger a WEA.

2. Considerable - Warnings tagged as having the potential to cause considerable damage are expected to contain at least 1.75 inch diameter (golf ball-sized) hail and/or 70 mph thunderstorm winds. These also will not trigger a WEA, but pose a higher level threat.

3. Destructive - Storms that pose a threat of destructive damage will be tagged as such and will trigger WEA alerts. The threshold for a destructive storm is at least 2.75 inch diameter (baseball-sized) hail and/or 80 mph thunderstorm winds. These storms are estimated to comprise less than 10% of all severe thunderstorms. Extra precaution is warranted (similar to actions taken during a Tornado Warning) given the level of damage they can cause - similar to a low-end tornado, particularly to weak structures.

So while additional alerts will be generated to your smart device, the number will be small and they will be high-end storms capable of significant damage. As a rough measure of their frequency, the NWS office in Memphis issued 223 Severe Thunderstorm Warnings in 2020. If ten percent of those were for "destructive" storms, that would be 22 warnings. And remember that is for all of west TN, north MS, east AR and the Missouri Bootheel! For your location, perhaps you could expect to receive ONE of these warnings per year. And remember that they are in essence based on your neighborhood - based on a cell tower location - not your county. This move by the National Weather Service and Federal Communications Commission is a good one and will hopefully draw more public attention to, and therefore result in a better rate of taking action, for the most destructive storms.

Want even more precise alerts and more control over those alerts you receive? Those that ONLY alert when your specific location is expected to be impacted by the type of alerts you select? Then StormWatch+ Alerts is for you! Add this upgrade to your MemphisWeather.net app and take control over which alerts you receive and for where (select multiple locations anywhere in the U.S.).

Erik Proseus
MWN Meteorologist

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"Real" summer is underway, and here to stay, across the Mid-South

Summer 2021 so far

While we saw some above normal temperatures in the month of June, the overall average for the month was 1.0 degrees below normal and the highest temperature recorded (officially) in Memphis was 94 degrees. July typically features highs in the low 90s and low in the mid 70s. Through the 23rd, we had only observed two days with above average temperatures and both were a single degree above average. Sixteen days were below average. So while it was hot, it wasn't abnormal, nor excessive.

Weather records for the first 24 days of July. The temperature departures from normal for each day are in the red box. The warmest temperature, relative to normal, so far this month was yesterday. (NWS)

That changed on Saturday. The high of 95 degrees was the hottest so far this year and today will likely meet or exceed that. Combined with dewpoints in the mid 70s, which is sultry and means there is a great deal of moisture in the air that makes it harder to sweat off the heat, the first Heat Advisory of the summer was issued. Today was the second. Tomorrow will be the third. Heat indices are making it to 105 degrees or higher in the afternoons. But how long will this hotter pattern last?

Early this week - scattered relief

A weak front (I almost hesitate to call it that) will move into northern sections of the Mid-South. So while we will start Monday on track for similar conditions to this weekend (disgusting upper 70s for low temps), clouds will increase and scattered showers and thunderstorms are expected mainly in the afternoon. We'll still reach the low 90s for highs, but there's a good chance many areas will get some relief as thunderstorms form - whether it be from actual rain or rain-cooled air spreading out from nearby thunderstorms. With the front nearby, dewpoints will likely "pool," meaning they build-up just ahead of the front. Since the front will not move through, we'll basically just sit in the soup. Expect extremely muggy conditions where rain or outflows are not helping a bit.

HRRR model radar simulation from Monday morning through Monday evening shows the likelihood of scattered showers and thunderstorms during the warmest part of the day. Exact storm location is not predictable, but overall coverage in a region is. Model ≠ gospel. (WeatherBell)

Tuesday will be fairly similar to Monday with warm and muggy conditions to start the day, heat building into the low 90s and afternoon scattered storms, though maybe a few less than Monday, as the front washes out to our north. Both days will likely see heat indices reach 105 or worse, at least until rain-cooled air invades an area. These are the invasions we root for.

Wednesday-Friday - more heat

As high pressure aloft builds back over the area from the west by Wednesday and for the rest of the week, oppressive conditions return as any shower than tries to form in the heat will be squashed quickly by the downward motion of air under the ridge aloft. Very little relief is expected overnight with lows in the mid to upper 70s. Afternoon highs should have no trouble reaching the mid 90s, and could touch the upper 90s late in the week in spots. Wind will be light. Sweat will be plentiful. Feels like temperatures will exceed 105, thus Heat Advisories are likely.

The European model ensemble shows a massive ridge of high pressure aloft over all but the northeast portion of the country between Wednesday-Sunday. The center of the high is over the central Plains and stretches southeast into the Mid-South. Warm colors indicate anomalously high (or warm) values. A 5-day average of 594 (or 5,940 meters) is very strong high pressure. (WeatherBell)

Next weekend

Another front looks to try and make a push towards the region from the north. The best we can hope for now is scattered showers of relief in the afternoons, but highs remain probably toward the middle range of the 90s. Further in voodoo land, a summer frontal passage is shown in long-range models early the following week. That is about like seeing snow 8-10 days out on the models in the winter. Don't get your hopes up just yet, even though the weather crap apps on your phone may show 80s ten days out.

Heat caution

Heat is rough on a person's body, and it gets worse with time. The more consecutive days with little relief, the more it takes a toll. It hasn't been this hot yet this summer. Please take it easy. Frequent breaks, plenty of non-alcoholic beverages (especially water or sports drinks), and shade as much as possible if you have to be out. Watch out for those pets too. They need lots of water and shade if they can't come in. And finally, you would never do it on purpose, but check the back seat before exiting your vehicle. We don't want any unnecessary deaths from children left in vehicles!

Heat exhaustion and heat stroke is also real - I have recent experience with a healthy, young relative who passed out while driving after working outside all day and totaled his truck when he drove it into a telephone pole. (Thankfully, he was fine other than recuperating from the heat!) It's not worth pushing it "just a little bit longer."

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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Cooler temps and wet weather on the way

While it was hot out there today, it’s nothing unexpected this time of year. Average highs are in the low 90s, and we were right around that today. We’re now about halfway through the month and so far it has actually been cooler than average here in the Mid-South and for much of the southern U.S. as a whole! 

Temperature anomaly (departure from average) for the month of July so far across the U.S. (WeatherBell)

We are very lucky that we haven’t seen the extreme heat western states have been experiencing - some areas in the west are seeing high temperatures more than 15 degrees above average for the month, yikes! Wildfire season has already been awful out there and will only get worse in the coming months as the heat intensifies the terrible drought. High in the atmosphere wildfire smoke could blow over our area from western fires at times for the rest of the summer and into the fall, which could make our skies hazy and our sunsets more red periodically. Keep an eye out!

Trough sets up this weekend

More wetness and below average temperatures are on the way as we end this week and start the next one. Unfortunately, this means the weekend is looking pretty wet. We have seen persistent areas of low pressure that have affected the Memphis area all through the late spring and early summer, and as we head into mid-summer that trend looks to continue. By the weekend, a trough, or a dip in the overall atmospheric flow across the United States, will once again bring a period of wet weather to the region. This “dip” will be accompanied by a weak front that will stall out near or just south of the area and provide the focus for multiple rounds of showers and storms this weekend and early next week. No drought concerns here for the foreseeable future!

The European model depiction of the weak mid-level trough that will keep our weather unsettled and cooler than normal this weekend. No extreme heat on the horizon locally! (WeatherBell)

Friday

Friday looks to be a fairly typical summer day, with rain chances a bit higher than the past few days, particularly late afternoon and evening. As we quickly warm up into the low 90s again Friday afternoon, scattered showers and storms will pop up across the area. the Storm Prediction Center doesn't have our area highlighted for potential severe weather so general thunderstorms with heavy rain will be the primary threat. The sagging weak front begins to have more influence over the area beginning Friday night, with rain chances actually increasing a bit. 

Weekend

Showers and storms will continue through the overnight hours and into Saturday morning. Saturday looks quite wet overall. We’ll wake up to widespread showers and storms which will continue into the afternoon and evening, perhaps tapering into the afternoon and evening to scattered just rain showers. The clouds and rain will hold our temps down in the mid-80s, once again several degrees below average. 

Sunday looks to be just as wet, so it’s a good weekend for indoor activities. Some of the storms could contain heavy rainfall, so flash and urban flooding could be a concern for some spots, especially if the same areas see repeated heavy rainfall after receiving a good amount Friday night and Saturday. Highs will only top out in the low to mid 80s on Sunday, and it’s looking quite similar for Monday, with widespread rain and storms and highs in the low to mid 80s. 

Next week

As the front moves south of our area and the trough moves east, rain chances should diminish a bit as we head towards the middle of the week with more typical scattered afternoon showers and storms. Highs will slowly rebound back into the upper 80s to near 90 degrees by Wednesday. All of this added moisture will only increase humidity levels across the area, so feels like temps will be quite high in the afternoon sun. Rainfall totals will likely be wide ranging across the area as it will be highly dependent on storm location. A couple inches of rain is a good bet for all of us, with some areas likely seeing more and some seeing a bit less. As always, when thunder roars, go indoors, and stay tuned for any updates should a Severe Thunderstorm or Flash Flood Warning be issued this weekend.

The NWS Weather Prediction Center forecast of total rainfall through Monday shows that much of the area is likely to pick up 1.5-2.0" of rain with this next system. (WeatherBell)

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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Pattern shift brings highest rain chances in a month

Prior to yesterday's deluge (for some of you), the previous month has been abnormally dry. We started June with very wet weather, particularly south of I-40 and into north MS, but once it dried out, it did so for all of us. 

Below, images show the rainfall departures from normal for June 10-July 9 and Thursday's Drought Monitor for Tennessee. For the past 30 days, the metro had accumulated a deficit of 2-3" of rain, or roughly only 30-40% than normal. Parts of Shelby and Tipton Counties were officially classified in D0 status, or "abnormally dry." My lawn has needed water weekly for the past few weeks now to keep it from browning up.

Rainfall departure from normal for June 10-July 9. Precipitation deficits of 2-3" (or 60-70%) were observed in the metro. (HRAP Precip Analysis via WeatherBell)

The Drought Monitor on July 8 shows "abnormally dry" conditions in portions of Tipton and Shelby Counties.

That atmospheric pattern started to change yesterday though, and the new pattern will continue into the middle of next week, as an upper level low pressure system forms to our north.

Friday retroactively rated "outperform"

Before we look into the weekend ahead, Friday's event was definitely interesting, and admittedly not well-forecast. The setup was basically a remnant outflow, or surface, boundary that moved into the metro Thursday night. You may recall a narrow line of storms making it to northern Tipton County Thursday evening. Many of us north of I-40 had a pretty decent light show after dark from distant lightning (not heat lightning!). 

As those storms fizzled, the boundary slipped south to around the TN/MS state line. Our best computer models really didn't pick up on much activity along that boundary early Friday, other than maybe a few isolated showers. I honestly didn't expect much. (In fact, I left my passenger side car window cracked a couple of inches when I went to work by the airport Friday morning!) Well, "outperform" would have been the proper rating if this were the stock market. 

With moist air flowing up from the southwest over the boundary and very muggy and unstable air in place by mid-morning, storms fired up and moved east-southeast along the boundary draped along the state line, while continuously regenerating back to the west along I-40 in east AR. Over and over, storms trained along the boundary from southern Crittenden Co along the Shelby/DeSoto border, into northern Marshall County, a "state line special." By noon, 4-6" of rain had fallen in that corridor, a couple of inches fell at the airport (some into my front passenger seat!) - setting a daily rainfall record, and most of the rest of the metro was wondering what all the fuss was about! My home in Bartlett received exactly zero drops. 

Below is the radar estimation of rainfall totals for the day, including scattered storms that formed in the afternoon in northeast AR and made it into northwest portions of the metro and lingering light rain for Shelby County in the evening. It was quite a day!

Radar estimation of rainfall for Friday's localized deluge (MRMS data via NSSL)

This weekend - northwest flow

For those who still haven't gotten their "fair share" of rain, all hope is not lost. Yesterday was a prelude to a transition in which the upper air pattern becomes northwesterly, allowing storm systems from the north to move into the Mid-South - commonly called northwest flow. It is not unusual to see this pattern a couple of times each summer and it is also a difficult one to forecast details more than about 24 hours out. The northwest flow will be driven by the development of low pressure in the mid levels of the atmosphere over the Upper Midwest that drops into the Missouri over the next few days, before weakening and lifting northeast by about Tuesday night.

The mid-level (500mb or 18,000') flow pattern from Saturday morning through Tuesday evening features a developing low pressure center over the Missouri River valley, resulting in "northwest flow" for our area tonight into Sunday, then a trough over Arkansas to start the week. (Euro model via WeatherBell)

Today starts mainly dry as we haven't quite transitioned from a high pressure/summertime setup just yet. A few afternoon showers or thunderstorms are possible in the heat of the day as temperatures reach 90 degrees, but short-term high-res models disagree on the extent and intensity of any pop-ups. Don't be surprised by some thunder and localized downpours - remember to evacuate the pool if thunder and lightning are nearby!

As we head into tonight, the first of the "northwest flow" system moves in. This one seems to be fairly well predicted by the morning model data. A line of storms is likely to drop through Missouri this afternoon and into northern AR and northwest TN this evening. That line appears likely to reach the metro around midnight, or perhaps a bit before, midnight. 

The 7am model runs of the HRRR (left) and NAM3 (right) show what they think radar will look like at midnight tonight. Subsequent iterations of the HRRR, which runs hourly, are a touch earlier with storms. Prepare for strong wind and heavy rain late this evening. (WeatherBell)

We are outlooked in a Marginal to Slight Risk of severe weather (level 1-2), with the primary threat being strong wind gusts with the line. The threat appears to be highest to our north, and the line may be weakening a bit as it gets here. Sometimes these things don't go according to plan though. The tornado and hail risk is very low, but the heavy rain threat is high as showers continue overnight after the main line. Stay tuned throughout the day and evening for updates, and prepare for the possibility of scattered power outages and minor wind damage overnight, especially in northeast AR and west TN. You'll want to have multiple methods of receiving warning information, just in case!

By Sunday morning, lingering showers will likely be falling apart, but a muggy airmass is likely to recover (or become more unstable) by afternoon and scattered showers and thunderstorms are again expected. These could last well into the evening. Though it will be cooler (mid 80s for highs), it'll still be muggy with southwest wind becoming gusty at times and a bit of sun peeking through during the afternoon as well. I expect all of us will have received some decent rain by Sunday night. In fact, the NWS has outlooked parts of the area, mainly south of I-40, in a Slight Risk (level 2) of excessive rainfall (not severe storms) for Sunday.

Starting the work week with continued rain chances

As the upper level low spins over Missouri, more showers and thunderstorms are likely on Monday. These may be more diurnally driven, meaning they are most likely during the warmest hours of the day. Keep that in mind as you make your plans for Monday. Many of us could get more rain and a few storms, most likely below severe limits, on Monday as highs remain in the mid 80s.

Tuesday will see rain chances drop off some as the low starts to weaken to our north, however scattered showers and thunderstorms appear to be a good bet in the afternoon and evening hours. Look for temperatures to start to recover and humidity to remain high. High temps will be in the upper 80s.

The latter half of next week appears to be more typical of summer (and much like this past week) as high pressure builds back in. High temperatures in the lower 90s and lows in the mid 70s will be common with isolated to widely scattered storms Wednesday-Friday.

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

June 2021 Climate Report for Memphis, TN

June Climate Recap

The months of April and May were cooler and drier than average, and that trend continued for much of June. 17 of the days in June were below average and only five days were above average by more than two degrees, resulting in an average temperatures that was a degree below average for the month. The first 90 degree reading of 2021 finally occurred on June 11 (18 days later than average). The number of 90 degree days was right at average, however. 

Precipitation ended the month 0.75" above average at 4.74", however 88% of that rain fell in the first nine days of the month. Just south of the border, flooding occurred in the first week of June as up to 6+ inches of rain fell. By the end of the month, prior to a decent soaking on the 30th, abnormally dry conditions were found across the area, particularly north of I-40 where rain early in the month was much less than at the airport. (Just over 2 inches was recorded at MWN in north Bartlett.) The only severe weather of the month occurred from the afternoon of the 8th into the 9th when very heavy rain occurred mainly along and south of the TN/MS state line. Flooding was reported south of the immediate metro in north MS. About 2.5" of rain fell at the airport, but reports of 6-12" of rain were received to the south.

Memphis International Airport, Memphis, TN

Temperature 

Average temperature: 78.9 degrees (1.0 degrees below average) 

Average high temperature: 87.0 degrees (2.4 degrees below average) 

Average low temperature: 70.8 degrees (0.4 degrees above average) 

Warmest temperature: 94 degrees (12th, 13th, 29th) 

Coolest temperature: 62 degrees (22nd, 23rd) 

Heating Degrees Days: 0 (0 above average)

Cooling Degree Days: 426 (21 below average) 

Records set or tied: None

Comments: There were 15 days with high temperatures above 90 (0.5 day below average) with the first day being June 11 (18 days later than normal). The average first 90 degree day for the year is May 24.

Precipitation 

Monthly total: 4.74" (0.75" above average) 

Days with measurable precipitation: 9 (0.1 days above average) 

Wettest 24-hour period: 2.51" (8th-9th) 

Snowfall: 0.0"

Records set or tied: None

Comments: Two days recorded precipitation of more than an inch, while June averages 1.3 days.

Miscellaneous 

Peak wind: South/41 mph (7th) 

Average wind: 7.3 mph 

Average relative humidity: 70% 

Average sky cover: 53% 

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

 

Cirrus Weather Solutions / MemphisWeather.net, Bartlett, TN

Temperature 

Average temperature: 77.9 degrees 

Average high temperature: 88.3 degrees 

Average low temperature: 69.0 degrees 

Warmest temperature: 95.5 degrees (17th) 

Coolest temperature: 55.6 degrees (23rd) 

Comments: None 

Precipitation 

Monthly total: 1.95" (automated rain gauge), 2.18"(manual CoCoRaHS rain gauge) 

Days with measurable precipitation: 11

Wettest date: 0.94" (1st) (via automated gauge) 

Snowfall: 0.0"

Comments: None

Miscellaneous 

Peak wind: South/34 mph (7th)

Average relative humidity: 78% 

Average barometric pressure: 29.94 in. Hg

Comments: None

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

 

MWN Forecast Accuracy

MWN average temperature error: 1.51 degrees 

MWN forecast temperatures within 2 degrees of actual: 82% 

MWN average dewpoint error: 1.71 degrees 

MWN forecast dewpoints within 2 degrees of actual: 79% 

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

 

Climate Outlook - July 2021

The July climate outlook for the United States from the Climate Prediction Center is shown below. Above average temperatures are forecast for the western U.S. across the Upper Midwest into the Northeast with highest odds across the Rockies. Below average temperatures are forecast in the Southern Plains to Lower Mississippi Valley. Odds favor below average temperatures for Memphis (38%) versus a 29% chance of above or below normal temperatures. The average temperature for July is 82.8 degrees.

Precipitation is expected to be above normal for much of the southern U.S. into the Mid-Atlantic, with highest odds in the Lower Mississippi Valley. Below average precipitation is forecast for the northern tier of the U.S. For Memphis, odds favor above average precipitation (41%) versus a 26% chance of below average precipitation. Rainfall historically averages 4.82 inches.

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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