Saturday, August 10, 2019

Steamy heat settling into the Mid-South

By most standards, this summer has actually been relatively mild in the Memphis metro. While May was warmer than average, the hottest it got was 92°. June's average temperature was 2° below normal and once again the highest temperature was 92°. July also finished a little over a degree below normal despite some hotter days. However, the high temperature only eclipsed the average high (92°) on five occasions and the hottest we got was 95°. Granted the humidity in mid-July pushed the heat index close to 110° a few days, but the end of the month was actually quite pleasant as dewpoints backed off for a good stretch of time. And to start August? Well, Tuesday and Wednesday were in the mid 90s, but otherwise each day has averaged below normal. All that to say - summer isn't over!

Heat builds, humidity lingers

A strong ridge of high pressure in the mid levels of the atmosphere is centered over Texas this morning but will expand east into the Mid-South as we head into the beginning of the week. That ridge will help to push temperatures up into the mid to maybe upper 90s in a few spots by the start of the week.

The European model through Wednesday morning shows a mid-level (500mb, or 18,000 feet) ridge of high pressure expanding from Texas north and east into the area to start the week. Yellow colors show where high pressure is stronger than normal. Blues are anomalously lower pressure areas. You can see at the end of the loop how the yellows retreat though as high pressure weakens. (WeatherBell)

And as you know in the Mid-South, it isn't just the heat, it's the humidity! Plenty of moisture from recent rain, as well as southerly wind originating over the Gulf of Mexico, will keep our dewpoints well above even sultry Memphis standards - in the mid to upper 70s. That means high humidity levels will couple with the building heat to create conditions that could become dangerous.

The NAM model shows forecast dewpoints through mid-day Tuesday. There is no reprieve from mid to upper 70s dewpoints, which means high humidity values to go with the strengthening high pressure. That combination produces excessive heat conditions. (WeatherBell)

A hot forecast

"Typical" summertime heat can be expected today (Saturday) with highs near 90° but with dewpoints in the mid 70s, look for heat indices to top the century mark this afternoon. An isolated shower or thunderstorm can't be ruled out, but most of those will be southwest of Memphis and could affect north MS.

Sunday will see the upper level ridge expand closer. Coupled with low rain chances outside of a few possible morning showers, highs should reach the mid 90s. Dewpoints remain in the mid 70s or a touch higher, so expect heat indices to climb towards 110°. This will match the hottest days we've had so far this summer.

Monday will start even warmer as the ridge builds and dewpoints remain high with lows just below 80°. That will allow highs to climb to the hottest so far this year, around 97°. Dewpoints in the upper 70s will put heat indices at a dangerous level, near 115° in the afternoon, just in time for kids to return to school.

One more day of excessive heat occurs on Tuesday with similar conditions to Monday - heat indices topping out above 110° and high temperatures near 97°. We could start to see a few thunderstorms around the area by Tuesday afternoon and evening. Fortunately, Tuesday marks the end of the excessive heat, so while intense, it won't be prolonged.

A marked shift in the upper level pattern allows a cold front to move through Tuesday night or Wednesday morning. Additional showers and thunderstorms are possible during that period, leaving most of Wednesday dry with falling dewpoints and highs back down to average levels near 90°. The rest of the week should see highs just below average and (better yet) humidity readings also below average!

Heat Preparation and Safety

Excessive heat is nothing to mess around with. First remember that temperature and heat index is computed in the shade! Add multiple degrees if in direct sunlight. A heat index reading above 105° is considered dangerous. Physical effects to the body often build slowly, so it is important to make sure that you are prepared. Of course, avoidance is best. Stay in climate-controlled areas as much as possible and check regularly on those without air conditioning. Warm overnight temperatures will compound the issue.

If you must be out for any length of time, plan frequent breaks and drink plenty of water before before, during, and after exposure. Light-colored clothing that reflects heat and loose-fitting garments that allow the body to breathe are best. Listen to your body and know the effects of heat exhaustion and heat stroke.

You certainly also want to make sure you take care of your pets with plenty of water and a shaded place to stay if they are outside, otherwise allow them in during the hottest parts of the day.

And finally, it should go without saying, NEVER leave a young person unattended in your vehicle for any length of time. It only takes minutes for the inside of a car to get dangerously hot. LOOK BEFORE YOU LOCK.

Erik Proseus
MWN Meteorologist

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

Sunday, August 4, 2019

July 2019 Climate Data for Memphis, TN

July Climate Recap

While June featured below average temperatures nearly all month, July ended a bit below normal for the month, driven mainly by cooler than average temperatures in the latter half of the month. The first half of July was slightly above normal temperature-wise, but with a maximum for the month of 95 degrees, it didn't get exceptionally hot. The humidity from routine rainfall though made for very hot heat indices. The second half of the month had some above average days, but was well below normal (and much less humid) for about the last 10 days, resulting in slightly cooler than normal temperatures for the month. A low temperature record was tied on the 25th as much of the Mid-South outside the urban heat island fell into the 50s.

Following the fifth wettest June on record, July broke into the top ten wettest as well, almost 3 inches more than average at the airport. As in June though, the southeastern portion of the area was wetter than the northern part of Shelby County with 2 inches more rain at the airport than at MWN in Bartlett, resulting in a difference for the two months combined of about 8 inches between the two sites! The two-month total at the airport was just over 17 inches of rain, good for third wettest June-July on record. A daily rainfall record of 2.28 inches was set on the 16th as remnants of Hurricane Barry moved through the northern Mid-South.

Observed precipitation for July in the Memphis area. (NOAA/WPC)

Departure from average precipitation for July, expressed as percent of normal. (NOAA/WPC)

The main weather hazards in the metro during July were related to heavy rain with multiple Flash Flooding Warnings posted on the 14th and, especially, the 16th, when record rainfall occurred at Memphis International as the remnants of Hurricane Barry moved by to the north. Also on the 16th, a very large tree fell at Memphis Botanical Gardens. A single Severe Thunderstorm Warning was issued on the evening of the 15th for northern Shelby and Tipton Counties. Finally, a brief EF-0 tornado touched down on the 16th in Victoria, MS (Marshall County), causing some roof and tree damage.

Memphis International Airport, Memphis, TN

Average temperature: 81.5 degrees (1.2 degrees below average)
Average high temperature: 89.7 degrees (1.9 degrees below average)
Average low temperature: 73.4 degrees (0.4 degrees below average)
Warmest temperature: 95 degrees (8th)
Coolest temperature: 62 degrees (25th)
Heating Degrees Days: 0
Cooling Degree Days: 523 (26 below average)
Records set or tied: Record low tied (62 degrees on the 25th).
Comments: Twenty-two days recorded a high temperature of 90 degrees or warmer, 1.1 days more than the average for July.

Monthly total: 7.53" (2.94" above average)
Days with measurable precipitation: 10 (3.8 days above average)
Wettest 24-hour period: 2.28" (16th)
Snowfall: None
Records set or tied: Record daily rainfall set (2.28" on the 16th). Tenth wettest July on record. Third wettest June-July period on record.
Comments: The month ranked as the tenth wettest July on record. Five days recorded more than 0.5" of rain and three days recorded over 1.0" of rain.

Peak wind: West/45 mph (29th)
Average wind: 7.1 mph
Average relative humidity: 76%
Average sky cover: 50%

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

Cirrus Weather Solutions /, Bartlett, TN

Average temperature: 80.2 degrees
Average high temperature: 90.6  degrees
Average low temperature: 71.3 degrees
Warmest temperature: 96.3 degrees (9th)
Coolest temperature: 56.6 degrees (25th)
Comments: None

Monthly total: 4.86" (automated rain gauge), 5.39" (manual CoCoRaHS rain gauge)
Days with measurable precipitation: 9
Wettest date: 2.11" (16th) (via automated gauge)
Snowfall: None
Comments: None

Peak wind: South/28 mph (15th)
Average relative humidity: 81%
Average barometric pressure: 30.00 in. Hg

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

MWN Forecast Accuracy

MWN average temperature error: 1.43 degrees
MWN forecast temperatures within 2 degrees of actual: 86%
MWN average dewpoint error: 1.69 degrees
MWN forecast dewpoints within 2 degrees of actual: 75%

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

Climate Outlook - August

The August climate outlook for the United State from the Climate Prediction Center is shown below. Below average temperatures are expected across the Great Plains stretching east into the Great Lakes and Ohio Valley, though with lower confidence. Above normal temperatures are likely to be found in the Pacific Northwest and in the far southern U.S., extending up the east coast. Odds favor near average temperatures for Memphis in August. Memphis averages 82.0 degrees for the month, just under a degree cooler than July, and is typically the second warmest month of the year.

A wet July is forecast for the Central Plains west into the Rocky Mountains, as well as south Florida. Below average precipitation is expected in the Ohio Valley and central Great Lakes, as well as in south-central TX. For Memphis, odds favor near average rainfall, which historically averages just 2.88" in August, which is climatologically the driest month of the year.

Follow MWN on Facebook and Twitter for routine updates and the latest info!
Complete MWN Forecast: 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