August Climate Stats and MWN Forecast Accuracy

Memphis International Airport, Memphis, TN
August is typically a hot month in the Mid-South, but August 2010 set multiple daily heat records and will go down as the 3rd hottest August on record. Ten temperature records were tied or broken (listed below) and Excessive Heat Warnings were in effect on 14 days with Heat Advisories in effect another 4 days.

For the month, the average temperature was 86.6 degrees, which was 5.4 degrees above normal. The average high temperature was 95.8 degrees and the average low was 77.3, with only 29 of 31 days reaching a high of at least 90. Typically, only 17 days reach highs of 90 degrees or higher. The maximum temperature for the month was 104 degrees on the 4th and the lowest was 66 on the 27th. There were 7 days in which the high temperature was at or above 100 degrees and 12 days on which the low never dropped below 80.

Temperature Records for August - Memphis Int'l
Date	Temp.	Record Set/Tied
8-1	82	Record High Minimum
8-2	100	Record High (tied)
8-2	82	Record High Minimum (tied)
8-3	103	Record High
8-3	84	Record High Minimum / All-Time (tied)
8-4	104	Record High
8-4	83	Record High Minimum
8-18	80	Record High Minimum (tied)
8-19	100	Record High (tied)
8-21	81	Record High Minimum

For the summer months (June-July-August), 2010 will go down as the 2nd hottest summer on record with an average temperatures of 85.4 degrees, behind only the much-maligned summer of 1980, which averaged 85.6 degrees. The average low temperature was 76.3 degrees - the warmest ever. Unfortunately, there were also 21 heat-related fatalities during the summer months in Shelby County (compared to 83 in 1980). In addition, 85 days (of 92) reported high temperatures of 90 degrees or higher. (Source: Commercial Appeal)

As far as precipitation was concerned, the month continued the mainly dry trend of the summer period. Precipitation totaled 2.32" or 0.68" below normal. There were 9 days with measurable rainfall, but 6 of those saw less than one-tenth of an inch. A total of 1.18" of rain fell on the 22nd, or just over 50% of the month's total. The peak wind gust was 49 mph, recorded in a thunderstorm on the 13th, while the average wind speed for the month was 6.9 mph. Humidity averaged 64%. Click here for the NWS climate recap for August.

Bartlett, TN
Bartlett also saw a very hot and dry month. The average temperature for August at the WXLIVE! station in north Bartlett was 83.7 degrees with a maximum of 103.1 on the 4th and a minimum of 57.5 degrees on the 27th. The high temperature failed to reach 90 on only 5 days, all occurring after the 24th.

August precipitation ended up well below normal with a precipitation total of 1.77", with only 5 days or measurable rainfall. A co-located manual gauge used for the CoCoRaHS program measured 1.79" in August. The peak wind gust was 25 mph on the 22nd. Click here for a daily statistical recap on MemphisWeather.net.

MWN Forecast Accuracy
MWN Forecast accuracy is forthcoming and will be appended to this report when it becomes available.

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5 years ago: NWS-New Orleans sternly warns of incoming Katrina

Hurricane Katrina made landfall five years ago tomorrow - August 29, 2005 - devastating and re-shaping the Gulf Coast for years to come. While there will be plenty of media coverage of the event on this anniversary weekend, I'd like to re-visit a statement from the National Weather Service in New Orleans made five years ago today, in advance of the landfalling behemoth. I wonder what Louisiana residents were thinking when they saw this...

URGENT – WEATHER MESSAGE
NATIONAL WEATHER SERVICE NEW ORLEANS LA
1011 AM CDT SUN AUG 28 2005

…DEVASTATING DAMAGE EXPECTED…

.HURRICANE KATRINA…A MOST POWERFUL HURRICANE WITH UNPRECEDENTED STRENGTH… RIVALING THE INTENSITY OF HURRICANE CAMILLE OF 1969.

MOST OF THE AREA WILL BE UNINHABITABLE FOR WEEKS… PERHAPS LONGER. AT LEAST ONE HALF OF WELL CONSTRUCTED HOMES WILL HAVE ROOF AND WALL FAILURE. ALL GABLED ROOFS WILL FAIL… LEAVING THOSE HOMES SEVERELY DAMAGED OR DESTROYED.

THE MAJORITY OF INDUSTRIAL BUILDINGS WILL BECOME NON FUNCTIONAL. PARTIAL TO COMPLETE WALL AND ROOF FAILURE IS EXPECTED. ALL WOOD FRAMED LOW RISING APARTMENT BUILDINGS WILL BE DESTROYED. CONCRETE BLOCK LOW RISE APARTMENTS WILL SUSTAIN MAJOR DAMAGE… INCLUDING SOME WALL AND ROOF FAILURE.

HIGH RISE OFFICE AND APARTMENT BUILDINGS WILL SWAY DANGEROUSLY… A FEW TO THE POINT OF TOTAL COLLAPSE. ALL WINDOWS WILL BLOW OUT.

AIRBORNE DEBRIS WILL BE WIDESPREAD… AND MAY INCLUDE HEAVY ITEMS SUCH AS HOUSEHOLD APPLIANCES AND EVEN LIGHT VEHICLES. SPORT UTILITY VEHICLES AND LIGHT TRUCKS WILL BE MOVED. THE BLOWN DEBRIS WILL CREATE ADDITIONAL DESTRUCTION. PERSONS… PETS… AND LIVESTOCK EXPOSED TO THE WINDS WILL FACE CERTAIN DEATH IF STRUCK.

POWER OUTAGES WILL LAST FOR WEEKS… AS MOST POWER POLES WILL BE DOWN AND TRANSFORMERS DESTROYED. WATER SHORTAGES WILL MAKE HUMAN SUFFERING INCREDIBLE BY MODERN STANDARDS.

THE VAST MAJORITY OF NATIVE TREES WILL BE SNAPPED OR UPROOTED. ONLY THE HEARTIEST WILL REMAIN STANDING… BUT BE TOTALLY DEFOLIATED. FEW CROPS WILL REMAIN. LIVESTOCK LEFT EXPOSED TO THE WINDS WILL BE KILLED.

AN INLAND HURRICANE WIND WARNING IS ISSUED WHEN SUSTAINED WINDS NEAR HURRICANE FORCE… OR FREQUENT GUSTS AT OR ABOVE HURRICANE FORCE… ARE CERTAIN WITHIN THE NEXT 12 TO 24 HOURS.

ONCE TROPICAL STORM AND HURRICANE FORCE WINDS ONSET… DO NOT VENTURE OUTSIDE!

Many thanks to Meteorologist Bill Murray of ABC33/40 in Birmingham for bringing this statement back to light today on his blog, AlabamaWx.com. In his words, the words turned out to be prophetic.

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Why has it been so hot? And when is it going to end?

The Mid-South summer of 2010 will likely be remembered (after the flooding rains of early May) for the intense and prolonged heat and humidity. The vast majority of the comments and questions I get from folks run along the lines of "when is this heat/humidity going away?" This post will hopefully answer two questions for you: when and why.

First the why. While the ultimate "why" may not truly be understood yet from a scientific viewpoint, the reason for this summer's unrelenting heat across much of the eastern and central U.S. can be found by looking up - into the middle reaches of the atmosphere. A recent blog post by The Weather Channel's well-known Severe Weather Expert, Dr. Greg Forbes, helps to explain. While the main focus of the post attempted to explain the abnormal heat and lack of summertime thunderstorms across central FL, it's pertinent for this region of the country as well.

At about 20,000 feet up (meteorologists refer to this layer as the 500mb pressure level), a large and very strong ridge of high pressure has set up this summer over the southeastern portion of the U.S. Commonly referred to as the "Bermuda High," this summer it ended up being stronger and more well-entrenched than usual (see the image below showing the departure from normal of the pressures at the 500mb layer, courtesy The Weather Channel). This high pressure cell of warm air aloft kept frontal systems at bay well to our north for much of the summer, while also causing sinking air underneath it, which squashed the rising columns of air required to produce widespread thunderstorms.

The strength and blocking nature of the high is directly responsible for the generally uncomfortable conditions we experienced 20,000 feet lower - at the surface of the earth. The image below shows the departure from normal for surface temperatures, which correlates well to the same areas experiencing the strongest high pressure in the first image (also courtesy The Weather Channel).

So the next logical, or perhaps more pressing, question is, when does it end?? Well, I have good news! The frontal system passing through the Mid-South this weekend is actually the start of a transition we will be seeing over the coming days as the massive ridge of high pressure breaks down some and high pressure at the surface originates from the cooler northern climes rather than the tropics.

The image below (click for larger image) is one model's forecast of the temperature, dewpoint, and humidity trends for the coming week. Notice in particular the downward trend in temps and dewpoints (a measure of humidity in the air) for the next several days, as well as the reduction in relative humidity. While our dewpoints have predominantly been in the 70s this summer (with a few brief spells of drier air), the long-term trend shows dewpoints dropping into the 50s next week. While it will still be warm, the air will be drier, so there will be less talk of heat index and definitely some cooler mornings to look forward to! Hang in there! Fall is also just around the corner!

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Video time-lapse of asperatus clouds

For those who follow weather closely, you may have heard of a newly-recognized cloud type over the past year or two. This cloud type, officially called undulatus asperatus, or just asperatus (roughly meaning "roughened" or "agitated waves"), was proposed to be classified as a separate cloud type in 2009 by the founder of the Cloud Appreciation Society. The Weather Service describes it thus:

“Although they appear dark and storm-like, they tend to dissipate without a storm forming. The ominous-looking clouds have been particularly common in the Plains states of the United States, often during the morning or midday hours following convective thunderstorm activity.”

Below you will find an awesome time-lapse video of about 90 minutes of asperatus clouds condensed into 90 seconds of video, taken over State College, PA (home of one of the most widely-recognized schools of Meteorology - Penn State) by Accuweather meteorologist and blogger, Jesse Ferrell. As you watch, pay particular attention to the wave action in these clouds. Truly fascinating! Let me know what you think by commenting on this post. Jesse's blog and additional still pics can be found here.



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Heat abates slightly for the upcoming week

A cold front will move through the Memphis metro area this evening and stall across north Mississippi, bringing an end to the near-100 degree temperatures and Excessive Heat Warnings of the past week. It will also help to lower humidity levels a little by Monday, which was the second factor (besides the heat) contributing to the heat warnings. The Heat Warning will be replaced by a Heat Advisory along and south of I-40 (including the metro area) for Monday as it will still be hot by all accounts (mid 90s) with a little leftover humidity. Heat index values will be near 105 in the I-40 corridor.

As we head further into the week, the dewpoints (a measure of humidity) will slowly begin to rise again, though more cloud cover and daily rain chances (albeit low) will keep temperatures in the lower to mid 90s. Heat Advisories are possible, but we won't be dealing with the extreme heat like the past couple of weeks. There are some signs that point to a little more heat and humidity again heading into next weekend as the upper-level high pressure system rebuilds over the region. We'll wait to see how that pans out. In the meantime, check out the MWN Forecast for Greater Memphis for details on this week's expected weather.

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Recap of the record heat wave - more on the horizon?

The Mid-South suffered through a heat wave of record proportions this past week, the hottest since 2007. Due to a massive ridge of high pressure over the area, temperatures climbed into the triple digits for four consecutive days at Memphis International Airport and overnight lows remained in the 80s for five days as well. The map above (courtesy NWS-Memphis) depicts the 500mb (or about 18,000 feet) level of the atmosphere at mid-day on Tuesday, in the middle of the heat wave. The very strong ridge of high pressure is depicted square over the region, resulting in the extreme heat.

Accompanying the heat was moisture-laden air, that resulted in high dewpoint values (and high relative humidity), creating heat indices that routinely eclipsed 110 degrees and topped 120 in some locations. The high heat indices resulted in Excessive Heat Warnings for the entire area for several days. In fact, much of the southeast and south-central U.S. was under Heat Advisories or Excessive Heat Watches or Warnings by mid-week (see the image below showing the heat-related advisories on Wednesday morning).


Below is a summary of the high and low temperatures for August 1-5, with records set or tied marked with an asterisk (*). The all-time warmest low temperature for Memphis was tied at 84 degrees on the 3rd.

High/Low Temperatures for Memphis
August 1 - 98 / 82*
August 2 - 100* / 80 *
August 3 - 103 * / 84 *
August 4 - 104 * / 83 *
August 5 - 101 / 78

With the passage of a cold front on Friday, much of the Mid-South got a slight reprieve from the heat, but the break will be short-lived as another ridge of high pressure builds over the region beginning tonight. The ridge will once again help to push temperatures into the upper 90s and towards the century mark beginning Sunday.

Though it doesn't appear this heat wave will be quite as intense, highs near 100 will be possible throughout the next week, with lows once again only dropping to near 80 in metro areas. High temperature records may not be broken, but overnight lows could be. After last week's heat, the problem this coming week could be more in it's duration rather than intensity. Heat is a silent killer and the dangers multiply as the hot days tick by. Please take all necessary precautions this coming week to prevent heat illnesses and check on the elderly, very young, and your pets frequently.

If you are tired of all of this "heat talk," check out the first winter weather outlook of the year, issued by Accuweather.

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