September 2014 Weather Recap and MWN Forecast Accuracy

September Recap

A ten month streak of below normal temperatures was broken in August. September saw those above normal temperatures continue, averaging 1.0 degree above normal.  Despite the warmer than average month, the average temperature for the year through September ranks 30th coolest on record (a span of 140 years).

Precipitation-wise, it was a rather odd month. The summer dry pattern continued on 29 of the 30 days, but historic flooding in the metro and record rainfall at the airport on September 11th left the month wetter than an average September. However, a total of just 0.30" of rain fell for the month if one disregarded that single day. And after September 11, only a trace of rain was recorded. For the year, precipitation is still 126% of normal, or exactly 10" above normal. Severe weather was limited to the significant flooding event on the morning of September 11. We posted a thorough recap of the event previously on the blog. You can find it here.

Precipitation totals from the September 11, 2014 Flash Flood event.

Memphis International Airport, Memphis, TN

Temperature
Average temperature: 76.2 degrees (1.0 degrees above average)
Average high temperature: 85.6 degrees
Average low temperature: 66.7 degrees
Warmest temperature: 95 degrees (4th, 5th)
Coolest temperature: 54 degrees (23rd)
Records set or tied: None
Comments: 10 days had maximum temperatures at or above 90, two above the climatological average. For the year, the average temperature at Memphis is 64.0 degrees, which is 2.1 degrees below average.

Precipitation
Monthly total: 4.75" (1.66" above average)
Days with measurable precipitation: 4
Wettest 24-hour period: 4.45" (September 11)
Records set or tied: 4.45" on September 11 broke the previous record of 1.87" in 1965.
Comments: Besides September 11, only one other day had more than 0.02" (0.27" on the 6th). As of the end of September, the yearly precipitation has been 48.47", which is 10.00" above (or 126% of) average.

Miscellaneous
Peak wind: Southwest/35 mph (11th)
Average wind: 6.0 mph
Average relative humidity: 67%
Average sky cover: 50%

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

Cirrus Weather Solutions / MemphisWeather.net, Bartlett, TN

Temperature
Average temperature: 73.2 degrees
Average high temperature: 85.8 degrees
Average low temperature: 62.7 degrees
Warmest temperature: 96.5 degrees (4th)
Coolest temperature: 46.7 degrees (23rd)
Comments: 9 days had high temperatures at or above 90. The warmest low temperature was 77.1 on the 10th.

Precipitation
Monthly total: 8.39" (automated rain gauge), 8.46" (manual CoCoRaHS rain gauge)
Days with measurable precipitation: 5
Wettest date: 7.62" (11th) (via automated gauge)
Comments: As in Memphis, the vast majority of the rain fell on September 11 (91%). There was only one other day with more than 0.03" (0.71" on the 6th). Over 7" of rain fell in 3.5 hours on the morning of the 11th, with Bartlett one of the epicenters of historic flooding. For the period July-September, excluding September 11, Bartlett received only 4.25" of rain, or 40% of the normal Memphis average for that period.

Miscellaneous
Peak wind: Southwest/16 mph (10th)
Average relative humidity: 80%

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

MWN Forecast Accuracy

MWN average temperature error: 1.64 degrees
MWN forecast temperatures within 2 degrees of actual: 81%
MWN average dewpoint error: 2.02 degrees
MWN forecast dewpoints within 2 degrees of actual: 70%

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

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Unsettled weather week starts with a chance of severe storms Monday

A gorgeous, if breezy, weekend is in the books with warming temperatures and increasing rain chances this week. The main discussion point is the potential for severe storms on Monday.

Clouds increase overnight as southwesterly wind continues to bring in additional moisture. Lows will be much warmer than the 40s of the past couple of mornings, only dropping to near 60. On Monday, mid-level energy will rotate around a large trough north of the region. As temperatures warm to near 80 by afternoon, temperatures aloft will cool due to the approaching mid-level disturbance. The disparity in temperatures creates a scenario with high lapse rates (which is the rate at which temperatures decrease with height). In addition, wind energy will increase as the mid-level wind picks up with the approach of the disturbance,resulting in increasing wind shear. All of these ingredients together will create a scenario which promotes the formation of thunderstorms, some of which could become severe.

The primary severe weather mode will be individual storms or clusters/short lines of storms with the main threats being large hail and damaging wind during the afternoon and early evening hours (coincident with peak heating). A tornado or two will be possible in any strong isolated cells that can become supercellular. We expect storms will be most likely and strongest roughly near a line from near Nashville to Corinth to Clarksdale, MS, but severe weather will be possible throughout the TN Valley, west TN, and north MS. The entire metro is outlooked under a Slight Risk tomorrow with a 15% chance of severe weather within 25 miles.

Severe weather probability for Monday afternoon and evening, centered on the TN Valley/Mid-South.

Preparations should include monitoring the latest forecasts from your favorite local sources, securing loose objects ahead of time (if they haven't already blown away from the wind the past few days!), and protecting anything outdoors that could suffer from hail damage. Have your severe weather apps,including StormWatch+, setup and ready to receive any watches and warnings that are issued.

For the rest of the week, the weather looks somewhat unsettled as we're squeezed between high pressure over the Midwest/Great Lakes and the Bermuda High over the Southeast. Temperatures should average near normal during the day (mid 70s to low 80s) and above normal at night (60s).

Erik Proseus, MWN Meteorologist

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Visit MemphisWeather.net on the web or m.memphisweather.net on your mobile phone.
Download our iPhone or Android apps, featuring StormWatch+ severe weather alerts!