Sunday, August 7, 2011

Chance of evening storms "under the ridge," then a pattern shift means cooler weather

Massive high pressure has maintained a grip on Mid-South weather for several days, bringing nearly daily chances of eclipsing the 100 degree mark. A respite on Friday was caused by thunderstorms that managed to move under the ridge thanks to a disturbance in the mid levels of the atmosphere.

After nearly reaching 100 again today, another one of these disturbances is moving slowly across AR and causing scattered storms over the central part of the state. This impulse should move just south of the metro area this evening, but will bring a chance of t'storms, mainly over northwest MS and east-central AR, between 6-11pm.

As we head into the new work week and the first week of school for many area children, the strong ridge of high pressure will begin to retrograde to the west, putting the Mid-South in a northwest flow.  This means that the upper level wind will be flowing from northwest to southeast over the area.  In the summertime, this pattern lends itself to the possibility of repeated rounds of thunderstorms, particularly at night or in the morning hours.  These rounds of thunderstorms are hard to time more than a day or two in advance, so for now the MWN Forecast includes a daily chance of thunderstorms this week as the pattern could stick around for a while.

The bad part of this pattern is that, depending on the timing of the storms, they could bring chances of damaging wind and hail. The good news, other than the rain chances, is that it will also mean reduced high temperatures. So, the end of the upper 90s to lower 100s is within sight.  An Excessive Heat Warning remains in effect through Monday evening with heat indices near 110 again Monday.  Excessive Heat Warnings are not anticipated for the remainder of the week after Monday.

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For weather information for Memphis and the Mid-South, where and when you need it, visit MemphisWeather.net on the web, m.memphisweather.net on your mobile phone, download our iPhone or Android apps, or visit us on Facebook or Twitter.

Friday, August 5, 2011

July 2011 Climate Data and MWN Forecast Accuracy

An extremely hot June continued into July with the June-July period averaging 84.9 degrees - tied with 1980 as the warmest June-July on record in Memphis and was just 0.2 degrees warmer than the same period in 2010. Despite the very hot temperatures, only one record was set - the maximum record low was tied on July 12 at 82 degrees.  Precipitation was below average for the month.

Memphis International Airport, Memphis, TN

The average July temperature was 86.0 degrees, which was 3.5 degrees above normal. The average high temperature was 94.9 degrees and the average low was 77.2. The coolest temperature of the month was 72 degrees on the 1st and the highest temperature was 99 degrees on the 11th, 12th, and 31st.

Precipitation for the month of July totaled 2.95", which was 1.27" below average. There were 9 days with measurable rainfall; 3 of those measured more than one-half inch.  The greatest 24-hour total was 0.82" on the 24th-25th. The peak wind gust was 51 mph in a thunderstorm on the 3rd with an average wind speed for the month of 5.6 mph. Click here for a daily statistical recap for Memphis International Airport.

Cirrus Weather Solutions, Bartlett, TN

The average temperature for July at Cirrus Weather Solutions in north Bartlett was 83.8 degrees with a maximum of 100.4 degrees on the 11th and 12th and a minimum of 64.5 degrees on the 1st.  July precipitation ended below normal with a total of 3.07". A co-located manual gauge used for the CoCoRaHS program measured 3.13". The peak wind gust was 20 mph on the 21st. Average relative humidity was a high 72%. Click here for a daily recap on MemphisWeather.net.

MWN Forecast Accuracy

For the month of July, the average temperature error in all MWN temperature forecasts was 1.63 degrees, lower than all compared computer models and our most accurate month since August 2010. Nearly 80% of the MWN temperature forecasts for the month were within 2 degrees of the actual temperature. MWN's forecasts extend out five periods (or 2.5 days). For dewpoint accuracy, the MWN forecast beat all data sources, averaging 1.65 degrees error and falling within 2 degrees of the actual dewpoint 82% of the time. Historical accuracy statistics can be found here.

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For weather information for Memphis and the Mid-South, where and when you need it, visit MemphisWeather.net on the web, m.memphisweather.net on your mobile phone, download our iPhone or Android apps, or visit us on Facebook or Twitter.