Wednesday, August 26, 2015

MWN Lightning Round: awesome local weather, a west TN quake, KMEM is StormReady, and a note on T.S. Erika


Decided it would be a good idea to hit a few topics all at once today, so here comes another edition of the MWN Lightning Round!

Awesome weather week

I don't know many people complaining about this week's weather. For late August, you can't be disappointed with morning lows in the 50s for many, afternoon highs in the mid 80s, abundant sunshine, and low dewpoints! We have one more day to copy/paste that forecast, then humidity starts creeping back up as wind shifts back to the south.

By this weekend, we'll be back to "near normal" for this time of year - lower 90s afternoons, lower 70s morning, and a little more humidity. The good news is there still is no appreciable rain chance in the 7-day forecast. Looking further out, NOAA thinks the first 10 days or so of September will feature slightly higher rain chances and above normal temperatures (which means 90s). Don't worry, this week's weather will be back before long! Fall is not too far away!

Temperature outlook for September 3-9, 2015, which shows a 70% probability of above average temperatures in the metro during this period. Summer may not quite be done!

Tipton County Earthquake

Tuesday morning at 8:26am, a magnitude 3.5 earthquake struck the Mid-South, centered a few miles north of Covington in Tipton Co. There were many reports of people feeling the tremor, especially north of the metro, including Lauderdale County. Fortunately, it was too weak to cause damage, but it is a good reminder that the New Madrid fault lies very near the area. For those of you who saw our post on Twitter and Facebook (below) and shared, commented, or liked it, thanks. It was all in good fun (especially since there were no major ramifications). The post went viral with over 100,000 views in 24 hours (and climbing). :-)

We stand with Tipton County. #TNQuake #TiptonStrong
Posted by MemphisWeather.net on Tuesday, August 25, 2015


Memphis International Airport becomes StormReady

About a month ago, Memphis International Airport (KMEM) achieved an important designation. No, not the first airport with a "Grit and Grind" spokesperson, but the first airport in Tennessee (and  only the 16th nationwide) to earn the "StormReady" designation from the National Weather Service. From the Airport Authority newsletter, the designation is "for demonstrating excellence in the preparation and planning for severe weather."

Jim Belles, Meteorologist in Charge of the NWS's Memphis Forecast Office; Cedric Simon, Memphis Int'l Operations Duty Manager; Stephen Kearney, NWS meteorologist; Terry Blue, MEM Vice President of Operations; and Gary Woodall, NWS Warning Coordination Meteorologist. Photo courtesy MSCAA. 
According to the National Weather Service, "StormReady helps arm America's communities with the communication and safety skills needed to save lives and property--before, during and after the event. StormReady helps community leaders and emergency managers strengthen local safety programs."  So the next time severe weather threatens the airport, rest assured that airport officials have a plan and are ready to execute it at a moment's notice to keep patrons and operations safe.

Tropical Storm Erika struggling, but has potential

As of Wednesday afternoon, Tropical Storm Erika is being affected by moderate to strong wind shear as it moves towards the Caribbean. This shear has weakened the storm and will continue to affect it for a couple of days. However, if Erika can survive the shear, much more conducive conditions await as the storm approaches the Bahamas, and potentially Florida, in a few days.

Computer models have narrowed in on a track that takes the storm north of Puerto Rico and into the Bahamas this weekend, while also strengthening it as it leaves hostile conditions behind. From there, it's difficult to say what Erika will do, but those along the Florida east coast will need to closely monitor the system. Multiple scenarios take Hurricane Erika up the east coast of Florida early next week.

NHC Forecast track for T.S. Erika as of Wednesday afternoon. The last forecast point just off the Florida east coast is valid Monday afternoon and indicates a hurricane with 75 mph  maximum sustained wind.
By the way, Saturday marks the 10-year anniversary of Katrina's landfall on the Gulf Coast. That year, 2005, was also the last time a major (category 3+) hurricane made landfall in the U.S., a 10-year drought that is unprecedented in the modern era. Hate to say it, but we're overdue. For the latest information on Erika, see the MWN Tropical Page.

Erik Proseus
MWN Meteorologist

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Monday, August 17, 2015

A stormy week ahead also means slightly cooler temps

Though it's a bit early to be looking ahead to autumn, I've had several people comment that they are DONE with the 90s and ready to start looking forward to fall weather - highs in the 70s, lows in the 50s, pumpkin spice at Starbucks... :-)  I don't think we're there yet, but we've already lost an hour of daylight since late June and average highs drop back below 90 as the calendar turns to September.


In the meantime, we have a stormy week ahead as a fairly strong upper level trough (for August) approaches, combining with seasonal mid-August heat and humidity to produce a risk of severe weather by mid-week. Before that though, I expect Tuesday to be a similar day to Monday with widely scattered "airmass" thunderstorms that pop up, move little, and rain themselves out during the afternoon hours. High temperatures will be similar to Monday and about normal for this time of year - near 90.

Tuesday night begin to see the influence of the approaching trough to our northwest as thunderstorms progress into MO and AR. A chance of rain moves into the Mid-South by early Wednesday, but the best chances of thunderstorms will be during the afternoon and evening hours. Model data is still not quite in line with the timing of the front and subsequent impacts, mainly because the front will be slowing down as it nears the Mid-South as the low "pulling" the front ejects north into Canada. As of Monday night, west TN and northeast AR are under a Marginal Risk (category 1/5) for severe storms Wednesday with the better chances to our north. This will likely change a few time between now and Wednesday afternoon, so stay in touch with MWN for the latest details. The main severe weather threats will be isolated damaging wind gusts and large hail. Wednesday night activities definitely need a rain plan.


Forecast precipitation amounts through Saturday from NOAA's Weather Prediction Center, which indicates 2" or more of rain could fall this week.

A relative lull is expected Thursday as the front stalls over the region and most of the atmospheric dynamics are well removed from the Mid-South. A few showers or a thunderstorm can't be ruled out however. The best part of Thursday will be the temperatures - some areas may barely reach 80° for the high!

Forecast high temperatures for Thursday from the NOAA WPC. While 78° may be a bit cooler than we actually see, temps near 80 would certainly be welcome!
To start the weekend, the front remains stalled over the area but pulls back to the north as a warm front on Sunday. Combined with warmer temperatures, scattered showers and thunderstorms will once again be possible, though it is too far out to pinpoint any more likely times. This time of year though, typically afternoons provide the best chance of thunder.

Surface map valid Saturday morning showing Wednesday night's front still draped across the area, providing a focus for scattered showers and thunderstorms to end the week.
We encourage you to download our mobile apps and follow us on Twitter and Facebook for the latest details and updates on the potential severe weather threat Wednesday. Links are all below.


Erik Proseus
MWN Meteorologist

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Sunday, August 9, 2015

Summer heat and humidity abates as schools resume

A busy week in the the weather world started hot, included three separate Memphis metro severe weather events, and ends with another hot weekend. However, a cold front and upper level pattern shift early this week promises more comfortable late summer weather as schools resume.

Recapping last week

The past week included two lines of storms with high wind that resulted in accumulating power outages and downed trees on Wednesday. In sum, over 50,000 MLG&W customers alone lost power between these two systems that moved through late Wednesday afternoon then again just before midnight. As utility crews were busy repairing their infrastructure, temperatures were a bit more comfortable to end the week but ramped up this weekend with Heat Advisories back in place. In addition, one additional line of storms moved through the metro about rush hour Friday morning, sporting a very photogenic shelf cloud and prompting warnings, but doing little in the way of additional damage thank goodness!

The shelf cloud Friday morning approaches Arlington in this picture by Laney Borwick.

Looking ahead

Monday will be the last day of above normal temps and Heat Advisories for most of the area as a cold front and pronounced upper level pattern change ushers in cooler temperatures and much lower humidity by mid-week that looks to last into early next weekend at least.  Let's get into the details.

Heat Advisories and Excessive Heat Warnings in effect as of Sunday afternoon reflect the heat provided by high pressure at the upper levels and southerly flow escorting high dewpoints from the Gulf into the region.

Technical forecast discussion

At the upper levels, a large dome of summertime high pressure centered over Texas dominates the southern U.S.

Upper level (18,000' or 500 mb) high pressure is centered over the southern Plains Sunday evening. Graphic courtesy WeatherBell
However, as we head into the week, that high pressure will retrograde into the western U.S. while a large trough develops over the eastern U.S. with pressure lowering over the Mid-South in the wake of an early week cold front. As the upper high moves west, heat will abate, dropping temps to below normal levels from mid-week into the early part of the weekend.

Upper level (18,000' or 500 mb) high pressure moves west by Wednesday evening. Graphic courtesy WeatherBell

A good way to visualize the dry airmass that will move in behind the front is by looking at precipitable water (PW), which measures the amount of water vapor in a column of air if it condensed into rainfall and piled up on the ground. In other words, it's somewhat a measure of humidity, only it is not just surface humidity, but humidity throughout the whole atmosphere.

The first image below shows PW early Monday evening. Values in the metro (red) are near 2", which is roughly in the 90th percentile for this time of year (meaning only about 10% of the time is it higher than this). However, by Wednesday evening (second image below), those values drop to about 0.75", which is near the minimum observed this time of year!  So the atmosphere as a whole will be much drier by mid-week.

Precipitable water (PW) values on Monday evening, as described above. Graphic courtesy WeatherBell.

Precipitable water (PW) values on Wednesday evening, as described above. Graphic courtesy WeatherBell

Forecast for the week

As for what to expect this week, first remember that Heat Advisories remain in effect Monday. Temperatures will again be in the mid to upper 90s with heat indices above the 105° danger level. Take frequent breaks if outdoors and keep drinking water! Below is the forecast precipitation amounts with the frontal passage. As you can see, very little rainfall is expected ahead of the front locally and that will be in the form of widely scattered thunderstorms Monday afternoon and evening.


As for the severe weather threat, we are currently in a Marginal Risk (category 1/5), which is low, but not no-existent. The main threat will be that a few storms could produce damaging wind Monday afternoon and evening, though again, not a lot of storms are expected.


As for the rest of the week, temperatures will moderate to below normal levels by Wednesday, then back to near normal by the weekend. The 60s temps in the mornings will feel great! Plenty of sunshine is expected with low dewpoints, thus heat indices will not be a factor starting Tuesday.



Erik Proseus
MWN Meteorologist

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Tuesday, August 4, 2015

July 2015 Climate Data and Forecast Accuracy

July Recap

Temperatures and precipitation were above normal the past couple months and that trend continued in July. In fact, daily average temperatures were at or above normal on 16 consecutive, and 24 of 25, days after a cooler than normal week to start the month. Precipitation was well below normal with the exception of 2 days (the 3rd and 23rd) which produced  87% of the total monthly rainfall. Through July, Memphis International Airport has a year-to-date rainfall deficit of 2.64", or about 92% of normal.

On July 14th, a complex of severe thunderstorms swept through the metro, downing trees and power lines across southwest TN with wind speeds of 50-60 mph. An 87 mph peak gust was recorded in Atoka, TN. Over 30,000 MLGW utility customers lost power, which took over 3 days to fully restore. Earlier in the month, flash flooding occurred across the metro on the Independence Day weekend as rainfall totals of 3-5" were recorded across the area.

Precip totals for the period July 2-4, 2015. Flash flooding was common across the southern metro.

Memphis International Airport, Memphis, TN

Temperature
Average temperature: 84.5 degrees (1.8 degrees above average)
Average high temperature: 92.7 degrees (1.1 degrees above average)
Average low temperature: 76.4 degrees (2.6 degrees above average)
Warmest temperature: 99 degrees (20th, 29th)
Coolest temperature: 69 degrees (5th)
Records set or tied: 81 degrees (20th) - tied record for warmest minimum temp. 82 degrees (29th) - tied record for warmest minimum temp. The average minimum temperature for the month was 7th warmest on record. July 2015 was the 15th warmest July on record.
Comments: The first six days of the month were below average, then the rest of the month (except the 23rd which was 1 degree below average) featured above average temperatures. Only one day saw the low drop below 70 degrees (69 degrees on the 5th). Five days had low temperatures at or above 80 degrees.

Precipitation
Monthly total: 5.17" (0.58" above average)
Days with measurable precipitation: 9 (0.2 days above normal)
Wettest 24-hour period: 3.41" (2nd-3rd)
Total Snowfall: None
Records set or tied: 3.40" (3rd)
Comments: Over 4.5" of rain was recorded on just two days (3rd and 23rd). If those two days were discarded, it would have been the 7th driest July on record.

Miscellaneous
Peak wind: North/48 mph (14th)
Average wind: 6.6 mph
Average relative humidity: 69%
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: 83.0 degrees
Average high temperature: 92.3 degrees
Average low temperature: 74.0 degrees
Warmest temperature: 99.0 degrees (29th)
Coolest temperature: 65.1 degrees (31st)
Comments: None

Precipitation
Monthly total: 5.58" (automated rain gauge), 5.91" (manual CoCoRaHS rain gauge)
Days with measurable precipitation: 8
Wettest date: 3.04" (3rd) (via automated gauge)
Total Snowfall: None
Comments: None

Miscellaneous
Peak wind: West/35 mph (14th)
Average relative humidity: 79%

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

MWN Forecast Accuracy

MWN average temperature error: 1.58 degrees
MWN forecast temperatures within 2 degrees of actual: 80%
MWN average dewpoint error: 1.48 degrees
MWN forecast dewpoints within 2 degrees of actual: 80%

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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