Monday, January 16, 2017

Potentially Stormy Week Ahead in Memphis

Is this winter or is this spring? With a chance of showers and thunderstorms throughout the week ahead and temperatures in the 50s and 60s, many are wondering where Mother Nature sent away winter to and when it might come back.

Severe Potential on Monday Night

Showers and a few thunderstorms have been rolling through northern Mississippi, Arkansas, and western Tennessee throughout the day on Monday, but will increase in number and intensity into Monday night. A slow-moving system that helped bring lots of ice and wintry conditions to the Central Plains is driving a Marginal Risk (category 1 of 5) for severe weather this evening, mainly along and west of the Mississippi River.

With a Marginal Risk (category 1 of 5) of severe weather this evening across the Memphis metro, be on the lookout for heavy downpours, thunder, and some strong winds on occasion. These storms should weaken by the overnight hours. (NWS/SPC)
The key takeaways from the threat of these storms will be locally heavy downpours, thunder, and brief strong wind gusts. Not every passing shower or thunderstorm will produce these, however. Showers may continue into the overnight hours and early on Tuesday, but the thunderstorm threat should abate by about midnight tonight. Temperatures this evening will fall off into the mid to upper 50s. Winds continue out of the south between 10 to 15 mph.

Continued Showers Possible

More showers and an isolated thunderstorm are possible throughout the rest of the week as this expansive low pressure system slowly inches east. A cold front should be passing through the region early Tuesday morning, with a wind shift accompanying it from the south to the west. Temperatures will fall off slightly, with highs in the upper 50s to low 60s on Tuesday and Wednesday. Overnight lows should only drop off into the upper 40s to mid 50s, a far cry from how low those temps should be this time of year. (Our average low temperature in mid-January is near the freezing mark!)

The same system that brought very icy conditions to the Central Plains this weekend will slowly push east, bringing a continued chance of showers and thunderstorms through this week for the Memphis area. The map above is valid at 6pm Tuesday. (NWS/WPC)

Another round of rain/storms

Temperatures will rebound on Thursday, with highs in the mid-60s in the metro, but with an increased chance of showers and thunderstorms as the slow-moving stationary front to our south continues to push out and low pressure develops to our southwest and moves across the area. A couple of those storms could be severe Thursday afternoon and into the evening. However, that rain will give way to a good start to your weekend, with temps nearing 70 degrees and partly sunny skies on Friday into Saturday. Lows remain comfortable for January, in the mid-50s, just cool enough to need a light jacket when taking the kids to school in the morning.

Early next week

As one system exits our picture late this week, another is taking shape over the west coast. That system could once again bring showers and thunderstorms late in the weekend into early next week to the Memphis area, with the best chance coming on Sunday. A chance of showers continues to hold in the forecast through at least Monday, with temperatures taking a dive into the 50s for highs and 40s for lows to start your next work week.

Where is winter, you might ask? Most of the eastern U.S. has been under well above average temperatures for the past week or so. However, long range models suggest that warm pool will be cooling off and winter-like temperatures could make a comeback as soon as the end of this month.

NOAA's 8-14 day temperature outlook covering January 24-30 suggests that warmer temperatures across the eastern half of the country will weaken, letting old man winter back in. (NWS/CPC)
Be sure to stay on top of the human-powered MWN Forecast this week and into the next by downloading the MWN mobile app or bookmarking our website. We’ll provide continuous updates on our social media platforms as well. Links to all of these tools can be found below this post.

Alex Herbst, Meteorologist
MWN Social Media Intern

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Thursday, January 12, 2017

20s to 70s - it's winter in Memphis!

For those of you who were tired of the 88 hours of sub-freezing temperatures we had late last week and into the weekend, you got your wish. We're back in the 70s! Welcome to the bipolar weather of Memphis, where lingering snow one day is completely melted by 60s and 70s the next day!

Arrival of a cold front

A general warm pattern looks to continue well into next week, but we do get a reprieve of closer-to-average conditions tomorrow, as a cold front moves across the metro this evening, lingers just to our south into Saturday, then makes a return trip back to our north as a warm front this weekend. If you're out and about this evening, you'll likely notice the front between 8-10pm as warm and humid conditions give way to showers and then a shift in the wind to the north, accompanied by a roughly 20-degree temperature drop. Here's forecast radar for this evening and overnight showing the rain:

Forecast radar for the evening and overnight hours from the HRRR model. If the GIF doesn't animate, click here. (WxBell)

Friday into the weekend

With the front stalling just to our south, the much cooler surface air combined with a strong temperature inversion (warming air with increased height, rather than typical cooling) and abundant low-level moisture that produces a low cloud deck, will result in much cooler temperatures tomorrow. Look for morning bus-stop temperatures in the mid 40s and highs not much warmer, in the lower 50s. A cool northeast breeze will provide a stark contrast to today's tropical breezes and mid 70s highs!

A vertical cross-section of the atmosphere at 6am Friday, according to the NAM model, clearly shows the inversion and low-level moisture that develops behind tonight's cold front. The inversion will serve to trap low clouds in place until sometime Saturday, resulting in much cooler and overcast conditions.
The inversion and cloud cover remain in place Friday night and into Saturday, keeping temperatures nearly steady Friday night near 50° and introducing the possibility of areas of dense fog. By Saturday afternoon, some sun may break out as the front starts to return back to the north. allowing the mercury to climb back to 60° or higher. Sunday promises to be a day not unlike the last couple with highs once again pushing the 70° mark and some afternoon sun expected between the clouds. With the exception of a stray shower, or drizzle Saturday morning, most of the weekend looks to be dry.

Next week

Looking at next week, a large scale system to our west, that is held at bay through the weekend by the Bermuda High pressure system over the southeast U.S., will start slowly moving east. A few showers are possible Monday, mainly afternoon and evening, as highs reach near 70° again. By Tuesday and probably into early Wednesday, periods of heavy rain and some thunderstorms are possible as the system, and it's upper level low, cross the region. Temperatures will remain mild, so there are no winter weather concerns, but not as warm as Sunday and Monday. We'll be watching rainfall amounts closely as some flooding is possible if heavy rain is prolonged.

The NWS predicts a solid 2" of rain for the metro over the next week with heavier amounts to our west where some impactful icing is also possible this weekend. (WPC/NOAA)
For those looking for more "winter-like" conditions, there are some long-range signs of a pattern shift late in the month. Cross your fingers! You can always check for details out a week in advance in the MWN mobile app or on our website. Look for the human-powered MWN Forecast!

Erik Proseus
MWN Meteorologist

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MWN Interview: Dr. David Stephens, "Winter Weather in a Southern School District"

Earlier this week, meteorologist Erik Proseus had the opportunity to sit down with Bartlett City Schools Superintendent Dr. David Stephens to talk about winter weather, and specifically the process a southern school district goes through in preparing for and executing operations when winter weather is forecast. Though his answers apply specifically to Bartlett, from our conversation it was clear that the process is fairly similar in other districts in the area. What follows is a Q & A from our conversation, edited for length. At the end of the post, you'll find a link to the audio of the entire conversation, as well as a full transcript. I think you'll find it enlightening, especially if you are a parent of school age children.

Can you start with just giving me a little bit of the background of the district? How many schools, how many students do you serve, and staff?

Bartlett has 11 schools, six elementary, three middle schools, one Ninth Grade Academy, and Bartlett High School. We have approximately 8700 students and about 850 staff members, so a fairly large district. In fact, as far as the municipal and city districts in the state, we are the largest.

It's said with probably some truth that southerners really don’t handle snow and ice well, and for good reason. First we don’t have a lot of practice with it, so even when you do put together a plan and you get to exercise it, you don’t get to exercise it again with your best practices a week later. And then as we all know, winter weather is a challenging meteorological question as well. So how early do you start to think about what your plans are going to be for this year in case of inclement weather?

Once we get school up and running and we get into the end of September, end of October, we start having discussions about our communication plan, how we’re going to do that. We look at what we’ve done in the past, and usually at the end of the snow season, we kind of sit down and see what works and what doesn’t.

What sources are you using for your information and are you consulting with other districts as you’re making these decisions?

Yeah, there’s a lot of communication. What I do is I constantly watch the weather. Fortunately, I’m kind of a weather nut. If you looked at my computer, you’d see different websites. I always look at 10 and sometimes I’ll even look at 15-day forecasts just to see, moisture and temperature. But I’ll say, Erik, and I’m not saying this in a gratuitous way, but the work you’ve done and the relationship we’ve been able to have where I can reach out to you and you can reach out to me with has been extremely helpful. [...] I’ll take that text [you send me] and send it to on to some of my colleagues, cause we’re getting it from a lot of different sources. I look at the Weather Channel, that’s pretty global, but I have that [] information here [locally]. I do enjoy the National Weather Service site and we will get on their conference calls.

So leading up to that, we’re [superintendents] having conversations because, you know, it’s kind of the domino. Once one district [cancels], then the heightened sense of, all right, what are you going to do? So we try to coordinate, and it may not be the same [decision for each district] because you can have a situation where Bartlett may be doing pretty good, but down in Collierville/Germantown, they may be the ones getting those issues, so it’s not always that we’re going to be the same, but we do try to coordinate and have discussions.

[Dr. Stephens continues about the process of making the cancellation decision]

We have a group of three of us that get out and drive the streets of Bartlett. We’re up at 3:30 a.m. We get out, we look at the conditions around our house, then we get out in our cars and go. [...] Then I touch base with some of the other superintendents to see what [they're] seeing. Then we’ll pull over in parking lots and I will meet with our staff. [...] It’s something that I take very seriously, because the thing we always want to do is, if we’re going to err, we’re going to err on the side of caution. We do not want to put any student, staff member, parent, anybody at any risk. [...] Between 4:30 and 5:00, we have to make that call because buses are going to start rolling. The bus drivers appreciate [letting them know] as early as we can so we’re not getting them out on the roads. [...] When I can’t see the lane lines, I’m not going to put buses and kids out in this.

What about early dismissals and late starts versus just calling off the day?

We have a fleet of [over 50] buses and they run three tiers. That’s how we’re able to economize and save. [...] From a parent perspective, the sooner we can let them know, I mean, perfectly, we’d let them know the night before. It’s hard to do that based on a forecast because, as we know, at times, it’s difficult. We understand they have young children and they have to make arrangements, so we want to let them know as soon as possible. But once we’re in school, let’s say it’s 9:00 and the snow’s coming down. We have to dismiss. Well then our schools that dismiss at 2:00, we would have to start [dismissing] those from 9:00 to 10:00, then your middle tier schools 10:00 to 11:00, [then the late schools from] 11:00 to 12:00. So you’ve got a three-hour period where you’re running those buses.

As far as the academic calendar is concerned, do they [snow days] have to be made up?

We do go some extra time [on each school day] to stockpile a few snow days. And then at the end of the year, I have to make a recommendation to the Board [of Education]. It’s a Board decision. Do we extend the school year by a day or two, or do we use those stockpiled days? If you miss a big chunk, if we’re out two weeks, that’s a lot of instruction [time missed]. But two or three days, if you look at adding that after Memorial Day, you really think how much instruction [will take place]? [...] I never plan a vacation the first week in June because you just never know if we’re [going to be] out for a long, extended period of time.

With social media I know that you’re hearing from people, good or bad. Does that make those decisions any more challenging?

We just have to deal with the facts. And at the end of the day, you have to be able to look yourself in the mirror and say, we’ve made the best decision for our kids and our community and our parents. [...] We want kids in school. We want those those things that are happening in classrooms to happen, but if I ever put a kid in a situation where somebody was hurt, [...] that’s a superintendent’s nightmare.

Finally, with 850 staff and almost 9000 kids and all their parents, what do you want them to know, bottom line, about the decisions you make regarding inclement weather and operations?

Well, we’re gathering a lot of information. We’re talking to other districts. We’re looking at those forecasts and we are going to make the best decision to keep our kids safe. That is the bottom line. We just don’t have the experience of driving on snow. We don’t have the equipment to mitigate snow. So we’re going to make that decision and sometimes we’re going to get it right. But if we’re going to miss it, we’re going to miss it on the side of caution.

You can get the same accurate and updated information Superintendent Stephens and many other decision-makers across the metro use by visiting, following us on social media, downloading the MWN mobile app, or reading this blog. Many thanks to Dr. Stephens for taking some of his valuable time to speak with MWN and educating all of us on the process involved when winter weather affects his district!

Listen to the entire interview via the player below, or if the player does not work, click here.

A full transcript of the interview in PDF format can be found here.

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

Saturday, January 7, 2017

Snow day recap - perhaps it wasn't ideal, but it was interesting!

Well, many of you got your wish - a day at home for kids and many parents alike! Enough snow fell to call off school and many businesses. I heard from several of you who (like our family) enjoyed a bonus lazy day on the first weekend after school starts back to recuperate from getting back into the "routine." And for those decision-makers out there, it started early enough that calling off school, etc.

However, it probably wasn't the ideal snow day for some. Why?

  1. It was COLD. I know, it has to be cold to get snow, but it was *really* cold. I think many would prefer a "30-degree-no-wind" snow day to a "wind-chills-near-10" snow day. It was hard to stay out for very long.
  2. The snow quality was sub-par compared to what we're used to. Not only was there not quite enough in the heart of the metro (granted there was more in north MS and up north a bit), but it was too dry to pack. Hard to make snowballs and snowmen with dry snow.
  3. Though it was drier than we usually get, there was enough on the streets prior to sunrise that when cars did get on it, and weren't going very fast, it just packed it down, which resulted in a thin layer of ice by the afternoon and evening. So it was too cold, too dry of a snow, and hard to drive in.

For those keeping score though, it was still a Mid-South snow, and probably more typical of what we should expect than the occasional 3-6" event that we see every few years. MWN on the north side of Bartlett was in a sort of minima with heavier snow north and south. The snow total there was 0.9". The airport on the south side of town officially measured 2" as it got in on a heavier band late in the event between 8-9am that brought totals up to 3" to parts of DeSoto County. Here's the NWS snowfall total map of the event:

Overall, I think the forecasts generally panned out pretty well too. Yes, we all pretty much started with "less than an inch" in some form or fashion on Wednesday and early Thursday, but by Thursday night, most sources had upped that to 1-2". We were on the early side of calling for the increase, and also mentioned that a band would set up that was capable of producing 3" totals, when I posted this in the MWN Blog just before 2pm Thursday:

That "somewhere in the metro" ended up being along and just south of the state line. Model data really caught on to the scenario that played out on Thursday morning and the new high-resolution hourly model data generally did a nice job of pinpointing where that band would set up by very early Friday morning. Kudos to our model developers at the NWS and affiliated research institutions for some fine work being done well-behind the scenes.

The high-res HRRR model simulated radar from 3am Friday, looping through to 10am. Note the heavier (brighter blue) it's depicting along and south of the TN/MS line, on the southern side of the precipitation area. Pretty good job comparing to what actually happened! (WxBell)
There was very one interesting scenario that developed by mid-morning and continued playing out throughout a good part of the afternoon. Two different "drivers" of light snowfall were occurring at the same time, in the same place. Check out this mid-morning radar loop and see two areas of snow moving in completely different directions:

Radar loop from mid-morning Friday when light snow was moving in two directions - west to east with the main weather system, and north to south as snow bands at lower levels than the primary system. 
And see it still happening several hours later as the late afternoon band of light snow approaches the metro:

Snow moving in multiple directions is still seen at mid-afternoon. The north-south bands of snow continued for several hours on Friday.
There are a couple of possible hypotheses on this strange phenomena, which includes multiple snow bands moving from north to south over the metro and more organized areas of snow moving from west-to-east (which was the snow that was better forecasted and driven by the synoptic setup).

One scenario, and the one I find most plausible at this point, involves the influence that warm water can have on a very cold airmass. It's much like lake-effect snow off the Great Lakes, only at a smaller scale. Cold and fairly dry air moves over that much warmer body of water, picks up moisture from that water, and also starts to rise as it warms a bit from the warm water below (warm air is less dense than cold air and rises). As the wind pushes the air downstream and it begins to cool, the moisture falls from the cooling air, creating a "path" of precipitation in a band that parallels the wind flow. The tell-tale signs are cold air blowing over a fairly substantial body of warmer water and bands of precipitation that are exactly in line with the low level wind.

There were 3 bands that formed in the morning. The first (western band) is believed to be a lake-effect band from Big Lake, which is just west of Blytheville, AR in  Big Lake Wildlife Management Area. The second (center band) is downwind of Open Lake (which is also right next to the Mississippi River) west of Ripley, TN. The easternmost, third, band was a little harder to figure out, but could be traced back to the Mississippi River itself, in an area west of Paducah where the river is fairly straight for several miles and is exactly lined up with yesterday's wind flow. The "fetch" is the amount of warm water the wind traverses. The longer that is, the more moisture it picks up. In this case, the wind was blowing from 020° (or NNE), which lines up with a length of the river that is oriented in the same direction. It's conceivable that we had the perfect scenario for river-enhanced snowfall yesterday! See the map below.

Three morning bands of snow, possibly traced back to their origins if they were indeed lake/river-enhanced snow. The eastern band had a long way to travel from north of Union City, but it likely could have been snowing all along that path from Ripley to Dyersburg to west of Union City. The radar would have been "overshooting" the relatively shallow depth of those precipitation bands that likely only extended a couple thousand feet into the air. 
The second hypothesis, which seemed a little more reasonable as we got farther into the afternoon and the bands became less pronounced, was that the light snow over the metro was due to a cold air miniature version of "convective rolls" which manifest themselves as cloud streets, or lines of cumulus clouds that form parallel to the wind flow. (See the Facebook post embedded above that has the satellite image of snow, then look at the bottom of the picture for cloud streets over the northern Gulf formed by Arctic air blowing over the warm Gulf waters. Another example is below.) If this were the case, in this situation we didn't just have rows of clouds, but clouds that precipitated! Satellite imagery didn't show these clouds like they usually do when typical cloud streets form because the sky was covered in clouds. They would've basically been buried by the other clouds around them. A hidden explanation? Perhaps.

Horizontal convective rolls, or cloud streets, off the U.S. Atlantic coast. Credit Jeff Schmaltz - NASA Earth Observatory.
I don't know exactly what happened, but theorizing and learning with real world experiences is part of why meteorology is so cool. :-)  I hope you enjoy the weekend, even if it is still way too cold. Don't worry, it's Memphis, so you always have this to look forward to:
(If you receive this blog by email and the animations don't work, click here for the online version.)

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