TOTAL LUNAR ECLIPSE…NEXT WEEK!

You read that right! There will be a total lunar eclipse next week – early Tuesday morning (April 15th) – that you could see right here in Middle TN. I say “could” because, of course, we need the weather to cooperate. If it does, this is what it will look like:

eclipse-lunar-2004-Fred-Espenak

It’ll be reddish brown in color and appear dimmer than usual. That color change will be caused by refraction of the sun’s light through the Earth’s atmosphere on its way to the moon – essentially what happens to produce red sunrises and sunsets.

During a total lunar eclipse, the Earth passes directly between the sun and the moon. The Earth casts a shadow on the moon. As the eclipse begins, just part of the moon is covered.  Gradually, that shadow spreads across the entire moon, and becomes increasingly red as it does.  Then, the opposite occurs as the eclipse winds down and comes to an end.  The photo below from mikesastrophotos.com is the best I found to illustrate the various phases.

eclipse-phases-dec21-2010

TIMES TO SEE IT:

So when exactly will this be visible here in our area?  Check out the table below, from http://www.timeanddate.com/eclipse/lunar/2014-april-15

Event UTC Time Time in Nashville* Visible in Nashville
Penumbral Eclipse begins Apr 15 at 4:55 AM Apr 14 at 11:55 PM Yes
Partial Eclipse begins Apr 15 at 5:59 AM Apr 15 at 12:59 AM Yes
Full Eclipse begins Apr 15 at 7:08 AM Apr 15 at 2:08 AM Yes
Maximum Eclipse Apr 15 at 7:46 AM Apr 15 at 2:46 AM Yes
Full Eclipse ends Apr 15 at 8:23 AM Apr 15 at 3:23 AM Yes
Partial Eclipse ends Apr 15 at 9:32 AM Apr 15 at 4:32 AM Yes
Penumbral Eclipse ends Apr 15 at 10:36 AM Apr 15 at 5:36 AM Yes

WEATHER OUTLOOK:

As for the weather, right now, it appears a rain system will have just exited.  BUT, some of its clouds will linger.  All we can do is hope they move out quickly enough.  It may come down to part of the area being able to see the eclipse, but other parts being too cloudy.  We’ll update you on this as the event draws closer on Channel 4 News and http://www.wsmv.com.

IF YOU MISS IT:

Lastly, if you miss this one, don’t worry.  There will be three more total lunar eclipses soon!  They’ll happen this October 8th, as well as on April 8th and September 28th of 2015.

 

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Thursday Night Storms Update

Some strong/severe storms moved through the Midstate late last night, producing some 1″ diameter hail along the way…but the main threat of severe weather will take shape over the next 24 hours.

Let’s start with a somewhat tenuous severe threat this afternoon and evening.  It looks like scattered storms are going to develop, and some of those could become strong or marginally severe.  This Futurecast image shows that the best chance of these scattered afternoon storms will be along and north of I-40, and west of I-65:
HRRR 2P THU

Like with the storms last night, the main threats will be large hail (1″+) and damaging winds (60+mph).  The severe threat won’t be as high with these storms (compared to tonight) because while there will quite a bit of energy in the atmosphere, there won’t be much to organize these storms.  (Organized storms are much more likely to become severe.)  Because of that lack of organization, the exact timing (or even their development in the first place) is really hard to pin down — at any point this afternoon and evening, the atmosphere will be able to support thunderstorm activity.  The Storm Prediction Center does not anticipate issuing any watches for our area through early afternoon.

There are still a number of questions surrounding tonight’s severe weather potential, mostly relating to the timing of the squall line that will be moving in from the west.  My original thinking this morning was that storms could be moving into the Tennessee River valley a little before midnight, but some of the latest computer model guidance suggests that the squall line will only be reaching the Mississippi River at midnight, which means a later arrival time for us, within the time ranges shown here:
PAUL STORM TIMING

Usually as a severe weather event approaches, we’re able to narrow down the time frame as our confidence in the computer models’ output grows, but so far today that hasn’t been the case…thus, still a three-hour window from the earliest possible arrival time to the latest.  (One of the models is depicting a scenario with two strong storm lines moving through, so obviously things are still in flux.)  The later the storms arrive, the lower their severe potential will be…but that doesn’t mean we’ll be out of the woods.  As I wrote yesterday, the main threat with squall-line severe thunderstorms is associated with damaging straight-line winds in excess of 60 mph.  We’ll also face a severe threat in the form of large hail, and there may still be enough rotation within the storms embedded in the line to a produce a couple of isolated tornadoes:
PAUL SEVERE RISK GRAPH 2

The Storm Prediction Center has included the whole Midstate within a “Slight Risk” region for severe thunderstorms, with westernmost counties on the edge of the “Moderate Risk” region:
PAUL SEVERE RISK REGION

Breaking down the specific threats into categories, here’s the SPC’s map for the tornado threat — most of the Midstate is within the 5% risk of a tornado within 25 miles of any one location, 10% in extreme western counties:
Apr3_tor

The damaging wind map shows our greatest hazard, with a 30% risk for most of us, and even a 45% chance of 60+mph winds along the Tennessee River:
Apr3_wind

Hail, as I mentioned earlier, is also a concern…15% risk of 1″ hail within 25 miles for most of Middle Tennessee and southern Kentucky, but again those westernmost counties have a higher risk, in the 30% category:
Apr3_hail

The Nashville National Weather Service office released this summary graphic regarding tonight’s severe potential…it’s very similar to the information I’ve outlined above.
nws-graph

Overall, you’ve got the idea by now — the farther west you are, the storms will arrive earlier and they’ll be stronger.  The worst weather today and this evening will be in Arkansas and Missouri — they’re staring down the barrel of a significant tornado outbreak, with baseball-size hail thrown in for good measure.  Our severe weather threat is more borderline in comparison, but what I wrote yesterday still stands: storms will likely be severe as they move into the Tennessee River valley, not-as-strong-but-still-severe as they approach I-65, and marginally severe as they move into eastern Middle Tennessee.

Coincidentally (NOT ironically), today’s severe weather threat comes on the 40th anniversary of the “Super Outbreak” of April 3-4, 1974.  The NWS has put together a thorough look back at that event here, if you’re so inclined.

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Thursday Night Storms

After three consecutive months of below-average temperatures (via NWS Nashville), warmer than normal temperatures have made themselves at home over the Midstate the past few days.  And the reaction has been, well…
cookie-monster

But it’s springtime, which means that warm spells are often followed by cool spells (next week), and the transition is marked by severe weather possibilities.  That’s exactly our concern for Thursday night into Friday morning.  Before that though, we’ll continue to experience above-normal temperatures today and tomorrow, with highs near 80 degrees both days.  Some showers and storms are possible this evening and overnight, and again Thursday afternoon, as shown by these Futurecast snapshots:
RPM 8P WED
RPM 2P THU

Initially, I didn’t expect these storms to pose much of a severe threat…but dew points have risen into the upper 50s (indicating a favorable level of humidity for stronger storms), and the Storm Prediction Center has included the northwestern part of the Midstate in a “Slight Risk” region for this evening and tonight.
PAUL SEVERE RISK REGION 2

It’s a borderline severe weather scenario, with the yellow-shaded locations indicating where there’s a 15% chance (estimated) of severe straight-line winds or large hail happening within 25 miles of any given point.  For the most part, I think we’ll just see strong-but-not-quite-severe storms — the strongest ones could certainly be loud, producing a lot of lightning and thunder…but lightning and thunder don’t make a storm severe.  Lightning and thunder just make a thunderstorm, well, a thunderstorm.
back-off-man-Im-a-scientist

Our severe weather chances increase significantly Thursday night.  The greatest severe potential will take shape well to our west, in Missouri and Arkansas — that’s where a significant tornado threat will develop Thursday afternoon and evening (they could get baseball-size hail as well).  Those storms will move to the east, and by the time they reach the Mississippi River they’ll merge into a squall line (technically, a “quasi-linear convective system,” or QLCS), which will continue to advance eastward through West Tennessee.

Here’s where the forecast gets tricky.  The squall line will likely still be capable of producing damaging straight-line winds and large hail as it approaches the Tennessee River…but the severe weather threat will fade dramatically as the storms transit the Midstate during the night.  This sequence of Futurecast images shows our two favorite computer models’ version (RPM and BAMS, for the weather-dorks among you) of what the radar will look like through Thursday night:
RPM 12A FRI
RPM 2A FRI
RPM 4A FRI
RPM 6A FRI

Still some timing differences between the two models, but notice that the colors look less “angry” in the later images, showing the weakening trend as the storms progress into eastern Middle Tennessee.  The Storm Prediction Center’s severe-weather outlook for Thursday and Thursday night reveals the same pattern: the greatest severe potential cuts off at the Tennessee River, but the whole Midstate is still included in the “Slight Risk” region, indicating an elevated threat for severe weather (this outlook did not change much at all with the SPC’s afternoon update):
PAUL SEVERE RISK REGION

Smoothing out the differences amongst the various computer models, here are the arrival-time windows for the strongest storms Thursday night:
PAUL STORM TIMING

Squall lines are typically associated with damaging straight-line winds, and at this point that looks like our major cause for concern.  There will be enough instability in the atmosphere for hail to develop, but whether that hail could grow to severe criteria (1″ in diameter) is still questionable.  The tornado threat for Middle Tennessee and southern Kentucky will be low…not zero, but low.  Whenever storms develop, we’re always watching carefully for signs of rotation.
PAUL SEVERE RISK GRAPH 2

Overall, my expectations at this point is that storms will be severe as they move into the Tennessee River valley, marginally severe as they approach I-65 (meaning there will be warnings, but probably not much damage), and strong-but-not-severe as they move into eastern Middle Tennessee.  Plan on having a source of weather information handy before you head to bed Thursday night.  We’re still 36 hours from the storms even heading toward the Mississippi River though, so there’s a lot of time for the atmosphere to throw a curveball.
curveball

So if all of that has you doing this…
what
…here’s a shameless plug: you can join us Thursday evening for our severe-weather-awareness program, the “4WARN Weather Alert Tour” — we’ll be in Metro Nashville this week, at the Northside Church of Christ.  Lots of severe weather safety information, some interactive learning, trivia games…good stuff!  Doors open at 6pm if you want to come early and say “hi” (or ask questions about the severe weather later that night), the show starts at 7pm.

And of course you can find us on Twitter and Facebook as well!  (You can follow or like me on social media too, if you’re interested in my random brain droppings whenever I’m not talkin’ weather.)

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Sunday Night Ice

SUNDAY “UPDATE”: Really was planning on doing a full post today, but a stomach virus had other ideas about what I should do with my Sunday.

Freezing rain and sleet are still likely across the Midstate, heaviest amounts northwest of Nashville. Follow @WSMVweather and @NWSNashville for updates on Twitter and Facebook. I’ll be tweeting when I’m conscious today (@PaulHeggenWSMV)…and if course check in with Nancy Van Camp this evening on Channel 4 News. We’ll be on dark and early at 4am Monday to keep you updated as well.

——————

SATURDAY AFTERNOON: Not going to do a “full” post today — actually typing this on an iPad while manning the Channel 4 booth at the 2014 Severe Weather Awareness Day conference.

But I did want to put up a quick post regarding our freezing rain and sleet potential late Sunday into early Monday. Instead of a northward “wobble” to the projected storm track, the weather models are actually pushing things even farther to the SOUTH. Check out these images from our two Futurecast computers — these show a snapshot of the weather situation at 3am Monday. (The dividing line between freezing rain and sleet is hard to pick out — freezing rain is the southern part of the pink area.)

image

image

Obviously still some differences in the model data…I’m hoping that by the time I post a FULL blog update tomorrow, there will be better consensus. But right now things are looking “bad enough” that the National Weather Service offices in Memphis, Paducah, Louisville and Nashville have issued Winter Storm Watches and Warnings, Winter Weather Advisories, and Ice Storm Warnings, as indicated here:

image

Keep in mind, snow is NOT the primary concern — freezing rain and sleet causing significant ice accumulations will be the main hazard. Here’s how much ice the NWS Nashville office is expecting:

image

Again, I’ll have a full update posted by early Sunday afternoon…the upper-level heart of this storm system is still way out to our west, so there’s still time for this to change. We can hope!

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More Winter? Really?

Tomorrow is the first day of March!  Springtime!  Warm weather!  Hooray!
colbert-gif

But wait…
NotSoFastMyFriend

Yet another winter storm is going to trek through the middle of the country over the next 72 hours, and yet again the Midstate will be very close the dividing line between “hey, it’s just rain” and…well:
ice-storm-geneva1

Okay, so it won’t be THAT bad…but it looks like folks along and north of the Ohio River are going to be dealing with a significant freezing rain event late this weekend.  Could it impact us?  Sure.  But here’s why I think the worst of it will avoid us…

Our pattern this winter (over and over and over) has been for winter storms to give us a lot of cold rain, but then the bulk of the moisture moves off to the east by the time the atmosphere gets cold enough to produce freezing rain or sleet or snow.  As of right now (mid-afternoon Friday) that’s looking like the most likely scenario for Sunday night and early Monday.

Here’s the latest sequence of Futurecast images for Sunday evening, Sunday night, and Monday morning, showing rain (green), freezing rain/sleet (pink) and snow (white/blue):
RPM 6P SUN
RPM 9P SUN
RPM 12A MON
RPM 3A MON
RPM 6A MON
RPM 9A MON

The computers have some significant differences regarding exactly where the rain/freezing rain dividing line will set up — the left-hand images (RPM model) pretty much equate to being the “best-case” scenario, the right-hand images the “worst-case” (BAMS model).  I lean toward the RPM model (left) at this point, but since we’re still more than 48 hours away from this developing, there’s still lots of us time for us to re-evaluate things.

“But,” you say, “what about that ‘worst-case’ scenario?  What if that model is right?  What if it’s not worst-case enough?  WHAT’S GOING TO HAPPEN???”
confused-fillion

It’s going to be a close call…but the storm system itself is still waaaaaaaaay out to our west.  In fact, it’s still off the west coast.  Out over the Pacific Ocean, we’re not able to get much “sampling” data of the upper atmosphere from weather balloons and wind profilers.  The computer models that simulate the atmosphere’s behavior rely on that data to set their “initial conditions” — what the storm is doing now.  If the initial conditions aren’t right, then the computer’s output won’t be right (the non-technical phrase is “garbage in, garbage out”).  So, while we KNOW that the storm is out there (we can see it on satellite, and we’ve got some ocean buoy and ship reports), we won’t have a lot of the necessary information to put into the weather computers until the heart of the storm moves onto the west coast early Saturday.  To make a long story short…
Clue_TooLate2
…we could still see some significant fluctuations to the forecast path of the entire storm system.  But given what’s happened over and over this winter, a “wobble” of the storm track to the north seems like the most likely scenario.

So far, the National Weather Service in Nashville is being wisely non-specific, just outlining the areas most likely to see any problems whatsoever:
NWS_Mar2_early

The NWS offices in Memphis, Paducah and Louisville have already issued Winter Storm Watches for the counties shaded in white (notice that counties in the Channel 4 viewing area are on the fringes of all of the watches):
PAUL WATCH

I’ll wrap this up by once again stealing Peter King’s idea of “10 things I think I think”:
1) I think we’ll see above-normal temperatures both Saturday and Sunday
2) I think we’ll get some spotty showers during the day both Saturday and Sunday
3) I think the heaviest rain (1″+) will fall late Sunday night…and it will be rain
4) I think that most of the Midstate will stay on the warm side of this system until very early Monday morning
4) I think we’ll see a brief changeover to ice/snow as cold air moves in Monday morning
5) I think that by the time temperatures drop, only a scrap of moisture will remain…so ice/snow will not accumulate across most of the Midstate, including Nashville
6) I think the western half of southern Kentucky and northwest Middle Tennessee have the best chance of seeing freezing rain or sleet that would actually accumulate
7) I think the worst problems due to accumulations of ice, sleet and snow will stay just outside the Channel 4 viewing area to the north and northwest
8) I think the “worst-case” computer models are too pessimistic right now
9) I think I’ll probably have to make a few adjustments to this forecast over the weekend
10) I think that if the month of March was a fictional character, it would be Jim Moriarty
moriarty-changeable

Watch for updates this weekend!

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Thursday Evening Storms (P.M. Update)

As promised, here’s your afternoon severe-weather update.  There really aren’t too many changes to the forecast situation, so I’ve done a copy-and-paste of this morning’s post, and made some relevant edits.  So…as you’re reading the subsequent paragraphs, a lot of what you read will seem very familiar.  But rest assured, the information is either updated or still valid.  Enjoy!

Ahead of the front that will cause this evening’s storms, the atmosphere is really getting “squeezed” by the rapid change in air pressure associated with the whole storm system.  This produces very strong winds — sustained winds around 20-30mph through the evening, with gusts over 40mph (the highest wind gust so far in Nashville has been 43mph, at 2pm).  The National Weather Service has issued a Wind Advisory for the entire Midstate through this evening:
PAUL WATCH

The main event, of course, is the severe weather event that continues to look likely for Middle Tennessee and southern Kentucky. Before the storms arrive, we look not only at computer-model forecasts, but also at information from weather balloons (to give us a look at conditions in the upper atmosphere).  Here’s this morning’s weather balloon data from Nashville — don’t worry, I’ll explain what it means:BNA_12z_Feb20
waitwhat

Okay, here’s what it means (skip down to the paragraph below the Doctor Horrible “Science” meme if you’re not interested in the weather nerdiness):
1) The temperature data (red line) indicates an inversion — a layer of warm air (in the black circle, where the red line squiggles to the right) a little over a mile above our heads that will act like a “lid” to suppress any daytime development of storms.  The front headed our way, combined with warm temperatures near the ground this afternoon and evening, will likely be able to break that lid to produce strong storms this evening.
2) The moisture data (green line) shows a layer of dry air just above the inversion (in the blue circle).  I think the strong winds from the south today will adequately mix the lowest couple of miles of the atmosphere to reduce that dry layer…but if there’s still a dry pocket in place when the storms develop, the evaporation of rain in that dry air could help to further accelerate the downdrafts that produce strong straight-line winds.
3) The wind data (red box, toward the bottom) shows already-impressive levels of wind energy in the atmosphere over our heads, and that wind energy will only increase throughout the day.  “Helicity” lets us quantify wind shear (change of speed and direction as you go up in the atmosphere) — it’s already over 200, and will probably be over 400 by this evening, which is significant.
4) The one factor working for us is the limited instability in the atmosphere.  We measure that with “CAPE” (Convective Available Potential Energy, highlighted in the yellow box at the bottom)…right now it’s zero, but it’s forecast to be “high enough” (500-1000) for at least some potential for storms to grow tall enough to produce tornadoes.  (It’s well over 1000 in Little Rock this afternoon, which is “upstream” and a good indicator of how our atmosphere will behave.)  Storms have to grow vertically for a significant tornado threat — more “stretching” accelerates the rotation within the storm.  The low CAPE numbers also indicate low hail potential.

So, now you have an idea of all the factors we’re looking at when we’re putting together these forecasts.
science3

I had hoped the afternoon weather balloon data would be available by the time we published this update, but as of 3pm it’s still not there.  Once that data becomes available, I’ll post some quick analysis on Twitter to let you know if anything has changed.

If you slipped the geekiness, welcome back.  The Storm Prediction Center has placed most of the Midstate within a “Moderate Risk” region for severe weather (the red area in the image below), with the remainder of our area still included in the “Slight Risk” region (yellow).  No real change to this since this morning:
PAUL SEVERE RISK REGION

Within 24 hours of a severe weather event, the SPC also breaks down their outlooks into specific threat forecasts — tornadoes, straight-line winds, and hail.  Those maps indicate a significant straight-line wind threat, a low-but-still-there tornado threat, and a low potential for large hail:
day1probotlk_2000_wind
day1probotlk_2000_torn
day1probotlk_2000_hail

In case you’re not into reading the fine print, I’ll turn it into regular print…the percentages on those maps show the probability of that particular phenomenon occurring within 25 miles of any given point.  So, for most of the Midstate, here are the odds of these types of severe weather happening within 25 miles of you this evening:
WIND: 45% chance of 60+mph wind gusts (10% chance of 75+mph gusts)
TORNADO: 5% chance areawide
HAIL: a 5% chance in western Middle TN, less than a 5% chance elsewhere in the Midstate

Don’t like numbers?  Here are the threat levels in chart form:
PAUL SEVERE RISK GRAPH 2

As of mid-afternoon, the first watches have been issued by the Storm Prediction Center…a Tornado Watch is now in effect for roughly the western one-third of the area (this watch doesn’t include the Nashville metro):
PAUL WATCH 2

Important: THIS WON’T BE THE ONLY WATCH ISSUED.  It’s just the first.  Remember, a “watch” means that conditions are favorable for severe weather, a “warning” means that severe weather is actually happening.

My hope this morning was that cloudy skies would prevail, keeping temperatures cooler and reducing our damaging-storm potential.  But alas, those hopes have been dashed — with breaks in the cloud cover allowing the sun to shine through, the temperature in Nashville has already reached a record-tying 78 (at 2pm).  The warmer air at ground level will have a better chance of breaking the “lid” on the atmosphere…and it increases our tornado potential as a result.

Okay, we’ve covered what’s likely to happen…but what about the when?  Here’s the latest regional radar image (complete with fronts!) as of 3pm:
VIDEO VIPIR

And here are the latest Futurecast simulations of what the radar will look like throughout the evening…right now I lean toward the left-hand images being more accurate — that particular model matches up quite well with the 3pm radar image:
RPM 5P THU
RPM 7P THU
RPM 9P THU
RPM 11P THU
RPM 1A FRI

As I mentioned yesterday, it’s been my experience that computer models tend to slow down the arrival times of storm systems like these.  Factoring that in, here’s the latest estimate of when the storms will arrive:
PAUL STORM TIMING

Like yesterday, our colleagues at the National Weather Service are thinking along not-identical-but-very-similar lines:

image_full5

BOTTOM LINE: Plan on staying weather-aware this afternoon and especially this evening.  Of course, as a loyal Channel 4 employee, I recommend that you hunker down and watch the Winter Olympics, and we’ll be there to let you know when the weather becomes threatening.  We’ll also be streaming any weather coverage on WSMV.com and on our mobile app.  (By the way, if we’re in NBC’s Olympic coverage on Channel 4, we could also be doing non-stop weather coverage on the live-stream, so check both!)

This is not going to be a good evening for heading out and about…if you’re going to be away from the TV, you can keep up with us on Twitter (@WSMVweather and @PaulHeggenWSMV) and Facebook.  (SOCIAL MEDIA NOTE: Twitter is by far the better resource in situations like this, because it’s a chronological stream.  Facebook filters out posts and presents them out of order, which isn’t very helpful.)

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Thursday Evening Storms (A.M. Update)

Two blog posts planned today — this one, with more weather geekiness than you can shake a stick at…and an update this afternoon (hopefully posted by 3pm) to handle any last-minute adjustments to this evening’s severe weather forecast.

Ahead of the front that will cause this evening’s storms, the atmosphere is really getting “squeezed” by the rapid change in air pressure associated with the whole storm system.  This produces very strong winds — sustained winds around 20-30mph through the evening, with gusts possibly over 40mph.  The National Weather Service has issued a Wind Advisory for the entire Midstate:
PAUL WATCH

The main event, of course, is the severe weather event that continues to look likely for Middle Tennessee and southern Kentucky. Before the storms arrive, we look not only at computer-model forecasts, but also at information from weather balloons (to give us a look at conditions in the upper atmosphere).  Here’s this morning’s weather balloon data from Nashville — don’t worry, I’ll explain what it means:BNA_12z_Feb20
waitwhat

Okay, here’s what it means (skip down to the paragraph above the Storm Prediction Center graphic if you’re not interested in the weather nerdiness):
1) The temperature data (red line) indicates an inversion — a layer of warm air (in the black circle, where the red line squiggles to the right) a little over a mile above our heads that will act like a “lid” to suppress any daytime development of storms.  The front headed our way, combined with warmer temperatures near the ground this afternoon and evening, will likely be able to break that lid to produce strong storms this evening.
2) The moisture data (green line) shows a layer of dry air just above the inversion (in the blue circle).  I think the strong winds from the south today will adequately mix the lowest couple of miles of the atmosphere to reduce that dry layer…but if there’s still a dry pocket in place when the storms develop, the evaporation of rain in that dry air could help to further accelerate the downdrafts that produce strong straight-line winds.
3) The wind data (red box, toward the bottom) shows already-impressive levels of wind energy in the atmosphere over our heads, and that wind energy will only increase throughout the day.  “Helicity” lets us quantify wind shear (change of speed and direction as you go up in the atmosphere) — it’s already over 200, and will probably be over 400 by this evening, which is significant.
4) The one factor working for us is the limited instability in the atmosphere.  We measure that with “CAPE” (Convective Available Potential Energy, highlighted in the yellow box at the bottom)…right now it’s zero, but it’s forecast to be “high enough” (500-1000) for at least some potential for storms to grow tall enough to produce tornadoes.  Storms have to grow vertically for a significant tornado threat — more “stretching” accelerates the rotation within the storm.  The low CAPE numbers also indicate low hail potential.

So, now you have an idea of all the factors we’re looking at when we’re putting together these forecasts.
science3

If you slipped the geekiness, welcome back.  The Storm Prediction Center has placed most of the Midstate within a “Moderate Risk” region for severe weather (the red area in the image below), with the remainder of our area still included in the “Slight Risk” region (yellow):
PAUL SEVERE RISK REGION

Within 24 hours of a severe weather event, the SPC also breaks down their outlooks into specific threat forecasts — tornadoes, straight-line winds, and hail.  Those maps indicate a significant straight-line wind threat, a low-but-still-there tornado threat, and a low potential for large hail:
day1probotlk_1300_wind
day1probotlk_1300_torn
day1probotlk_1300_hail

In case you’re not into reading the fine print, I’ll turn it into regular print…the percentages on those maps show the probability of that particular phenomenon occurring within 25 miles of any given point.  So, for most of the Midstate, here are the odds of these types of severe weather happening within 25 miles of you this evening:
WIND: 45% chance of 60+mph wind gusts (10% chance of 75+mph gusts)
TORNADO: 5% chance areawide
HAIL: a 5% chance in western Middle TN, less than a 5% chance elsewhere

Don’t like numbers?  Here are the threat levels in chart form:
PAUL SEVERE RISK GRAPH 2

There are still reasons for optimism, particularly with cloudy skies so far this morning.  Our best hope is for skies to remain cloudy, which would reduce our afternoon temperatures, and thus reduce the amount of energy available to fuel the evening storms.

Okay, we’ve covered what’s likely to happen…but what about the when?  Here are the latest Futurecast simulations of what the radar will look like throughout the evening…right now I lean toward the left-hand images being more accurate:
RPM 5P THU
RPM 7P THU
RPM 9P THU
RPM 11P THU
RPM 1A FRI

As I mentioned yesterday, it’s been my experience that computer models tend to slow down the arrival times of storm systems like these.  Factoring that in, here’s the latest estimate of when the storms will arrive:
PAUL STORM TIMING

Within those windows, I would lean toward the earlier arrival times…but until the storms actually start to develop, it’s hard to know for sure.

Like yesterday, our colleagues at the National Weather Service are thinking along very similar lines:
Feb20_NWS_timing

BOTTOM LINE: Plan on staying weather-aware this afternoon and especially this evening.  Of course, as a loyal Channel 4 employee, I recommend that you hunker down and watch the Winter Olympics, and we’ll be there to let you know when the weather becomes threatening.  We’ll also be streaming any weather coverage on WSMV.com and on our mobile app.

This is likely not going to be a good evening for heading out and about…if you’re going to be away from the TV, you can keep up with us on Twitter (@WSMVweather and @PaulHeggenWSMV) and Facebook.  (SOCIAL MEDIA NOTE: Twitter is by far the better resource in situations like this, because it’s a chronological stream.  Facebook filters out posts and presents them out of order, which isn’t very helpful.)

Again, I’ll post an update this afternoon to address any adjustments to the forecast.

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