Thursday Storms: ETA + Hail? Damaging Winds & Tornadoes? Heavy Rain?

ETA

This afternoon our NWS updated its ETA. Storms are forecast to arrive between 8am and noon Thursday.

Hail?

Probably not much, if any. Our NWS:

WHILE THE FRONTAL SYSTEM TRAVERSES WESTERN TN AND APPROACHES MIDDLE TN
...SREF SEVERE PARAMETERS...CONVECTIVE AVAILABLE POTENTIAL ENERGY MORE 
THAN ANYTHING...PLUMMETS WITHOUT DAYTIME HEATING. THIS SEEMS TO BE A 
SHARED OPINION ACROSS THE MODELS. THIS WOULD CALM THE FEARS OF MANY 
IN THE WAY OF HAIL.

Damaging Winds & Tornadoes?

There’s a decent chance of both. Our NWS gets technical:

FORECAST SOUNDINGS ARE STILL INDICATING SUB 1000 FT LCLS AND 0-3 KM 
SRH VALUES ABOVE 300 M2/S2 AHEAD OF THE LINE. HODOGRAPHS CANT LOOK 
MUCH MORE CLASSIC FOR CYCLONIC TURNING IN THE LOW LEVELS. ALOFT...
A BROAD AND STRONG AREA OF 250 MB DIVERGENCE DOES APPEAR TO COINCIDE 
WITH A THIN AREA OF STRONG 850 MB FLOW, THUS DYNAMICAL LIFT IS STILL 
A PLAYER AS WELL.

That’s weather-speak for “the conditions are forecast to favor damaging straight-line winds, and possibly a tornado.” Thankfully, the NWS included a summary:

TO SUMMARIZE...THE THREATS OF NOTE ARE GOING TO BE LARGELY HEAVY
RAIN...DAMAGING STRAIGHT LINE WINDS...AND THE THREAT OF BRIEF
TORNADOES ALONG THE LINE. THE BULK OF THIS THREAT WILL BE IN CLOSE
PROXIMITY TO THE COLD FRONT ITSELF.

Heavy Rain?

Yes. Here is the “How Much We Think It’ll Rain” map from NOAA’s Weather Prediction Center. This covers 7pm Wednesday through 7pm Thursday:

Our local NWS office estimates 1.37″ in Davidson County and 1.51″ in Williamson County.

You’ll find more updates on Twitter (@NashSevereWx). I’ll update this site as more information becomes available.

Thursday’s Squall Line ETA & “Will There Be Tornadoes?”

Storm Prediction Center (SPC)

The SPC has included us inside their “SLIGHT” risk category for severe weather Thursday. The outlook map below begins at 7am Thursday. Given the fact we’re on the west edge of the outlook area, we can conclude the SPC thinks the squall line will arrive Thursday morning after 7am.

National Weather Service (NWS)

Our National Weather Service office agrees. They think our ETA is Thursday morning:

IMPORTANT DIFFERENCES REMAIN BETWEEN MODELS CONCERNING CONVECTIVE TIMING 
WITH THE GFS MODEL REMAINING A CONSISTENT FAST OUTLIER. WE ARE TRENDING 
TOWARD THE SLOWER NAM AND EUROPEAN MODELS, WHICH WILL FOCUS STORM CHANCES 
IN THE LATE WED NIGHT TIME FRAME WEST...THURS MORNING I-65 CORRIDOR...THEN 
LATER IN THE AFTERNOON ON THE PLATEAU.

Those of you who read last night’s post saw the European model advertising a Thursday night ETA. Well, no more. The latest run of the European model sends in the squall line just after noon. The other models send in the line before noon (one waaaay before noon). The models aren’t giving us the exact same ETAs, but confidence is increasing the line will be here Thursday morning.

Will There Be Tornadoes?

The NWS wrote in a Special Weather Statement issued at 8:14am that the main threat will be damaging winds. “Tornadoes cannot be ruled out . . . given the amount of wind shear forecast across the area.” (Wind shear is a change in direction and speed of the winds the further up the atmosphere you go). So, yes, there could be tornadoes embedded inside the squall line. Don’t discount the damaging wind potential. Severe thunderstorm winds are widespread and can be as strong as — and occasionally stronger than – weak tornado winds. Look for more updates as tonight, tomorrow, and certainly Thursday.

There Will Be (Severe?) Storms Thursday. We Don’t Know What Time.

Discussing Thursday’s severe weather this afternoon, our NWS said:

TIMING REMAINS QUITE UNCERTAIN FOR WHEN PRECIP ARRIVES ... LATE WEDNESDAY NIGHT 
OR THURSDAY...AND HAVE GONE WITH A BLEND OF THE TWO MODELS FOR NOW IN 
COORDINATION WITH SURROUNDING NWS FORECAST OFFICES. DESPITE LOW CONFIDENCE IN 
TIMING...THERE IS HIGH CONFIDENCE IN WIDESPREAD SHOWERS AND STORMS OCCURRING...

“Quite uncertain.” Helpful, isn’t it?

Blame the weather models for the uncertainty. Let’s look at four of them and their varying ETAs.

1.  American NAM Model. ETA – wee hours of Thursday morning, while (most of us) sleep.2.  American GFS model. ETA – Thursday morning rush hour.

3.  American Short Range Ensemble Forecast model, aka the SREF for those of you wanting to impress your friends out yourself as a weather nerd. ETA – Thursday, mid morning.

4.  The European model, which actually does great here in the U.S.A. It was the only model to accurately predict Superstorm Sandy would strike the northeast. Like all models, it’s not perfect. ETA – Thursday around 9pm.

Hello Euro

The NWS thinks if the NAM and SREF are right, the storms will arrive weaker. So, let’s all hope for the storms to show up mid-morning Thursday.

DESPITE THIS...NAM AND PARTICULARLY THE SREF WEAKEN THE LINE OF STORMS 
AS IT MOVES INTO AND ACROSS THE MID STATE. THUS SEVERE WEATHER POTENTIAL 
REMAINS QUITE UNCLEAR WITH THIS SYSTEM.

Squall Line Expected Sometime Thursday. Damaging Winds Likely. Few Tornadoes Possible

Just got off the weekly NWS conference call with media and emergency management. Here’s the scoop:

1.   Expect a squall line of storms to arrive Thursday. Damaging “straight line” winds are the most likely threat. A few tornadoes are also possible.

2.  We aren’t sure what time the storms will be here. Notice the three models, below. Two bring the storms in the morning. One brings them in around sundown.

American GFS model – ETA 7am:

Hola GFS

American NAM model – ETA 10am:

Hola NAM

European Model – ETA 7pm

Hola_Euro

3.  Expect about 1″ of rain Thursday. Some areas may get close to 2″. Rain is not the main concern.

Storms are expected to be strong/severe regardless of when they arrive. The best ETA for us would be early Thursday morning, which would help depress storm intensity.

Consult reliable weather sources this week. We should have a much better idea about the ETA as we move closer to Thursday.

NWS: We May Have Severe Weather (A Few Tornadoes?) Thursday

During the afternoon discussion about Thursday’s storm potential, our NWS said:

THE SETUP LOOKS LIKE A QLCS EVENT FOR MID TN WITH THE POTENTIAL FOR A FEW 
TORNADOES. THERE ARE STILL A LOT OF UNCERTAINTIES REGARDING TIMING AND 
DETAILS...SO PLEASE MONITOR UPDATED FORECASTS AND OUR HAZARDOUS WEATHER 
OUTLOOK CLOSELY OVER THE NEXT FEW DAYS.

This means we think there will be a squall line – with the potential for a few tornadoes – either (1) early Thursday morning or (2) Thursday afternoon. (QLCS is weather-speak for Quasi Linear Convective System, best referred to as a squall line).

(1)   The American (GFS) model gives us a 7am Thursday ETA:

(2)   The European model gives us a 1pm Thursday ETA:

Euro Hope

There are real uncertainties about the timing and nature of these storms. Monitor reliable weather sources this week as the picture becomes clearer and more details are evident.

I’ll let the NWS break the good news to you:

THE GOOD NEWS IN THE EXTENDED FORECAST IS THAT VERY NICE WEATHER IS EXPECTED 
AGAIN NEXT WEEKEND.

 

Tomorrow’s Small Rain Chance. Storms Thursday?

Sunday 51/73

Clouds will file in Sunday afternoon. Light rain is possible. Here’s what the models think:

European (ECMWF):

European Model as of Sunday at 1pm. This is very, very light rain.
European Model as of Sunday at 1pm. This is very, very light rain.

American (GFS):

American (GFS) model, also at 1pm Sunday. The 4pm run takes the precip N of Davidson & Williamson Counties

Any rain is forecast to be light. It should not ruin any outdoor activities.

Monday 55/76

Cloudy, but no rain is forecast.

Next Week’s Storm Potential – Thursday?

The dynamics are in place for strong & potentially severe weather this week, but there is uncertainty if it’ll all come together, and if it does, when it’ll arrive. Right now, the best guess is it’ll arrive Thursday.

Yesterday, the European model gave a Thursday morning ETA. Today it thinks storms arrive Thursday night:

WunderMap®  Interactive Weather Map and Radar  Weather Underground 2013-04-06 16-30-57

The American (GFS) model thinks the storms will come Thursday morning:

The Storm Prediction Center (SPC) has identified West Tennessee as an area to watch for severe weather Wednesday and Thursday. Although we are not currently included in the SPC outlook, those storms will come in our direction. Here’s that SPC outlook:

Thursdays are starting to look snakebit for outdoor activities.

 

Beautiful Saturday! Sunday Almost as Great. Mid-Week Storm Update.

Tomorrow 42/73

It will be awesome!

Sunday 49/73

The NWS includes a “slight chance of showers.”

The GFS and NAM weather models think we will be dry here, but it will rain in southern Kentucky. If the models are wrong by 50-75 miles, we will get wet.

The European model says we might see a few hit or miss showers Sunday afternoon.

It probably won’t rain. More on this tomorrow night.

Mid-Week Storm Chances

Anyone who says they know what will happen is lying.

When weather models are consistent run-to-run, and are then consistent with each other, forecasters can have confidence about what kind of storms to expect, and when we can expect them. With this week’s storm system, the models aren’t consistent.

The European model thinks storms will arrive Thursday morning. Here it is Thursday at 7am:

Euro Thu 7am

The GFS (American) model has been wildly inconsistent with (1) it’s prior runs and (2) the European model. The latest GFS model run delivers storms Wednesday afternoon, almost a day before the European model:

As usual, our NWS expresses the forecast quandary best (ECMWF is the European model; “Ensembles” are multiple runs of the same model). Our NWS likes the European solution better because it has been consistent with its prior runs:

FORECAST PROBLEMS ABOUND MIDWEEK...WITH THE LATEST GFS AND ECMWF SHOWING VERY DIFFERENT TIMING WITH THE NEXT WEATHER SYSTEM. THE LATEST GFS BRINGS A COLD FRONT THROUGH MID TN TUESDAY NIGHT...A FULL 24 HOURS EARLIER THAN MOST PREVIOUS RUNS AND MORE THAN 36 HOURS AHEAD OF THE ECMWF. PER WPC GUIDANCE AND CONTINUITY WITH PREVIOUS FORECASTS...WE WILL LEAN TOWARD THE ECMWF ENSEMBLES AND MAINTAIN EXPECTED FRONTAL PASSAGE THURSDAY MORNING. EARLIER WE UPDATED THE HAZARDOUS WEATHER OUTLOOK TO MENTION THE POTENTIAL FOR STRONG STORMS...AND THE VERY UNCERTAIN POTENTIAL FOR SEVERE WX.THE POTENTIAL STILL EXISTS...BUT THERE ARE STILL TOO MANY
UNCERTAINTIES TO OFFER ANY ADDITIONAL DETAILS AT THIS TIME.

Those wanting a more technical analysis, and sometimes a slightly different take, are welcome to visit Eric’s Forecast page (a link to that is in the menu at the top of this page). Eric is studying meteorology. You know him as @RuthSevereWx.

 

Rain Leaving. Beautiful Spring Weekend. Storms Next Week?

The chilly rain is leaving tonight. We’ll have a dry and chilly Friday morning, then quickly warm into the mid 60s. Expect a beautiful Spring weekend, with high temps in the mid 70s.

images

Expect temps in the mid to upper 70s next week.

Weather models suggest the arrival of a possibly-robust storm system sometime during the middle of next week.

GFS_3_2013040412_F168_DPTF_2_M_ABOVE_GROUND

Why the concern? Consider one model – the GFS – above. Notice the warm, humid air streaming in from the south, which is colliding with the cold, dry air coming in from the west.  There are other dynamics in play, but they aren’t worth breaking down this far out because they’ll likely change. The timing will probably change, too. Just be aware of a potential mid-week storm threat, and keep checking reliable sources for weather information next week. As our NWS said this afternoon:

NEWER MODEL RUNS AND FORECAST REASONING/DISCRETION WILL BE NEEDED TO GIVE THE MID STATE A CLEARER PICTURE OF WHAT IS IN STORE WEATHER WISE FOR THE MID PORTION OF NEXT WEEK.

Backpedalling (a Bit) on Tomorrow’s Rain

Yesterday’s forecast called for about 1.25″ of rain tomorrow. Time to backpedal!  Looks like the rainmaker is going to move further south and way east of us. We still think it’ll rain, just not that much.

NWS forecasts 0.53″ for Davidson Co., 0.55″ for Williamson Co.

Here’s the Weather Prediction Center’s rainfall map:

d12_fill

Friday we clear out the clouds while Spring drives in and unpacks its things. Spring will have taken up residence Saturday, arriving gloriously, with early morning temps in the mid 40s, warming into the low 70s in the afternoon.  Perfect weather for the WillPower5K!  Sign up here: signupWP5K.com

Weather models continue to advertise severe weather potential for the middle of next week. Any severe weather forecast more than three days away is magic, so any details would ultimately be meaningless. I mention this to remind you we are in the middle of severe weather season. Spring is a saucy lass, but she has a violent side. Stay tuned.

How Much Rain on Thursday? (Enough to cancel soccer practice)

I coach my daughter’s under-8 soccer team. We practice every Thursday at 5pm. I’ve already canceled practice for this Thursday due to rain (well, that, and we’ve already played a night game this week).

Our NWS lists a 100% chance of rain Thursday. The Weather Prediction Center thinks between 0.50″ and 0.75″ of rain will fall through Friday, almost all of it on Thursday. Here are their estimated totals:

Our local NWS office thinks this map underestimates rainfall totals. They’re calling for 1.24″ in Nashville and 1.28″ in Williamson Co. Friday we clear out, then….

Behold, Spring Arrives This Weekend!

High temps Sat-Sun-Mon-Tue are forecast to be 72-72-71-76.

There’s some indication of spring storms forming during the middle of next week, but it’s way too far away to say anything more than that. We’re watching it.