Beau Dodson's WeatherTalk Blog

August 30, 2017: Special Harvey Update

Evening updated graphics

The trend in the evening data was to shunt the higher totals a bit further south and east.  There is a VERY sharp gradient in the rain totals.  Portions of the region will receive no measurable rain or very light totals.  Keep that in mind.

Northern and northwest counties of southeast MO and southern IL are most likely to miss the bigger rains.

Here are the new forecast numbers

Afternoon update

To view previous update you should scroll down.

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AFTERNOON UPDATED GRAPHICS

CONCERNS

  1. Heavy rain with flash flooding likely Thursday night and Friday morning over portions of western Kentucky and Tennessee.  See graphics below.
  2. Isolated tornado risk for portions of Kentucky/Tennessee.
  3. High winds likely Thursday night into Friday.  Highest winds will likely be from the Missouri Bootheel into extreme southern Illinois, western Kentucky, and western Tennessee.   Winds may gust above 50 mph.  Be aware of this.  As the center of the remnants of Harvey moves through our region there could be high winds.

The heaviest rain should arrive late Thursday afternoon into Friday morning.  Peak rainfall will be on Thursday night.  High confidence in this.  Keep in mind, portions of the area will see very little rainfall.  Portions of the region will likely have flash flooding (see graphics below).

We have been upgraded to a high risk of flash flooding (parts of Kentucky and Tennessee)

Keep in mind, the atmosphere will be loaded with moisture.  It won’t be unusual, under the heaviest cores, to experience 0.50″ to 1″ of rain per hour.  This could cause flash flooding.

Avoid flooded roadways.  See flood/flash flood probabilities below.

Use common sense.  Don’t drive through rapidly flowing water.  Water may be deeper than you realize.  Every time we have flash flood someone drives into the flood waters.  Avoid flooded roads.

The flash flood threat will be highest at night.  That could mean you won’t see the road flooded until it is too late.

Strong and gusty winds are possible Thursday night into Friday.  Winds will likely range from 20 to 30 mph with gusts above 45 mph.  Some data suggest 50+ mph winds will be possible.  These winds could cause some damage.  Just be aware of the potential.  There remains some uncertainties on wind speeds.

Highest winds will likely be from the Bootheel into extreme southern Illinois and then Kentucky/Tennessee.

Here is the high resolution 3K NAM model.  These are wind gusts.  Again, some uncertainty on if this will be accurate or not.  There is at least the potential of strong wind gusts.  Highest winds may end up over Kentucky/Tennessee.

10 PM Friday

1 AM Friday

4 AM Friday

7 AM Friday

10 AM Friday

1 PM Friday

Let’s take a look at four models.  These are their opinions on rainfall totals.

Models do not handle tropical moisture all that well.  Models are for guidance and not gospel.  You can see my actual rainfall forecast in the probability section below.

With that said, here are what the models are spitting out.  Huge differences between certain models.  Notice the sharp gradient in Missouri and Illinois.  Some areas won’t receive all that much rain.  Keep that in mind, as well.

GFS

Click images to enlarge

NAM

NAM 3K high resolution

Canadian

Click all images to enlarge

Future-cast radar.  What radar MIGHT look liked based on the 3K NAM guidance.  Again, this is the models opinion.  It may not be exact.  Take the general idea from it.

Heaviest rain arrives Thursday night.

7 AM Thursday

We may have a band of showers and thunderstorms moving northward through the area.  This should weaken with time.

4 PM Thursday

7 PM Thursday.  We can see the main rain band moving into the region from the south.  It will move east/northeast overnight.

10 PM on Thursday.  Heavy rain in the region.

1 AM Friday.  Heavy rain in the region.  Flash flooding possible.  High winds possible, as well.

7 AM Friday

1 PM Friday

7 PM Friday

Saturday and Sunday should be dry.  Small chance for Saturday morning showers over Kentucky.  Most of the rain will have ended.

Sunday should be dry.  Small rain chances on Monday.

Tornado risk graphics.  Here are the probabilities for a tornado warning being issued.  The greatest risk will be Thursday and Thursday night.

Occasionally tropical systems can produce short lived tornadoes.  Sometimes there is not a tornado warning.  They can last seconds to a few minutes.  They can occur without a thunderstorm present.  In other words, they can occur in showers without lightning.

Click graphic to enlarge

Here is the 10% risk zone

What are the chances for a flood or flash flood warning?

I have update these numbers as of 3 PM on Wednesday afternoon

 

 

 

 

It is important to remember that historically the dying remnants of tropical systems have produced flash flooding in our region. Isolated pockets of extreme totals are not uncommon along the path of a dying system.

The heaviest rains can be to the north and northeast of the center.

One of Paducah’s worst flash floods was caused by a dying tropical system.

We don’t want to let our guard down no matter what the eventual track of the lows center.

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This forecast update covers southern Illinois, southeast Missouri, western Kentucky. and northwest Tennessee.
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August 30, 2017
Wednesday night:
Forecast
:  Increasing clouds.  A chance for showers and thunderstorms (mainly after 11 pm).  A band of showers and thunderstorms should move into the region from the south.  It will be moving northward out of Tennessee.  A few downpours possible.
Temperatures:   MO ~ 62 to 66      IL ~ 62 to 66       KY ~ 65 to 70       TN ~ 65 to 70
Winds: East and northeast winds at 4 to 8 mph
What impacts are anticipated from the weather?  Maybe wet roadways.  Spotty lightning.
My confidence in the forecast verifying: High.  This forecast should verify.
Is severe weather expected?  No
The NWS defines severe weather as 58 mph winds or great, 1″ hail or larger, and/or tornadoes
What is the chance of precipitation
?  MO ~ 40% (mainly far southern counties)   IL ~ 40% (mainly far southern counties)    KY ~ 60%  late tonight   TN ~ 60% late tonight.  A band of rain may approach from the south
Coverage of precipitation
: Perhaps scattered.  Increasing from south to north.
Should I cancel my outdoor plans? No, but check radars.

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August 31, 2017
Thursday F
orecast Details
Forecast: Cloudy.  Showers and thunderstorms becoming likely (mainly the southern half of the region).  Precipitation would be moving northward out of Tennessee.  Rain chances will be less from Poplar Bluff, Missouri towards Mt Vernon, Illinois.  Northern counties have the least chance for precipitation.
Temperatures:  MO ~ 78 to 84    IL ~ 78 to 84     KY ~ 76 to 82     TN ~ 76 to 82  Temperatures could be a bit warmer if we end up with a little more sunshine.  Clouds are likely to keep temperatures down just a bit.
Winds:  East and northeast winds at 8 to 14 mph with gusts to 18 mph
What impacts are anticipated from the weather?  Wet roadways.  Isolated lightning.  Small risk for tornadoes in Kentucky and Tennessee during the afternoon.
My confidence in the forecast verifying:  High.  This forecast should verify.
Is severe weather expected?  Isolated tornado risk.  This would mainly be for Tennessee and Kentucky.
The NWS defines severe weather as 58 mph winds or great, 1″ hail or larger, and/or tornadoes
What is the chance of precipitation
?  MO ~ 50%    IL ~ 50%    KY ~ 70%    TN ~ 80%
Coverage of precipitation
:  Scattered to perhaps numerous.  Increasing from the south towards the north.
Should I cancel my outdoor plans?  Have a plan B in case rain moves into the region.
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Thursday Night Forecast Details:
Forecast
:  Cloudy.  Rain.  Some lightning possible.  Heavy rain likely over portions of the region (see graphics above).  Monitor updates.  Windy.  High winds possible.  Best chance for heavy rain will be the Missouri Bootheel into extreme southern Illinois and then Kentucky/Tennessee.
Temperatures:   MO ~ 62 to 66      IL ~ 62 to 66        KY ~ 62 to 66        TN ~ 62 to 66
Winds: East and northeast at 15 to 25 mph becoming gusty.  Gusts above 40 mph possible.
What impacts are anticipated from the weather?  Wet roadways.  Isolated lightning.  Heavy rain.  Isolated tornado risk.  Flash flooding risk, esp for KY/TN.  High winds possible.
My confidence in the forecast verifying:  High.  This forecast should verify.
Is severe weather expected?  Isolated tornado risk.  Flash flooding possible.
The NWS defines severe weather as 58 mph winds or great, 1″ hail or larger, and/or tornadoes
What is the chance of precipitation
? MO ~ 70%    IL ~ 80%    KY ~ 100%    TN ~ 100% (keep in mind that far northern counties will see lower rain chances vs southern half of the region)
Coverage of precipitation
: Widespread.
Should I cancel my outdoor plans?  Have a plan B

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September 1, 2017
Friday F
orecast Details
Forecast: Cloudy.  Rain likely before 4 pm.  Lightning possible.  Windy with high winds possible.  Precipitation may dwindle from southwest to northeast as the day wears on.  More precipitation in the morning vs late afternoon.  Rain will linger longer over the Pennyrile area of western Kentucky.
Temperatures:  MO ~ 76 to 82     IL ~ 76 to 82     KY ~ 76 to 82     TN ~ 76 to 82
Winds:  South and southeast at 15 mph with gusts to 40 mph with higher gusts possible
What impacts are anticipated from the weather?  Wet roadways.  Isolated lightning.  Gusty winds.  Flash flooding possible.  Tornado risk should have dwindled.
My confidence in the forecast verifying: Medium.  Some adjustments are possible.
Is severe weather expected?  The tornado risk may have ended.  Monitor updates and see risk charts above.
The NWS defines severe weather as 58 mph winds or great, 1″ hail or larger, and/or tornadoes
What is the chance of precipitation
?  MO ~ 60%    IL ~ 60%    KY ~ 90%    TN ~ 90%
Coverage of precipitation
:  Numerous the first half of the day.  Rain ending from southwest to northeast as the day wears on.  Rain will likely linger into the evening hours (esp over KY/TN)
Should I cancel my outdoor plans?  Have a plan B
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Friday Night Forecast Details:
Forecast
: Cloudy.  Showers and any remaining thunderstorms should have ended or be coming to an end.  Cooler.
Temperatures:   MO ~ 56 to 62     IL ~ 56 to 62        KY ~ 56 to 62        TN ~ 56 to 62
Winds:  East and southeast at 8 to 16 mph with gusty winds, at times.  Winds will depend on where the remnants of Harvey track
What impacts are anticipated from the weather?  Wet roadways and lightning early in the evening.
My confidence in the forecast verifying:  Medium.  Some adjustments are possible.
Is severe weather expected?  No.
The NWS defines severe weather as 58 mph winds or great, 1″ hail or larger, and/or tornadoes
What is the chance of precipitation
? MO ~ 20%    IL ~ 30%    KY ~ 50%    TN ~ 30%
Coverage of precipitation
: Ending.
Should I cancel my outdoor plans?  Have a plan B just in case rain lingers longer over KY/TN

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September 2, 2017
Saturday F
orecast Details
Forecast: Partly to perhaps mostly sunny.  Rain should have ended.
Temperatures:  MO ~ 76 to 82     IL ~ 76 to 82     KY ~ 76 to 82     TN ~ 76 to 82
Winds:  South and southeast at 6 to 12 mph.  Gusts to 15 mph.
What impacts are anticipated from the weather?  Most likely none.
My confidence in the forecast verifying: Medium.  Some adjustments are possible.
Is severe weather expected? No
The NWS defines severe weather as 58 mph winds or great, 1″ hail or larger, and/or tornadoes
What is the chance of precipitation
?  MO ~ 10%    IL ~ 10%    KY ~ 20%    TN ~ 10%
Coverage of precipitation
:  Rain should have ended.
Should I cancel my outdoor plans?  No
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Saturday Night Forecast Details:
Forecast
: Clearing.  Patchy fog possible.
Temperatures:   MO ~ 62 to 64      IL ~ 60 to 64        KY ~ 62 to 64        TN ~ 62 to 64
Winds:  Southeast at 5 to 10 mph
What impacts are anticipated from the weather?  Patchy fog.
My confidence in the forecast verifying:  Medium.  Some adjustments are possible.
Is severe weather expected?  No.
The NWS defines severe weather as 58 mph winds or great, 1″ hail or larger, and/or tornadoes
What is the chance of precipitation
? MO ~ 0%    IL ~ 0%    KY ~ 0%    TN ~ 0%
Coverage of precipitation
:  Most likely none
Should I cancel my outdoor plans?  No

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September 3, 2017
Sunday F
orecast Details
Forecast: Mostly sunny.  Perhaps some morning fog.
Temperatures:  MO ~ 78 to 84     IL ~ 78 to 84     KY ~ 78 to 84     TN ~ 78 to 84
Winds:  Becoming north at 6 to 12 mph
What impacts are anticipated from the weather?  Most likely none.
My confidence in the forecast verifying:  Medium.  Some adjustments are possible.
Is severe weather expected?  No
The NWS defines severe weather as 58 mph winds or great, 1″ hail or larger, and/or tornadoes
What is the chance of precipitation
?  MO ~ 0%    IL ~ 0%    KY ~ 0%    TN ~ 0%
Coverage of precipitation
: None
Should I cancel my outdoor plans?  No

Sunday Night Forecast Details:
Forecast
: Mostly clear.  Patchy fog possible.
Temperatures:   MO ~ 62 to 66      IL ~ 62 to 66        KY ~ 62 to 66        TN ~ 62 to 66
Winds:  North at 4 to 8 mph
What impacts are anticipated from the weather?  Most likely none.
My confidence in the forecast verifying:  Medium.  Some adjustments are possible
Is severe weather expected?  No.
The NWS defines severe weather as 58 mph winds or great, 1″ hail or larger, and/or tornadoes
What is the chance of precipitation
? MO ~ 10%    IL ~ 0%    KY ~ 0%    TN ~ 0%
Coverage of precipitation
:  Most likely none
Should I cancel my outdoor plans?  No

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September 4, 2017
Monday F
orecast Details
Forecast: Partly to mostly sunny.  Isolated thunderstorm possible.  Mild.
Temperatures:  MO ~ 82 to 86     IL ~ 82 to 86    KY ~ 82 to 86    TN ~ 82 to 86
Winds:  Variable at 5 to 10 mph
What impacts are anticipated from the weather? Isolated wet roads and lightning.
My confidence in the forecast verifying:  Medium.  Some adjustments are possible.
Is severe weather expected?  No
The NWS defines severe weather as 58 mph winds or great, 1″ hail or larger, and/or tornadoes
What is the chance of precipitation
?  MO ~ 10%    IL ~ 10%    KY ~ 10%    TN ~ 10%
Coverage of precipitation
:  None to isolated
Should I cancel my outdoor plans?  No.
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Monday Night Forecast Details:
Forecast
: Partly cloudy.  A slight chance for a shower.
Temperatures:   MO ~ 62 to 66      IL ~ 62 to 66        KY ~ 62 to 66        TN ~ 62 to 66
Winds:  Variable at 5 to 10 mph
What impacts are anticipated from the weather?
My confidence in the forecast verifying:
Is severe weather expected? No
The NWS defines severe weather as 58 mph winds or great, 1″ hail or larger, and/or tornadoes
What is the chance of precipitation
? MO ~ 20%    IL ~ 20%    KY ~ 20%    TN ~ 20%
Coverage of precipitation
:  None anticipated
Should I cancel my outdoor plans?  No

 

Previous update below

August 30, 2017

Wednesday Morning Update

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The remnants of Harvey will be the main concern in this update.  The eventual track of the remnants of Harvey are not certain.

A few things to remember

  1. Confidence on the eventual track of Harvey is now medium.
  2. Confidence on rainfall totals for Missouri and Illinois are medium.  Confidence for Kentucky and Tennessee are high.
  3. Historically, dying tropical systems have the potential to produce extreme rainfall totals.  Extreme meaning greater than six inches of rain.  Flash flooding is a concern, especially for Kentucky and Tennessee.
  4. Portions of the region may receive very little in the way of rainfall.  Most likely that would be areas from Poplar Bluff, MO towards Mt Vernon, Illinois.  In other words, the west/northwest part of our region
  5. Isolated tornadoes are not uncommon from weakening tropical systems.  They tend to be brief and difficult to issue warnings on.
  6. The bulk of the rain will arrive Thursday into Friday morning.  Precipitation should dwindle Friday afternoon and night.
  7. Flash flood watches already cover portions of western Tennessee.  Additional watches will be issued by the Paducah, KY National Weather Service.

Confidence in the forecast is as follows

Southeast Missouri ~ Medium
Southern Illinois ~ Medium
Western Kentucky ~ High
Western Tennessee ~ High

Models over the last 12 to 24 hours seem to have settled on a track for the remnants of Harvey.

The general idea is to take the area of low pressure to Memphis, Tennessee and then move it northeast towards south central Kentucky.

This would place portions of our region in a risk for torrential rainfall.   Rainfall totals greater than four inches are not out of the question.

The bigger question may be how much rain falls in some of our counties.  Can we exceed six inches of rain?  It would certainly not be unheard of from a weakening tropical system.

Paducah, Kentucky, had it’s greatest flash flood on record from a dying tropical storm.  That system, back in the late 1980’s, produced 6 to 8 inches of rain in a few hours.

There is no way of forecasting extreme rainfall totals this far in advance and sometimes not at all.  We can, however, forecast general amounts and then mention the potential for higher totals.

The system’s track may cause portions of our region to escape the bulk of the rainfall.  The area that may remain dry or fairly dry would include Poplar Bluff, Missouri, Farmington, Missouri, and Mt Vernon, Illinois.  Those areas may end up on the fringe of this system.

Any shift in track could change the forecast.  Keep that in mind.

This is my current (as of 7 am Wednesday) forecast.  Changes are LIKELY to occur moving forward.  These are my initial thoughts.

These are for the entire event from today (not much happening today) through early Saturday morning

If the system is a bit further west and northwest than anticipated then these numbers will be adjusted higher/upwards.  This will need to be monitored as new data arrives today.  Keep this in mind moving forward.

Here are the probabilities for 0.50″ to 1″ of rain

Confidence in the 0.50″ to 1″ forecast is high

Click to enlarge

Here are the probabilities for 1″ to 3″ of rain

Confidence in the 1″ to 3″ of rain is high

Click to enlarge

Here are the probabilities for 3″ to 6″ of rain

Confidence in the 3″ to 6″ rain totals is low

Click to enlarge

Here are the probabilities for 6″ or more of rain

Confidence in the 6″+ rain totals is low

Click to enlarge

Again, I want to remind you that historically weakening tropical systems can produce isolated very high rainfall totals.  Someone could end up with a lot of rain from this system.

There is also a risk for short lived tornadoes.  These type of tornadoes are nearly impossible to issue warnings on.  They can last for seconds to a few minutes.

We had an event a few years ago that produced numerous short lived tornadoes.  The probabilities for tornadoes is fairly low, but certainly not zero.

Here is the Thursday Severe Weather Outlook from the Storm Prediction Center.  The brown represents a risk for a few tornadoes.

This may need adjusted depending on the actual track of the center of low pressure.

A low end risk on Thursday.  Friday will need to be monitored, but it appears the main concern will shift eastward on Friday.  Monitor updates, as always.

The National Weather Service has issued a flash flood watch for portions of western Tennessee from this evening through Friday evening.

Light colored green counties are in the flash flood watch.  Additional counties may need to be added.  Additional watches are likely for at least portions of western Kentucky.

Here is the latest official track forecast from the National Hurricane Center

No significant adjustment in this map since the last update.  Model guidance may have settled on a solution.

Here is the latest rainfall forecast from the National Hurricane Center

You can see the NHC has painted some orange in our region.  That represents rainfall totals greater than five inches.

Don’t put too much stock on the exact placement of these colors.  Take the general idea that some heavy rain will be possible and perhaps enough to cause some water issues.

Here is the excessive rainfall outlook from NOAA for today through 7 am Thursday

Western Tennessee and the Missouri Bootheel are in a marginal risk for flash flooding.  This is mainly for tonight for northwest Tennessee.

Here is the Thursday 7 am to Friday 7 am excessive rainfall outlook from NOAA

This outlook is for Thursday morning through Friday morning.  An additional outlook map will be necessary for Friday 7 am through Friday night.  That outlook will be issued later today.

Southeast Missouri and southern Illinois are currently in a marginal risk for flash flooding on Thursday/Thursday night.  Far western and northern counties are not in the risk.

The yellow zone is a slight risk for flash flooding.  The red zone (small area) is a moderate risk for flash flooding.

Here is the NOAA rainfall outlook.  Click to enlarge and view.   NOAA lowered rainfall totals from previous forecasts.

Zoomed in for a better view.  Scale is on the right.

Click to enlarge

Let’s take a look at a few model projections for rainfall totals.

Keep in mind, the models continue to shift around a bit.

Keep in mind, models handle precipitation totals poorly.  Don’t walk away looking at one graphic and thinking that is how much rain will fall at your location.  Models are guidance and NOT gospel.

Take the general idea from these maps.

There are many models that forecasters use.  Typically a blend of models work best when forecasting.  We don’t just use one model.

The models used most often are the following

NAM rainfall forecast

Click to enlarge

GFS rainfall forecast

Click to enlarge

EC rainfall forecast

Canadian rainfall forecast

Notice the differences from one model to the next.  The main reason for the differences is track of the storm.  Some models track it a bit further south and east than other models.

A general track from Memphis and then northeast towards Nashville and south central Kentucky seems most likely.  I will continue to monitor trends.

Gusty winds will be possible Thursday afternoon into Friday morning.  Gusts above 40 mph are possible.  The highest gusts would likely be from the Missouri Bootheel and western Tennessee into Kentucky.

NAM model wind gusts for Thursday night.  Higher gusts possible.

 

Let’s take a look at the timing of the rain.

I am going to use the high resolution Hrrr and 3K NAM models for showing you this.  Keep in mind that the NAM guidance is a bit further west than some of the other guidance.

This gives you a general idea.

We could have some rain bands into the southern portions of the region later today and tonight.  That would include the Missouri Bootheel into western Kentucky/Tennessee.

These are future-cast radar images.  This is what radar MIGHT look like at the different time stamps.

Again, this model is more west than some other data.  The western and northern parts of our region may not receive as much rainfall.  This will depend on the track.  Keep that in mind when viewing these projections.

Wednesday 11 pm

Click images to enlarge

Thursday at 4 am

Thursday at 10 am

Thursday at 7 pm

Friday at 1 am

Friday at 10 am

Friday at 1 pm

Friday 7 am

Friday at 1 pm

The system may move out fairly quickly on Friday.  This is still a question, as well.

There is plenty to monitor over the coming days.

Confidence in the forecast is as follows

Southeast Missouri ~ Medium
Southern Illinois ~ Medium
Western Kentucky ~ High
Western Tennessee ~ High

 

 

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