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TN valley heavy rain/flooding week of whenever

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21 minutes ago, McMinnWx said:

The 18z NAM seems to think the Valley is going to get around 5 inches between Monday afternoon and Tuesday. 

This is normally when I say that the NAM tends to overdo precip, but that totally contradicts my experience from the weekend snow event. 

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Impressive:maprain:

 

Huntsville

ECMWF Deterministic FORECAST FOR: MDQ    LAT=  34.87 LON=  -86.55 ELE=   755

                                            18Z FEB09
                6 HR    6 HR    FROZN   TOTAL    SFC     2 M    1000    1000 
                 QPF     CVP     PCP     QPF     PCP     TMP     500     850 
                (IN)    (IN)    (IN)    (IN)    TYPES    (C)     THK     THK 
SUN 18Z 09-FEB                                          13.4     551     134    
MON 00Z 10-FEB                          0.00            11.3     554     135    
MON 06Z 10-FEB  0.01    0.01    0.00    0.01             9.2     556     135    
MON 12Z 10-FEB  0.14    0.11    0.00    0.16             8.1     557     135    
MON 18Z 10-FEB  0.74    0.53    0.00    0.89            12.1     560     136    
TUE 00Z 11-FEB  0.99    0.33    0.00    1.88            14.3     562     138    
TUE 06Z 11-FEB  0.68    0.09    0.00    2.56            14.9     563     137    
TUE 12Z 11-FEB  1.37    0.14    0.00    3.93            13.6     564     137    
TUE 18Z 11-FEB  0.48    0.02    0.00    4.41            14.0     559     135    
WED 00Z 12-FEB  0.01    0.00    0.00    4.42            11.5     558     135    
WED 06Z 12-FEB  0.10    0.00    0.00    4.53             6.8     558     134    
WED 12Z 12-FEB  0.11    0.00    0.00    4.63             7.8     560     135    
WED 18Z 12-FEB  0.05    0.00    0.00    4.68            14.4     564     137    
THU 00Z 13-FEB  0.03    0.01    0.00    4.71            18.3     567     139    
THU 06Z 13-FEB  0.02    0.01    0.00    4.73            19.0     567     139    
THU 12Z 13-FEB  1.17    0.11    0.00    5.90            11.0     561     136    

 

Cha

ECMWF Deterministic FORECAST FOR: CHA    LAT=  35.03 LON=  -85.20 ELE=   689

                                            18Z FEB09
                6 HR    6 HR    FROZN   TOTAL    SFC     2 M    1000    1000 
                 QPF     CVP     PCP     QPF     PCP     TMP     500     850 
                (IN)    (IN)    (IN)    (IN)    TYPES    (C)     THK     THK 
SUN 18Z 09-FEB                                          10.0     549     133    
MON 00Z 10-FEB                          0.00             7.6     553     134    
MON 06Z 10-FEB  0.00    0.00    0.00    0.00             6.4     554     134    
MON 12Z 10-FEB  0.06    0.05    0.00    0.06             6.1     556     134    
MON 18Z 10-FEB  0.46    0.17    0.00    0.52             9.6     558     135    
TUE 00Z 11-FEB  0.79    0.41    0.00    1.31            11.4     560     137    
TUE 06Z 11-FEB  0.93    0.10    0.00    2.24            13.2     562     137    
TUE 12Z 11-FEB  1.68    0.15    0.00    3.92            14.0     562     137    
TUE 18Z 11-FEB  1.03    0.07    0.00    4.95            17.4     561     137    
WED 00Z 12-FEB  0.00    0.00    0.00    4.95            12.5     558     135    
WED 06Z 12-FEB  0.06    0.00    0.00    5.01             8.4     558     134    
WED 12Z 12-FEB  0.08    0.00    0.00    5.09             7.4     560     135    
WED 18Z 12-FEB  0.04    0.00    0.00    5.13            12.7     563     136    
THU 00Z 13-FEB  0.06    0.03    0.00    5.19            15.2     565     138    
THU 06Z 13-FEB  0.01    0.00    0.00    5.20            17.7     566     138    
THU 12Z 13-FEB  0.25    0.05    0.00    5.45            16.9     565     138   

 

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High Risk out now to almost Chatt...WPC says there is still some uncertainty as to where to put the High Risk, could be moved north or south in further updates. For SE TN:

Further downstream we have a Moderate risk across portions of 
northern GA into southeast TN and the far western Carolinas. 
Significant flooding is still possible here today/tonight. 
Slightly lower QPF and the expectation of weaker rates this far 
northeast, precludes the need for a High risk here. However, a 
Moderate Risk does cover these areas, which is still a significant 
and potentially life threatening risk level.

20200210_074334.jpg

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31 minutes ago, TellicoWx said:

Comparing the NAM, 3k, GFS, HRRR, Euro..with what has currently fallen here (.13). The Euro was the only one to have the rainfall into SE Monroe at this point.

The 18Z GFS yesterday said the rain wouldn't start until mid-afternoon today. I've been discounting it for getting the start time so wrong.

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43 minutes ago, dwagner88 said:

The 18Z GFS yesterday said the rain wouldn't start until mid-afternoon today. I've been discounting it for getting the start time so wrong.

Big question mark to me for today is around storm motion and orientation return flow. If the motion/return sets up more oriented ENE across N. AL then the results will be lowered (storms firing/training south of the area cutting off some of the flow from the gulf, plus a downslope component off the plateau)...HRRR/GFS. If it is orientated more NNE across N. AL, then the return up the southern valley will be greater and minimal downsloping (Euro Op/NAM).

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2 hours ago, dwagner88 said:

The 18Z GFS yesterday said the rain wouldn't start until mid-afternoon today. I've been discounting it for getting the start time so wrong.

Same here. This wasn't supposed to start until late afternoon here. Started raining steady at 7 am. 

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Started raining IMBY according to my weather station at 4am (northern Meigs county) currently since it started I'm sitting at .72 inches for the day with rainfall rates bouncing between .12" up to as high as .29" an hour so far.

Sent from my SM-G965U using Tapatalk

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Looks to me like the Euro has the best grip on reality right now. It is the only one not significantly behind the surface qpf obs. Showed KCHA in the 0.60-0.80 range since start of precip. Actual obs shows we were at 0.81 as of 11:45. It unfortunately has in excess of 5" qpf falling from this first round. It is much lighter with the second round, as it appears to show intense convection over northern MS blocking moisture return in the area Wednesday. We finish out by noon on Thursday with just over 6".

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Had a leaky chimney.  Got up there and fixed it yesterday evening.  Very thankful that is done and fingers crossed that the new sealant works!  6" of rain by Thursday.  Not good!

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.91 in the bucket since around 3am this morning. MRX has most of the area in the 4-6 inch range by Thursday.  Not sure that flash flooding will be an issue but a lot of slow rising water issues will happen at that point. I'm now at 8.17 inches of rain already for the month and had 7.35 last month. So already 8 inches or so above normal for 2020. 

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Up to 1.14" at KCHA. Still running ahead of everything, even the Euro. MRX issued a pre-emptive flood warning for South Chickamauga creek for meeting flood stage at 18 ft. It crested at 23 ft. with less rain last week. Not sure where that forecast comes from.

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New MCD out for southern valley:

 

Discussion...Moisture is streaming in from the west-southwest
within an atmospheric river moving into the region.  Precipitable
water values are currently 0.8-1.3".  Inflow at 850 hPa is
west-southwest at 30-50 knots per nearby VAD wind profiles,
similar in direction and magnitude to the 850-400 hPa mean wind. 
MU CAPE remains under 100 J/kg for much of the area, though trends
are upward across northern AL.  Recent observations show hourly
rain totals of 0.15-0.30", roughly 1/5 of the current precipitable
water value, due to the lack of instability.

With time, hourly rain totals are expected to rise to 0.5-1" as MU
CAPE rises to 500+ J/kg across northeast AL and northern GA and
convective elements become more common within the mostly
stratiform rain areas.  Mesoscale guidance generally advertises
local amounts ~2", but 3" can't be ruled out during the next
several hours.  Two week precipitation anomalies are 150-300%+ of
average, which has led to fairly saturated soils.  Flash flooding
is considered possible through 8 pm EDT.

20200210_143159.jpg

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MRX has changed the Flood Watch to a Flash Flood Watch:

The National Weather Service in Morristown has issued a

* Flash Flood Watch for portions of southwest North Carolina,
  east Tennessee, and southwest Virginia, including the
  following areas, in southwest North Carolina, Cherokee and
  Clay. In east Tennessee, Anderson, Bledsoe, Blount Smoky
  Mountains, Bradley, Campbell, Claiborne, Cocke Smoky
  Mountains, East Polk, Grainger, Hamblen, Hamilton, Hancock,
  Hawkins, Jefferson, Knox, Loudon, Marion, McMinn, Meigs,
  Morgan, North Sevier, Northwest Blount, Northwest Cocke,
  Northwest Monroe, Rhea, Roane, Scott, Sequatchie, Sevier Smoky
  Mountains, Southeast Monroe, Union, and West Polk. In
  southwest Virginia, Lee.

* Through Tuesday evening

* Rainfall amounts of 2 to 3 inches with locally higher amounts
  expected. The heaviest rainfall will occur the rest of this
  afternoon and early evening across southeast Tennessee and
  southwest North Carolina with another round Tuesday morning
  area-wide.

* This amount of rainfall could cause flooding. People in the
  watch area should be aware of the possibility of heavy rainfall.
  Avoid low lying areas...and be careful when approaching highway
  dips and underpasses.

 

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Rare High Risk and large Moderate Risk of flooding is quite significant for the South. Due to the high impact of this event, please share with your fiends on social media. Make sure the graphic comes up on the post. Date it and make it public too. (just change back to friends your next post.) I went through Thursday, though the High is through Tuesday. This is going to be bad from rivers down to streams and low areas.

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I have to say I'm pretty pleased with the way the convection in central MS and AL has shut off the taps up here. We are having a heavy shower at the moment, but it looks like we may get a couple hour's reprieve after this. The radar is drying out across North Alabama. At some point this evening that front will lift north and bring the convection with it, but this may help limit qpf somewhat this far north.

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42 minutes ago, dwagner88 said:

I have to say I'm pretty pleased with the way the convection in central MS and AL has shut off the taps up here. We are having a heavy shower at the moment, but it looks like we may get a couple hour's reprieve after this. The radar is drying out across North Alabama. At some point this evening that front will lift north and bring the convection with it, but this may help limit qpf somewhat this far north.

The concern among alot of mets (including MRX.. the reason they switched from an Areal Flood to Flash Flood Watch) is going up. The first wave has overpefomed even compared to the 06z Euro (Chatt is approaching 1.5"-2" of rain so far). The main show is what's building over MS and the Arklatex. From MRX AFD:

For Tonight, this first wave will move east allowing for a lull
in the rainfall but another round of jet dynamics along a quasi-
stationary over the region for late tonight through Tuesday
morning. Models show a regeneration of rainfall coverage and
intensity into the flash flood watch area. Favorably high PWs and
warm rain process to produce a period of moderate to heavy rains
with this next band.

There is a good deal of differences on placement and strength of
the low-level jet. The NAM is the most aggressive showing strong
low-level moisture transport into this boundary while the GFS is
weaker.

Main question is exactly where this boundary becomes more quasi-
stationary. Current thinking is that this boundary will remain
across the central/southern areas into the central/southern
Tennessee Mountains. Training of moderate to heavy rain is a major
concern for these areas as PWs and thermodyanmic profile for
favorable warm rain process will be unseasonably high. Given low
FFG (saturated ground) and high stream flows, flash flood
potential is a major concern through Tuesday morning.

Model QPF ensembles depict around 3 inches at CHA and RHP, and 2
inches at TYS through Tuesday. Due to the potential of high
rainfall rates and already saturated soils/high stream flows,
decided to change the flood watch to a flash flood watch. Several
river warnings have been issued as well.

6z Euro:

 

20200210_164709.jpg

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1 hour ago, TellicoWx said:

The concern among alot of mets (including MRX.. the reason they switched from an Areal Flood to Flash Flood Watch) is going up. The first wave has overpefomed even compared to the 06z Euro (Chatt is approaching 1.5"-2" of rain so far). The main show is what's building over MS and the Arklatex. From MRX AFD:


 

Oh I have no doubt that there will be significant urban and flash flooding tomorrow morning, but I don’t think we are going to see 24 hour totals over 5” like earlier runs of the Euro and NAM were showing last night. I have 1.76” in the gauge at the house, and all of the streams are now bankfull. The next round will put them over the edge. 

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1 hour ago, nrgjeff said:

We got almost an inch more overnight. Apparently it all ran off. @dwagner88 was I seeing things or the creek was almost up to the bridge by Food City Jenkins and EB Rd?

It got pretty close. I know Davidson Rd was closed this morning. It is further downstream on that creek and is subject to backup from South Chickamauga. Storm total for me when I left the house this morning was 2.76", which is quite a bit less than the globals were showing during the day Monday. The HRRR and RAP were correct in showing lighter amounts overnight.

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I'm ready to see that MDT Red on the SPC charts instead of the WPC charts. Can it just be April yet?

12Z QPF progs are not quite as bad East, but still there Mid-Tenn. Trouble there is double whammy of daytime rain and then the squall line.

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Mesoscale Precipitation Discussion 0051
NWS Weather Prediction Center College Park MD
552 PM EST Wed Feb 12 2020

Areas affected...Portions of the TN & OH Valleys

Concerning...Heavy rainfall...Flash flooding possible

Valid 122251Z - 130451Z

Summary...A band of heavy rainfall is expected to move across
central portions of TN and KY.  Hourly rain totals to 1" and local
amounts of 2" are expected.

Discussion...A developing atmospheric river extending from the
Mid-South towards the Ohio River Valley along with increased low
level moisture convergence/frontogenesis has led to a band of
heavy rainfall producing hourly rain totals to 1" per KY mesonet
observations.  This band is progressive, though it is moving over
and into an area with two week precipitation at 200-300% of
average, more to the south across northern AL, which has led to
saturated soils.  Precipitable water values of 1-1.3" lie here per
GPS values.  Inflow at 850 hPa is south-southwest at 55-80 knots
per VAD wind profiles.  MU CAPE is negligible per SPC mesoanalyses.

The best guess is that increasing moisture convergence/
frontogenesis has played the main role in hourly rain totals
approaching the precipitable water value.  The 18z HREF
probabilities of 0.5"+ per hour increase to likely as the band
moves eastward across central KY and Middle TN with a small
percent chance of 1" an hour.  KY mesonet obs suggest the HREF
probability guidance, as well as WSR 88D hourly rainfall totals,
are underperforming here.  Local amounts of 2" are possible before
the line accelerates as it reaches into eastern KY and eastern TN,
which could cause issues over saturated soils and area coal fields.

Roth

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