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TN valley heavy rain/flooding week of whenever


janetjanet998
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3 hours ago, Holston_River_Rambler said:

Hopefully it doesn't come to fruition, but the GFS/ Euro showing a way that a system between the 14th and 16th could get hung up across the area. Still a ways to go, but this has been shown as a possibility on several model runs now. 

Yea it is not a good look on the models that is for sure. Do not know where we are going to put the couple inches we should get this weekend. No telling what would happen if we got that as modeled

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Found this off a blog about Iowa weather:

https://www.tswails.com/single-post/2019/03/07/FINAL-FLOOD-OUTLOOK-AN-EYE-OPENER?fbclid=IwAR3p0YRgKuuc3wOuRE7UZj1tN-Pl9C1vIJyDSPgaHAWI_mDBb7KjbbYyWxM

Not exactly sure how specifically this could/ would impact our western areas and areas further down the Mississippi, but I can't image it is good news to have a big, quick melt in those midwestern areas where so much snow has fallen and then have more rain in our TN upstream areas. 

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Now a little good news, hopefully...

Columbus AFB, Miss. and adjacent radars show some bright banding this morning (Monday). Dual polarization confirms it's mixed precip aloft. Radar estimated (and human estimated) rainfall from the bright reflectivity is probably high. I figure totals are down around a quarter inch. Monday rain was always forecast light.

Midweek system even improved a bit. Looks like it'll be moving just enough to keep totals 1-2 inches. Few days ago looked like another 3-4 in. This pattern anything can happen, but think positive.

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  • 1 month later...

ECMWF comes out after the Day 2 from SPC. Evidence now supports a slight risk Saturday from North Alabama into North Georgia. NAM and Euro both have a lot of CAPE along and south of a lifting boundary. I thought the 12Z NAM was nuts showing a right mover there; other CAMs do not. 

Now.. Euro introduces a mesolow on the said boundary. Low level winds are veered off, and the upper levels are not robust. However it's May which is CAPE season. While the Day 2 update is still Marginal, I figure on waking up to Slight. No I'm not staying up, lol! Something to watch Saturday though.

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  • 2 months later...

Today Monday July 22, National Weather Service is hitting flooding hard along and north of the I-40 and I-81 corridors. Good call considering all of Today Monday July 22, National Weather Service is hitting flooding hard along and north of the I-40 and I-81 corridors. Good call considering Observation posts from @John1122 up that way. Ground won't hold anything before flooding quickly. Locally 2 inches of rain could fall quickly, with isolated 3 inch bursts.

Hope we can all avoid flash flooding. Might be worth sharing NWS posts on regular social media too. It will still be hit or miss. Hopefully more miss.

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Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1205 PM EDT Mon Jul 22 2019
 
Day 1
Valid 16Z Mon Jul 22 2019 - 12Z Tue Jul 23 2019 

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS 
OF THE CENTRAL APPALACHIANS INTO THE MID ATLANTIC...

...Lower Mississippi Valley, through the Tennessee Valley and 
Central Appalachians, into portions of the Mid Atlantic and 
Northeast...
The expansive band of Slight to Moderate Risk was generally 
maintained with minimal changes on this forecast update, 
stretching from Arkansas to southern New England. Among the minor 
changes were to extend the length of the Moderate Risk on both 
ends: (1) along the Kentucky and Tennessee border to account for 
an alignment of ongoing convection in a zone of low-level 
confluence and on the northern periphery of a pool of stronger 
instability; and (2) from the NYC metro area into southwest 
Connecticut as hi-res models have a fairly robust signal for 
heavier QPF (2+ inches) into Connecticut. The Slight Risk area was 
drawn further northwest in parts of southeast Ohio and southwest 
Pennsylvania to account for the position of developing convection 
along the front in those areas. The overall forecast reasoning 
remains similar, with a ribbon of precipitable water values near 
or above the 95th percentile along a gradually advancing front. 
HREF probabilities indicate a high likelihood of pockets of at 
least 2-3 inches of rainfall over most of the Slight and Moderate 
Risk regions, and individual members show widespread rain rates of 
1-2 in/hr with isolated maxima approaching 3 in/hr. This seems 
reasonable based on the combination of moderate instability and 2+ 
inch PW values. 

Several areas of greater concern exist. First, from eastern 
Pennsylvania into the NYC metro area hi-res models generally have 
a stronger signal for rain rates exceeding 2 in/hr. The nose of 
stronger low-level moisture transport will be focused in this area 
as well, and GOES-16 visible satellite imagery indicates limited 
cloud cover as of 16Z, so considerable instability should be able 
to build (supporting higher rain rates). The second area of 
concern is near the Kentucky-Tennessee border, where convection is 
becoming aligned with the deep layer mean flow already, and the 
inflow region over Tennessee is strongly unstable with SBCAPE 
around 3000 j/kg at 16Z. Once again, the stronger instability may 
support a concentrated region where higher (2+ in/hr) rain rates 
are more likely. Finally, there is concern from far eastern 
Kentucky into West Virginia and far southwest Pennsylvania. A 
stronger westerly component to the low-level flow may support a 
greater concentration of convection in the upslope regions of the 
Appalachians, and these areas of terrain can be more vulnerable to 
flash flooding. Furthermore, GPS observations just upstream in 
south-central Ohio show PW values near or in excess of 2 inches, 
which indicates significant, deep moisture impinging on the 
Appalachians. Therefore, flash flooding could also be more 
prevalent in these areas.
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National Weather Service Nashville TN
1152 AM CDT Mon Jul 22 2019

.UPDATE...
FOR 18Z AVIATION DISCUSSION.

&&

.DISCUSSION...

Our FFA will be expanded to cover most of our area. Showers and
thunderstorms with locally heavy downpours should expand rapidly
across the area going into the afternoon. The approach of a trough
and embedded MCVs will help initiate the activity in a very moist
environment. The 12Z OHX upper air showed about 2 inches for
precipitable water, and models are focusing a northeast to
southwest band of moisture convergence across Mid Tn this
afternoon. Our previous FFA area did show the zone of most
persistent lift, but potential for localized flash flooding seems
just as high extending back across our southwest counties where
heavy rainfall has occurred during the past few days. 1 hour
flash flood guidance values are under 2 inches for much of the Mid
State, and we will likely have episodes of rainfall rates well in
excess of these amounts. We do not expect a widespread flood
situation, but locations where heavy convective bands set up could
be dealing with several inches of rain and significant local
impacts.

Thanks LMK for collaboration.
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  • Mr Bob unpinned this topic
  • 2 months later...
  • 3 weeks later...
54 minutes ago, janetjanet998 said:

the start of a 2020 redux? 

 

Both the 12z Euro and 18z GFS have huge amounts 8+ inches over TN over the next 360 hours..GFS 14 in

a dumping the next 2 days..a decent break but then very active

 

and soil moisture is currently already high (70-80 percentile)

 

 

She's back,that's not good..lol

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1 hour ago, janetjanet998 said:

the start of a 2020 redux? 

 

Both the 12z Euro and 18z GFS have huge amounts 8+ inches over TN over the next 360 hours..GFS 14 in

a dumping the next 2 days..a decent break but then very active

 

and soil moisture is currently already high (70-80 percentile)

 

 

DzpTphsX4AA2aR4.png

 

Looks like earlier this year into FEB but this is Jan

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18 minutes ago, AMZ8990 said:

Wow

Right now the Euro shows a warm front lifting northward next weekend.As the WF  lifts  you should anyways see even a chance of the thunderstorms possibly severe into next weekend As the LLJ starts to strenghten more or less this drives up the Thetea-E along with SB Capes with DP'S getting into the lower 60's,impressive for Jan.With convection some of those totals might be much higher..IMO

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  • 4 weeks later...
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
258 PM EST Sun Feb 02 2020
 
Day 3
Valid 12Z Tue Feb 04 2020 - 12Z Wed Feb 05 2020 

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS 
OF THE LOWER MISSISSIPPI AND TENNESSEE VALLEYS...

21z update...
No significant changes to the previously issued Marginal Risk. Any 
changes were based primarily on model trends in the placement of 
the axis of maximum rainfall. 

Model soundings showed that the best instability remains south of 
KY/TN, with the best MUCAPE values relegated to the Lower MS 
Valley and central Gulf Coast (which is not unusual for a cool 
season system). However, model soundings did  show some elevated 
instability across these areas, with MUCAPE values generally less 
than 100 J/KG. There is some spread on how models distribute the 
elevated instability, which has some effect on where the heaviest 
rainfall axis ultimately resides. 

Moisture is plentiful, with precipitable water values between two 
and three standard deviations above the mean transported into the 
upper TN Valley and lower OH Valley, where three hour flash flood 
guidance values are as low as 1.50 inches. While there is some 
model spread regarding the highest rainfall amounts, each of them 
placed the axis west of the lowest flash flood guidance. Based on 
this, the Marginal Risk was left in place. If there is better 
agreement concerning the placement of the heaviest rainfall 
(especially if it impacts areas with lower flash flood guidance 
values), a Slight Risk could be needed in later forecasts.
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