Summer-Fall 2024 Weather Disco Med/Long Range

[*Flash*]

 

Watch 6:15-7:13. We could be seeing a Fujiwhara effect taking shape over our state in a few days. 

[*Flash*]

Last Thursday's USDM Outlook. Many locales still needing a lot of rain to bust the drought, especially east of the TN River's western extent. I'm knocking on the door of D3 IMBY as Francine didn't move the needle in our area.

[dwagner88]

Looks like this area may get a PRE ahead of Helene midweek. That will be very interesting to watch. Flash flooding will be a huge concern with the very hard and dry ground. The last one I can remember was in 2011 from a TS that hit LA and interacted with a front across the TN valley. We got 12" of rain from it.

[Carvers Gap]

The 18z GFS paints a bleak picture for western NC with this next tropical system.  With the upslope, that would have the potential for significant flooding IMHO.  Downslope would protect most of E TN with the exception being SE TN.   

[Daniel Boone]

4 hours ago, Carvers Gap said:

The 18z GFS paints a bleak picture for western NC with this next tropical system.  With the upslope, that would have the potential for significant flooding IMHO.  Downslope would protect most of E TN with the exception being SE TN.   

Yeah, sure looks that way. If it takes a more Eastward track as it moves North it could dump enough to cause some issues in the Great Valley. Also, a remote possibility it doesn't keep moving NW as it gets to our Latitude but kind of stalls and washes out . That could result in flooding for the Valley.

[Carvers Gap]

12 hours ago, Daniel Boone said:

Yeah, sure looks that way. If it takes a more Eastward track as it moves North it could dump enough to cause some issues in the Great Valley. Also, a remote possibility it doesn't keep moving NW as it gets to our Latitude but kind of stalls and washes out . That could result in flooding for the Valley.

The system two weeks ago was handled very poorly by modeling.  Just kind of saying that as a caveat, the 12z NAM would be a drought buster.

[Windspeed]

Becoming more concerned with the potential predecessor rain event (PRE) advancing north of Helene for the eastern Tennessee Valley under interaction with the frontal/upper level setup and block. The actual event where the core of the TC moves across the Southern Appalachians may be a much bigger impact for Western NC/Blue Ridge region (Asheville, Lenior, Boone, etc.). At any rate, I've prepped today, making sure gutters are cleaned out and checked the roof. Had to replace a few vent pipe boots and touched up with some Flex Seal. Hoping totals for KTRI don't exceed 6 inches.

[Carvers Gap]

@Met1985, did you see the 18z RGEM.  How much rain falls in W NC on that run!?  @Windspeedthe 18z NAM looked a little more tame.  The RGEM is "turn out the lights" bad for many areas in the mountains.

[Met1985]

9 minutes ago, Carvers Gap said:

@Met1985, did you see the 18z RGEM.  How much rain falls in W NC on that run!?  @Windspeedthe 18z NAM looked a little more tame.  The RGEM is "turn out the light" bad for many areas in the mountains.

I have not seen it. Go ahead and post it. We are keeping a very close eye in things over this side of the mountain.  The trend is NOT our friend.

[Windspeed]

Here's the WPC's rainfall forecast that includes the PRE and TC.

[Carvers Gap]

33 minutes ago, Met1985 said:

I have not seen it. Go ahead and post it. We are keeping a very close eye in things over this side of the mountain.  The trend is NOT our friend.

 

[Carvers Gap]

13 minutes ago, Windspeed said:

Here's the WPC's rainfall forecast that includes the PRE and TC.

That isn't a whole lot different than the 18z RGEM.  That is a pretty aggressive forecast.

 

[Met1985]

8 minutes ago, Carvers Gap said:

 

Yeah this is exactly what we are worried about.  I talked in our thread about this being a historical event for us...

[1234snow]

0z HRRR:

The hurricane at hour 48 was just across the state line in Georgia.

[Matthew70]

This hurricane is going to be impacting over a very large area.  It’s going to be flying towards middle TN then comes to a crawl.  The rubber band snaps the other way.  From drought to flooding in areas. 

[Daniel Boone]

1 hour ago, 1234snow said:

0z HRRR:

The hurricane at hour 48 was just across the state line in Georgia.

You can extrapolate to how much more is probable from Helene's remnants. Also, IF some guidance is correct in Helene reaching middle Tn then turning back ENE you can bet some eye popping Totals will be the case once all is said and done. Some serious flooding even in the Great Valley is looking more and more likely.

[Matthew70]

Definitely agree.  This one has a high ceiling high impact IF it does what the models are saying.  IF!!!  

[jaxjagman]

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
855 PM EDT Tue Sep 24 2024
Day 3
Valid 12Z Thu Sep 26 2024 - 12Z Fri Sep 27 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHEAST...

...2030Z Update...

In coordination with all of the impacted offices, the Moderate Risk
was expanded north to include much of the east facing slopes of the
Southern Appalachians with this update.

What is forecast to be Major Hurricane Helene is forecast to make
landfall in the Big Bend Region of the Florida Panhandle Thursday
evening. Around and well ahead of the arrival of the center of
circulation, bands of locally very heavy rain will impact all of
the Florida Panhandle and portions of the west coast of the Florida
Peninsula. PWATs with Helene are expected to be nearly off the
charts, as the much larger than normal hurricane draws nearly
unlimited moisture from the much warmer than normal eastern Gulf
and efficiently converts it to heavy rainfall. Areas of the Florida
Peninsula east of the track will contend with storm surge along
the coast, which will impact drainage from the heavy
rain...resulting in excessive rainfall flooding due to poor
drainage. Thus, the Slight continues along the Florida Peninsula,
with the Moderate closer to the track.

Fortunately, Helene is likely to be moving at its fastest forward
speed when it makes landfall in the Big Bend region. This should
somewhat reduce the impact potential of the heavy rain. Thus, for
now, a High Risk along the Gulf Coast is not yet anticipated, but
will certainly continue to be considered with new and changing
guidance.

Further north, the intensifying southeast flow ahead of Helene's
center will advect increasingly deep tropical moisture into Georgia
and the Carolinas. The previous day's PRE will give way to the
primary rainfall shield with Helene, only resulting in increasingly
heavy rainfall into north Georgia and the Carolinas, especially
overnight Thursday night. The Moderate Risk was expanded north to
account for the PRE, Helene's rainfall, and the much more dangerous
nature of the impacts from nighttime flash flooding. Mudslides and
landslides will become increasingly common in the southern
Appalachians as rainfall amounts approaching 12 inches are
expected. Despite recent dry conditions in this area, PWATs
exceeding 3 inches in some areas will support storms easily capable
of overwhelming the soils resulting in a very healthy percentage of
the rainfall converting to runoff.

The area from metro Atlanta, much of north Georgia, the western tip
of South Carolina, and much of the mountains of western North
Carolina are considered in a higher-end Moderate Risk, with
increasing potential of eventually needing a High Risk upgrade for
this area. This is for a few reasons: 1) The PRE shifting east (as
mentioned in the D2 discussion) will prime many of the same
southeast facing slopes much more efficiently than in previous
forecasts. 2) Increasing rainfall totals with PWATs potentially
getting as high as 3 inches in some areas means that much more
efficient warm rain processes. 3) Southeast flow perpendicular to
the southwest to northeast orientation of the southern Appalachians
will maximize the upslope component of the flow, resulting in more
rain. 4) Terrain issues, especially after multiple inches of rain
Wednesday could mean multiple mudslides and landslides which could
cut off whole communities from the road network.
For Atlanta, any ERO risk upgrades will be dependent on significant
rain from the PRE on Day 2/Wednesday in the city, as otherwise on
Day 3 the rainfall in Atlanta will likely be similar to surrounding
areas.

The surrounding Slight Risks have generally been expanded in all
directions: In the Florida Peninsula, convergence along the East
Coast with the expansive wind field may result in heavy rain in
urban areas from Orlando to Jacksonville.

Given the eastward shift in the guidance and that much of Helene's
moisture will shift northeast well after landfall, the Slight has
been expanded to include all of South Carolina and central North
Carolina.

Finally, the Slight has also been expanded west to cover nearly all
of Tennessee. Much of the westward shift in the guidance will be
with some of Helene's moisture as it dissipates being absorbed into
a cutoff low over the Mississippi Valley, resulting in a conveyor
belt of moisture and heavy rain over much of Tennessee. That heavy
rain will continue westward with a jet eventually moving into
Missouri and Arkansas by Day 4/Friday. Flash and urban flooding
across the major Tennessee cities from Chattanooga, Nashville,
Knoxville and maybe as far west as Memphis will be possible.

Wegman

[Windspeed]

Nice mosaic of the precipitation and moisture feed out of the GOM. This is all still due to the frontal/upper trough, which is getting cut off and driving south through the Mississippi Valley. A soaking pre to the PRE...

[Carvers Gap]

45 minutes ago, Windspeed said:

Nice mosaic of the precipitation and moisture feed out of the GOM. This is all still due to the frontal/upper trough, which is getting cut off and driving south through the Mississippi Valley. A soaking pre to the PRE...

That is impressive.  Drought buster.

[jaxjagman]

Cant imagine driving to Atlanta and the nightmare that could happen,especially with potential mudslides/winds in the mountains,hopefully people take detours.But you cant fix stupid can you ?

[Carvers Gap]

We are already dealing with some flooding in NE TN, and the main system isn’t even here.  Decently bleak afternoon disco by MRX.  

[Windspeed]

Some of these model runs now aggressively capture Helene, advancing its core into the Eastern Tennessee Valley with haste. I wonder if some record surface pressures may be broken. Also, the 850-700 hPa vorticity maximum remains intense all the way across the Smoky Mountains. Might some areas NE of the circulation experience some very high wind gusts due to downsloping effects with such a tight gradiant and E to ESE flow in the NE and E quadrant? Combined with saturated water-logged soils, becoming concerned about uprooted and downed trees. Most trees are still in full foliage.

[1234snow]

We are already dealing with some flooding in NE TN, and the main system isn’t even here.  Decently bleak afternoon disco by MRX.  

Several counties in NE TN are under a flash flood warning currently until 10 pm. The firehose doesn’t seem to end soon.

[Windspeed]

RE: Potential downsloping and wind gusts. Granted, this is just one model (HAFSB) and the most recent run. Hopefully, overdone.

[Daniel Boone]

Some locations near Coeburn VA have recorded over 6 inches of rain since Midnight.

[ShawnEastTN]

Not very often see in the Morristown CWA "Tropical Storm Conditions" in their point forecasts. Have to say this in many respects seems eerily reminiscent of Hurricane Opal in 1995. I was in high school then and remember they closed school where I live for 2 days but some systems were closed up to a whole week for flooding and number of trees down.

[John1122]

Similar here. Probably the highest wind potential mentioned in a forecast I've seen outside of severe thunderstorm predictions. 

 

Friday

Tropical storm conditions possible. Showers likely in the morning, then showers with a slight chance of thunderstorms in the afternoon. Highs in the lower 70s. East winds 30 to 40 mph with gusts up to 70 mph, becoming south 15 to 25 mph with gusts up to 45 mph in the afternoon. Chance of rain near 100 percent.

[Carvers Gap]

FXUS64 KMRX 261117
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
717 AM EDT Thu Sep 26 2024

...New AVIATION...

.SHORT TERM...
(Today through Friday) Issued at 353 AM EDT Thu Sep 26 2024

Key Messages:

1. Flooding potential remains high as heavy, tropical downpours
affect the area today into Friday.

2. Winds will be high in the mountains, which are areas that are
used to strong winds. There is also the potential for widespread
strong winds in the TN valley late Thu night through Fri morning.

Discussion:

Hurricane Helene is in focus for the period, and the impacts the
decaying tropical system brings to our are are expected to be major.
The current NHC track has it coming ashore then track north before
curving northwest across southeast TN early Friday before being
absorbed into the upper low to our west. The two main concerns with
this system for us will be heavy rain/flooding and very strong
winds.

A precursor rain event has been ongoing, and we`ve already had a lot
of rain across areas mainly along/east of the I-75 and I-81
corridors (in excess of 4 inches in spots). We will see additional
heavy rain over these areas today, with a downtrend for a period
west of the mountains for a period later today into tonight as the
downslope winds increase and the axis of the more significant rain
shifts south and west, then likely another increase area wide late
tonight into early Friday as the tropical system approaches. WPC has
rainfall from now through Friday evening of around 3 to 4+ inches
over most of our area, with even higher amounts across portions of
SW NC and the eastern mountains. The flood watch will be expanded
into our northern Cumberland Plateau counties with this issuance.
Both flash floods and river flooding is expected.

For winds, some of the higher elevations of the mountains will see
wind gusts in excess of 70 mph, but valleys are likely to see strong
wind gusts as well later tonight into Friday morning. Mean HREF wind
gusts are showing values of 50+ across much of the area outside of
the mountains. While we may not reach actual wind warning wind
speeds in most locations outside of the mountains, we will likely
see a lot of trees down and power outages especially given the soggy
ground. Given the uncertainties of exactly how strong Helene will
get before landfall and it still being second period, and in
coordination with neighboring offices, will leave the watch out for
one more cycle. Will continue the high wind warning in the
mountains. Will also continue the Tropical Storm warning for our SW
NC counties in accordance with North Carolina partners.

 

[Holston_River_Rambler]

Did Hugo have a upper low slinging it inland too? I was just looking at a model for Helene and the long outflow cloud deck aiming at the upper low seems to remind me of Hugo:

Helene: 

 

Hugo:

 

Color schemes aren't the same, but the long outflow upper cloud deck kind of seems similar to me. 

 

Actually, I just realized I could go look at reanalysis and yeah, Hugo had a deep south upper low: