Spring/Summer 2021 Medium/Long Range Forecast Discussion.

[Carvers Gap]

I am not seeing the aggressive totals with the Euro or Canadian.  Is the American model more accurate with this type of set-up?

[PowellVolz]

I am not seeing the aggressive totals with the Euro or Canadian.  Is the American model more accurate with this type of set-up?

Noticed that also. I didn’t look but I’m assuming the GFS has a more favorable Floyd track for us.


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[Carvers Gap]

2 hours ago, PowellVolz said:

Noticed that also. I didn’t look but I’m assuming the GFS has a more favorable Floyd track for us.


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There are two potential rainmakers.  The flow from the GOM with Floyd and a potential front late next weekend.   MRX has a pretty decent rainfall map on social media.  That looks reasonable to me.  What will be interesting is whether we get significant rainfall in day6-10.  That could be a problem on the heels of Fred.  Right now, we could use the rain.  

[dwagner88]

I got over 4" just last night with the stalled boundary over the area. I really don't need any more from Fred. The Euro is lighter than the GFS (under 2" additional), but ALL of the models blew the heavy rain last night.

[Windspeed]

I am not seeing the aggressive totals with the Euro or Canadian.  Is the American model more accurate with this type of set-up?

Sorry for just now responding. The GFS has been more aggressive with totals from Fred over the Ridge and Valley and western side of the Blue Ridge. The SPC/WPC has the highest totals on the eastern side into the W. Carolinas. Euro is more in line with that, however some of this likely depends on how far west Fred's mid-level circulation pivots around the high and how strong Fred becomes prior to landfall. The GFS has been stronger than forecast and also keeps the heavier totals further west. We do need the rain but obviously not too much too fast and I hope I didn't seem like I was "model hugging".

Here are the highest totals forecasted for Fred as of 3AM. Below is the latest GFS totals through 96 hrs as presumably Fred should be out of the region.

[Met1985]

44 minutes ago, dwagner88 said:

I got over 4" just last night with the stalled boundary over the area. I really don't need any more from Fred. The Euro is lighter than the GFS (under 2" additional), but ALL of the models blew the heavy rain last night.

Yeah you are right. No model saw what happened last night and with Fred strengthening then all bets are off.

[Daniel Boone]

5 hours ago, Met1985 said:

Yeah you are right. No model saw what happened last night and with Fred strengthening then all bets are off.

Ive noticed in recent years , more times than not, HPC guidance underforecasts TC intensity as close in as a day in advance of landfall..They also almost always underforecast rainfall amounts, particularly in northern remnant track locations.

[John1122]

The track has shifted East so the rainfall totals are shifting East too. I can probably live without it. I've had 5 inches of rain this week and it's rained off and on most of today. 

[Windspeed]

Latest from WPC...

[dwagner88]

Looks like the GFS was correct with the rain amounts. The precip shield is more displaced to the NW from the LLC than on the other globals. MRX said 025"-0.50" today. Already over 1" and it's pouring down.

[Windspeed]

Looks like the GFS was correct with the rain amounts. The precip shield is more displaced to the NW from the LLC than on the other globals. MRX said 025"-0.50" today. Already over 1" and it's pouring down.

I-75 corridor is getting pummeled right now as coverage continues to increase. I-81 coverage is beginning to increase as well. Should we make a new thread specifically for a heavy rain event as to not clutter up the medium/long range too much going forward?

[Carvers Gap]

Headed down to @waltrip country last night in order to get some XC running on their course last night.  As soon(and I mean right when we put the truck in park and got out), it started to thunder.  So, we got back into the truck to wait, and wait, and wait.  Those storms were coming off the mountains heading NW.  All it would take would be a little ripple.  As soon the storm come off the mountain, it unloaded and trained over east Greeneville.  Finally got on the course around 7:15 after about a two hour wait.   You can see the same deal on the radar above.  As the rainfall descends the mountains - nada.  As soon as it hits flat land....rain appears.  This is textbook as to why during winter that the valleys do better with storms that come from the GOM.  The foothills get the shaft in this set-up though(on the west side....east side gets hammered.)

[PowellVolz]

I-75 corridor is getting pummeled right now as coverage continues to increase. I-81 coverage is beginning to increase as well. Should we make a new thread specifically for a heavy rain event as to not clutter up the medium/long range too much going forward?

Rain seems heavier on the ground than what the radar is showing. I’m under moderate feedback on RadarScope but it’s absolutely a monsoon on the ground.


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[PowellVolz]

Cell in NE Georgia has a confirmed tornado. Don’t think it would make it but it’s track would take it into SE Tennessee


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[Windspeed]

Rain seems heavier on the ground than what the radar is showing. I’m under moderate feedback on RadarScope but it’s absolutely a monsoon on the ground.


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A common trait of tropical system rainfall. It's steady moderate rain here at my location south of Bristol but the radar dbz echoes aren't really that impressive.

[PowellVolz]

A common trait of tropical system rainfall. It's steady moderate rain here at my location south of Bristol but the radar dbz echoes aren't really that impressive.

Interesting, never heard that.


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[Daniel Boone]

Kmrx Rainfall forecast Graphics are way too low along the plateau and SE KY. I don't know how they derived that, tbh.

[Windspeed]

1 hour ago, PowellVolz said:

Interesting, never heard that.


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Nice article explaining how radar rates and dbz can be deceiving in tropical systems.

https://radarlab.wordpress.com/2015/06/22/whats-so-special-about-tropical-rainfall/

Quote

Tropical rainfall is generally formed by a different process that does not involve ice, and is known as “warm rain”. In this process, some liquid rain drops grow just large enough to start falling (still relatively small for rain drops). As they fall, they collide with other droplets that are smaller and not falling as fast (possibly moving upward with the wind). Often the two drops involved in the collision merge together into a larger drop that falls even faster and collides with more small drops. Collisions between drops can also cause the drops to break up into two or more smaller ones. Though this process can result in some large drops, it also results in very many small drops. These small drops contribute quite a bit to the rain rate but not very much to the reflectivity. The tropical rainfall formula accounts for these small drops, which is why it yields much higher rain rates for the same reflectivity.

The difficulty for meteorologists is often in knowing when to apply the tropical formula and when to apply one of the “normal” ones, because tropical rainfall can occur far from oceans or locations that would normally be considered tropical if there is a warm, humid air mass present (like one would often expect to find in the tropics). The most important characteristics of the air mass that supports tropical rain are high relative humidity through a deep layer, low cloud bases, and a high freezing level. In years past, analysis of these environmental factors was the key to knowing whether to switch to the tropical rain rate formula or not.

However, the recent dual-polarization upgrade allows for better characterization of the drop size distribution by using reflectivity and differential reflectivity (Zdr) together. The differential reflectivity essentially measures the average shape of the particles. Spherical particles have Zdr that is near zero, and particles that are “pancake-shaped” have positive Zdr. A fortunate property of rain drops is that they are spherical when small, but become increasingly “pancake-shaped” as they get bigger, so the Zdr can be used to infer the size of the drops as well. Methods to estimate precipitation that incorporate this information (such as PQPE) can handle both tropical rainfall and “normal” rainfall without having to switch from one formula to another.

Because we know that tropical rainfall has unusually large numbers of small drops, and small drops have low Zdr, we would expect that tropical rainfall would have unusually low Zdr for a given reflectivity.

 

[John1122]

Noticed the small raindrops as I drove across town earlier.  

Last night a cell popped up overhead and just drenched down huge drops for about 30 minutes, it had thunder embedded. This rain is a whole lot of small drops. 

Either way, closing in on 5 inches in the last 72 hours and 7 inches over the last week. 

[PowellVolz]

Some pretty big isolated totals around the region. Most areas seen between 1-3” but a few areas outside the higher elevations did well. One in particular was 5 miles north of Jefferson City in Granger Co picked up 5” and no one close to that area seen more than 3”. Cherokee Co in SWNC picked up almost 8”.


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[Daniel Boone]

7 hours ago, PowellVolz said:

Some pretty big isolated totals around the region. Most areas seen between 1-3” but a few areas outside the higher elevations did well. One in particular was 5 miles north of Jefferson City in Granger Co picked up 5” and no one close to that area seen more than 3”. Cherokee Co in SWNC picked up almost 8”.


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Picked up 2 day total of about 3.4 here. 5 day, 4.6".

[Carvers Gap]

What is crazy is that it rained like crazy here, but barely raised many of the urban streams.  On a positive note, my yard turned green almost over night!

[John1122]

Ended up with 6.15 inches of rain since Saturday and just over 8 inches in the last 6 days. Big storms are firing to the west of me in Fentress Co. Not sure if they make it this evening but they probably will by tomorrow if nothing else. 

[1234snow]

What is crazy is that it rained like crazy here, but barely raised many of the urban streams.  On a positive note, my yard turned green almost over night!

I was confused by this as well considering the rains we had over the weekend. I guess the ground needed a good soaking.

[Carvers Gap]

On 8/19/2021 at 10:47 AM, 1234snow said:

I was confused by this as well considering the rains we had over the weekend. I guess the ground needed a good soaking.

I think we are very fortunate.  Folks in western North Carolina have been slammed.  Looks like Carter and Johnson counties are having problems as well.  

https://www.usatoday.com/story/news/nation/2021/08/19/fred-flooding-missing-people-north-carolina-tornado-warning-northeast/8191424002/

[Carvers Gap]

First snows of the season are falling in the Big Horns today.  Bout' time to create a fall thread........

[Carvers Gap]

La Nina extended summer looks locked-in.  That is very counter to what LR models were showing just a few weeks ago.  I suspect we see a very sudden flip, but until then....going to be HOT!!!!  Some modeling is showing a pattern which gets progressively warmer against the norms.  On the bright side, again, I think that might bode well to an early start to winter.  Really though, I don't like this pattern all.  Of all the patterns I really dislike, this is number one - August extending into September and the first part of October.  Boy, I hope I am wrong.