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Joaquin/ULL inland flooding threat


BullCityWx

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Models continue to suggest there is Going to be a really tight precip gradient  in georgia or the western flank of wherever that band sets up . 30 or 40 miles could mean the difference between a foot and  just a couple of inches or even that. 06z only shifted very slightly east vs the 0z run and it dropped totals here by 6 inches. It should be noted the 0z canadian, 0z uk, and 4km nam keep the band/extreme amounts in sc as well. A bit anxious  to see the 12z guidance suite to see if that was a one off or a start of a trend which would keep the truly excessive amounts in sc. Although the new nam says otherwise and spreads it around a good bit more and to the west...but I have virtually zero faith in the nam at this point with it's silly and incredibly annoying run to run inconsistency.

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The NAM looks pretty excited about precip totals from Asheville to GSP to Columbia through 42. Laurens County is in the bullseye so far, FWIW.

Yep! That new map they just showed on TWC has the 12+ inch bullseye creeping ever closer to Greenville! It looks to be touching S parts of the county and as you stated, Greenwood bullseyes!

I'm still in the 8-12" range!

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Yep! That new map they just showed on TWC has the 12+ inch bullseye creeping ever closer to Greenville! It looks to be touching S parts of the county and as you stated, Greenwood bullseyes!

I'm still in the 8-12" range!

If this were a winter storm, I think we'd be saying that were exactly where we want to be. Not in the bullseye yet but moving closer as the storm approaches.

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Counter clock wise flow in Louisiana is the ULL. You can see it start to wrap up. As it does, the energy it creates will bring the rain. Also, you can see the interaction the the cat 4 of the coast of FL. I assume the radar will begin to pop as we head through the day. This is also backed up by recent short range modeling as noted about by other posters. 

 

I am new to this. Please explain. TIA!

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Counter clock wise flow in Louisiana is the ULL. You can see it start to wrap up. As it does, the energy it creates will bring the rain. Also, you can see the interaction the the cat 4 of the coast of FL. I assume the radar will begin to pop as we head through the day. This is also backed up by recent short range modeling as noted about by other posters. 

Got you. So it is essentially pulling moisture from the Gulf and the Atlantic? Will it pull in winds from the cane or just the moisture from the Atlantic?

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I am new to this. Please explain. TIA!

The upper level low on strongwx's image has dropped down from the northwest.  It will bottom out and crawl east to a position near Jacksonville by Sunday night.  As it does this, the rains will work west from the coast, and pivot across the Carolinas.  A lot of times these heavy precip bands can setup farther north than modeled, that's why I mentioned the southern half of NC earlier could be hit hard even though the models are targeting SC more at the current time.  There's going to be a focused area of intense rains.

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Great explanation. 

The upper level low on strongwx's image has dropped down from the northwest.  It will bottom out and crawl east to a position near Jacksonville by Sunday night.  As it does this, the rains will work west from the coast, and pivot across the Carolinas.  A lot of times these heavy precip bands can setup farther north than modeled, that's why I mentioned the southern half of NC earlier could be hit hard even though the models are targeting SC more at the current time.  There's going to be a focused area of intense rains.

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GFS gives Spartanburg County 18+ inches by Monday. Amazing that it's still spitting out these totals as we get closer to the event, whether they're right or not (and probably not).

 

*edit - Sorry upon closer inspection that Cherokee County, or on the border anyway - Greenville is in the 12-15 range, along with CLT

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The moist dynamics are going to play a huge role in where the axis of heaviest precipitation sets up. The intense precipitation ongoing in coastal NC/SC is ultimately going to impact the enhancement of the easterly flow in the southeast. I'll step through it using the 6Z GFS forecast...

 

At 12UTC, we know there was intense precipitation along the NC/SC coastline as evidenced by the vertical motion contours (red contours) below. The resultant diabatic outflow (outflow due to the heavy precipitation) pushes westward against the upper-level PV contours (grey contours). 

 

Stepping forward to 18UTC (the 12-hour forecast), there is still intense convection along the coastline and we can see that the PV gradient along the eastern flank of the trough has been pushed slightly westward.

 

This trend continues through the 18- and 24-hour forecasts. The diabatic outflow builds the downstream ridge and "erodes" the PV though the Ohio Valley such that the orientation of the trough/downstream ridge eventually produce southeasterly flow into the Carolinas bringing in that tropical moisture plume. 

 

I took the time to go through that because if the precipitation is slightly over or underdone in the model, it is going to affect the ultimate location and orientation of these dynamic features and the resultant QPF. Since most models don't use a hot start, there are going to be non-trivial errors in the precipitation forecast that may well have important implications for where the heaviest precipitation occurs.

 

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post-659-0-25232200-1443800466_thumb.png

 

post-659-0-68390700-1443800472_thumb.png

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