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Pattern December 2023

Mesoscale discussion out for heavy rainfall.....

Mesoscale Precipitation Discussion 1222
NWS Weather Prediction Center College Park MD
656 AM EST Tue Dec 26 2023

Areas affected...portions of the Southern Appalachians & Piedmont

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

Valid 261156Z - 261756Z

Summary...Showers and thunderstorms with heavy rain are expected
to continue through the morning. Hourly rain totals to 2" with
local amounts to 4" are possible.

Discussion...Surface observations indicate that a coastal
front/thermal boundary has progressed into the Piedmont of the
southern Appalachians due to surface southeast flow to the
northeast of a surface low in GA. Precipitable water values of
~1.25" lie in the area. MU CAPE of 250-500 J/kg lie to the
southwest, and are being advected into the region by southwest
winds within the cyclone's warm sector at 10-15 kts at 850 hPa per
VAD wind profiles. There is some evidence for 850 hPa
frontogenesis near the convective activity which is moving
north-northeast along the lines of the mean 850-400 hPa wind.
This above has led to a bit of precipitation efficiency, with
radar estimates exceeding 1.5" totals in an hour at times.

Instability trends are very slowly declining, which fits in with
06z HREF expectations for a slow drop off in hourly rain totals
with time. Still, there is enough of a signal, and for the time
being enough instability for 3" totals within convection that
forms near and poleward of the coastal front, particularly in the
very short term, to be concerned about flash flooding within area
terrain despite recent dryness as they would exceed the 3 hourly
flash flood guidance in the area. Until instability declines,
hourly rain totals to 2" and local amounts to 4" would remain
possible.

Roth
 
Cad Wedge NC said:
Mesoscale discussion out for heavy rainfall.....

Mesoscale Precipitation Discussion 1222
NWS Weather Prediction Center College Park MD
656 AM EST Tue Dec 26 2023

Areas affected...portions of the Southern Appalachians & Piedmont

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

Valid 261156Z - 261756Z

Summary...Showers and thunderstorms with heavy rain are expected
to continue through the morning. Hourly rain totals to 2" with
local amounts to 4" are possible.

Discussion...Surface observations indicate that a coastal
front/thermal boundary has progressed into the Piedmont of the
southern Appalachians due to surface southeast flow to the
northeast of a surface low in GA. Precipitable water values of
~1.25" lie in the area. MU CAPE of 250-500 J/kg lie to the
southwest, and are being advected into the region by southwest
winds within the cyclone's warm sector at 10-15 kts at 850 hPa per
VAD wind profiles. There is some evidence for 850 hPa
frontogenesis near the convective activity which is moving
north-northeast along the lines of the mean 850-400 hPa wind.
This above has led to a bit of precipitation efficiency, with
radar estimates exceeding 1.5" totals in an hour at times.

Instability trends are very slowly declining, which fits in with
06z HREF expectations for a slow drop off in hourly rain totals
with time. Still, there is enough of a signal, and for the time
being enough instability for 3" totals within convection that
forms near and poleward of the coastal front, particularly in the
very short term, to be concerned about flash flooding within area
terrain despite recent dryness as they would exceed the 3 hourly
flash flood guidance in the area. Until instability declines,
hourly rain totals to 2" and local amounts to 4" would remain
possible.

Roth
Click to expand...

Yup. Added .50” in the last 50 minutes here.


Sent from my iPhone using Tapatalk
 
Under the Areal Flood Advisory and Flood Watch. Already have gotten 3.5” and it looks like we are getting training (pause) here with huge downpours right now. Probably smoother 1-3” is pretty likely. So much for that drought thing from the fall.
 
iGRXY said:
Under the Areal Flood Advisory and Flood Watch. Already have gotten 3.5” and it looks like we are getting training (pause) here with huge downpours right now. Probably smoother 1-3” is pretty likely. So much for that drought thing from the fall.
Click to expand...
I would not have believed it after looking at the radar most of yesterday, but we are up to 2 inches here and it is still raining, although it is much lighter now. I'm a little surprised that a couple of counties in the mountains are not under flash flood warnings. I guess the heavier stuff shifted east just in time.
 
Definitely an over performer gets imby.
Apparently Gsp agrees putting most of N GVL county in a flood advisory from early this morning thru now.
 
weatherfide said:
Not a clap of thunder during this entire event for me. Most of the time the rain was not even showing up on radar. I'm sitting at over 1.35" for the event and from the radar, you wouldn't think I found .25".
Click to expand...
Stormed like hell here this morning...early and often!
 
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