1/10-1/12 Southern Slider

[John1122]

GFS was fantastic. 

[Runman292]

1 minute ago, John1122 said:

GFS was fantastic. 

Could you post a map?

[Runman292]

49 minutes ago, Runman292 said:

MRX AFD:

Discussion:

Bottom line up front: No change will be made to the Winter Storm
Watch at this time, due to the lowered confidence in p-types and
snow amounts. To issue a Warning beyond 24 hours, confidence must be
high that Warning criteria will be met and that impacts will be
significant.

Model trends and differences:

The NAM has thrown a wrench in the forecast with its depiction of a
warm nose spreading well northward into our area, due to its strong
southerly low level jet. This potential for mixed p-types adds much
uncertainty to the forecast snow amounts in southern sections and in
the lee of the mountains. The main difference in the NAM is that it
develops a secondary surface low in northern AL on Friday afternoon,
which tracks NE along the Cumberland Plateau to WV through the
evening. This creates a strong pressure gradient across the TN
mountains, and a 40-50 kt LLJ. However, it is noteworthy that this
is not a typical mountain wave/downslope enhancement pattern, which
is usually characterized by a 850 mb jet max to our NW, so perhaps
the NAM is overdone with the downslope warming. Also, the NAM is an
outlier in its solution, as the GFS and ECMWF do not develop this
secondary low and LLJ, and keep warm advection to our south. The
HRRR seems to be a compromise solution, and is not as aggressive
with the warm nose and LLJ as the NAM.

Precipitation types:

At onset Friday morning, temperatures profiles will support all snow
as top-down moistening evaporatively cools a dry low level layer.
HREF p-type probs show a snow/sleet/fzra mix entering southern
sections between 1 PM and 4 PM EST. The northward extent of this mix
is a big uncertainty, but for this forecast, the HREF probs look
reasonable, and keep the mix mainly to the south of I-40. The
strength of the downslope wind will affect the p-type in the
foothills north of I-40 and the Tri-Cities, and the potential for a
brief period of mixed p-types may result in lowered snow amounts
there.

Snow amounts and confidence:

The area of highest confidence in the snow amount forecast is north
of I-40 and west of I-81, in the northern Cumberland Plateau area
and KY border counties, where the p-type is highly likely to remain
all snow. In this area, amounts are expected to be in the 4-6"
range. As we go south and east from there, confidence lowers due to
the above mention p-type issues. In the southern Valley and SW NC, 1-
3 inches of snow is expected, mainly during Friday morning and early
afternoon before the mix takes over, with the potential for up to a
tenth of an inch of ice accumulation in the mid/late afternoon and
evening. Another factor in the snow amounts will be the loss of
moisture in the dendritic growth zone from the dry slot Friday
evening, which may shut off accumulating snowfall sooner than
previously forecast. The chance of accumulating precip drops rapidly
between 7 PM and midnight EST as the dry slot moves overhead.
Freezing drizzle may be a concern during this period.

Timing:

Not much has changed from previous forecasts regarding the timing of
snow onset Friday morning. Expect that the morning commute in the
Chattanooga area could be impacted by snow, potentially starting as
early as 7 AM EST but accumulating mainly in the 9-11 AM time frame
as snowfall rates increase. In Knoxville, 10 AM to noon appears to
be the likely time frame for snow to start accumulating, with Tri-
Cities being in the noon to 2 PM window. Peak precip intensity
appears to be during the afternoon, from around 1 PM EST to 7 PM
EST. Precip will begin to end near or after 7 PM from SW to NE as
the dry slot moves across the area and brings drying in the dendrite
growth zone. This end time is faster than previously forecast, but
the end time of the Winter Storm Watch will be kept at 7 AM EST
Saturday. We transition to a NW flow pattern Friday night, which may
result in some additional light snow accumulation in SW VA and the
TN mountains into Saturday morning.

WVLT Mets:

 

[John1122]

4 minutes ago, Runman292 said:

Could you post a map?

 

[BlunderStorm]

4 minutes ago, Runman292 said:

Could you post a map?

GFS sticks to its guns and ups totals slightly.

[TellicoWx]

4 minutes ago, John1122 said:

GFS was fantastic. 

Just from a global op stand point...it's running 3hr increments vs 6hr. Timing of the DGZ drying will play a big role in the final totals. Wondering if it's able to time it up better?

[John1122]

To me, the ICON is the middle ground between the Euro and GFS. The Euro is dry, the GFS loaded. The ICON is close to the middle.  RGEM is as well. 

 

That's discounting the oddball NAM runs for now. 

[John1122]

5 minutes ago, TellicoWx said:

Just from a global op stand point...it's running 3hr increments vs 6hr. Timing of the DGZ drying will play a big role in the final totals. Wondering if it's able to time it up better?

That, I don't know. I've never thought that time frames would make a difference, but that's possible. 

I'm trying to remember what resolution the GFS runs at now. The Euro is 9k, the ICON 13. 

[Runman292]

It's pretty cool to stay up all night and talk weather with everyone. I really enjoy learning a lot with these conversations.

[Mrwolf1972]

06z GFS hammers state no warm nose

[John1122]

Gonna see what the RAP throws out. I believe it's the seed for the HRRR, who honestly wasn't too far off the GFS except for the bit of sleet. 

[John1122]

The RAP looks just like the GFS. It pops the low in Alabama but it goes up the east side of the Apps and we get dumped on. 

[TellicoWx]

For Chatt folks...you can always drive south to Ft. Payne. HUN went 2"-4" there lol.

[AFranklin88]

They may be right and the NAM scores a huge coup, but it just trended towards all other modeling in 6z suite. While others (gfs for one) are doubling down and rap/hrrr seem to make a big move onboard. baffling move by MRX in that AFD

[John1122]

The 9z 51hr  RAP will factor into the 12z 48 hour HRRR. 

 

 

[TellicoWx]

7 minutes ago, John1122 said:

The RAP looks just like the GFS. It pops the low in Alabama but it goes up the east side of the Apps and we get dumped on. 

Yeah the 10:1 is near a carbon copy

[BlunderStorm]

The 6z Ukie 10:1 looks good staying true to its prior run but leaves some to be desired for SWVA folks. The 9z RAP meanwhile was perfect for SWVA but left Chatty and some other eastern valley locations a bit sketchy.
 

[John1122]

It's basically everything vs the NAM currently. 

[ChattZ]

[John1122]

06z Euro was basically a carbon copy of 0z. Its generally 3 to 6 inches for most of us. More to the west as it continues to lose punch as it heads east. 

It remains on the low side qpf wise. Lower that the AI version and the EPS. 

[fountainguy97]

1 hour ago, BlunderStorm said:

The 6z Ukie 10:1 looks good staying true to its prior run but leaves some to be desired for SWVA folks. The 9z RAP meanwhile was perfect for SWVA but left Chatty and some other eastern valley locations a bit sketchy.
 

09z RAP jumping on the colder/wetter side is big. Everything has ticked better overnight for Estsern areas. Even NAM/HRRR.

 

hopefully the RAP move is a sign and the NAM jumps again at 12z! 

[Carvers Gap]

2 hours ago, TellicoWx said:

To me MRX broke the cardinal rule...if you have a drastic outlier that has zero support...simple toss it. You don't include it in your package or totals. Better hope they are close to right, or once again going to look like fools to general public. Especially south of 40. As far as the DGZ, that's been showing for several days now. 

I knew all I needed to know when I saw the forecast package of WSWs on a straight line along the SW VA border last weekend and nothing below.  That has never verified, and it didn’t last weekend.  All of that despite clear modeling trends which depicted the possibility for wintry precip south of that line.  Due to lack of proper advisories this week around TRI, I actually have a family friend who got caught in jt and likely totaled their car.  I just about didn’t make it home Sunday due to their forecast (I should not have listened to it).
 

Unimpressed this week, and that is very rare criticism from me.

With the ground so cold, impacts from any frozen precip will be immediate and impactful around TRI.  Are they going to make the same mistake a third time this week?  I am all for conservative forecasts 48-72 hours out.  This areas is tough to nail down, but we have already seen two misses this week alone due to waiting until the event is underway to issue winter wx products.  We have school systems in this area(we all know who they are) which will open if the forecast isn’t clear.

[tnweathernut]

6 minutes ago, Carvers Gap said:

I knew all I needed to know when I saw the forecast package of WSWs on a straight line along the SW VA border last weekend and nothing below.  That has never verified, and it didn’t last weekend.  All of that despite clear modeling trends which depicted the possibility for wintry precip south of that line.  Due to lack of proper advisories this week around TRI, I actually have a family friend who got caught in jt and likely totaled their car.  I just about didn’t make it home Sunday due to their forecast (I should not have listened to it).
 

Unimpressed this week, and that is very rare criticism from me.

With the ground so cold, impacts from any frozen precip will be immediate and impactful around TRI.  Are they going to make the same mistake a third time this week?  I am all for conservative forecasts 48-72 hours out.  This areas is tough to nail down, but we have already seen two misses this week alone due to waiting until the event is underway to issue winter wx products.  We have school systems in this area(we all know who they are) which will open if the forecast isn’t clear.

Kind of like the school system in middle TN sending texts to parents yesterday telling them to have a ride prepared for their children Friday, they were going to attempt to start school.  Why?  From the first 10 minutes of flakes you are certain to have road problems and the start time has been well modeled between 8-10 am for the last 48 hours now.  Hopefully they backtrack and don’t meet at all tomorrow in northern middle TN.  If they do I’d question the sanity of the people making these high level decisions.  

[Holston_River_Rambler]

Local news (WBIR and WATE haven't had a chance to see WVLT yet) this AM seem to be leaning into the more snow than not, but I think they have the problem of the MRX graphics totals cut in southern and eastern areas of east TN. Also a lot of times the in house models they show on TV are Hi res CAMs that show some of the mixing potential. 

[Kasper]

Just now, Holston_River_Rambler said:

Local news (WBIR and WATE haven't had a chance to see WVLT yet) this AM seem to be leaning into the more snow than not, but I think they have the problem of the MRX graphics totals cut in southern and eastern areas of east TN. Also a lot of times the in house models they show on TV are Hi res CAMs that show some of the mixing potential. 

I just watched WVLT, she was all snow, but of course mentioned an ever so slight chance of mixing basically, polk, Bradley, Hamilton! 
I’m sure they’ve read MRX and mixed the AFD in their forecast 

[matt9697]

5 minutes ago, tnweathernut said:

Kind of like the school system in middle TN sending texts to parents yesterday telling them to have a ride prepared for their children Friday, they were going to attempt to start school.  Why?  From the first 10 minutes of flakes you are certain to have road problems and the start time has been well modeled between 8-10 am for the last 48 hours now.  Hopefully they backtrack and don’t meet at all tomorrow in northern middle TN.  If they do I’d question the sanity of the people making these high level decisions.  

Here is the most recent statement on the Sumner County Facebook page.....

[Holston_River_Rambler]

1 minute ago, matt9697 said:

Here is the most recent statement on the Sumner County Facebook page.....

[matt9697]

And not to be outdone, here is one of the statements on the Nashville NWS Facebook page with just one of the comments  

[matt9697]

1 minute ago, matt9697 said:

And not to be outdone, here is one of the statements on the Nashville NWS Facebook page with just one of the comments  

Which is different from their website which displays this graphic....I could not imagine being an administrator trying to decide about tomorrow! 

[Holston_River_Rambler]

Welp, still over an hour for the SREF, so might as well look at the EPS:

 

10th through 90th percentile snowfall (this is NOT an increasing Mean)