December 2025 Short/Medium Range Forecast Thread

[Carvers Gap]

The 18z HRRR has decent returns over @John1122's and @Shocker0's places. Mix ove TRI.  Snow over SW VA and SE KY. If that stays the same, I would expect MRX and JKL hoist winter wx products tomorrow evening at the very lates...maybe tomorrow morning once the actual axis of precip is determined.

[Carvers Gap]

This kind of shows the idea.  The 3k name is decidedly SE of 12K.  The 18z ICON is north.  I am using the two models which serve me decently well at short range.  They are just about where I can rely on them decently well

 The 18z RGEM is running now.   Similar to 12z.  It has more ZR.  See MRX comments above.

[John1122]

Hard to trust it, but the RAP just delivered big for 40 and North across the forum. Bullseye around Jax. 

[Holston_River_Rambler]

I would say the 18z Euro ticked SE just a hair too. 

Apologies, I was still comparing the 6z and 12z. 

[Holston_River_Rambler]

36 minutes ago, John1122 said:

Hard to trust it, but the RAP just delivered big for 40 and North across the forum. Bullseye around Jax. 

 

Like John said, probably the best run of any model for this potential event so far. An outlier for now. 

[BNAwx]

56 minutes ago, John1122 said:

Hard to trust it, but the RAP just delivered big for 40 and North across the forum. Bullseye around Jax. 

RAP it up.  I’ll take it…

[Carvers Gap]

It would not at all surprise me to see this trend SE or NW.  LOL.  The cold could push more than expected...we have seen that trend on a lot of models at 18z.  OTH, we have all seen systems jog northwest at the last minute.  I need to look at the 500 vort map.  The RAP is a good model.  To some extent, we see that same setup on other models...just not as juicy.  Plenty to track beyond this event as well.  In the valleys, we are trying to get a head start on climatology.  

[Carvers Gap]

46 minutes ago, Holston_River_Rambler said:

 

Like John said, probably the best run of any model for this potential event so far. An outlier for now. 

Looks like a little lee side slp???

[Carvers Gap]

MRX noted in their disco that soundings indicate all snow in NE TN but light.  Again, time of day is important.  If this comes in at night, could be frozen for many areas.  

[Carvers Gap]

What is crazy is that the Euro Weeklies had this timeframe as a bullseye before they infamously had an infinite loop of feedback over the Southwest...and pumped crazy temps into the East.  Now, we are tracking a potentially light winter wx event for northern areas of the forum.  I wouldn't be surprised for glaze to show up further south.

[Holston_River_Rambler]

0z HRRR looking a little RAPish, about 40 SE with the snow wrt 18z:

 

I'll wait until 12z tomorrow to get my hopes up for the inevitable flop though. 

 

 

[Carvers Gap]

HRRR looks like it is has some downslope over the eastern valley. Looks very similar to its 18z run.

[Carvers Gap]

Let’s see what MRX notes with their next update in regards to soundings.

[jaxjagman]

lol...glad i'm not the Met at OHX

[Carvers Gap]

Some nice trends on both the NAM and RGEM if you like frozen.  To me, this also bodes well for future systems.  It looks like modeling under-did the NW shield of the precip.  So this super dry sliders which follow tomorrow night...might have a bit more juice.   Good luck on overnight modeling to everyone.  I hope someone gets an early season snow!

[Carvers Gap]

The 18z Euro has a light upslope clipper around the 8th....need to keep an eye on that one.

[John1122]

The 03z RAP looks similar to the 21z with a decent strip of 2-3 inches of snow in the same areas. 

The RAP and HRRR are more stark with rain or snow vs freezing rain or mix. 

[John1122]

The NAM, HRRR and RAP all look somewhat similar now. 

[John1122]

The Rufus is similar, and a bit south with the snow line, to the other hi-res models. The Rufus is supposed to replace the NAM and NAM 3k at some point. 

The Rufus has 1.5 inches across downtown Knoxville. 

[John1122]

OHX has issued WWA for snow, sleet, and freezing rain for their Plateau areas.

[John1122]

Quote

- A Winter Weather Advisory is in effect for portions of the
  Cumberland Plateau tonight for ice accumulation up to 0.10".

- Mixed wintry precipitation is likely across all of Middle TN
  this evening from roughly 6PM-2AM. Some slick spots may develop
  tonight. Be cautious when travelling anywhere in the mid state.

- Temperatures warm above freezing Friday afternoon.

 

[Carvers Gap]

This pretty much sums it up...models are all still all over the place.

National Weather Service Morristown TN
606 AM EST Thu Dec 4 2025

...New AVIATION...

.KEY MESSAGES...
Updated at 601 AM EST Thu Dec 4 2025

 Dry weather today before increasing precipitation chances tonight
into Friday.

- Probabilities for minor impacts from ice and snow are trending
upwards across the northern Cumberland plateau, southwest VA and
extreme northeast TN for tonight into Friday morning

- Very low probability of rainfall this weekend.

&&

.DISCUSSION...
Issued at 1240 AM EST Thu Dec 4 2025

Dry today with continued below normal temperatures. Increasing
precipitation chances tonight into Friday morning. The good news is
that the latest HREF probs mostly align with the previous forecast.
The bad news, the last two runs of the HRRR are well above the HREF
means in terms of snowfall amounts. This makes for a low confidence
forecast.

Latest HREF guidance shows probs for at least 0.5 inches across
southwest VA are in the 30 to 50% range. Probs for at least 0.5
inches for extreme northeast TN are generally from 50 to 70%. There
are also low probs, 10 to 20%, of at least 0.5 inches across the
northern Cumberland Plateau and areas along and near the TN/KY state
line. Upping the prob amounts to 1 inch yield much lower values,
around 30%, but for very isolated locations for both southwest VA
and extreme northeast TN.

The LREF members shows slightly higher prob values, and with more
spatial coverage, for the 0.5 and 1 inch prob values. LREF shows
moderate probs of 1 to 2 inches across southwest VA and into extreme
northeast TN. The REFS output aligns fairly well with the LREF
ensemble probs.

Then we have the HRRR. The latest two runs of the HRRR show even
higher values than what the REFS and LREF ensembles means suggests.
The HRRR wants to paint a solid 2 inches in across the northern
Plateau, and 3 to 4 inches in across southwest VA and extreme
northeast TN.

Because of all this, uncertainty in snowfall amounts is high. These
higher end amounts would result in travel impacts while the lower
HREF amounts suggest little to no impacts. With this forecast
package, have trended snowfall amounts slightly upward, above NBM,
based on latest model data and trends. In addition to the snow, NBM
also painting in some light icing across these same areas. Please
stay tuned to the forecast as the snowfall forecast will likely
continue to change given the current variability. Please plan ahead
for potential impacts with this system.

Areas from Knoxville and south should remain all rain through the
event. The bulk of the precip will have ended by Friday afternoon,
but a few light showers may linger into the evening hours. NBM still
wants to hold on to some slight chance POPs for Saturday and Sunday
but it seems warranted so will leave them in the forecast.

Rain chances continue into next week as an active pattern will be in
place across the country. As of now, Tuesday look like it should be
dry though and is most likely to be the nicest day of the forecast
period.

 

[Holston_River_Rambler]

HRRR was keeping me and I 40 north snow overnight but has trended NW and warmer since 6z. 

Both RAP and HRRR have a warm nose between 850 and 750mb:

HRRR:

 

RAP"

 

That's not a huge one, but it's there. Keep in mind this is also just for my area in and around Knoxville, and Oak Ridge. Just one county to the north near Oneida, both of the above models keep snow around, but it does look to me like there is a NW trend the past few runs of the Hi Res models. 

On to 12z. 

[John1122]

The 12z RAP and HRRR are relatively steady regarding the arc of snow compared to 06z. I still have my doubts about each.

[jaxjagman]

Look at the SOI around the 23 of Nov then next week,this is when the models get chaotic with the MJO,but even  that  today, look how negative the SOI is today,the LaNina base state has been taking out and it   is acting more Nino now,seems like the JMA and Euro are going into the COD,then back into the WH afterwards possibly and should probably climb back out the COD,actually the GEFS isnt far behind

[Carvers Gap]

Jax, looks like basically a reload.  Lots of conflicting signals there.  Great share.

[Carvers Gap]

33 minutes ago, John1122 said:

The 12z RAP and HRRR are relatively steady regarding the arc of snow compared to 06z. I still have my doubts about each.

Yeah, I don't trust any model at this point.  Glad I don't have to put out a product tonight to the public!  This is one of those which could bust either way.

[jaxjagman]

Keep seeing it being to warm  while the clown maps keep saying you'll get IP and SN,looks more cold rain here

[housemtnTN]

So snow in the tn valley is basically a crapshoot at the moment?

I've been trying to educate myself on what makes this particular area so difficult to forecast, it's really fascinating to me.

[John1122]

16 minutes ago, housemtnTN said:

So snow in the tn valley is basically a crapshoot at the moment?

I've been trying to educate myself on what makes this particular area so difficult to forecast, it's really fascinating to me.

The warm nose that Holston mentioned in a prior post is often a problem for valley areas. It tends to be more prevalent towards Nashville and from Chattanooga to Knoxville. In this case there's also a general lack of heavy precip on some modeling and that doesn't cool the column as efficiently.