December 2018 Pattern And Forecast Discussion

[1234snow]

I’m pretty sure the FV3 GFS incorrectly assumes sleet and freezing rain as snow on the clown maps. But it is colder overall. Even gives Chatty a front end thump of snow.

[TellicoWx]

7 minutes ago, 1234snow said:

I’m pretty sure the FV3 GFS incorrectly assumes sleet and freezing rain as snow on the clown maps. But it is colder overall. Even gives Chatty a front end thump of snow.

The algorithms each site uses varies to a degree, so you end up with two different totals from the same run. The difference between the 12z GFS and 12z FV3 is in the soundings. As the 850 vort passes over N AL/N GA, the GFS has a slightly stronger warm nose that pushes the temp between 700/800 above freezing, the FV3 is weaker and keeps the temp at that column right at or below freezing.

[TellicoWx]

12z GFS sounding @156 (rain) top vs 12z FV3 sounding (snow/sleet). On the GFS the DP has already advected warmer vs the FV3.

[TellicoWx]

Another view of the temp affection difference between the two, GFS (top) vs FV3 (bot):

[Chattownsnow]

wow, new Euro has me at 33F at the height of precipitation at hr162 now. Sooo close even for Chattanooga. This thing is trending really really well. 

[TellicoWx]

Still a long ways out, and things will trend one way or the other, but right now the key piece to me is how strong and where does the 850 vort track. The stronger it is the more advection and rain we see.

[Holston_River_Rambler]

I do like that the trend today seems to have to a more consolidated vort rather than a strung out one with the 500 center one place and the 700 and 850 another and washed out. Hope that is a sign of things to come. As Tellico says for 40 south folks it would help if nothing except the 500 center passed at our latitude 

 

[Carvers Gap]

Like I said, at this time frame a lot of options are still on the table.  Looks like the range right now keeps the forum alive for hopes of snow.  Very good 12z suite.  Of course, I am pulling for MBY, but if Chattanooga/northern MS/northern AL get hammered...I can live with that!  The folks in Memphis and Chattanooga get to see the rest of us talk snow and patiently wait.  They are over due!  I suspect the EPS should have some fun individual solutions as well.   That got pretty wild at the end of that event. Looks like part of it went OTS and the other part formed a coastal that goes to NC.

[Carvers Gap]

Bout all we can say today and bout all we can ask for at this time frame from the 12z model suite:

1.  System is south of us.  Check

2.  High pressure over the top.  Check

3.  Storm.  Check.

[BlunderStorm]

5 minutes ago, Carvers Gap said:

Bout all we can say today and bout all we can ask for at this time frame from the 12z model suite:

1.  System is south of us.  Check

2.  High pressure over the top.  Check

3.  Storm.  Check.

In other words that's the recipe.

[Carvers Gap]

4 minutes ago, BlunderStorm said:

In other words that's the recipe.

Unless it keeps trending south.  The Euro has trended south for like six runs straight.  The EPS will give us a good look.  I said it earlier, this is the time frame where weather models are notorious for losing storms or washing them out.  The end of the Euro operational was a bit wonky at the end of that event.  That hp over the top is 1039.  If real, that will not cut and will be held easily south.  But for us in the northern valley, we need it to turn the corner.  But really, I feel no different about this system today than I did two days ago.  I feel better that it might remain to the south of us(the low road).  The high pressure over the top is the question.  Do we get it?  If so, how strong?  But I have to admit, what a fun suite of models to watch today.

[AMZ8990]

2 hours ago, Carvers Gap said:

Those maps are about to give me a heart attack!  LOL.  That is my absolute favorite track to follow.  I hope(fingers crossed) that it continues to take the low road.  That and we get strong enough hp over the top.  I am pleased to see the trend of the hp coming back into play...it was absent a couple of days ago.  I remind myself that great solutions come and go at this range.  But yeah, I ain't gonna lie...I like a good clown map.  LOL.

Me and you both, ha!!  Clown maps are like a good side salad, it’s a great buffer before the main course.  Hopefully the main course leaves us all happy.  

[BlunderStorm]

4 minutes ago, Carvers Gap said:

Unless it keeps trending south.  The Euro has trended south for like six runs straight.  The EPS will give us a good look.  I said it earlier, this is the time frame where weather models are notorious for losing storms or washing them out.  The end of the Euro operational was a bit wonky at the end of that event.  That hp over the top is 1039.  If real, that will not cut and will be held easily south.  But for us in the northern valley, we need it to turn the corner.  But really, I feel no different about this system today than I did two days ago.  I feel better that it might remain to the south of us(the low road).  The high pressure over the top is the question.  Do we get it?  If so, how strong?  But I have to admit, what a fun suite of models to watch today.

I feel much better than yesterday about the system. The weather models have really went for the southern track in a big way. Right now a cutter is looking a lot less likely. Miller A's and Sliders are what I'm hoping for and that's what I'm seeing. There is plenty of time for the models to sort through this mess and with our storm in the pacific atm there is a ton of time for the NW trend. (Maybe too much time.) If this storm has to be a near miss I'd rather it hit south of here than north of here. I hate being excited for this as it seems too good to be true too far out.

[TellicoWx]

The algorithms on weather us site must be goofy, cause if not the Euro just told the FV3 "hold my beer, watch this" lol. 

[Carvers Gap]

3 minutes ago, TellicoWx said:

The algorithms on weather us site must be goofy, cause if not the Euro just told the FV3 "hold my beer, watch this" lol. 

WxBell has the same look.  Like I said, the storm gets wonky at the end.  The storm hits the coast and part of it "appears" to go OTS and then part of it goes to Hatteras.  Due to that, the storm pivots over the pink spot.  It could happen.  We are going to see some wild solutions as long as this stays where it is which is the low road.

Wxusaf stated in the MA forum that the confluence for this run was different which allowed for the different result.  Still, pretty fun to watch models spit out those kinds of totals.  

[BlunderStorm]

5 minutes ago, TellicoWx said:

The algorithms on weather us site must be goofy, cause if not the Euro just told the FV3 "hold my beer, watch this" lol. 

I dunno it showed persistent heavy snowfall for 48 hours in northern SC.

[AMZ8990]

33 minutes ago, Carvers Gap said:

Like I said, at this time frame a lot of options are still on the table.  Looks like the range right now keeps the forum alive for hopes of snow.  Very good 12z suite.  Of course, I am pulling for MBY, but if Chattanooga/northern MS/northern AL gets hammered...I can live with that!  The folks in Memphis and Chattanooga get to see the rest of us talk snow and patiently wait.  They are over due!  I suspect the EPS should have some fun individual solutions as well.   That got pretty wild at the end of that event. Looks like part of it went OTS and the other part formed a coastal that goes to NC.

Been hoping for a big dog storm for a long time now.  I can’t remember the last time we got over 4” In one storm.  If we could get into that 4+ range I would be ecstatic!! Lol

[Holston_River_Rambler]

Griteater just posted in the SE forum that EPS mean is south. Low in the mean goes from Brownsville, south of NO, to Jacksonville.

[Holston_River_Rambler]

Another person just posted a UKMET map with precip. that goes out to 168 and it looks gorgeous. 

Stole it. Hopefully they won't mind. 

[PowellVolz]

Interesting that this time last year parts of Atlanta had over a foot of snow and here we are again.


.

[TellicoWx]

Euro Ensembles say OP may not have been off it's rocker.

[Carvers Gap]

When you look at the individual EPS members, there are very few that have accumulations as far south at the operational.  There are also several slps north of the mean.  To me, looks like there is room for it to come north.   We need that high pressure to be strong.  The actual mean is quite good.  Against my better judgement this far out...here is that map.  We can use it for trends.  Pretty good look for Tennessee. 

 

[nrgjeff]

Monday edits in bold.

Few quick thoughts in case work load shuts me out of the Board Monday. This is a rare Sunday post. Here is my take on 12Z data.

1. GFS Para (FV3) is closer to that ECMWF run which slams MEM to CHA. Watching vort max track south and high press staying very firm north. No wavering!

2. ICON I infer is warmer most areas, less favorable esp south. Just one model and this is way out at its end at 180 hr.

3. Still a week out. I expect more shifts south; then, shifts back north. No idea where that ends up.

4. I have no reason to get hopes up yet this far south (CHA) but I'm interested and watching. I-40 still has better odds based on climo.

5. Yes the thunder then snow rule might verify. We laugh, but it has some meteorological reasoning. Both require amplified long-wave troughs, meridonal vs zonal flow.

Discussion in this thread is exemplary. Hopefully this builds up into a real event for most of us!

[Reb]

20+ members of the EPS show at least 2” for Central Valley of ETN. Not bad...I still think the warm nose will give us the screw job but there’s definite hope and worth watching. 

[Carvers Gap]

MRX with another great write-up...

.LONG TERM...(Monday night through Sunday)...

Extended period remains active with two main systems to impact
the forecast area. Monday night, quasi-zonal flow will dominate
the mid to upper levels across a large portion of the central
CONUS with a fairly compact shortwave trough moving off the Great
Lakes. Closer to the surface, an area of high pressure will begin
to move into the central plains with surface troughing across New
England and into the Mid-Atlantic region. Aforementioned mid-level
shortwave will begin to eject northeast as stronger mid-level
energy dives south into the Midsouth and Ohio river Valley.
Northwest flow showers will likely begin to develop as early as
Tuesday before coverage increases Tuesday afternoon/night.
Precipitation type likely starts out as rain or rain/snow mix, but
as cold air advection moves in and wet-bulbing effects cool the
column, expect a transition to snow. QPF remain light on all
numerical guidance with only a few hundredths of an inch progged.
Thus not expecting much in the way of snow accumulations with
mainly a dusting to maybe an inch in the higher elevations.

Surface high pressure quickly builds into the region Wednesday
through Thursday with a northwest flow regime aloft.  Would not be
surprised to see a few snow showers or flurries continue through
this period in the highest elevations where boundary layer moisture
(1000-850mb RH > 80%) still remains sufficient.  Otherwise expect a
drying trend as a low amplitude ridge moves through the Southeast
before another quick shortwave moves out of the Great Lakes Thursday
night.  An associated cold front will drop through the area and will
likely increase cloud cover.

The greatest divergence in numerical guidance occurs over the
weekend in what looks to be a significant storm system.  A lot of
inconsistencies in placement of synoptic scale features.  The
morning guidance speeds up the southern stream branch and keeps it
flatter, which is more in line with the ECMWF guidance.  Do expect
to see a large rain shield to develop from the south Friday night
and spreading northward by Saturday. Precip type continues to be
uncertain and wintry precipitation is possible across portions of
the area.  Any slight changes in the track of this system will
change the thermal profile and eventual precip type.

[TellicoWx]

Here's the breakdown on the Euro individual members: Loc / % 3+/ % 1+ (% 6+)

NE TN: 58/78 (28)

TYS: 42/56 (18)

CHAT: 52/70 (26)

PLAT: 62/74 (36)

MTNS: 72/90 (48)

Pretty decent numbers being this far out.

[Carvers Gap]

The 12z Euro has support from the JMA this evening.  Slider for southern areas of the Upper South.  Strong high over the top.  Grabbed that info(not verbatim) from the SE forum and agree.

[AMZ8990]

18 minutes ago, Carvers Gap said:

The 12z Euro has support from the JMA this evening.  Slider for southern areas of the Upper South.  Strong high over the top.  Grabbed that info(not verbatim) from the SE forum and agree.

JMA shows 850mb temps below freezing for the entire forum from HR120 thru HR168 as well.  Good look for sure.  

[BlunderStorm]

24 out of 50 give or take a few of the 12z ensemble members are winter storm material for me. The minor event preceding it makes it hard to determine if 4 inches falls or not.

[Carvers Gap]

Interesting trends at 18z, not all bad and not all good.  The high pressure is not as strong and positioned differently than 12z regarding the FV3.  In a nutshell, this allows the 18z GFS-FV3 to bring the precip shield north as mostly rain.  The plain old GFS is similar to the 12z Euro and slides the system to the coast with some redevelopment.  I know folks talk about confluence, northern stream influence, etc.  However, IMHO this is going to come down to how much high pressure is overhead, how strong the slp is, and indeed, also how it interacts with that northern stream.  I think the confluence is a by product of those things.  If we get the decent high pressure over the top, IMO someone in the forum area is going to see frozen precip.  But one can see the differences among the American suite at 18z.  The placement of that high is going to make a huge difference along with how long strong that high is.  That is just a complicated way of saying that we need cold air available that limits the progress north of the system and forms frozen precip on the northern shield.  Still, a long way to go with many twists and turns.