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Pattern Nippy November

SD

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It’s like Shane pointed out . The model uses algorithms in order to spit out a solution . You can’t just blanket a model and say it has a cold bias . There is a reason it spits out a cold solution . Now maybe there are flaws with how it comes up with those solutions but it’s not like it’s just spitting out cold to be cold


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Yup a cold bias is 5 models with the same setup and 1 model is 10 degrees colder and this happens over and over. A cold bias is a not model constantly arriving at a western ridge eastern trough solution past D5. That's a pattern flaw/bias that leads to a colder solution
 

weatherfide

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Haven't looked at any 12z runs, but I can probably fairly accurately predict how they look, simply based on this:

View attachment 26289
I thought the 12z GEFS was interesting, especially after 12/1. Just entertainment, though. I am looking forward to the chance of 1 to 2 more inches of rain. I missed the heaviest accumulations on the past two events.
 

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Yup:


View attachment 26291

View attachment 26292

GEFS mutes the signal a little bit in the LR, but still maintains the general pattern shape in place. Unfortunate. Hopefully, the EPS is better.
Yep. Below was the best I could find. 2014 ish. Cold -EPO, but no more -NAO. Right after this the trough goes into the west and ridging starts to poke up in the SE. Been there done that for the last 10 years. :(

1574360653731.png
 

GaWx

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By "cold bias" does that mean the pattern its modeling is correct and temp departures are being over estimated? Or is it not even getting the pattern right?
Excellent question! There's been during the 6-10 day a tendency for too much W US ridging along with too much E US troughing thus leading to a tendency for the E US to be too cold and some of the west being too warm. In essence, a good bit of this is the SER being badly undermodeled just as was the case last winter. The Maxar met (who is very smart and knowledgeable), as you'll see below, says that is still an E US "cold bias". But on top of that there actually has also been a same day cold E US bias. Here's this Maxar met's response to me, which was a reply to my asking the same Qs you asked as I wanted to make sure I wasn't mistaken in calling having too cold a pattern in the E US a "cold bias":


"Hi Larry,
Cold bias is used to reference the model being too cold versus reality. This could be for varying reasons, including a simple miss in the pattern (arguably what we see in longer range projections). Here is an example using the current 6-10 Day maps comparison to when the period was in the 11-15 Day period (note the Southeast ridge in the more recent runs compared to troughing when in the 11-15 Day):

That said, the model has also been too cold in its same day projections (i.e. morning projection for the day of), so some bias even when the larger scale pattern is figured out.

I hope this helps. Let us know if you need anything else."
 

Myfrotho704_

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Yep. Below was the best I could find. 2014 ish. Cold -EPO, but no more -NAO. Right after this the trough goes into the west and ridging starts to poke up in the SE. Been there done that for the last 10 years. :(

View attachment 26293
Hard to get both patterns at the same time, I’d take my chance with threading the needle with the -EPO before the pattern switches since a -EPO delivers our best cold, we have done that to much this past decade, also note the STJ undercutting the ridge/split flow, this is a good pattern for a miller B winter storm setup, little bit similar to early last December if I’m not mistaken
 

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Next tuesday/Wednesday the euro has a low pressure system in a favorable place for severe weather in the southeast 😶 prateptype_cat_ecmwf.conus.png
 

KyloG

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Excellent question! There's been during the 6-10 day a tendency for too much W US ridging along with too much E US troughing thus leading to a tendency for the E US to be too cold and some of the west being too warm. In essence, a good bit of this is the SER being badly undermodeled just as was the case last winter. The Maxar met (who is very smart and knowledgeable), as you'll see below, says that is still an E US "cold bias". But on top of that there actually has also been a same day cold E US bias. Here's this Maxar met's response to me, which was a reply to my asking the same Qs you asked as I wanted to make sure I wasn't mistaken in calling having too cold a pattern in the E US a "cold bias":


"Hi Larry,
Cold bias is used to reference the model being too cold versus reality. This could be for varying reasons, including a simple miss in the pattern (arguably what we see in longer range projections). Here is an example using the current 6-10 Day maps comparison to when the period was in the 11-15 Day period (note the Southeast ridge in the more recent runs compared to troughing when in the 11-15 Day):

That said, the model has also been too cold in its same day projections (i.e. morning projection for the day of), so some bias even when the larger scale pattern is figured out.

I hope this helps. Let us know if you need anything else."
Thanks for the response! That's kind of what I thought you guys meant but wanted to be sure.
 

pcbjr

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Unless every major model is really wrong, we're all going to be more or less a tad AN into December ... but two things: 1) models could be wrong (like when are they dead nuts on anyway?), and 2) there are potentially some good signs down the road ... so hang tough and enjoy the anticipation ... without having an aneurysm in the process of all this weather watching every 6 hours ...
 

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Here's a summary of the 12Z GEFS/EPS and what it portends for the SE US from my perspective:

- Both models much colder in the 1st 5 days of Dec vs the last 5 days of Nov, when they're all (including CMC suite) clearly warmer than normal
- For the 1st 5 days of Dec. averaged out, the GEFS is colder to much colder than normal whereas the EPS is near normal
- Based on a clearly cold biased GEFS in recent weeks (largely due to too cold of a pattern) and a much closer to reality EPS, which I think has recently had only a small warm bias, my educated guess is that Nov 26-30 will average solidly warmer than normal and that Dec 1-5 will cool off a lot to the near to slightly colder than normal category averaged out, which I'd take in a heartbeat. Betting on the B to MB of the 12Z GEFS would not be a wise bet.
 

Brick Tamland

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Here's a summary of the 12Z GEFS/EPS and what it portends for the SE US from my perspective:

- Both models much colder in the 1st 5 days of Dec vs the last 5 days of Nov, when they're all (including CMC suite) clearly warmer than normal
- For the 1st 5 days of Dec. averaged out, the GEFS is colder to much colder than normal whereas the EPS is near normal
- Based on a clearly cold biased GEFS in recent weeks and a much closer to reality EPS, which I think has recently had only a small warm bias, my educated guess is that Nov 26-30 will average solidly warmer than normal and that Dec 1-5 will cool off a lot to the near to slightly colder than normal category averaged out, which I'd take in a heartbeat. Betting on the B to MB of the 12Z GEFS would not be a wise bet.
Just in time for the Christmas season.
 

Ollie Williams

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Here's a summary of the 12Z GEFS/EPS and what it portends for the SE US from my perspective:

- Both models much colder in the 1st 5 days of Dec vs the last 5 days of Nov, when they're all (including CMC suite) clearly warmer than normal
- For the 1st 5 days of Dec. averaged out, the GEFS is colder to much colder than normal whereas the EPS is near normal
- Based on a clearly cold biased GEFS in recent weeks (largely due to too cold of a pattern) and a much closer to reality EPS, which I think has recently had only a small warm bias, my educated guess is that Nov 26-30 will average solidly warmer than normal and that Dec 1-5 will cool off a lot to the near to slightly colder than normal category averaged out, which I'd take in a heartbeat. Betting on the B to MB of the 12Z GEFS would not be a wise bet.
GEFS FWIW has a few members with a southern slider
 
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12z EPS looks great for early December. -EPO, -NAO, upper level high breaks down. This is actually good! It's still holding on what I was talking about last night. We may have a shot at a winter event some point in early December.
 

ForsythSnow

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Based on what?
Decembers have been mostly warm, and we are headed into a pattern that will result in transient warmth, but as soon as that -epo erodes the NAO, it'll open the door to the SER developing. Historically, when the models hint at it's arrival, it'll stick for a week or two. We may have transient cold in there but always bet the SER will overstay it's expected time. Also if you read, the supposed nice setup near the end of December is highly subject to chance and usually we end up being warm right until after Christmas before we chill.
 

pcbjr

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Decembers have been mostly warm, and we are headed into a pattern that will result in transient warmth, but as soon as that -epo erodes the NAO, it'll open the door to the SER developing. Historically, when the models hint at it's arrival, it'll stick for a week or two. We may have transient cold in there but always bet the SER will overstay it's expected time. Also if you read, the supposed nice setup near the end of December is highly subject to chance and usually we end up being warm right until after Christmas before we chill.
FS, I was about to reply to Brick with one word ... "History" ... but felt uncomfortable replying to a question directed to you. You expanded on the "History" thought very, very well ... ;)
Phil
 

Brick Tamland

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Decembers have been mostly warm, and we are headed into a pattern that will result in transient warmth, but as soon as that -epo erodes the NAO, it'll open the door to the SER developing. Historically, when the models hint at it's arrival, it'll stick for a week or two. We may have transient cold in there but always bet the SER will overstay it's expected time. Also if you read, the supposed nice setup near the end of December is highly subject to chance and usually we end up being warm right until after Christmas before we chill.
Okay, but so far the models have only shown the SER showing up for a little while. Right now it has been the opposite of what we're used to, with the SER showing up on the models only to be beaten back. Maybe this December will be different. We'll see.
 
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