Bob Chill

I'm surprised on how violent the flip is and how strong the +ao looks on ens guidance now. Early Dec is usually a fight to get snowfall in the corridor. A -epo driven pattern without help elsewhere is not a good way to run a weeniefest. NW zones are in a much better place. Wouldn't surprise me one bit if we open met winter with a forum divider storm. Lol. I'm not stressed at all for the first half of Dec as any snowfall is usually a gift. However, I really don't like seeing features than imply we may have a rough go for an extended period. Guidance isn't just converging on a run of the mill +ao... it's converging on a quite strong +ao.

This is an abrubt regime change. Seasonal/weekly guidance has been showing a +AO Dec for a long time but seasonal guidance isn't exactly reliable. Eta: hot linking images is annoying on this site sometimes. I linked the current image at CPC but it's showing an old one. Eta2: here's the current ao gefs ens spread. https://imgur.com/a/kGAUv5w

Are we nervous yet? Lol Seeing such a drastic flip of the ao/nao could be a sign that this Nov is the headfake kind and not the early season clue month it can be. Opening Dec with a strong +ao is usually a bad omen. Way too early to jump to conclusions but won't lie... seeing all guidance converge on the same idea of a fairly robust +AO to kick off Dec is not a positive development. Entirely possible it all flips back to a blocked look quickly. Not going to overthink anything yet. Prime climo is still a month away.

This post is for @leesburg 04 Seems we now have unanimous agreement for an amplified -epo/+nao pattern during the first week of December. Should deliver some sig cold but that type of pattern can easily shuffle around to a disasterous pattern. Don't be surprised if meltdowns begin within a week.

GEFS continues to look very cold during the first week of Dec. -EPO driven patterns are volatile with temps so the smoothed mean can be deceiving in that it shows cold to very cold temps for the first 7 days of Dec. If the GEFS is right in transitioning to a -EPO driven progressive pattern the ground truth will be a series of fronts and big temp swings and not 7-10 straight days of cold weather. While the pattern isn't perfect or one that makes me think easy snow, the fact that Dec looks to start off with some sig cold shots is very encouraging. Haven't had a Dec kick off with legit cold around since 2013.

Helena's climate is like a desert. It's in the shadow of the rockies and doesn't get much precip in general. They don't benefit from upslope like denver, boulder, ft collins, etc.

Taking current d10+ ens guidance verbatim, looks like we play with some fire. Epo ridge is a bit too west and there's no coupled +pna so that implies some very cold air dumps right down into the rockies before bleeding east. There will be a battleground between airmasses. It's entirely possible the mjo is influencing the pna. Could be any # of things really. -PNA periods in late fall are as normal as the redskins having losing seasons.

If we lose the -ao/nao and get a massive epo ridge going like we're seeing it changes the way we can get snow. It's a tradeoff because we basically need sig temp help in early Dec. Especially I95 eastward. The big epo can def deliver big cold and it's looking more likely as we move towards Dec. The bad part of the pattern is cold highs will be on the move and luck/timing becomes more important. Rain, flawed, and mixed events are the most common during -epo/+nao patterns and they can be very frustrating with cold running away before precip. I'll only get worried if a shutout pattern shows up. Right now all signs point to early Dec not being hostile. Can't ask for much more than that.

My biggest question is whether or not the models are rushing or flat wrong about the ao/nao going positive in 2 weeks or less. The nao block coming up was totally missed from long range.

One thing that can be very misleading about ind ens member output is the resolution is lower than the op and if you loop the members that produce, some always do it in a way that's pretty much not possible irl. I agree about clusters though. Get a nice group of similar solutions and outcomes and it increases confidence in the opportunity. Conversely, if there are a few giant hits embedded in an otherwise crappy run the snow mean can be very misleading. One thing we can all agree on is ens member snow output is massively biased to the upside and is a very unreliable way to assess our chances.

Not that I think the GFS has discrete features modeled accurately d10-11 but the run is a great example on how we can still score with a -PNA. It's all about the NAO and 50/50. If the NAO is real then it could provide an extended window.

Check out the h5 loops on the 18z gfs & gefs and stare at Greenland. Starts in 4 days and never lets up through the end of the run

18z gefs is loaded with members showing height patterns that make me think snowstorms are possible in early Dec. Looks like an active pattern with plenty of cold near or overhead. STJ would be juiced on most of these solutions too

Yea, we seem to be getting played similar to last year except this time it's breaking in our favor. Cfs weeklies have been a total dog turd lately. Here's week 2 from a week ago: A week later week 1 looks like this: Completely missed the -nao from just 2 weeks out. Lol. Anyone who worries about the crappy look on the cfs for weeks 3+ needs to look at these panels and ignore weekly/seasonal guidance. My skepticism of Dec being good is slowly becoming confidence that we kick off met winter tracking threats in the med term.

Yep, the whole atmosphere is full of good and bad features upstream and down. Normally a tendency for a -pna is a dagger in our area with one exception... add in a -nao.

I'm excited about the med term and what it implies down the line... in just 4-5 days we should have the strongest -nao we've seen early during season since 2010. Complete agreement the upper level ridge closes off and parks for a while.

Yea man, I keep liking the entry into Dec more and more. The big epo ridge makes complete sense and is what I've been expecting to roll forward. The nao is even more interesting because it's in the med range and all models agree on it. These types of features can be stubborn and models don't do well with figuring out when it's going to relax. My gut says the neg nao will likely be stubborn and it's happening at a perfect time. We need extra help through most of Dec. Get the ao,nao, and epo working in our favor and it's actually not that hard to get an event out of it. I'm expecting the eps to cave to the gefs with the nao. We'll have a stout neg nao in just 4-5 days...

The numerical calc is 1000mb pressure but we all know what a good h5 look is no matter the numerical index. These type of long range op looks keep happening and it's intriguing. Not that I think the gfs is right or anything but seeing these solutions are a potential clue that an extreme blocking event is possible

I generally don't pay much attention to the SOI honestly. However, very unlikely for there to be a direct connect to the NAO. The only reliable precursor I know of for predicting a -NAO in the future is to have one in the present.

Strong agreement for a pretty strong storm cutting west leading into Turkey day. Right now it looks like the front will clear just before or on Thanksgiving. Delay that a little and the holiday could be really warm. Personally, I don't care one way or the other. If it's warm then fine and if it's cold then better. We'll have a clear view of early Dec by then and that's 100% of my focus. I'm warming up to the idea of a broad conus trough with enough blocking help to make it interesting. GFS/GEFS are going hog wild with a nasty -EPO ridge popping and a lot of ens members are showing cold to very cold temps in the conus stretching from the intermountain west to the east coast. GEFS has nearly unanimous agreement for a pretty stout -NAO building D5+. I'm impressed with how this month is shaking out and agree with PSU about how there seems to be some persistence building with features that have been sorely missing for quite a few years now. Majority of our snow events happen with a flawed pattern. Early Dec doesn't look like a perfect pattern or anything but so far it sure looks like one that can work out to me.

This is just for the eye candy aspect ofnthe panel. I don't need a reminder that it's d15+ on an op run. This is one way to turn a trough in the west to a big storm pattern. Lol

I totally agree and it could have sig implications down the line as climo gets better. As we start moving though Dec normal temp regimes can work here. A stable -ao/nao can overcome other flaws like a so-so Npac. Last year's pac base state was too much to overcome for most of winter but we had literally no help from above.

Simplistic view would be to just watch the EPO/PNA. We're going to be fighting those teleconections for at least a week it seems. Probably longer. However, ens are certainly hinting towards a -EPO reload and the PNA trough rolling forward. If that does in fact happen then our first legit "snow window" should present itself sometime during the first 10 days of Dec. OTOH- if we keep getting teased with a +PNA/-EPO in the long range only to have a hostile pattern dominate then it could spell trouble for at least a portion of Dec even if we do have some help in the AO/NAO domains. As I've said multiple times... I have mixed feelings about Dec as a whole. Kicking the month off with a window where it can snow would be our first win. If the AO/NAO continue to cooperate into late Dec then it's possible to overcome a sh!tty Pac. That's way too far down the line to speculate on. Let's finish shoveling our early Dec storm before freaking out about the rest of the month.

Hey man, my bong is too small and you don't hear me bitching about it.

Lol. Yea, it's tenuous depending on which way it breaks... My gut instinct is telling me that the -pna rolls forward and a -epo ridge builds. Retro the weeklies pattern and we're toast. Literally.... Eta: no sign of a se ridge popping and that's always a good thing.