griteater

So the MJO deals with where convection is being enhanced / suppressed in the tropics, and this typically has a large influence on the EPO and PNA patterns across the Pacific and North America. For this time of year, when the convection is enhanced from the Eastern Indian Ocean, to the Maritime Continent (Indonesia), to the Western Pacific (phases 3-6), a +EPO / -PNA pattern is favored (central / eastern U.S. ridging). When the convection is suppressed in those same regions (phases 7-8-1-2), a -EPO / +PNA pattern is favored (central / eastern U.S. troughing). But that is what is "favored". Other processes will influence the overall pattern. With the NOAA MJO update I posted a few pages back, they favor the MJO making a quick trek through phases 3-4-5 in week 1, before making a move toward phase 7 in week 2, and they state that the MJO is not expected to have a large influence on the pattern. In spite of that, for a cold eastern U.S., we never want to see the MJO in the warm phases (3-4-5-6), so it remains to be see whether forecasted -EPO / +PNA patterns come to fruition - https://www.americanwx.com/bb/topic/51836-mid-to-long-term-discussion-2019/?do=findComment&comment=5117686 The MJO does have some influence on the AO and NAO but the processes which produce AO/NAO blocking are complex and can be largely separate from the MJO, including stratospheric influences.

The day 15 EPS analogs have both Atlanta Snowjams, lol - Jan 1982 and Jan 2014 (image courtesy of @commoditywx)

From NOAA's latest MJO Weekly Update...

Winter temperatures to date

I asked Anthony (HM) about him seemingly predicting the upcoming polar blocking. Obviously, the Euro Weeklies and other weeklies are showing it, but it's nice to see that he feels there are legit physical mechanisms for the blocking. So when he says momentum loss, my interpretation is that he is referring to typical strong westerly flow in the upper atmosphere and stratosphere slowing down (post-SSW effect and other processes I'm sure), which opens the door for waviness in the flow and blocking. Also, he mentions typical Nino trough/ridge positioning to go along with the blocked flow (western ridge / eastern trough).

Last Thursday's Weeklies (above) compared to tonight's for the same dates (Jan 24 - Feb 13)

^ -NAO is much better in the analog composite compared to the actual EPS

In the meantime, here are the top 10 analog match dates (your favorite Mack, lol) for day 11-15 from the 12z EPS (courtesy of @ChrisDevitoWX) 12z EPS Day 10-15

It’s happened before - Jan 1994. Rainstorm sandwiched in between 2 big arctic blasts with single digit lows. 500mb configuration has to be right along with having the cold air

Yes, it was an official SSW with zonal winds reversing from westerly (+) to easterly (-) at 10mb in the stratosphere averaged over the globe at 60N, and also occurring at a time when the strat PV should be at its strongest of the winter. The wind reversal has lasted 10-11 days now and may end in a week or so (pending). The red/purple/orange line is this year. The blue line is last year, where the SSW wind reversal lasted 17 days in February. I don't know of the exact definition of an SSW split vs. displacement, but I would think this one qualifies as a split just based on the 10mb height images. However, it wasn't a violent split like we saw last year and in other years where there is strong heat flux that comes up from the troposphere in conjunction with heat flux in the stratosphere. With this one, the heat flux that weakened the strat PV was focused in the stratosphere alone - note the focused orange colors above 100mb in the stratosphere near Christmas. As far as the SSW's effect on the AO, we see that the effects have been hard to come by so far. "Northern Annular Mode" here is essentially the AO, so the blue coloring shows that the AO has turned negative in the stratosphere, and is trying to work its way down into the troposphere on the right side of the image, but it remains to be seen how forceful it will propagate downward.

Here's the WSI version of the Euro weeklies. Week 4 looks fantastic

Anthony Masiello tweets: "Stage 1 is complete (poleward, fast, less split jet stream with lots of Tropical Heat). Stage 2 has started (an increase in wave activity, loss of momentum and continued splitting of mean NH jet). Stage 3 is enhanced STJ/westerly AAM phase (think November)." "What is coming ahead is analogous to getting favorable intraseasonal oscillations at peak tropical season in early Sep. Predicting hurricanes in early Sep is kinda meh. Well, late Jan into early Feb will have favorable intraseasonal state for winter in E-C US/UK."

The best period on tonight's Euro Weeklies runs from Jan 24th to Feb 13th

Just don't have enough well-entrenched cold air to the south. We want to see both Tennessee and North Carolina full of cold air prior to the storm as opposed to cold air retreating in TN and hanging on via cold air damming in NC as the storm approaches. Cold air damming is great to have, just need it cold in TN prior to the storm as well for more snow.

Yeah GFS run was similar...it was a little warmer in the E Piedmont Canadian was colder at the sfc with freezing rain down into SC

Both NWS offices have become more apt to be bullish in the extended range over the years. Not sure why that is, but in the old days, they were typically conservative until it got close in.

The Greenville NWS "changes everybody to rain" wording is a bunch of bunk IMO, especially for the hardcore CAD areas in the foothills. Yeah, Raleigh NWS is going with more of a Miller A with mostly snow where temps allow and Greenville NWS is going with the Miller A/B Hybrid, mixed bag scenario. I favor the mixed bag scenario, but not "changing to rain in all areas".

New Euro Weeklies

Yeah GFS bumped south this run - puts more folks in NC in play for wintry precip this run compared to last

Happy hour GFS coming in - 500mb suggests this isn't going to be as far north as last run

Looking at the Euro Ensemble Trends thru today's 12z run, the western U.S. ridging and the amplitude of our storm wave over the Mississippi Valley have increased (at least on its backside)...but the storm wave is trending more positive tilt - so the amplitude/tilt trade off is kind of a wash. If you increased the amplitude, but kept the wave more neutral tilt, you'd have a farther north/warmer solution (but you can see that the angle of the height lines thru North Carolina really hasn't changed). The cold air damming signal is increasing as well, as to be expected. It kind of looks like a central/northern mtns, foothills, NW Piedmont (and north) wintry event at the moment IMO, but plenty of time for it to change.

From NOAA's Weekly MJO Update

I always find the whole self-limiting thing kind of funny. Like you said, if it's 28 degrees with NE winds and lots of steady precip, the only thing limiting is going to be the extent of the power grid. If it's 32 degrees, well that's a whole different story.

GFS is just more wound up with the storm wave closing it off over Missouri, so that throws the parent low up into Tennessee. Euro and Icon are more broad with the trough, with more of a weak Miller A sliding low

For the GFS and Euro, this fits well with their common biases nowadays IMO. It was opposite in the old days