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NotSparta

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  1. NotSparta

    Teleconnections: A More Technical Discussion

    I like this part of the thread that I link above too, some explanation of why we may expect -NAO for the end of 2018 rather than +NAO
  2. NotSparta

    Teleconnections: A More Technical Discussion

    Another nice thread. tl;dr comparison of yrs w/ Scandi blocks & the Nov-Dec NAO values, between yrs that have +NAO and -NAO. 2018 thus far has featured little W1 & anoms similar to the +NAO yrs, but is quickly transitioning to something more similar to -NAO yrs.
  3. Weak clipper moving thru. Expected trace-2cm, about 1cm has fallen so far, currently 30 & SN. Big cooldown on the way here, some of the coldest values I've seen for November. Also, this is the second system so far this season to give us accumulating snow. The first time there was accumulating snow in 2017/18 was December.
  4. Wow, retrograding all the way from Scandinavia to central Canada. Really shows how weakened the tropospheric PV is
  5. Look for a brief warmup in around a week as a shortwave ridge passes by, then a negative trough with help from the blocking ridge that has retrograded all the way to the Baffin Bay
  6. Now, I'm not much of an expert so I can't really provide a very detailed outlook like some other posters have made, but I'll outline my thoughts here: From looking at PV graphics recently, you can see the pattern setting up that has the potential to persist for some time. The 10mb height shows a well-organized, strong vortex. As can be seen, the strat PV is quite strong - centered very near the pole, w/ an impressive gradient. Little disturbance can be found (though there is some slight displacement), and there is little sign of any WA. In most cases, this would mean the winter will be predominantly warm, w/ little blocking and progressive, Pacific flow. However, this assumes that the tropospheric vortex is in the same shape. As can be seen here, this is not the case. The trop vortex is quite different looking from the stable strat vortex. It is elongated, and while it is located near the pole, the strongest area is displaced into Siberia. It can be seen being affected by wave disruption, w/ areas where high heights intrude, and lower heights move equatorward, leaving a lopsided and thus weaker vortex. This is forecast to continue for the short-term (wrt seasonal timescales), where confidence is high enough to know. However, in my earlier post, it's likely that at least the NAO blocking will stay in place, which allows for continued disruption of the trop vortex, even if the strat vortex remains stable. Thus, it appears that the PV will be decoupled between the troposphere and stratosphere, so the stratospheric indexes may not be indicative of the patterns on the sfc, as is happening currently. The SSTs can also shine some light on the possible patterns. The NP has an area of warm water in the far northern area. This causes anomalous ridging in those areas, and sometimes CWB activity, leading to a -EPO. This thus causes height rises over the Western CONUS, which, w/ help from what could be the dominant NAO pattern, would help lower heights around the Eastern CONUS, leading to +PNA conditions. The effects of this on the pattern in general will be discussed later. Looking closer to home, SSTs can also shed light on situations during the season. Though a prolonged -NAO would cool off these waters, the currently anomalously warm waters near the coast exist. While very close to the coast, this may present more problems than usual w/ PTYPES, it provides more energy and moisture for passing storms. BREAKDOWN Region definitions: NW CONUS: Anomalous ridging and warmth due to -EPO patterns and +PNA. Below avg precip expected, as S/Ws move to the north and leave the area w/ less precip. SW CONUS: Near normal temperatures w/ below-near normal precip. El Niño pattern w/ strong STJ, and cool, wet wx partially overridden by EPO, PNA, and the dominant pattern this yr. Midwest - North: Near normal temperatures in the west w/ avg precip. This area will be the barrier between the warmth to the west and cold to the east. In the rest of the region, NW jet flow on the west side of the dominant trough w/ active storm track will cause below avg temperatures w/ avg-above avg precip. Midwest - South: Predominantly cool and wet conditions, due to strong STJ & nearby troughing, esp as you move to the east. NE CONUS: Cold, w/ periods of wetter wx. Core of troughing brought on by mix of interactions from NAO, EPO & PNA teleconnections act to only allow short periods of warmth. Regions in the eastern area of this box likely wetter w/ slow-moving lows sometimes traversing the region. SE CONUS: Cool and wet, strong troughing w/ stronger than avg STJ allowing snow events anomalously south. Possibility of more severe wx than usual in Florida, due to strong STJ and associated favorable dynamics, as well as anomalous temp gradients brought on by anomalous troughing to the north. Note: I am not a meteorologist. For official forecasts, please consult the NWS.
  7. yeah, signals are pretty strong for this thing. still hard to believe that such an event is coming directly after the lack of blocking patterns during the summer / fall.
  8. Before diving into what's going on behind the sudden reversal of NAO conditions (I'm finding the sudden favorability for blocking quite interesting), I have to show this loop of NATL pressure anoms as the -NAO begins to get into place, then matures. First, it's the seemingly age-old pattern that has persisted for months on end. Lows that get into the ATL quickly propagate eastward, due to the strong westerly jet that has been in place due to the +NAO/AO. However, it's quickly apparent that something is off. The red blob in the top-right becomes a bigger force, eventually beginning to retrograde, ripping apart the current gyre, one piece rocketing NWward, another indication that the strong westerly jet pattern is being disrupted. As the retrogration continues, some lows can be seen actually moving from the east, as the westerlies get eroded. Near the end of the loop, the westerlies are nearly gone; the major NATL low is actually stalled, and the NAO block is strong and mature. If you've looked at teleconnections this year, you'll likely have noticed something. The NAO (and to a lesser extent the AO) have been quite persistently positive. Other than the SSW-induced -NAO in March, the only negative NAOs have occurred when a zonal wave propagated across the Atlantic, causing Greenland ridging and very transient -ve NAOs. Obviously, this time is different. The most obvious factor is a Scandi block, which is associated w/ longer lived -NAOs. Higher SLPs/heights across the upper latitudes are also apparent, which is another sign of longer lived, stronger -NAO events. Something that'll keep it in place is its contributions to the surrounding pattern. As the loop shows above, it ends w/ a stalled and even slightly retrograding low. Obviously, you can't have the ridge move away in a progressive pattern when the pattern is completely jammed up. What else can end a -NAO event? There are many things that can, and one thing is ACWBs (anti-cyclonic wave breaking). The nature of them cause wave activity to move poleward. This forces the Icelandic low north into Greenland, and causes anticyclogenesis in the mid-latitudes, both of which act to cause the NAO to become more +ve. ACWBs have been king in the Atlantic this yr, w/ little CWB (cyclonic wave breaking) activity. This was one of the reasons there was little -NAO activity in 2018. Conveniently, a CWB event is expected to occur while the Scandi block retrogrades. Cyclogenesis in the mid-latitudes coupled w/ equatorward wave activity pushing the Icelandic low north, and ridging created to the north cause the NAO to be more -ve than w/o one. This expedites the arrival of the event, and given a pattern w/ more of them, would help lengthen it. So I've explained why it will be long-lived, but how did it even occur in the first place? The pattern that has been in place for months has been against exactly what is occurring right now. Luckily, this can be explained. A rise in AAM and MT has occurred, leading to a NP jet extension. The Scandi block formed, and the events in the Pacific have caused a more El Niño-like response in the ATL, w/ equatorward wave activity and a better environment for CWBs. Thus, a recent major atmospheric change has created much better conditions for a -NAO/AO, and when they get established, conditions look good for a long-lived event, helping chances for a bigger start to the winter.
  9. Seems that basically, the wavebreaking occurring is currently against -NAOs, but the type of wavebreaking is changing, which makes things much more favorable for a -NAO event that then ends up meaning a snowier cooler dec down the road
  10. NotSparta

    The Banter Thread

    Does anyone know where the AAM/MT charts are located?
  11. @antmasiello_HM has an amazing twitter thread about the transition from ACWB patterns over the ATL to more CWB and equatorward thus allowing for -NAO conditions
  12. I don't want a 95-96 repeat, but there are some similarities so I wouldn't be surprised for this winter to be similar
  13. Amazing horseshoe like pattern for blocking but the -EPO position causes there to be a trough it appears so that the PNA is more -ve which could make things warmer
  14. Yes, but I'm not too sure of the total. Going by how the snow has buried all but the very tallest blades of grass, probably about 3 to 3 1/2 inches. However, there is more on the way, so I could end up with something like 4 or so inches by the end, which is pretty impressive by Toronto standards in November, as there usually isn't enough moisture to produce this kind of precip which such cool temperatures if they occur.
  15. Decent rate of snow here, but that band is moving out soon. However it looks like something else formed behind it and is heading in this direction
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