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  1. 27 points
    Geopotential heights are likely to correct more positive over the PNA, NAO and southern AO domains as an ineluctable consequence of stratospheric alterations ongoing D10-12. By December 15th-16th, the geopotential structure alteration will have overspread most of North America and Greenland, as the stratospheric vortices are perturbed / displaced toward Eurasia. Robust w1 hit will impact the SPV via the felicitous tropospheric precursor pattern, and once the nascent blocking encompasses the NAO region, wave 2 will be enhanced again. This final follow-up w2 hit circa Dec 23-31 will be the primary opportunity to induce a technical SSW. I have thought that we'll come close, but near miss. Regardless, the tropospheric impacts will be quite significant. MJO should circulate should through p3, thereupon, rapidly losing coherency during passage in p4-5 by mid December. GWO should be back into/approaching phase 5 by about the solstice in my opinion. The momentum reversal processes are already beginning, as this negative/removal mini cycle will be efficiently overshadowed / dampened by the background, resuming +AAM state. +EAMT will increase in the coming week, with more rossby wave dispersion events and wly momentum injection. Classic walker cell forcing resumes again by the 18th, and we will see the retrogression of the GOAK trough into an Aleutian low position on or about December 20th/21st. As a consequence of which, temperatures neutralize/near normal by the 18th-19th, supportive of snow in the coastal Northeast as early as around the 18-20th, then cooler than normal air begins developing shortly following the EPO diminution via GOAK retrogression. December 20th-31st is colder than normal and active w/ an undercutting STJ, with SPV perturbation continuing. In other words, everything's on track. There are heterogeneous stances on initiation/timing among our colleagues here, but by and large, I see the disparities as fairly immaterial and we accord on the larger scale forcing mechanisms. Continue to keep in mind that the snapshots for D 11-15 in particular on the EPS and GEFS are not static, and expect those to improve for the 17th-22nd period (like many of us argued regarding the faster cessation of the warm-up, which is now effectively a few very mild days).
  2. 25 points
    Hi everyone, first time poster here. Saw this discussion and wanted to jump in. I recently finished my PhD in atmospheric science and a large aspect of it was data assimilation and observation impact. That latter topic, obs impact, uses numerical methods to quantify the impact that any arbitrary component of the total observing system (i.e., radiosondes, sat wind, amdar, etc.) may have on a particular forecast cycle. With that said, 1) fresh observational data is fully assimilated at every cycle (00z, 06z, 12z, 18z), it is not merely just data from the previous off hour (06z and 18z) runs; 2) there is not a significant skill difference between the main synoptic time and off hour runs; and 3) balloons make up a very, very small portion of the observing system, and any one platforms relative importance is completely flow dependent. It is almost impossible to determine a priori which system will be most important for a particular forecast.
  3. 23 points
    There's still a pretty large discrepancy between modeling, and most of it comes down to the direction of PVA and the strength/direction of the confluent flow. The 12z CMC had a pretty favorable solution for the MA and NE regions. This is for a couple of reasons. 1) Look at the direction of the 500mb wind barbs circled. They are right up the coast, which allows for PVA into the MA and NYC metro region. PVA is extremely important in the development of precipitation because of its ability to create divergence aloft. In the same way that an ice skater spreads their arms to slow their rotation while spinning to conserve momentum, an air parcel that moves from an area of high vorticity to low vorticity will also diverge. This promotes surface convergence, which then leads to precipitation. The WAA into the colder established air mass also leads to some frontogenic forcing over S NJ and SE PA, which also leads to enhanced precipitation. 2) Look at the direction of the 500mb winds over SE Canada and N NY. They are almost completely out of the east once they reach the EC's longitude. This allows for increased expansion of precipitation due to vorticity being able to advect northward more vigorously. Now let's take a look at a much different scenario aloft, the FV3 GFS: The positive features that lead to significant snowfall in the MA and NYC metro regions on the CMC are nearly gone here. 1) Looking at the 500mb wind barbs, one can see that the PVA is completely offshore once at Delaware's latitude. This means that favorable forcing is never able to reach far enough northward, and the N MA region gets no significant precipitation. This is partly due to the trough being much less amplified. 2) The confluent flow shown on the FV3 is much less favorable for significant precipitation, as it's a strong NW flow right into the N MA. Instead of the flow being southerly at NYC's latitude, it's almost completely westerly, which destroys any chance of seeing snowfall in the area. In my opinion, this feature is the most influential. If the confluent flow remains so, there is almost no shot at significant snowfall in the NYC metro. Overall, we want to see trends toward a less hostile flow out of SE Canada along with a more amplified trough. We have seen some of these shifts over the last model cycle, and there are sure to be dramatic changes in the modeled evolution of this storm, so hang tight. It's certainly something to monitor closely. This is already a major threat for the southern MA, and it could possibly become one up north, too.
  4. 22 points
    The second half of December has always held more potential, and to me, anything before mid month was/is a bonus. The principal inimical issue w/ this short range threat is the pacific jet extension induced upstream ridge collapse which halts downstream s/w amplification, reduces PVA, limits consolidation of energy, thereby obviating a more poleward climb of the sfc low. Yes, the confluence is robust, but if the PNA did not collapse prematurely, this would have been a snowstorm up into the N-Mid Atlantic. The fact that this threat appeared at the very onset of an unfavorable period was an issue. There's still time left for Washington DC to receive meaningful snow, but no one north of the Mason-Dixon line in my opinion (I'm doubting even DC receives much). Again, the problems seen with the storm itself are symptomatic of the upstream ridge deterioration, the provenance of which, paradoxically, is one of the very mechanisms that will aid in leading to significant SPV/TPV perturbation and resultant blocking in the second half of December.
  5. 20 points
    Here is a fresh pic from a friend in Brigantine, NJ:
  6. 18 points
    Long range ensemble modeling is beginning to see the favorable pattern forming for the final third of December into January. There are a couple of notable features here: 1) The strength of the blocking in N Canada into the Davis Strait and Greenland has become more intense in the past couple model runs. This is a direct result of the increase in strength of the modeled Scandinavian blocking over time. We've seen this story before, and if this comes to fruition, it will provide blocking in the AO and NAO regions. This is also a very defined signal for 300 hours out. 2) The lower than normal heights in the GoA and AK have begun to retrogress. This allows for higher than average heights in the PNA domain, which is much needed for adequate cold air into the E US. I am not worried about the ridging shown over the E US here, as long range modeling has overdone this ridging all season. There will be a period of moderation, but the SE ridge shown here will slowly wash out as time goes on, especially given the +PNA/-AO/-NAO. Also, any snowfall that occurs over the next week will help lower heights over the E US. The strong blocking shown is partly a result of the strong stratospheric warming and the subsequent perturbation of the SPV into Siberia. This displacement allows for higher heights to build into the NAO and AO regions, and since the blocking is also being driven from above, there is a higher chance of the blocking being prolonged. The warming is also becoming more prominent as we move closer to the end of the month, and this will increase the strength of the blocking signal as time goes on. As @Superstorm93 showed, the 12z EPS has the same idea with a strong SSW and resulting high latitude blocking. The lower than average heights in the S US shown by the EPS also indicate an active STJ. Overall, I am becoming more and more confident that the period from December 20 to January 10 will be an exciting one due to a much more favorable hemispheric pattern. There will be a relaxation, but it most likely last less than a week. Afterwards, the perturbation of both the TPV and SPV will lead to high latitude blocking, and the retrogression of the lower than average heights near AK will promote rising heights in the PNA domain. Buckle up.
  7. 18 points
    H5 evolution has changed dramatically again on the GFS. We are still in a period of very wild change among forecast model guidance and I would not be surprised to see major changes still in the forecast evolution of the storm.
  8. 17 points
    LOVE IT! Great surprise! Up to 7” for November and early decsmber...nice.
  9. 17 points
    Hey everyone, Just wanted to stop by and do a quick scan of an observation of something i've begun to notice on ensembles (GEFS, GEPS, EPS) and to add; those weeklies have merit. Look at this below; Does this look familiar in anyway pertaining to that anomalous High east of Greenland and centered over and near Scandinavia? That configuration was seen very recently.... I do ask to ignore the z500mb depiction across Alaska/Western Canada for now for the point i'm making. What you see in the composite led to over a 1 S.D. from normal (right below) in the negative territory. Below are the GEFS and the last 13 runs (could only fit an animated gif of one ensemble suite, but basically GEPS is almost a near carbon copy). EPS? Right below... (just couldn't add the gif either). What is the point? After carefully observing the z500mb rossby wave synoptic pattern while taking into consideration "smoothing" subjectivity from ensembles, it stands to reason that we're looking at a clear shift towards yet another potential retrogression/incipient positive geo. heights backing into the NAO domain. BUT, it's manifesting yet again near and within the vicinity of Scandinavia! Just look at the signal magnify with decreasing lead time! Did we not just experience this? (EPS...) But wait, now lets go back to the top and my mentioning of disregarding the ridging seen across AL/W.Canada. Below, just the top row is what you need to concern yourselves with (fig. a and b), as this study (published from Judah C. and partner - Justin Jones) essentially shows what the SLP depiction looks like BEFORE a PV displacement and then AFTER. Hmm, that looks awfully familiar! So, not only are we getting yet ANOTHER incipient signal from the Scandinavia region and its correlation to a retrogression/-NAO, but the type of pattern being displayed in the medium term yields distress of upwelling momentum (via W1, but increased support for a W2) towards the stratosphere. All of this while a "brief moderation" to the cold discharges, thus, if we add all of this together in conjunction with westerly momentum in the tropics about to deposit into extra-tropics/mid-latitudes, the period after ~12/18th-ish.... I say game on! (Sorry to take away from the upcoming storm and the great analyzations going on!)
  10. 15 points
    Regardless of the volatility, it does seem inevitable that there's going to be some sort of PV streamer enhancing the confluence at the wrong time for this storm to climb the coast. A bit frustrating to see this on all of the guidance, but it does make me think that this storm is not the same "inevitable northward trender" as some others in the past. This confluence also seems to come independently of our storm's amplification, as it remains so cleanly split from the flow. That also makes me wary.
  11. 15 points
    We hold... These are numerical solutions from a great distance covering a massive amount of space over time. It`s why you see volatility in every model when resolving the atmosphere. The reason you see " rogue " members hitting you are because when they are run with different variables or initialization`s their solution 5 days out can be drastically different than say a member closer to the mean. But that is all it takes. Even though you see a " trend " or a tightening of a mean that`s less favorable doesn`t mean the model isn`t showing you that option can`t have an equal chance to verify. And when it`s 120 hours away , you really have to wait until everything is absorbed. My forecast has been focused between the Philly and NYC corridor up I - 95 , more S , less N and I can`t believe that after all these years and seeing how things break down or come together in the 11th hour or the eastern seaboard , with so many different moving parts and multiple variables could someone dance at a 5 day solution and spike the ball. I am not moving until 12z Friday and that`s not wish casting , it`s simply waiting for all of the data to be absorbed. I hope for my sake there`s a fairy vort hiding somewhere.
  12. 14 points
    Act 1 winter 2018-19 will conclude after this weekend's major Lower Middle Atlantic/Southeast snowstorm. The scenario painted by the return of a generally positive EPO and periodically positive Arctic Oscillation (AO) has shown up for some time on the ensembles. A look at where we have been is helpful. Scene 1 saw a historic November snowstorm in parts of the East. Cities such as Newark and New York had their biggest ever snowfall so early in the season. Heavy snow blankets the New York City area (November 15) Scene 2 featured an exceptional Arctic blast for Thanksgiving Day and the day after. Central Park's 15° temperature was New York City's lowest November temperature since the mercury fell to 12° on November 27, 1932. Select record-breaking and record-tying low temperatures for November 22: Albany: 8° (old record: 9°, 1969) Allentown: 14° (old record: 15°, 2014) Bangor: 5° (old record: 11°, 1978) Binghamton: 3° (old record: 10°, 1989) ***Tied November Record set on 11/30/1976*** Bridgeport: 16° (old record: 18°, 1987) ***Tied November Record set on 11/28/1951 and tied on 11/23/1972*** Hartford: 9° (old record: 14°, 1969) Islip: 18° (old record: 20°, 1987) Manchester: 9° (old record: 12°, 1969) Mount Washington: -26° (old record: -11° set in 1969 and tied in 1987) ***Broke November Record (old monthly record: -20°, 11/30/1958)*** New York City-JFK: 18° (old record: 20°, 1987) ***Broke November Record (old monthly record: 19°, set on 11/30/1976 and tied on 11/21/1987)*** New York City-LGA: 19° (old record: 21°, 1987) Newark: 17° (old record: 19°, 1987) Portland: 6° (old record: 11°, 1888) Poughkeepsie: 10° (old record: 14° set in 1972 and tied in 1984) Providence: 15° (old record: 16° set in 1969 and tied in 1987) Saranac Lake: -19° (old record: -2° set in 1972 and tied in 1987) ***Broke November Record (Old monthly record: -14°, set 11/26/1938 and tied on 11/28/1951)*** Scranton: 9° (old record: 15° set in 1969 and tied in 1987 and 2014) Worcester: 7° (old record: 11°, 1987) Record-breaking and record-tying low temperatures for November 23: Albany: 4° (old record: 5°, 1972) Allentown: 11° (old record: 16°, 1964 and 2000) Binghamton: 0° (old record: 12°, 1989 and 2008) ***Broke November Record (old record: 3°, set on 11/30/1976 and tied on 11/22/2018)*** Bridgeport: 13° (old record: 16°, 1972) ***Broke November Record (old record: 16°, set on 11/28/1951 and tied on 11/23/1972 and 11/22/2018)*** Burlington: -1° (old record: 2°, 1888 and 1972) Hartford: 5° (old record: 12°, 1972) Mount Washington: -13° (tied record set in 1994) New York City-JFK: 15° (old record: 25°, set in 1949 and tied in 1964, 1972, 2000, and 2008) ***Broke November Record (old record: 18°, 11/22/2018)*** New York City-LGA: 17° (old record: 23°, 1972) ***Tied November Record set on 11/29/1955*** Newark: 13° (old record: 21°, 1932) Portland: 4° (old record: 7°, 1888 and 1978) Poughkeepsie: 6° (old record: 9°, 1989) Providence: 13° (old record: 14°, 1972) Saranac Lake: -17° (old record: -11°, 1932) Scranton: 5° (old record: 13°, 1972) ***Broke November Record (old record: 6°, set 11/29/1929 and tied on 11/26/1938) Trenton: 13° (old record: 16°, 1880) Westhampton: 6° (old record: 14°, 1964 and 2000) ***Broke November Record (old record: 9°, 11/24/2000)*** Worcester: 7° (old record: 9°, 1929, 1972, and 1989) Scene 3 featured a blizzard on November 25-26 that brought heavy snow from Kansas to the Great Lakes Region. That storm dumped 8.4" snow at Chicago and 11.7" at Rockford. Scene 4 saw an inverted trough bring a localized 3"-6" snowfall (with some higher amounts) to a portion of New Jersey, including Atlantic City where 4.8" fell. Scene 5 will star a major early December Lower Mid-Atlantic/Southeast snowstorm. There had been a window of opportunity during the first two weeks of December. By the time that period ends, Scenes 4 and 5 will have been put into the weather records books. That the northern Mid-Atlantic and southern New England regions will very likely miss out given the 500 mb pattern (which, in this case provided above normal lead time for the area at greatest risk of significant snow) does not mean that the potential did not exist. It did. Act 2, courtesy of the onset of a positive EPO, variable Arctic Oscillation (including positive values), and the MJO's move into milder phases will be defined by a pause. Typically, such pauses last 2 and sometimes 3 weeks. Unlike some recent Decembers, it does not appear that this pause will see exceptional warmth. It will likely see above normal readings in the means. Act 2 is not the closing Act of December, much less winter. Unlike such "non-winters" as 2011-12, the SSTAs in the Pacific favor a negative EPO. Those SSTAs are remarkably similar to those that were present during winter 2002-03. During that winter, the EPO went positive and remained predominantly positive into the first week of January. Afterward, it went negative and was largely negative through the remainder of what proved to be a very snowy meteorological winter. Already, some of the guidance suggests an end to the positive EPO that will likely develop in coming days. Whether the EPO will go negative toward the end of the December or start of January remains to be seen, as there remains uncertainty concerning the timing of such an evolution. Nevertheless, my guess has been and remains that the last week of December could feature a growing risk of wintry weather. First, the trough will begin to redevelop. The weekly guidance strongly suggests the development of a sustained trough in the East in the longer-term. As that happens, colder air will return and opportunities for snow will increase. The last week of December could be volatile as the pattern evolves toward a stable colder pattern--the kind of pattern that defined such winters as 1977-78, 2002-03, and 2009-10. During that last week of December, I believe it is more likely than not that New York City will see accumulating snow. Waiting might be challenging, but I believe the patience will be rewarded so to speak. At present, there remains no meaningful indication that the promising start to Winter 2018-19 will end in heartbreak. Overall, things remain on track for a very widespread winter with cold anomalies and greater than normal snowfall. The coming pause does not change things. It is part of a larger transition that will see the winter increasingly gain the attributes one has seen in past Central Pacific-based El Niño winters during which both Atlantic and Pacific blocking predominated.
  13. 14 points
    122 people be waiting for the next model like...
  14. 14 points
    To further this discussion, we can look at a fast-moving trend of the last 10 operational runs for some ideas as well. Two very notable things are clearly visible here. 1) The operational model has adjusted the northern stream disturbance completely out of the picture (this may change again, but it's trending away from that for now). Notice how the compressive heights and vorticity were in New England at one point and are now in Eastern Canada 2) There is a trend toward much more organization of the shortwave itself. This is a result of the above factor among other things, including a more amplified and better positioned Pacific ridge. Notice how much more organized the main disturbance appears as a whole 3) There may be other streams involved as well. As the amplification of the pattern becomes more clear and the mid/upper level jet streaks become more apparently, the models are suggesting some potential for phasing. All in all...we are still well within a period of major change. While i'm not exactly expecting a huge snowstorm here, and I think the overall pattern has some serious limits for us in regards to how "big" this gets, it's important not to fall asleep at the wheel here from a forecasting perspective. Major changes are still well within the realm of possibility.
  15. 13 points
  16. 13 points
  17. 13 points
    John hits the nail on the head with regards to recent trends & why operational and certain ensemble guidance may take time to hone in on what to expect from this system. Just to expound upon that a bit further... I think there have been some meaningful trends that we can entertain in the short/early medium range which have more credence right now than say an operational cyclonic vorticity/heights map 138 hours out. 1.) The initial 50/50 low has demonstratively become stronger as we've moved up on time across nearly all guidance. In association with upstream ridging (will get to that) - This assists in letting the pieces come together so to speak. The consolidation we're seeing in the medium range further out on guidance is evidence of this. Additionally, its position has moved closer to the actual 50/50 position as our various pieces of vorticity begin to culminate into a storm. If this was to stay too far south, it could act as a suppressive mechanism. I don't think it's coincidence that we see the CMC with the further north solution as it's position is higher in latitude vs other guidance. The confluence over southern QC/NE is further N, which allows the track to come north, as discussed ad nauseum on the board in recent times. Noting that this is the 0z run of the ECMWF vs the 6z runs of the FV3-GFS & CMC, it's of course six hours behind the FV3 with regards to the positioning. Yet you can still see a deepening low which positioned further NE when moving up in time. 2.) Upstream ridging (PNA) changes: The CMC has displayed a more amplified ridge in this domain with some intrusion into the EPO domain as well. Keeping the ridge axis further west before it begins to roll over allows for a slower evolution & more time for consolidation. The ECMWF is less bullish on this idea. So therefore, the downstream changes don't translate as favorably. The FV3-GFS tends to show a similar trend as the CMC, but is not quite as pronounced. 3.) Shortwave sampling... This can be a contentious topic sometimes. Thanks to modern satellite data, we do tend to get a decent idea of how these disturbances are going to evolve before they ever make it to land. But I do think there is something to be said for true sounding data. As the many different pieces start traversing over AK & Canada, that additional data should make at least a marginal different in how the models begin resolving the medium range. Marginal in a case like this may mean big differences downstream. 4.) Diabatic outflow: I made a joke on the banter thread of what the over/under will be on how often we'll hear "latest heat release" in the coming days. It's true, a potent enough system (especially a Miller A) featuring strong convection may vent out ahead of itself in order to increase heights off the coast in a scenario like this. Problem is, first, we need to see that consolidated system materialize & we need to see the confluence continue to trend weaker/further N. Once we do that, then we can start talking about more favorable positive vorticity advection & latest heat release assisting to give the surface low a chance to come north. We're far from that right now Meanwhile, the EPS has been rather consistent in its idea of a true southern slider. There's no denying that its a generally reliable model in the medium range. That being said, I don't believe we'll truly have a good idea on how far north, or south for that matter the surface low pressure ends up positioning itself until tomorrow night. The next 36-48 hours should feature some "model mayhem" to some extent as these features start to become clearer. That being said, I wouldn't expect any major changes on a model like the Euro right away, they'll mostly be incremental in nature. But yes, now is the time to start looking for those short range trends, if they're there of course. Stay tuned!
  18. 13 points
    There was a pretty notable trend toward a more amplified back half of this storm system on the latest GEFS. They remain extremely underdispersive as a whole, but it's always interesting to try to start and pick out some of the subtle trends or movements. The big thing we continue to see with this storm system is a trend toward a slower evolution with more consolidation. There are still a ton of moving parts involved from multiple streams. While the northward extent of the system is inherently limited by the pattern, it would be downright foolish for anyone (including operational forecasters) to ignore the potential for major track changes. The storm is still 5 days away.
  19. 13 points
    Surface, 500mb, 700mb, 250mb, frontogensis, temps, shortwaves, other semi important tidbits Hope that helps.
  20. 13 points
    Can't tell if Weeklies Control run thinks we're headed into a snowy period or not.
  21. 12 points
    This is coming. It will likely overwhelm the pattern. The PV will displace and possibly split. We will snow. We will snow a lot. Nothing else matters.
  22. 12 points
    Just for fun, and no, I swear I didn't look at this beforehand......check the progression of the Euro Control at H5: Then we start setting up for the next one lol
  23. 12 points
    And anticipating the rebuttal from any naysayers out there in cyberspace - yes, it's not a very cold pattern initially, but strong positive geopotential heights and warmer than normal z850 temperatures in Canada with an undercutting jet signal would probably yield surface temperatures slightly colder than normal (U30s maybe) with no precip, and in the lower 30s if we are precipitating. 850s are generally sub 0c on both the EPS and GEFS by the 18th-19th. We should be conducive for a winter event as early as the 18th-20th (in other words the pattern will support snow from this point onward).
  24. 12 points
    I know you all are kinda miffed about this threat, but I'm really happy. This could be the biggest storm I've ever seen (I've only seen a 9" storm, and when I was visiting family up north. I've seen 8" twice back in Raleigh.).
  25. 12 points
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