CAPE

Mount Holly updated AFD for severe threat this evening and tomorrow-

Yeah pretty much all the CAMs are onboard for tomorrow. Might be legit.

September edition of the CanSIPS is out. My glass half full overview- Overall it looks less torchy for the winter months than the previous run. For December, not a half bad look, and verbatim just about average temps. At h5 the positive heights in the EPAC are such that the mean ridge is decently placed..close enough for perhaps a +PNA at times. Beyond that the heights shift westward in Jan, but still not a terrible look for the east coast- maybe a gradient type pattern. By Feb the EPAC ridge is a monster, max +height anomalies south of the Aleutians, and whatever winter there was would be over. Up top, December looks like a neutral AO/NAO, Jan a somewhat +AO/NAO, Feb ++AO/NAO. So not much help in the high latitudes.

Slight risk today. From the Mount Holly AFD this morning- With sufficient CAPE and fairly strong shear expected (30-40 kt 0-6 km bulk wind difference) along with alarmingly high values of storm- relative helicity (150+ J/kg), I am concerned storms will be capable of producing severe wind gusts and possibly a couple of tornadoes. As alluded to, the threat is conditional on the degree of instability that develops, but the tropical nature of the vertical profiles suggests to me that CAPE will need not be that large to promote an environment favorable for organized/rotating storms. SPC maintains a slight risk of severe storms today across the entire region, and this seems reasonable to me.

If the NAM is correct, Saint Michaels may be close to 20" for the month by tomorrow. Sitting at 15.62" currently.

A snippet from the updated AFD from Mt Holly- Hot and humid into the early evening hours ahead of an approaching shortwave. Showers and thunderstorms over central Pennsylvania will continue to track east, and additional storms will fire up ahead of that main area. Temperatures remain in the 80s to around 90 with surface dewpoints in the upper 60s to low 70s. As a result, surface-based CAPE values are up around 2000 J/kg across Delmarva and from 1500-2000 J/kg across southern New Jersey and southeast Pennsylvania. Across Delmarva and southern New Jersey, DCAPE values are up around 1000 J/kg. 0-6 KM Bulk Shear is minimal, generally around 25 kt, but up to 40 kt across far northern New Jersey. Finally, PWATs are from 1.5- 2.0 inches. Thunderstorms moving into the unstable airmass, especially across the southern half of the forecast area, will become strong to severe, with damaging winds and heavy rain the most likely impacts.

Are you seeing a low level dust cloud kicked up as the heavy rain falls?

Too much inverted V. This will probably congeal nicely on the lower eastern shore.

Storms dropping southward to the east, storms dropping southward to the west... nada in between. Mostly what the latest runs of the mesos were advertising.

Just wait till winter.

Pretty good stuff here from Mt Holly- At 250 mb a subtropical jet was noted around KWAL with another ~90 kt speed max located over western Ontario. The subtropical jet is forecast to re-orient and center over the NC/ VA border. This would place the DELMARVA in a Left Front Quadrant (LFQ) or under upper level divergence. The northern stream jet is forecast to propagate east through the base of the trough axis and center over northern NJ. This would place central and southern NJ in a Right Rear Quadrant (RRQ), or upper level divergence. The jet structure isn`t completely coupled, but some interaction appears likely. At 500 mb strong height falls are occurring over central Quebec (~100 m) with mostly weak height falls across central NJ (~30 m). The overall idea is for this wave to continue to amplify as it digs southeast. The primary DCVA will be located over New England, and the northern Mid- Atlantic States. At 700 mb a weak wave was noted across the Great Lakes region and is forecast to continue to dive southeast towards WV and VA. Overall this wave feature appears to track too far south and west of the region to affect our area. Earlier this morning there was some precipitation that tried to move into the region from the west, but quickly fell apart. This has allowed for the entire CWA to be under mostly full sun for the entire day. As a result the entire area has destabilized, with the greatest destabilization being across the DELMARVA with ML CAPE values around 2000 J/kg. A surface cold front is currently located across west/central NY into western PA and is heading southeast. The orientation of the cold front will slowly transition from SW/NE to more of a W/E orientation. Forecast soundings continue to advertise mostly unidirectional tropospheric flow with effective bulk shear values around 25 kts. The latest 18z KWAL sounding was slightly different than initially expected with a descent amount of dry air in the 300/500 MB layer. Lapse rates in the 500 to 700 mb layer were around 6.6 degrees C though, with DCAPE values around 1000 J/kg. The general idea is for convection currently in central PA to continue to head southeast towards MD and the DELMARVA. The anvil storm relative flow vectors with these storms is easterly, and this can clearly be seen on visible. As the anvil debris continues to spread east, cold pool reinforcement and amalgamations appear likely. This means the convection will likely continue to take on a more linear appearance. The primary threat with these storms will be damaging winds.

The damaging wind threat looks legit for later today where convection develops/propagates. Pulled this forecast sounding off the 3km NAM . Steep lapse rates in the low/mid levels, dry air aloft, impressive Dcape.

Excellent write up. The bolded is the bottom line, and pretty much what I expected would be the case. Another "thought". With SSTs basin wide on fire lately, can a weak Nina even produce the same sort of atmospheric response as it would have say 20 years ago? At some point you would think a sliver of slightly negative sst anomalies would get overwhelmed, and have about the same 'impact' on the atmosphere as a neutral/warm neutral ENSO... more variable/less "typical".

Excerpt from Mount Holly AFD this morning on tomorrow's potential- As we move into the day on Tuesday, the weather looks like it will become quite interesting. Guidance continues to indicate a convective complex should develop Tuesday morning.. . A stronger shortwave will track from the Great Lakes towards the Mid Atlantic quickly during the day and push the convective complex towards the southwest. Strong deep layer shear, and steering flow in excess of 40kts should lead to forward propagating storms. Equilibrium levels will be quite tall and so storms will likely become quite tall with >40kft echo tops possible. With quite a bit of instability out ahead of the lifting mechanism, up stream initiation looks likely. As was mentioned by the day shift yesterday, wet bulb zero heights appear to be too tall to see large hail, so the main threat for any severe will be strong to possible damaging winds.

Since it is pretty clear we are heading towards a weak Nina for the winter at this juncture, how many weak Ninas/cold neutrals(just to expand a bit) over say the last 50 or so years have featured a -AO/-NAO for at least a third of the winter? Not that this correlates to above normal snowfall because we already know it doesn't the majority of the time with a Nina. Just trying to gauge the prospects of at least somewhat mitigating what will probably be a less than favorable Pacific, to at least improve the odds for some decent cold periods, and perhaps luck into a few well timed fluke events. Not that we will ever actually see a -AO/NAO in winter again lol.

Sorta like my bigfoot(Daryl) analogy with a -NAO.

Likely depends on the strength of the Nina. A moderate to strong Nina and +QBO likely eliminates any chance of HL blocking. A cold neutral/weak Nina AND a severely negative QBO may allow for either some HL blocking episodes or some favorable EPO periods, providing a mechanism for cold outbreaks in the east. PSU is saying his research finds no correlation, during a Nina winter, specifically between QBO and snowfall for the MA.

Not surprising. As I have said, the QBO correlations seem nebulous, but in theory it impacts the strength of PV, and thus potentially the AO/NAO phases, so I would expect to see better correlation(-QBO) during a Nino, when HL blocking episodes are more prevalent (and we tend to get more snow).

CFS is on one of its better "runs" lately, Big picture h5 for Dec and Jan look pretty decent, and is a 'believable' look for a typical weak Nina. Feb doesn't look bad either, but with the massive +height anomalies it has in the EPAC, there would probably be more of a ridge in the east, although it also suggests a -NAO lol.

This area rarely sees big snow totals from a Nina, but can do ok with smaller events and scraps, and sometimes make it to average. That is a hell of a lot better than the crap we dealt with last winter. Ofc you have to completely tune out the fact that places further north are getting hammered from miller Bs while our region mostly gets jipped. We are who we are here, and we sure as fuuck aren't NNE.

This is pretty much how it went in 2017-18. The early Jan period was memorable for folks in the eastern MA, esp right along the coast with the blizzard. The snow also stayed around for a week or so with the cold, before moderating a bit.

Something to keep in mind with the general gloom and doom/early predictions for a warm winter- wrt the "new" normal/base state of the Pacific, in conjunction with a Nina, it doesn't necessarily translate to a crap winter. The last Nina we had was just 3 years ago, and it did produce a very respectable cold period, the bomb cyclone, and for some of us, normal snowfall. My yard was literally right at or maybe a tad above average. Point being these changes in the Pacific certainly existed to some extent then, and this stuff waxes and wanes each season even if the general trend is headed in an 'unfavorable' direction going forward. Nina winters can be an exercise in frustration wrt snowfall for the MA, but an anomalous cold period. even in an overall warmish winter, does happen- we just need to time it up and get lucky.

The most reliable indicators we have about the character of winter are ofc ENSO, and then the recent persistence of the background state in the Pacific. At this point its hard not to have visions of a persistent pig ridge sitting over the EPAC exactly where we don't want it.

Chuck needs to expand on the stock market/crude oil correlation to the global weather patterns. He might be on to something. Probably cant be any worse than the SAI/AO bullshit.

The PDO seems to be heading back to a predominately negative phase, and it might stay that way for a while. I never know what to think of it anyway, as it is clearly a response to multiple influences, and not an atmospheric driver itself. Most of the patterns/temp/precip anomalies that the PDO is associated with, have a stronger correlation to the ENSO state itself. So I suppose it is an enhancer/moderator in certain cases. We have had a recent tendency for a massive ridge in the EPAC/suppression of the Aleutian low, and combined with SST anomaly persistence, seems to argue for negative phase. The ENSO has an impact on the elements that drive the PDO (like the Aleutian low). Looking at the distribution of SSTs associated with the -/+ PDO phases, it seems logical that the cool phase should be generally favored in a Nina, and vise versa, esp during stronger ENSO events. Ofc it doesn't always work out this way.