andyhb

https://twitter.com/antmasiello/status/698172872704028672 Brilliant,

This looks to be what most recent guidance has suggested.

Continued strong signal from the EPS and GEFS for a large western trough developing later next week, thanks to a very impressive jet over the Pacific and a lack of a blocking ridge along the W Coast. Favorable teleconnections with troughing in the Gulf of Alaska (+EPO and -PNA) look to be in place to get this moving into the CONUS. Wouldn't be surprised if 2015 has at least one last go of it in the severe department should this end up verifying, especially considering the location of the SE ridge axis out ahead and what may be quite a moist warm sector (especially by December's standards) by the time the upper level jet pushes eastward of the Rockies. Deep moisture trajectories on the Euro look pretty prototypical for what you would want to see in a cold season event, coming right through the Caribbean. Then it comes down to what character the trough ejection assumes, and whether it will be sheared out if the ridge amplifies too much ahead of it, or whether it amplifies too much and becomes too meridional. This is of course barring any complications from the active southern stream, i.e. shortwaves disrupting the return flow. The more reliable Euro has not been showing this to the extent that the NA models have though, thus has more instability. Regardless, as usual this time of year, the biggest question is always moisture quality and from what I'm seeing, this system does have a reasonably good chance of achieving that. With a very potent jet like this moving onto the W Coast, that is definitely an eyebrow raiser.

HGX had quite the discussion for Mon/Tues in their most recent AFD.

FWIW, the message I'm getting from basically every AFD I've read (OAX, EAX, TOP, LSX, SGF, ILX, DMX, etc.) is concern for just how dynamically impressive this system is, as I've stressed from the beginning with this thing. Troughs like this can and often do pull a lot out of very little thermodynamic wise. Then you start concerning with areas that actually have appreciable buoyancy like closer to the 500 mb low. I also noticed that the Euro was showing some better 700-500 mb lapse rates further south on Wed, although still very little CAPE.

I wouldn't be surprised if this thing peaks severe wise on Wed from 12-18z over the E Plains and Lower MO Valley. Both the Euro and GFS are showing some appreciable instability there closer to the triple point where colder 500 mb temps will result in steeper mid level lapse rates on the nose of the LLJ.

Instability looks rather low, what was once looking like a solid warm sector has shrunk into almost nothing.

This was changed upon further survey. Several homes that were bolted down to their foundations were swept away and these received an EF5 rating. Briarwood was discovered to have had multiple construction flaws and was downgraded.

Expecting a 2013-like fall any year would be a tall order, considering that year had not one but two really significant severe events (10/4 and 11/17). However, I would lean more on the active side this fall given that previous ones heading into Ninos have featured some substantial fireworks and especially if this new regime that has taken over the E Pacific continues deeper into October/November (i.e. Gulf of Alaska/western N. America trough).

The EF5 rating was at least partly based (haven't read the survey in awhile) on manhole covers that were thrown from their locations and also concrete parking stops.

Seems to be the suggestion of a rather strong shortwave trough dropping SE out of the Gulf of Alaska towards the early part of next week via the deterministic guidance (supported a pronounced lowering of the heights across the Prairie Provinces and N Plains on the ensembles in this same timeframe). Northern stream has been quite active this summer so this doesn't seem to be too farfetched. Does seem that there may be some low latitude troughing that could cause problems with moisture availability though.

Yeah that whole idea fell apart fast. Looks as if we'll go all of Spring and June without a high risk or PDS watch at this juncture.

Just a few thoughts about the 00z guidance (focusing on the operationals): There are two camps in this set of model runs. One, consisting of the Euro and GGEM, is more progressive with the closed low that breaks off the main northern jet branch in the NW in a couple days (this is mainly due to it not retrograding west as far) and eventually leads to a rather messy, disjointed troughing across the N tier of the CONUS late next week since the aforementioned low does not phase very well with the incoming southern stream that undercuts the Aleutian ridging. The other, potentially more volatile scenario is shown by the GFS and likely an extrapolated UK. These two model retrograde the closed low far enough so that it is not picked up by the northern stream for a slightly longer period of time (both in a similar position at 144 hours). It then (on the GFS) is picked up by the northern stream afterwards and phases with the southern branch more effectively, eventually leading to a very potent shortwave trough ejecting across the Northern Plains around D8-9 with some extremely impressive wind fields for June (and likely higher end severe potential as it seems a large reservoir of seasonably high instability will be in place for whatever does come down the chute then). In conclusion, while it seems all guidance would indicate at least some severe possibilities late next week (as they have for several days now), it's going to be crucial to monitor the evolution of this closed low off the West Coast over the next few days as it could have major implications downstream for the northern CONUS. Should also add that the northern stream shortwaves that eventually lead to the closed low being picked up are also highly important. Overall, a lot of moving parts and it should be awhile before anything is settled on.

Some of these longer range GFS/ensemble runs as of late have really fallen into the "holy crap" category.

Man 18z GFS has a trough with a 90 kt 500 mb and 120+ kt 300 mb speed max moving across the Northern Plains next week, that would be seriously impressive.

What I seem to be seeing on the recent ensemble guidance is a tendency to shift high latitude ridging eastward over central Canada past the first week of June. Should this happen, it would likely open up an opportunity for the Aleutian low to slide east and allow a relatively open path for its associated jet to the West Coast (with an accordingly active pattern downstream).

-EPO block is going to be a problem through the next week at least, need that to break down/slide east a bit so the jet from the Aleutian low can advance east. Until then, might be more nickel and dime setups vs. bigger events.

We still haven't had that bigger event/outbreak to accent the season yet. There will likely be moisture in spades, just a question on whether the Pacific cooperates. A northern shift will help with the EML situation, with more favorable 700 mb trajectories.

June 1957 and June 1958 also had some bigger events in the N Plains and Upper Midwest (F5 in Fargo on 6/10/57 and F5 in Colfax, WI on 6/4/58).

Late May-June 2004 showing up a ton in the CPC 8-14 day analogs today.

Not sure about the Euro weeklies, but the monthly forecast from the CFSv2 for June looks pretty favorable currently. Strong northern stream on the 200 mb U-wind anomalies plowing into the Pacific NW with net troughing in the Gulf of Alaska, cool temp anomalies across the western/central CONUS and warm in the east.

I'll send him an NARR loop of late May 04 if it helps.

Mark can you hack Ian's computer?

Might want to mention that there is a very nice W TX/E NM setup showing up next week (5/19) on the 12z GFS.

Gonna need a pretty deep eastern trough to have any appreciable affect on the Plains this time of year.