andyhb

The 500 mb height gradient across the SW is total garbage for this weekend especially on the Euro and the most recent 18z GFS.

For now all I will say on that is a warm sector as extensive (with quality BL moisture) as is being progged by the GFS and Euro for Saturday generally yields problems in the cold season. A lot of details to be sorted out surrounding the influence of the strong SE ridge and the trough's ejection though.

12z Euro was showing a fairly significant severe weather setup (first of the year if it comes into fruition) over the Red River Valley eastward into the Arklatex on Tuesday.

Pending enough moisture return, Tuesday (9/19) could offer a fairly substantial severe risk across the Dakotas mainly. Consensus for a strong, negatively tilted shortwave pivoting east/northeast out of that large trough in the northwest with a broad, 40-50 kt southerly/south-southeasterly LLJ axis becoming established by 21z Tuesday. Don't see many problems with forcing for ascent (so much so that fairly quick linear transition is more of a concern than a cap bust), and if enough southwesterly 500 mb flow can overlap the LLJ axis, deep layer shear shouldn't be an issue either. Seems to me like it could be the first healthy risk of the "second season". Also, the primary trough/ULL remains in the west in behind, which could lead to further potential later in the week, although that's still TBD.

Georgia has gotten absolutely raked this year. It has fit with an overall SE shift closer in to verification with a lot of the threats through April.

Positioning of subtropical ridging is going to have to change here. It's anchored too much over the central US shunting the storm track north (almost reminiscent of a late June/July-type pattern) before any shortwave can eject into the Plains. Need to get that shifted east. So far this year, the Pacific jet has been overwhelming these western/central US ridging episodes with time. The cycles in AAM/MJO activity have been driving jet extensions generally towards the tail-end of the months. Some of the mid-range ensembles are generally indicative of this occurring again, but probably don't want that ridge to become too dominant in the meantime.

A veered low level jet to that degree would decrease convergence along the dryline and makes it harder for storms to form. Considering the forecasted EML, that would be a fairly substantial issue. If moisture is any less than forecast, that would really throw a wrench in it.

Can't say I'm not impressed with the 12z GFS on Tuesday in the PPA-CDS-FDR corridor. Those are some pretty hellacious looking soundings with a very high degree of turning between the surface and 6 km, very low LCL heights (we'll see how moisture behaves) and a pretty classic arcing dryline configuration. Synoptically, especially at 500 mb, there appear to be quite a few similarities to significant early season High Plains events in the past with a large, slow-moving ULL generally near/just east of the Four Corners. Dryline position will probably end up being west of where the GFS depicts it, and there seems to be some concern regarding displacement of the stronger 700 mb flow away from overlapping the effective warm sector. Oh, and there's definitely some indication of after dark problems, of which this region is no stranger to with early season events.

00z Euro might have enough instability for an issue in W IA/NW MO on Monday just eyeballing it. 500-1000 J/kg would probably be enough for some fast moving/low-topped cells with a tornado threat if anything can get going in that highly sheared environment on the western periphery of the LLJ. Might also be worth watching further south down the dryline towards KS/OK although better moisture would certainly be appreciated. GFS is too fast for the former threat.

Seems like a dipole severe event is possible Tuesday with the stronger vort coming through the Four Corners + dryline and then the lead low over the Lakes/OV. Cap does look breakable further SW and if you do get backing (deeper vort leading to stronger lee cyclone/etc.), the shear profiles become rather conducive for tornadic supercells. Deep layer shear is already on the high end across basically all of the warm sector.

Really going to come down to the strength/amplification of that polar shortwave dropping out of the Pacific NW and the incorporation of the ULL that is currently driving a rex block over AK and the Aleutians. This will largely determine whether the thing ejects in pieces and gets sheared out by the confluence resulting from the SE ridge (or the fact that the northern and southern streams are out of phase). Euro has definitely been raising my eyebrows for the past few runs though although the extent of the effective warm sector shrank a bit along with the strength of the LLJ with the 12z run. Chiclet chart earlier was hitting next week hard, with the strongest hit being Tuesday unsurprisingly.

Quite a bit of damage via the scanner traffic, was quite a strong signature associated with the QLCS now moving towards College Station/Bryan.

Seems to be a suggestion of severe potential increasing across the central Plains towards the beginning of next week. Broad cyclonic flow looks to become anchored across the western half of the country at 500 mb with periodic shortwaves passing through the flow leading to amplification of the LLJ. Should be sufficient instability for severe wx and perhaps supercells given the lack of linear forcing.

That southern stream wave ejecting this upcoming Tuesday bears watching for the southern Plains and perhaps one last kick at the can for the chasers there. The last three runs of the Euro have shown a setup that looks conducive to tornadic supercells in KS and N OK with a moderate LLJ and a respectable, sub-1000 mb surface low along with 40-50 kt 500 mb flow (the latest run also increased the instability). I am really a fan of these kinds of lower amplitude waves that tend to not force major height rises to the east and create conditions favorable for VBV profiles. The GFS is faster and less favorable, although it appears to be a progressive outlier among the full suite and even its ensemble mean to some degree.

If we get at least a piece of this ejecting into a typical June warm sector, yowza.

4/10-11/2001. High risk on 4/11 for IL/IA, fairly prolific tornado outbreak in the Plains/Middle-Upper MS Valley.

Well, there goes the Monday system on all four model runs tonight.

If that Euro run slows 6-12 hrs and the 144 frame turns out to be more around peak heating, can't ask for much more than a potent negatively tilted shortwave with a 60+ kt southwesterly/west-southwesterly H5 jet and H85-H7 flow of 40-50+ kts this time of year.

It's convectively contaminated.

Eh, this run of the Euro wasn't so favorable. Trough gets more blocked in the west and the waves tend to shear out as they eject eastward. Need the larger scale trough to make it further east on its initial amplification.

Last four runs of the Euro (and three runs of the EPS) suggest a more progressive pattern in the mid range than the GFS/GEFS with that large upper trough amplifying in the W later this upcoming week then ejecting eastward (or at least pieces of it) by 5/22-5/24 and really amplifying the flow fields across the Plains. Might be quite the start to many chasecations (including possibly mine) if it turns out to be more on the right track. Would like to see more multi-model consensus on this less blocked idea though.

Seems like most of the models aside from the GFS want to eject a lead southern stream wave that basically screws the setup by stealing away the LLJ from the second trough (i.e. Monday's system) and shunts moisture southward.

12z GFS is basically suggesting a potential outbreak over a large area of the central/S Plains on Monday. Thing that really gets my attention is how broad the LLJ axis is, with 40-50 kt H85 flow covering much of OK, KS and N TX ahead of the dryline. The low amplitude nature of the shortwave trough was another red flag. Looked at some soundings basically from I-20 north to I-70 and my eyes just about popped out of my head. Euro isn't as enthused, showing a more disjointed trough ejection with weaker wind fields overall, but still plenty of CAPE. Finding it interesting that 5/9 produces majorly (anniversary of last year's CO, KS and Cisco tornadoes) and now 5/16 may try to do it as well (Elmer).

While it could obviously screw things up like the wind fields, I'm less inclined to believe it portends a lack of moisture return, especially into the High Plains. We've reached the time of year now where any sliver of the Gulf open to poleward advection for at least a day means there likely will be sufficient BL moisture. If this was March, obviously it would be an exercise in futility.

50 kt LLJ over ICT on the 00z Euro at 00z Wed, shear seems to be ramping up here in the last runs. Not to mention there's already 2000-3000 J/kg SBCAPE at 12z Tuesday across a significant portion of OK and KS.