andyhb

GFS was definitely more promising than the 00z run though.

I'm pretty impressed with the overall synoptics with this system (especially the strong LLJ throughout the afternoon), looks like a fairly prototypical earlier season High Plains event. Also a strong LLJ like that will help counteract any negative effects the ongoing drought might have on moisture return. Need that lead system to both help recover the Gulf sufficiently after the FROPA this weekend but also stay a bit less amplified so as to not suppress the cyclogenesis/warm sector behind it.

Certainly taking more note of Friday with the recent model runs aside from the GFS (which looks to be too fast). The 500 mb winds over the southern half of the threat especially have definitely shifted more straight out of the SW as opposed to the SSW, partly due to the somewhat more positive tilt nature of the trough. Not all of guidance is indicating a wash out in the morning/early afternoon either now. Curious to see how far north the destabilization gets closer in proximity to the surface low, it seems possible that we could have an arcing band of semi-discrete storms up in that area. Low level shear should be rather favorable over most of the threat area, although I do have some questions regarding more boundary-parallel deep layer shear in some portions of the risk. Should note that a lobe of vorticity (especially apparent on the latest Euro run) on the SW side of the ULL may lead to pressure falls further south and subsequent convergence/low level wind response.

2010s post-2012 are fun, eh? This entire regime that we've been in for most of the last half decade has been very testing on my patience for following this stuff (and that says a lot). Fortunately there was 2016 to have success with chasing to keep the interest high, but aside from that, not a whole lot. All of this bupkis on Twitter/etc. about calling the season now isn't helping either.

The idea shown on the Euro/EPS mean is a more low amplitude pattern that doesn't necessarily mean a big SE ridge.

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.

Bumping this since it is the 5 year anniversary today and I've worked on some graphics in Python to display radar loops using both Level II and III data. One below is of the New Pekin/Henryville EF4 and then the West Liberty EF3 (two deadliest tornadoes of the outbreak).

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.