Central/Western Medium-Long Range Discussion

[Chreeyiss]

25 minutes ago, jojo762 said:

18z NAM was incrementally faster than 12Z but verbatim it actually expanded the area of best parameters. The speed of the system, eastward movement of the dryline, in addition to the effects (and/or actual existence) of morning convection will all play a significant role in how Friday plays out. Euro/NAM both indicate a fairly active day across a large portion of the country. 

STP obviously does not present the whole picture, but gotta admit I was fairly impressed by this. Likewise, the tornado threat is probably limited by mid/upper level flow that is oriented nearly parallel to the dryline... However, if the system ends up just incrementally slower, we could be talking about more favorable wind profiles.

Ive seen discussion on other sites, as well as a couple of AFDs that courser models tend to be a little overzealous in mixing the dryline eastward. I like the prospects of how that might give us a better setup than the models currently depict, but it does concern me that this episode might "sneak up" on the general public at the last minute, when the convective allowing models finally get within close range. And only a few hours' difference in timing could have pretty big implications on wind profiles as you mentioned, as well as CAPE. 

[bjc0303]

Hard to write off tornado potential for Friday. Personally I have seen this song and dance in recent time and expect this to shift west such that CI along the dry line very well could end up along I-35 rather than on the border of the TSA region.

I do think OK sees first tor of the season Friday, but that will hinge on wind profiles aloft. Subtle changes in the flow, nothing which is impossible at this range, could enhance tornado potential in the mesoscale. Won't be chasing this one, but will be forecasting/nowcasting for it and enjoying the view.

[Quincy]

The models are converging and a severe weather event is appearing increasingly likely on Friday, particularly from eastern portions of the southern Plains into parts of Arkansas, Missouri and possibly Iowa.

Models bring a seasonably strong surface cyclone from the central Plains Thursday night to a position in the lower Missouri Valley vicinity by Friday evening. Ahead of a cold front, a plume of low to mid-60s dew-points is favored in the warm sector likely covering much of Missouri, eastern Kansas, eastern Oklahoma, Arkansas and East Texas. This would support at least a narrow zone of moderate instability, i.e. CAPEs of at least 1000-2000 J/kg, particularly along areas from eastern Kansas, southward to East Texas, immediately ahead of the cold front.

Due to cooling aloft, an upper level low approaches, convective initiation is expected during the afternoon with little to no capping, in a broad swath immediately ahead of the cold front and possibly in the open warm sector as well. It should be noted that the size of the warm sector is a bit of a question mark, leaving the greatest confidence to convection closer to the cold front. Areas displaced farther east may see more capping, along with less influence from the attendant upper level trough.

More than adequate deep layer shear for severe thunderstorms is a given with a >70 knot jet streak rounding the base of the upper level trough. Probably the biggest issue limiting this from a more widespread tornado threat is the largely unidirectional wind fields in the mid and upper levels. Forecast soundings up and down the region from southern Iowa to East Texas show relatively straight hodographs in the 1-6km layer, with some subtle veer-back-veer signals as well. With that said, there is enlargement of 0-1km hodographs, as near-surface winds ahead of the southwesterly mid/upper level flow should be S to SSE in the warm sector. Take it with a grain of salt, but NAM forecast soundings in a wide area do show a bit of a sickle-shape in the 0-1km portion of the hodograph, but show kinks in the mid-levels. There may even be a tendency for winds to back a bit above 500mb, so the lack of a more veering-with-height throughout the column profile suggests there are some limiting factors in place in respect to tornado potential.

There is some concern that convection may develop quickly over a broad area Friday afternoon with a tendency for storms to merge into line segments. Unlikely some recent severe weather events, mid-level lapse rates appear more modest, so large hail will probably be overshadowed more by the threat for damaging winds and isolated tornadoes.

In terms of storm chasing potential, the threat one does not exactly look to fall over favorable terrain, but there is some silver lining. Assuming the model progs do not speed up the system, then eastern Kansas may get in on the action. Eastern Oklahoma and other points east are far from ideal. The Iowa vicinity is a bit more of a wildcard, depending on how the surface low evolves. If a more wound-up low moves across Iowa, there could certainly be a play near the surface low/triple point. If the low is more elongated, like some data suggests, then I would be concerned about limited instability and messier storm modes with northward extent.

Mesoscale details can be ironed out as the event nears, but the general area surrounding the AR/KS/MO/OK border region seems to have the greatest likelihood for severe thunderstorms, near and just ahead of the cold front. Issues arise further north (Iowa) and it's unclear how convection may evolve farther south, away from stronger large-scale forcing (East Texas).

Given the synoptic pattern, at least scattered severe reports (including all hazards of hail, tornado and wind) are likely. Storm mode expectations lead me to believe that the window for tornadic supercells and large hail may be relatively narrow, but wind fields suggest that brief tornadoes may remain a possibility later in convective evolution, even if storms consolidate into a line or line segments. Damaging wind could end up being the more widespread story, given the strength of the expected wind fields.

[Chinook]

Yes, it looks like Kansas and Oklahoma are in the game. The last 2 runs of the NAM show some 2000-3000 J/kg of CAPE (or more like 1500 J/kg at 00z) in a narrow east-west zone (see STP chart posted above). This is much more CAPE than the GFS was forecasting in this area. So perhaps the SPC will eventually extend the slight risk to far northeast Kansas, northwest Missouri, and parts of Iowa. I think a dryline will extend up to Tulsa, and a cold front will be the forcing mechanism north of that.

[jojo762]

00z NAM definitely shifted west a bit. Also upped the ante a noticable amount from Eastern Kansas into Southeast OK, also showing a potential dryline bulge somewhere from E OK into SE KS... Most significant change this run seemed to be in the QPF fields supporting more of a scattered discrete/semi-discrete supercell mode along the entire dryline. Really curious to see what the SPC does with the D3 outlook. Almost certainly will expand the SLGT risk area north and westward (pending the Euro), and perhaps add an enhanced risk area (which seems warranted for at least large hail and damaging winds if not tornadoes too) somewhere between eastern Kansas and southeastern Oklahoma.

NAM forecast sounding from near KC at 7pm Friday, clearly some backing above 500mb but it seems doable. However, that is a very impressive -- almost ideal, low-level hodograph. All with very low LCLs and very impressive low-level instability. If we get discrete convection that isn't messy and/or closely spaced (leading to deleterious storm interactions), its hard to believe we wouldn't be able to get low-level mesocyclones on almost every storm capable of producing tornadoes, some potentially strong and long-tracking.

[andyhb]

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.

[Radtechwxman]

Why isn't there a thread for this event yet? Just curious

[bjc0303]

Well, I am pretty intrigued in the Thurs/Fri timeframe for a severe weather event over the high plains. Big differences between ECMWF and GFS ensembles.. but worth keeping an eye on. Won't bother posting deterministic guidance from GFS with apparent differences between both models, but if that verified I'd be out there no question.

[bjc0303]

15 hours ago, bjc0303 said:

Well, I am pretty intrigued in the Thurs/Fri timeframe for a severe weather event over the high plains. Big differences between ECMWF and GFS ensembles.. but worth keeping an eye on. Won't bother posting deterministic guidance from GFS with apparent differences between both models, but if that verified I'd be out there no question.

Day 7 outlook and I can’t say I’m surprised at all. The general threat area has been highlighted well by most guidance. Considering GFS likely underforecasting instability, forecast wind fields on the GFS/ECMWF look pretty impressive..by 21z. Going to be one to keep an eye on. 

[andyhb]

4 hours ago, bjc0303 said:

Day 7 outlook and I can’t say I’m surprised at all. The general threat area has been highlighted well by most guidance. Considering GFS likely underforecasting instability, forecast wind fields on the GFS/ECMWF look pretty impressive..by 21z. Going to be one to keep an eye on. 

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.

[bjc0303]

16 minutes ago, andyhb said:

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.

Which is my biggest concern. Time of year says amplification is a big worry. 12z euro while still impressive did not have the best overlap between instability and shear. 

 

If we can get it worked out, would be a pretty nice event I’d think. Shear vectors would favor discrete mode as progged by both GFS and ECMWF. Low level shear looks very impressive, so here’s to hoping it all lines up. 

[andyhb]

1 minute ago, bjc0303 said:

Which is my biggest concern. Time of year says amplification is a big worry. 12z euro while still impressive did not have the best overlap between instability and shear. 

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

[bjc0303]

Just now, andyhb said:

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

For sure. I definitely think an event happens, just would love to see us maximize our potential for once lol. 

[andyhb]

Just now, bjc0303 said:

For sure. I definitely think an event happens, just would love to see us maximize our potential for once lol. 

On the other hand, the CMC and UK have basically nothing because they aren't nearly as amplified with Friday's trough. Thing more or less just slides through the large scale flow as opposed to really digging.

[bjc0303]

Looking at individual members for Fri from EPS, I’m more encouraged. 

[WhiteoutWX]

GFS and EURO with sub-60 degree dewpoints even in west/central Texas has me underwhelmed for Friday. The low-level shear is good but that’s some pretty meager moisture for this time of year. I’ve been following this for days waiting for this aspect to improve but models have been very consistent. I find it hard to expect anything more than a low end threat exists at this time. 

Eventually the gulf will stop getting bombarded with crashing cold fronts but doesn’t seem like that will stop for the foreseeable future.

[Quincy]

32 minutes ago, WhiteoutWX said:

GFS and EURO with sub-60 degree dewpoints even in west/central Texas has me underwhelmed for Friday. The low-level shear is good but that’s some pretty meager moisture for this time of year. I’ve been following this for days waiting for this aspect to improve but models have been very consistent. I find it hard to expect anything more than a low end threat exists at this time. 

Eventually the gulf will stop getting bombarded with crashing cold fronts but doesn’t seem like that will stop for the foreseeable future.

Sounding climatology suggests that 60F dew-points would be high-end for the time of year.

MAF sounding climo suggests a 55F dew would move into the 90th percentile, while lower 60s is the max for the 64+ year period of record. 
At AMA, 50F is already well above the 90th percentile, with almost no soundings eclipsing 60F dews in April.

Remember that West Texas has a similar elevation to the CO/KS border region, as higher terrain does not necessitate higher dew-points as lower terrain areas. Dew-points in the mid and especially upper 50s would be sufficient. Mean mixing ratios of 11+ g/kg (which GFS shows) will get it done. With that said, I don't think there's any reason to believe this will be a major event, but it certainly has the ingredients for a respectable April event in the High Plains, assuming storms remain at least somewhat isolated. 

Let's keep an eye on it and see how moisture return looks. If it trends lower than it is now, then maybe we'll have a problem. At the very least. the setup should bring some much needed rain to the panhandle region, which has been plagued by a major drought and destructive fire season as of late.

[WhiteoutWX]

8 minutes ago, Quincy said:

Sounding climatology suggests that 60F dew-points would be high-end for the time of year.

MAF sounding climo suggests a 55F dew would move into the 90th percentile, while lower 60s is the max for the 64+ year period of record. 
At AMA, 50F is already well above the 90th percentile, with almost no soundings eclipsing 60F dews in April.

Remember that West Texas has a similar elevation to the CO/KS border region, as higher terrain does not necessitate higher dew-points as lower terrain areas. Dew-points in the mid and especially upper 50s would be sufficient. Mean mixing ratios of 11+ g/kg (which GFS shows) will get it done. With that said, I don't think there's any reason to believe this will be a major event, but it certainly has the ingredients for a respectable April event in the High Plains, assuming storms remain at least somewhat isolated. 

Let's keep an eye on it and see how moisture return looks. If it trends lower than it is now, then maybe we'll have a problem. At the very least. the setup should bring some much needed rain to the panhandle region, which has been plagued by a major drought and destructive fire season as of late.

I guess I should have been more specific as to which part of Texas I was referring to. I meant more in the Big Spring to Wichita Falls area which is at a much lower elevation. On closer inspection though the dryline will likely be much further west and you’re right those dews would go further at higher elevations.

And agreed on the much needed rainfall! Will help with ongoing fire fighting efforts in some of those areas as well

[bjc0303]

Yeah as far as the moist axis goes... it’s totally fine. The meager instability is not owed to the quality of moisture (at least not near the dry line). 

[andyhb]

With a pitiful pattern it looks like heading towards May I might add. Upper flow over the CONUS dies with the unfavorable +dAAM/dt tendency.

A lot of bad in the CPC analogs too with 2006 and 1987 showing up at/near the top (easily two of the worst Mays for chasing).

[CheeselandSkies]

51 minutes ago, andyhb said:

With a pitiful pattern it looks like heading towards May I might add. Upper flow over the CONUS dies with the unfavorable +dAAM/dt tendency.

A lot of bad in the CPC analogs too with 2006 and 1987 showing up at/near the top (easily two of the worst Mays for chasing).

Can I rage quit the atmosphere?

[HailTracer]

The program "2018instability.exe" has stopped working. Please restart.

[bjc0303]

I don’t care too much for the analogs honestly. Severe wx depends too much on mesoscale factors to even care, in my opinion. People are crying too much about things we have zero control over and little (if any) predictive ability over. May could suck, May could also go out with a bang a la 2013. We won’t know for weeks, so as awful as the pattern looks ahead (and it does look quite awful), we are nowhere near reaching any respectable level of predictability wrt severe potential in May. 

The GEFS GWO phase space plots do have me somewhat concerned but again, even that hardly touches on May at this point. At some point it comes crashing down and climo wins out. If we still see progs like this by May 10th, then I’ll talk about reaching “awful May” status. 

[jojo762]

Even the CFSv2 looks god awful for the entirety of its run in May. Yikes... But like BJC said, we cannot accurately predict anything with any level of certainity at this point in time. But the current indications are fairly saddening. 

[WhiteoutWX]

22 hours ago, bjc0303 said:

The GEFS GWO phase space plots do have me somewhat concerned but again, even that hardly touches on May at this point. At some point it comes crashing down and climo wins out. If we still see progs like this by May 10th, then I’ll talk about reaching “awful May” status. 

Can you elaborate on why the GWO phase space plots have you concerned? From everything I’ve read Phases 1/2 are the best phases for tornado activity in the US. The current GEFS forecast has us solidly in phase 2 in about 5 days, with the long range taking it into high magnitude phase 2 territory. Is there something else you were seeing?

[bjc0303]

36 minutes ago, WhiteoutWX said:

Can you elaborate on why the GWO phase space plots have you concerned? From everything I’ve read Phases 1/2 are the best phases for tornado activity in the US. The current GEFS forecast has us solidly in phase 2 in about 5 days, with the long range taking it into high magnitude phase 2 territory. Is there something else you were seeing?

Need to look at bias-corrected GEFS forecast:

 

[Quincy]

At least we should finally start backing out of the historic fire weather concerns and exceptional drought in the southern High Plains. The operational models and ensembles are in very good agreement for at least 0.5-1 inch of rain by Friday night over a broad area that has seen virtually no meaningful precipitation since last fall. 

[Chicago Storm]

See you in June.

[Quincy]

41 minutes ago, Chicago Storm said:

See you in June.

I actually looked closer at the data tonight and it's downright ugly.

• The weeklies show AOA 500mb heights over the central/southern Plains for 35 out of 36 days between 4/26 and 5/31. 
• The CFS has all blue chiclets through May 3rd. (The CFS is not God, but it has support from other data)
• Overall synoptic pattern advertised on the GEFS/EPS over the next two weeks is not favorable.

To be cautiously realistic, there is some potential for the pattern to amplify a bit around the last weekend in April, but even there, some ensembles suggest that we get some sort of cutoff low over the California region, which would not be very favorable either.

Overall, the next two weeks, at least, look quiet. One cannot rule out one or two days that either overperform or come up on short notice, but aside from that, I'll go back to sleep as well.

[WhiteoutWX]

There always the chance for late May magic, I’m reserving calling the season for at least another few weeks, even as bad as things look at the moment.