Central/Western Summer Medium/Long Range Discussions

[Jon]

I see some interesting hodos for day 3 in western OK....might be a little something before the main event! Haven't really seen the white/black on the CAPE output on Maue's models yet...impressive.

[1900hurricane]

00Z GFS reeks of weekend chasing road trip.

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[andyhb]

00z GGEM/UK also falling more into the Euro's corner.

[andyhb]

And the 00z Euro is backing it up so far, that is one monster trough on Sunday, might be a tad slower on Saturday, but still threatening nonetheless. Well organized surface low on both days, won't be surprised to see the D4-8 light up tonight.

 

With that said, it almost looks like one of those cases with this run where the in-between timing of the second vort makes D2 less favorable with the two surrounding days having higher potential.

[Radtechwxman]

Which setup are you referring to?

 

If it's 4/3 or 4/6-7, it was the veering low level winds (especially near the surface) that caused many of the problems there (also allowing further mixing in MO in 4/3's case), rather than the actual strength of the LLJ.

 

Also, sometimes you don't need really strong low level winds when you have high instability and 35 kts is more than sufficient in many of these cases (5/15/13 is a good example, although that setup was quite different from this one and not as impressive as the large trough involved here).

 

Yes those were the days I was referring to. I agree with you on that, the veering sfc winds were the main killer of tornadic potential. now that I have thought about it you are def right. with that kind of thermodynamics low level wind fields wouldn't have to be too strong for a tornado threat. 0z gfs was a major cave to the euro. lets hope this trend holds and we will finally have our first really solid chase days of the year. looks like we may get a brief lull after this system with a nasty cold dump behind it however pattern looks to reload. sometime around may 9th looks to have another threat. but don't wanna get off topic. my focus is def on this weekend.

[OceanStWx]

I think this is a perfect summation of where everything stands.  Let's not make this more convoluted and confusing by introducing massive amounts of conjecture and bad science at this point.  The bottom line is that if the pattern evolves along the more progressive route, we're dealing with a potentially big problem on Sunday and Monday.  If it becomes more amplified, the threat is less.  The more reliable guidance/more of the guidance is currently indicating the more progressive solution.  That could change, but that's where it stands now.

 

Sounds a lot like New England after a bad run of winter storms.

 

I do like what I see as far as overlap of lower level theta-e lapse rates and upper level winds go.

[jojo762]

For posterity 

 

day48prob (1).gif

Very disconcerting to see the SPC using that kind of rhetoric this far out. Albeit more than warranted IMO.

[Quincy]

A reminder that there's a separate thread now for the weekend threat. (which does look awfully significant at this point)

[brettjrob]

12z ECMWF brings a broad, low-amplitude trough into the western CONUS mid-late next week (5/6-5/8), with at least a couple days of Plains potential. There hasn't been a lot of consistency between runs or models for this period yet, though. Frankly, I'm just relieved to see that major eastern troughing will abate (at least for a period) after this weekend.

[andyhb]

12z ECMWF brings a broad, low-amplitude trough into the western CONUS mid-late next week (5/6-5/8), with at least a couple days of Plains potential. There hasn't been a lot of consistency between runs or models for this period yet, though. Frankly, I'm just relieved to see that major eastern troughing will abate (at least for a period) after this weekend.

 

Yeah the long-lived, Gulf-scouring runs from earlier clearly were off base as the main ULL lifted north.

[Chicago Storm]

12z ECMWF brings a broad, low-amplitude trough into the western CONUS mid-late next week (5/6-5/8), with at least a couple days of Plains potential. There hasn't been a lot of consistency between runs or models for this period yet, though. Frankly, I'm just relieved to see that major eastern troughing will abate (at least for a period) after this weekend.

The GFS is on-board as well with a multi-day potential.

[andyhb]

The CPC analogs almost appear to be a reload of the same pattern over the North Pacific that lead to the current event, with a very long, strong jet streak.

[brettjrob]

30/00z ECMWF has a stationary longwave -PNA pattern from 168-240 hours with a lee cyclone parked over E CO the whole time... wow. Wavelength isn't quite as large as I'd like to see (trough not far off the east coast), but we're finally getting to the time of year where that may not be a show-stopper.

[thewxmann]

I think moisture return could be a problem in the beginning of the period, but definitely towards the end of the period (closer to Day 10) there's quite a bit of potential.

 

I picked the wrong weekend to go out to the Plains. 

[HM]

A few interesting signals this year I wanted to throw your way:

 

1. The most widespread events, with a tendency to focus away from best chasing territory so far, tend to occur with a strong MJO/KW passage through the western hemisphere. At the same time, we are in a general relative maximum in angular momentum, but seeing a notable negative tendency on threat dates (makes sense with downstream, lee-cyclones in Mid Latitude Asia-America). These events include: 2/20-21, 3/27-3/28, 4/23-4/25, 4/26-4/28. If this pattern continues, the next potential may be around 5/20 +/- a few days for the next outbreak. The weaker the low-frequency wave, the weaker the response on our winds, jet stream etc.  

 

2. Plains-only events, that were somewhat tornadic, tend to occur during the weaker KW passages across western hemisphere as the MJO progresses through the niña-phases of the IO-Indonesia regions. This happened on 3/15, 4/2, 4/12-4/14, 4/20-21. Something like this is possible as soon as 5/16 or so, +/- a few days before the more low-frequency wave arrives a bit after. This will be the harmonic wave of the more impressive MJO wave that just passed through our longitude belt.  

 

3. The quiet periods have basically the opposite conditions mentioned above. So, presumably, this next week fits perfectly with that and it really has already started for the Plains. This is when the MJO-forcing is shifting back into the eastern hemisphere, GLAAM has fallen and the mountains relax.

 

After the last MJO wave in Feb, things were generally quiet until the next wave late March on 3/27, outside of 3/15 (which was non-tornadic). Things then were still very much in winter mode. I expect a more active post-MJO outbreak period, mostly because of climo. If this wave can remain robust through the nina phases, it will exhibit a 2013 like progression again. If it just falls to the nino-dominate stuff, there will be some chase days for sure but nothing significant. Pretty much, we'll repeat those events of early-mid April as the weakened pulse pulls through.  

[HM]

Just a small note: I wanted to focus on the LR, outside of where models can take us for the time being. Clearly later next week is a potential period of interest with the western trough being signaled. The MJO will have progressed into the IO and there is a jet extension day 6-10 across the N PAC. This leads to an amplifying high in the NE PAC and a downstream trough over western USA. It should allow for a couple of interesting days in between some boring stretches for sure.

[brettjrob]

Just a small note: I wanted to focus on the LR, outside of where models can take us for the time being. Clearly later next week is a potential period of interest with the western trough being signaled. The MJO will have progressed into the IO and there is a jet extension day 6-10 across the N PAC. This leads to an amplifying high in the NE PAC and a downstream trough over western USA. It should allow for a couple of interesting days in between some boring stretches for sure.

 

Good stuff. Your LR expertise is much appreciated, and a lot more valuable than the rest of us just picking at model solutions in the MR!

 

At this point, a two-week period on par with 2013 would be a godsend -- hopefully centered a touch more NW away from populated corridors, of course.

 

Any general thoughts on June and the influence of rapidly-developing Nino conditions? It's remarkable how inactive June has been through the heart of the Plains for three consecutive years now. The most recent ENSO analog, 2009, was quite active and in fact June basically amounted to most of the Plains season. Your last post a couple weeks back mentioned 72, 91 and 97 as the strongest analogs; all had June Plains tornado activity at least within the realm of climo and well above the past couple years (which isn't saying much).

[Ground Scouring]

Good discussion by HM, as usual. Models are definitely trending slower with the arrival of a large-scale Western trough pattern.

 

As an aside, the 12Z operational GFS and its ensembles have since 00Z shown a noticeable trend toward a flatter, more zonal/progressive pattern by day six. What seems fairly certain is that we will have a large EML establishing itself over the srn Plains in this time frame, with nice advection of a high-quality warm layer from the Sonoran region of nrn MX. We will probably see good, seasonably deep low-level moisture return from the Gulf at least two days prior to the possible event(s). Big issues continue to be timing and the possibility of capping, but so far the signs look good. In fact we may be looking at multiple events in the srn Plains based on the overall pattern.

[brettjrob]

Good discussion by HM, as usual. Models are definitely trending slower with the arrival of a large-scale Western trough pattern.

 

As an aside, the 12Z operational GFS and its ensembles have since 00Z shown a noticeable trend toward a flatter, more zonal/progressive pattern by day six. What seems fairly certain is that we will have a large EML establishing itself over the srn Plains in this time frame, with nice advection of a high-quality warm layer from the Sonoran region of nrn MX. We will probably see good, seasonably deep low-level moisture return from the Gulf at least two days prior to the possible event(s). Big issues continue to be timing and the possibility of capping, but so far the signs look good. In fact we may be looking at multiple events in the srn Plains based on the overall pattern.

 

Good summary. The consensus has perhaps shifted over the past 2-3 days toward a slightly "junkier," positive-tilt trough. Regardless, southwest flow atop at least seasonably decent low-level moisture should be in place for several consecutive days. This is the type of pattern that would be awesome to see in late May or June, when rich moisture is almost a foregone conclusion and marginally-favorable kinematics/dynamics give rise to great localized setups. At this point in the season, I'm not sure that we'll get great results unless a well-timed shortwave (lol at the very idea, so far this year) ejects one day, most likely Wed or Thu. As usual, widespread SW drought may compound any capping issues, but I'm sure we'll get at least one day of warm sector convection in the Plains.

[Ground Scouring]

Good summary. The consensus has perhaps shifted over the past 2-3 days toward a slightly "junkier," positive-tilt trough. Regardless, southwest flow atop at least seasonably decent low-level moisture should be in place for several consecutive days. This is the type of pattern that would be awesome to see in late May or June, when rich moisture is almost a foregone conclusion and marginally-favorable kinematics/dynamics give rise to great localized setups. At this point in the season, I'm not sure that we'll get great results unless a well-timed shortwave (lol at the very idea, so far this year) ejects one day, most likely Wed or Thu. As usual, widespread SW drought may compound any capping issues, but I'm sure we'll get at least one day of warm sector convection in the Plains.

With model consensus tightening, I've started a thread for May 7-9:

 

http://www.americanwx.com/bb/index.php/topic/43567-severe-threat-srn-plains-states-may-7-9/

[jojo762]

SPC Issued Day 6, mentioning Large Hail and Damaging wind being likely, with some tornado potential...

"AS MODELS BRING THE UPPER TROUGH EWD INTO THE PLAINS DAY 6 /THU 5-8/

HOWEVER...MORE COMPLETELY MODIFIED GULF MOISTURE APPEARS LIKELY TO

HAVE SPREAD INTO THE CENTRAL U.S. PERMITTING DEVELOPMENT OF MORE

SUBSTANTIAL CAPE. AS THE SURFACE LOW SHIFTS NEWD ALLOWING A

TRAILING FRONTAL ADVANCE ACROSS THE CENTRAL PLAINS

VICINITY...DEVELOPMENT OF AFTERNOON SURFACE-BASED STORMS APPEARS

LIKELY. WITH THE GREATEST JUXTAPOSITION OF FAVORABLE SHEAR AND

MODERATE CAPE LIKELY TO EXIST FROM ROUGHLY OK NEWD ACROSS KS/MO/IA

AND INTO IL AND SRN WI...IT APPEARS THAT INCLUSION OF A 30

PERCENT-EQUIVALENT RISK AREA CAN BE INTRODUCED ATTM WITH MODERATE

CONFIDENCE...WITH HAIL/DAMAGING WINDS LIKELY ALONG WITH SOME TORNADO

POTENTIAL."

[ZackH]

There's already a thread for the threat above.

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[jojo762]

There's already a thread for the threat above.Sent from my LG-LS980

Oh, whoops. Thought I was posting in the May 7-9 thread

[andyhb]

12z Euro actually brings yet another strong trough through the country's midsection from 192-240.

[Ground Scouring]

12z Euro actually brings yet another strong trough through the country's midsection from 192-240.

I was just going to mention that…the long-range pattern looks quite good, actually. It's definitely a replay of May 2013 in some respects.

[nwburbschaser]

12z Euro actually brings yet another strong trough through the country's midsection from 192-240.

I like the look of the 12z Euro.  One of my trips this year starts on the 10th and the GFS has been making me worried about the first half of it with a constant eastern trough so I will take anything positive at this point.  

[ZackH]

Our first university chasing class trip starts on May 21st... for 7-10 days... teleconnections are looking promising

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[andyhb]

00z Euro also shows the strong second trough that the 12z suggested (with increasing suggestion from its ensemble mean as well). If something like this were to materialize, it would likely have quite a large amount of potential given a well established moisture trajectory fed by a potent Bermuda high developing in latter portions of next week, leading to a very broad/potentially latitudinally extensive warm sector.

[Ian]

Looks like plentiful ridging by our trip

[brettjrob]

After what currently looks quite underwhelming by May standards for 5/7-5/8, the ECMWF continues to advertise another shot just a few days later (5/11-5/12). Its own ensembles are somewhat supportive, while GEFS members are overwhelmingly unsupportive for now.