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Central/Western Summer Medium/Long Range Discussions


Srain

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I'm still rather skeptical, given that the HPC discussion mentioned the fact that even a blend of the GFS and ECMWF ensembles supports a strong polar surface high near Hudson Bay. It's better but far from ideal re: moisture return and could well bust. Additionally, while the 12Z GFS shifts the NE low farther east, it also shows a deeper low, thereby keeping the surface warm front from retreating northward. If, on the other hand, the ECMWF trends toward a broader-based trough, and if the GFS continues to shift the NE low farther east, then I'll consider getting excited. But not now. I'll need to wait for persistence. (I'm personally favoring the ECMWF's handling of the trough, but not by much.)

I definitely hear you. Maybe if we'd had a single good day this season so far I'd be able to temper my excitement better. The rational side of me agrees with you entirely, for sure.

 

The thing is, I think Saturday might have the best shot to still pull something off in the event that downstream troughing is a problem. Everyone is focused on the major-league potential in Sunday and/or Monday farther E, but that's only going to be more problematic if the pattern is at all blocky. The trough would at minimum start getting pinched and meridional, and at worst, stable air might undercut most of the upper jet and dynamics. On Saturday, even the GFS with its still-undesirable solution gets a wedge of unstable air into the southern High Plains and shows an impressive setup.

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I definitely hear you. Maybe if we'd had a single good day this season so far I'd be able to temper my excitement better. The rational side of me agrees with you entirely, for sure.

 

The thing is, I think Saturday might have the best shot to still pull something off in the event that downstream troughing is a problem. Everyone is focused on the major-league potential in Sunday and/or Monday farther E, but that's only going to be more problematic if the pattern is at all blocky. The trough would at minimum start getting pinched and meridional, and at worst, stable air might undercut most of the upper jet and dynamics. On Saturday, even the GFS with its still-undesirable solution gets a wedge of unstable air into the southern High Plains and shows an impressive setup.

 

You get an idea of the type of environment and you do have continued moisture advection after 0z from the sfc-850mb as the LLJ cranks with also a nice precip signal on the nose of the theta-e axis into south central KS. 

 

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Trough ends up being a bit shallower this run, but it's still a significant, multi-day severe setup for Sat 4/26 to Mon 4/28.

Open Gulf + monster jet streak w/cold temps aloft = 3500-4000J/kg CAPE on the southern plains Sunday and 2500-3000J/kg of CAPE on Monday in the Tennessee Valley down to the I-20 corridor Monday w/50 kt SW winds at 850 mb.

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Trough ends up being a bit shallower this run, but it's still a significant, multi-day severe setup for Sat 4/26 to Mon 4/28.

Weaker 850 mb winds + weaker forcing + Plains drought = cap bust, veered winds at 00Z on 28 April. If the ECMWF is moving toward the GFS's shallower, bowling-ball cut-off low solution after H156, then moisture return over the srn Plains / MS Valley will definitely not be nearly as great as currently suggested.

 

Next.

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Weaker 850 mb winds + weaker forcing + Plains drought = cap bust, veered winds.

 

Next.

 

What?

 

I) The Euro lights up the dryline in Western OK at 132.

 

II) The 850 mb winds are strong (certainly sufficient at the least) and are nearly southerly (SSW at most).

 

III) The surface winds are backed pretty strongly east of the dryline.

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Weaker 850 mb winds + weaker forcing + Plains drought = cap bust, veered winds. If the ECMWF is moving toward the GFS's shallower solution, then moisture return over the srn Plains / MS Valley will definitely not be nearly as great as currently suggested.

 

Next.

Did you even bother to look at the output?  I mean, did you?  I can't really be nicer about this.  You clearly didn't.  The Euro has 40-60kt DUE SOUTH TO BARELY SSW (180-190°) FLOW AT 850 mb Sunday evening.

 

I get that this has been an incredibly slow severe wx season, but for the love of God, at least LOOK AT THE OUTPUT before posting something about a model run.  And this goes for everyone.

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Did you even bother to look at the output?  I mean, did you?  I can't really be nicer about this.  You clearly didn't.  The Euro has 40-60kt DUE SOUTH TO BARELY SSW (180-190°) FLOW AT 850 mb Sunday evening.

 

I get that this has been an incredibly slow severe wx season, but for the love of God, at least LOOK AT THE OUTPUT before posting something about a model run.  And this goes for everyone.

Yes, I looked at the output, and the trend is not impressive. I mean that the trend toward a cut-off low solution and/or shallower trough means that low-level flow will be MORE veered/weaker than on previous runs, meaning the moisture return will be shallower/not as great (especially with the srn Plains drought), more vulnerable to mixing, which puts the spectre of a cap bust on Saturday / a narrower, less rich warm sector on Sunday, which could ruin the entire event.

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Weaker 850 mb winds + weaker forcing + Plains drought = cap bust, veered winds at 00Z on 28 April. If the ECMWF is moving toward the GFS's shallower, bowling-ball cut-off low solution after H156, then moisture return over the srn Plains / MS Valley will definitely not be nearly as great as currently suggested.

 

Next.

 

Except it's not, if anything this run is more progressive with less potential for that.

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Except it's not, if anything this run is more progressive with less potential for that.

I'm not convinced given the fact that the seasonal trend is also in favor of a less progressive solution per HPC, in addition to my other points.

 

WHILE TELECONNECTIONS

RELATIVE TO THESE TWO FEATURES YIELD DIFFERENT RESULTS OVER THE

WRN-CNTRL CONUS THERE IS A COMMON THEME OF TROUGHING CLOSER TO THE

EAST COAST... WHICH LEADS TO SOME SKEPTICISM OF THE 00Z

ECMWF/ECMWF MEAN THAT BRING THE SFC FRONT RATHER FAR NWD DUE TO

HIGHER HGTS ALOFT.

http://www.hpc.ncep.noaa.gov/discussions/pmdepd.html

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Yes, I looked at the output, and the trend is not impressive. I mean that the trend toward a cut-off low solution and/or shallower trough means that low-level flow will be MORE veered/weaker than on previous runs, meaning the moisture return will be shallower/not as great (especially with the srn Plains drought), more vulnerable to mixing, which puts the spectre of a cap bust, which could ruin the entire event.

There is NO TREND THAT WAY IN THE EURO.  Again, I'm being as nice as I can be about this.  The trend is AWAY from that on the Euro, as you can see in the 00z to 12z run comparison below for Sunday evening (00z Monday).  Slightly weaker troughing ALWAYS means that the tendency is going to be AWAY from a closed low because those result from HIGH AMPLIFICATION with downstream blocking.  And the trend on the GFS is toward great wave spacing between the midweek and weekend systems, which would also again trend AWAY from that solution.

 

post-97-0-99247700-1398109944_thumb.png

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I agree with you Andy. too early to nit-pick every little detail. yes euro may not be completely right and gfs could be onto something but 12z gfs did make an improvement from its previous run regarding severe weather potential. the system is still days away from being sampled. the pattern this yr has been very progressive

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There is NO TREND THAT WAY IN THE EURO.  Again, I'm being as nice as I can be about this.  The trend is AWAY from that on the Euro, as you can see in the 00z to 12z run comparison below for Sunday evening (00z Monday).  Slightly weaker troughing ALWAYS means that the tendency is going to be AWAY from a closed low because those result from HIGH AMPLIFICATION with downstream blocking.  And the trend on the GFS is toward great wave spacing between the midweek and weekend systems, which would also again trend AWAY from that solution.

 

 

Def a lot less amplified on the east coast. i am liking that. thanks for posting these images. nice comparison

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There is NO TREND THAT WAY IN THE EURO.  Again, I'm being as nice as I can be about this.  The trend is AWAY from that on the Euro, as you can see in the 00z to 12z run comparison below for Sunday evening (00z Monday).  Slightly weaker troughing ALWAYS means that the tendency is going to be AWAY from a closed low because those result from HIGH AMPLIFICATION with downstream blocking.  And the trend on the GFS is toward great wave spacing between the midweek and weekend systems, which would also again trend AWAY from that solution.

Good images. Now that I'm re-checking my assumptions, I realize that you are right; meteorologically, the trend is more favorable than I presented it. I admit that I am overly skeptical due to the way the severe wx season has evolved thus far (in terms of observable tornadoes in the rural Plains). Next time I will abstain from posting something that doesn't stand up scientifically. I will read instead.

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Good images. Now that I'm re-checking my assumptions, I realize that you are right; meteorologically, the trend is more favorable than I presented it. I admit that I am overly skeptical due to the way the severe wx season has evolved thus far (in terms of observable tornadoes in the rural Plains). Next time I will abstain from posting something that doesn't stand up scientifically. I will read instead.

 

I think the important thing is not to fixate on the nitty-gritty details right now and look at trends and overall patterns. We have an intense upper-level jet streak nosing into the western CONUS with a warm, moist, and unstable air mass over the GOM. We have various models that suggest the extent of that air mass may or may not be modulated based on the interaction of the first system with a PV over the Hudson Bay. And that's all we can really say. The ceiling is high, but there are large-scale caveats whose trends we will monitor over the coming days.

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I think the important thing is not to fixate on the nitty-gritty details right now and look at trends and overall patterns. We have an intense upper-level jet streak nosing into the western CONUS with a warm, moist, and unstable air mass over the GOM. We have various models that suggest the extent of that air mass may or may not be modulated based on the interaction of the first system with a PV over the Hudson Bay. And that's all we can really say. The ceiling is high, but there are large-scale caveats whose trends we will monitor over the coming days.

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.

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Looking at only the 04/21 12z model suite, both the Euro and GFS light up the dry line over west central OK at hour 132.  Gfs has more surface cape than the Euro, but either is more than adequate.  Crossover winds on both models are favorable, while speed shear is somewhat lower than I would like to see for a major outbreak on the Euro, again it's adequate. Even the GFS ensemble means show PW values near the 35mm range.  While it's to early for a high confidence event next Saturday evening, it's certainly got my attention.  If tonight's runs holds with this solution, I would expect the SPC, if they don't highlight that area will strongly hint at it in their written disco.gfs-ens_mslp_pwat_us_23.png 

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I feel like this might be the first time I've said this so far this year, but I'm feeling pretty optimistic about getting a few nice severe weather days this weekend. Saturday looks to be most likely out of my cruising range, but I'm already starting to clear out everything for Sunday. Things are still nearly a week out, but prospects look pretty encouraging from my perspective.

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I know earlier it was said not to get caught up in the little details this far out but I can't help to notice on GFS how the LLJ isn't very impressive in the warm sector Sun. Like 35knts max. The LLJ core is really displaced to the northeast of the ULL. I haven't seen Euro yet but I remember with the last setup LLJ weakness was a major issue. What do you guys think?

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I know earlier it was said not to get caught up in the little details this far out but I can't help to notice on GFS how the LLJ isn't very impressive in the warm sector Sun. Like 35knts max. The LLJ core is really displaced to the northeast of the ULL. I haven't seen Euro yet but I remember with the last setup LLJ weakness was a major issue. What do you guys think?

 

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).

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Saturday looks like such a frickin' great chase day on the 00z GFS... wow.

 

Not like it's really a linear trend from last night's to this morning's to tonight's runs, especially regarding the Hudson/Northeast cyclone, but the practical impacts on this system have been to improve it drastically each run.

 

We're not totally out of the woods, but the prospect of the warm front not lifting past the Red River or something like that looks to be dwindling. Really, the only other complaint I can see having is timing, if it slows down some (could be a cap bust Saturday, and then Sunday could still be messy). But that's getting ahead of ourselves. This looks really solid for now.

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