2018 Short to Medium Range Severe Thread

[bjc0303]

20 hours ago, Hoosier said:

I'd also watch if there's a lead system like the 12z Euro showed.  That can really up the threat level for a following system by priming the moisture pump so to speak, especially if there's a favorable synoptic evolution. 

It can if it doesn’t induce a stronger-than-wanted cold frontal surge, which it kind of has been in more recent runs. 

 

Recent runs have this wave occluding fast, too. 

[bjc0303]

On 4/5/2018 at 10:54 AM, andyhb said:

Would be nice if I saw more than just statements about the Plains there.

That's all I'm going to say about that.

You’re shocked that a website dedicated to storm chasing focuses on the best region FOR storm chasing? Lol 

[Hoosier]

4 minutes ago, bjc0303 said:

It can if it doesn’t induce a stronger-than-wanted cold frontal surge, which it kind of has been in more recent runs. 

 

Recent runs have this wave occluding fast, too. 

Right.  Preferably the lead system would track as far north as possible with a cold front that doesn't sweep too far south, and then the next system doesn't occlude as fast.

[Hoosier]

12z GFS bottoms out the surface low around 972 mb.  That is about as deep of a surface low as you can get at that latitude at this time of year.

[CheeselandSkies]

3 minutes ago, Hoosier said:

12z GFS bottoms out the surface low around 972 mb.  That is about as deep of a surface low as you can get at that latitude at this time of year.

Very narrow band of marginal surface CAPE along the front though...looks like moisture will be an issue. Dew not even up to 60. Lapse rate map is rather eyebrow-raising, though, at least at 18Z.

[hlcater]

44 minutes ago, Hoosier said:

12z GFS bottoms out the surface low around 972 mb.  That is about as deep of a surface low as you can get at that latitude at this time of year.

Occluding low doesn't lend itself to a tornado threat real well. But these systems almost always have a strongly forced line/QLCS along the cold/occluded front in that narrow axis of instability. At this time, I'm more interested in areas further south. But I guess we can hope the trough deamplifies someand the surface low doesn't occlude as fast can't we . Should the surface low not occlude(which I think is unlikely for our area), a more significant event could be in the cards.

[andyhb]

1 hour ago, bjc0303 said:

You’re shocked that a website dedicated to storm chasing focuses on the best region FOR storm chasing? Lol 

No, I'm annoyed by some of the lack of objective analysis for anything that isn't focused on the Plains.

My analysis now is that this thing is too amplified and its wavelength is too short. How quickly everything turns to a lesser threat these days.

[Hoosier]

33 minutes ago, NWLinnCountyIA said:

Occluding low doesn't lend itself to a tornado threat real well. But these systems almost always have a strongly forced line/QLCS along the cold/occluded front in that narrow axis of instability. At this time, I'm more interested in areas further south. But I guess we can hope the trough deamplifies someand the surface low doesn't occlude as fast can't we . Should the surface low not occlude(which I think is unlikely for our area), a more significant event could be in the cards.

I looked up the pressure records for that region in April and they are high 970s. So if you had to bet on it at this distance, there's a good chance it doesn't come in quite so deep.  I agree that our areas are probably going to get screwed out of a more significant threat, but perhaps the extreme deepening and eventual occlusion can get delayed a little for areas farther west.  

[Quincy]

1 hour ago, andyhb said:

No, I'm annoyed by some of the lack of objective analysis for anything that isn't focused on the Plains.

My analysis now is that this thing is too amplified and its wavelength is too short. How quickly everything turns to a lesser threat these days.

I said that it doesn't look like anything "big" at that point. Yeah, a surface low below 990mb over the central Plains is pretty impressive, but with an event so many days out and models continuing to evolve on the details, I'm not getting overly excited yet.

Taken literally, the latest 12z Euro is pretty impressive across portions of Arkansas/Kansas/Missouri/Oklahoma next Friday, but that's seven days out. Earlier model progs were faster and some showed potential Wednesday and Thursday over the Plains, while the warm sector on Friday was progged to be fairly narrow across the Midwest. Now, it's slowing down and adjusting west a bit. This may have switched from an Iowa/Illinois/Missouri event, back into the Plains/Ozarks.

Since it's a week out, there's a lot more room for things to change. The synoptic pattern does favor severe weather, but with model disagreement and still at least some issues about downstream troughing over the Northeast, there is not a lot of wiggle room. In years like 2011, due to the persistent early spring pattern and ridging over the eastern U.S., storm systems went nuts over a large area. This year, especially with it still being relatively early in the season, you do have to wonder about the size of the warm sector and moisture transport with northward extent. Having an intense surface cyclone may help offset some of those concerns a bit, but there is a reason why SPC did not highlight a risk zone yet in their extended outlook.

Let's see how it evolves. Yeah, I'm a bit biased toward the Plains, but if something big shows up for areas east of the Mississippi River (I drove overnight to Alabama for the March 19th event...), I'm still going to have my interest piqued. If the last few years have taught us anything, it's to not get too excited 7+ days out from a potential event, especially with details. A lot can and often will go wrong, unless a historic event is expected, then models often tend to zero in on the threat many days in advance.

While the surface low itself looks impressive, the synoptic upper level pattern is similar to what you'd expect to see at least once or twice a year in April. It's nothing to write off, but for many reasons, it does not look like a major event at this time.

Model variability is huge. The 12z Euro on Wednesday had a 970mb low in eastern Iowa at 18z Friday, while today's run has a 985mb low over the Colorado/Nebraska border at the same time. Extrapolate that out another few days and it's easy to see how much more models could change.

[CheeselandSkies]

If nothing else, the end of next week's system is at least a sign we might be turning the corner toward a less frigid and more convectively active pattern. The biting northwest wind today was not pleasant.

[andyhb]

1 hour ago, Quincy said:

I said that it doesn't look like anything "big" at that point. Yeah, a surface low below 990mb over the central Plains is pretty impressive, but with an event so many days out and models continuing to evolve on the details, I'm not getting overly excited yet.

I mean, my frustration is more arising from Twitter than anything else, where people are basically trolling while not offering anything productive regarding actual meteorology. You're fine.

That was probably the wrong thread to quote on that.

[Chicago Storm]

Is there potential, yea.

But it's too far out to get too interested, especially given several fail options on the table.

[Hoosier]

00z GFS somehow managed to outdo itself with the surface low intensity

Posted for posterity

[Jackstraw]

Day 4-8 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0354 AM CDT Sun Apr 08 2018

   Valid 111200Z - 161200Z

   ...DISCUSSION...
   The primary feature of interest during the extended period will be a
   deep/amplified mid-level trough that will reach the central US by
   D6/Fri. As it does so, strengthening west/southwesterly flow aloft
   will transport steep lapse rates over much of the southern/central
   Plains. Meanwhile, a robust low-level mass response will feature a
   narrow corridor of enhanced poleward theta-e transport, generally
   from eastern Texas to the lower Missouri Valley. As a dry line and
   cold front accelerate east across the region, low/mid-level ascent
   is forecast to strengthen sufficiently to overcome convective
   inhibition and promote thunderstorms from eastern Texas to parts of
   the Midwest through Friday night. 

   While medium-range guidance continues to exhibit run-to-run
   variability with regards to the amplitude/timing of the trough, most
   deterministic/ensemble guidance suggest strong/severe thunderstorms
   will be most likely from eastern Texas to the Ozarks and Mid-South
   Friday afternoon through the overnight. Within this corridor,
   vigorous low/mid-level wind fields should overlap adequate
   surface-based buoyancy, such that all severe hazards may be possible
   with maturing convection. Therefore, a 15-percent probability has
   been introduced with this forecast cycle. Further refinements of
   this area (with some potential for a northward expansion) will
   likely be needed in future updates.

   The trough will advance further east through D7/Sat-D8/Sun, with
   pockets of strong/severe convection potentially persisting across
   areas from the Ohio Valley south to the Gulf Coast. Despite this
   potential, uncertainties regarding availability of adequate
   instability, the eastward evolution of the trough, and subsequent
   timing/placement of stronger convection remain too high to introduce
   probabilities beyond D6/Fri.

   ..Picca.. 04/08/2018

[Indystorm]

Sunday's 12Z GFS much more sensible with the strength of the low pressure for this coming Friday.  Not the extremes we have been seeing and puts more of IL and IN in realistic play.

[CheeselandSkies]

39 minutes ago, Indystorm said:

Sunday's 12Z GFS much more sensible with the strength of the low pressure for this coming Friday.  Not the extremes we have been seeing and puts more of IL and IN in realistic play.

Verbatim that run is pretty meh. Thursday would be a decent day over the Plains if it wasn't totally capped, and it speeds the system up with the front coming across the MS at 12Z Friday instead of ~21Z. Might be some gusty morning thundershowers for us before another ripping, chilly northwest wind takes hold. By the time it gets to you closer to peak heating, the system is occluded with deep layer flow parallel to the cold front.

[Chicago Storm]

Still 4-5 days out, but things are trending less favorable with time for anything decent on Thur/Fri.

[Hoosier]

Gotta agree with what was posted above.  With potential lingering strong wind fields and at least a small amount of CAPE, I could envision some severe threat into IL/IN but likely something toward the lower end. 

[Indystorm]

The 4/10 EURO is somewhat surprisingly looking better with svr prospects from eastern Nebraska southward for Friday.  Will this portend better chances for Sat. into IL and IN?  Stay tuned.  Some Indpls TV mets are now mentioning the possibility of svr storms for Saturday and saying the situation must be watched.

[HillsdaleMIWeather]

Looking like Wednesday and Thursday might give some us some severe

[cyclone77]

Looks like things could get somewhat interesting for parts of the sub next week.  Euro brings in some deep moisture by mid-week.  Depending on how things time out, and evolve somewhere in the Wed-Thu time frame may be something to watch.  Wednesday is looking pretty interesting out in the central/southern Plains.  

[HillsdaleMIWeather]

[Hoosier]

Should have decent moisture... hopefully the dews don't underperform too much as can happen at this time of year with the lack of vegetation.

[HillsdaleMIWeather]

Wednesday is still looking possibly good

[HillsdaleMIWeather]

12Z is looking better instability wise for Thursday compared to prior runs

[cyclone77]

Don't have much time to type much, but just took a quick look at the 06z NAM, and it looks pretty nasty for parts of southern and southeast Iowa, and down into northern MO for Thu.  Backed surface flow, plenty of juice, and nice jet support.  Forecast soundings look pretty nice.  Conditional setup of course.  If we can keep surface flow backed like in subsequent runs this could get interesting.

[HillsdaleMIWeather]

54 minutes ago, cyclone77 said:

Don't have much time to type much, but just took a quick look at the 06z NAM, and it looks pretty nasty for parts of southern and southeast Iowa, and down into northern MO for Thu.  Backed surface flow, plenty of juice, and nice jet support.  Forecast soundings look pretty nice.  Conditional setup of course.  If we can keep surface flow backed like in subsequent runs this could get interesting.

Only problem is their might not be that much instability due to cloud cover and rain

[Jonger]

May 1st and I have seen lightning 1 day all year.

[Hoosier]

Considering how dry it has been, almost hard to believe we may see mid/upper 60s dewpoints getting into areas near/north of I-80 in the next 1-2 days. But there are dews in the 60s in parts of Iowa right now so maybe something close will verify, though I still wonder if that's a little high given the dry spell and lack of vegetation.  The HRRR and RAP have generally been doing the best with temps/dews lately so will be watching those with interest.

[Hoosier]

Enhanced Risk was expanded in northern MO/southern IA, with a moderate risk farther west.

Also noticed this probabilistic breakdown at the end of the day 2 outlook.  Wonder if they are going to be doing this from now on.  It used to be sort of a guessing game on what the individual probabilities were for day 2.

 

...MAXIMUM RISK BY HAZARD...
   Tornado:  10% SIG - Enhanced
   Wind:     45% SIG - Moderate
   Hail:     30% SIG - Enhanced