10/22/04 FCST: Plains/midwest

[Mike Hollingshead]

For discussions about the BIG day Friday WILL be. Jinx. I really like the looks of tonights GFS for c NE and to the ene and south from c NE. SFC dews will hopefully be better up near the sfc low and west to the sfc trof. Looks like it has some potential to be big. 80knts at 500mb will assure some rather high storm speeds given this unfolds as is. Very nice dry punch aloft over the boundaries. Thoughts.............

 

[Glen Romine]

Seems rather silly posting on a day still so far out, but why not. Would tend to agree with Mike that the location of the surface moisture boundary is probably projected too far east - as this is a typical model bias to over mix the dryline to the east. So, forecast is for low-mid 60 dewpoints - which is pretty good for mid October. GFS has a strong jet streak rolling around base of trough on Friday, leading to cyclogenesis in the northern plains and will aid in backing of surface winds to SEerly, with surface low tracking from sw NE to sw MN from 12-00Z. Winds south of warm front expected to be SSW, and deep layer shear orientation is also expected to be from the SW, so little turning of the winds in the warm sector and hence along the dry line, which should rapidly then evolve into a convective line instead of discrete cells. So, might have to work the warm front instead, but cell motions will not favor long residence along the boundary, so most warm front convection should become elevated quickly. So, that basically leaves trying to play the triple point - which is not forecast to have favorable instability - but maybe due to over mixing of moisture. So, the early look I'd call this event marginal - but a lot can and most likely will change in this forecast.

Glen

 

[Robert Dewey]

Well, my 48 hour abstinance from the models didn't work out too well, and I am now looking at the 12Z data from the ETA...

Using ONLY the ETA (wishcasting basically), the best threat would appear to be from eastern OK into southern WI, with southern WI/IL/IA/MO area having a pretty unusual looking setup. Dewpoints actually climb into the upper 60's across this region, which is very rare for October - ETA also forecast CAPE of close to 3000J/KG (using forecast soundings with a parcel of 74F/64F temp/dewpoint averaged around the region), with close to 400m2/s2 of helicity!

As Glen said, this will change with time... But it is just interesting that this is even a forecast possibility, as we head towards the end of October!

 

[Mike Hollingshead]

Hope the eta's trend isn't going to continue with the veering sfc stuff(more positive tilt nature to the system.....trof is sort of "flat"). The good thing about looking at things so far out is when they don't look terribly good they have room to improve, I guess. This is the wrong direction though.

The Friday morning "lows" the eta is spitting out the last two runs is rather interesting...lol. 75?

 

[Glen Romine]

Yeah, the ETA forecast may not be very reliable (typically has less skill than the AVN until forecasting within 36 hours). Note the double warm front structure forecast, with persistent convection from 12Z onward north of the southernmost boundary - which usually doesn't materialize as forecast in my experience. But if it did, that would offer a more favorable scenario for tornadic potential than is present in last night's GFS. Mike understandably may not care for the eastward shift - but it strongly favors a better system by improving the deep layer directional shear - leading to more favorable storm motions. Since it is closer to my location - I hope the solutions come closer to the extended ETA.

Glen

 

[Robert Dewey]

Hope the eta's trend isn't going to continue with the veering sfc stuff(more positive tilt nature to the system.....trof is sort of "flat"). The good thing about looking at things so far out is when they don't look terribly good they have room to improve, I guess. This is the wrong direction though.

The Friday morning "lows" the eta is spitting out the last two runs is rather interesting...lol. 75?

I think it all depends on what area you plan on chasing... For us Midwesterners/Ohio Valley folks, the ETA would be an awesome setup (I haven't checked the GFS yet)... Of course this is the Plains thread though, so I will keep my mouth shut, LOL

 

[Mike Hollingshead]

There I fixed it, talk away...lol. I think GFS coming around to a real system and back west.

Edit:

LOL, yeah GFS knows what it's doing....go away eta!!! I'll take the 12z gfs for sure. That is pretty dang impressive to me. Early target remains the same based off new gfs. I wonder which model is more reliable with the strength/orientation of this system.

 

[Robert Dewey]

There I fixed it, talk away...lol. I think GFS coming around to a real system and back west.

Edit:

LOL, yeah GFS knows what it's doing....go away eta!!! I'll take the 12z gfs for sure. That is pretty dang impressive to me. Early target remains the same based off new gfs. I wonder which model is more reliable with the strength/orientation of this system.

Thanks for adding the midwest, LOL...

Anyway, I am changing my wishcast to the GFS as well (just took a look), though I would still settle with an ETA solution. I think once this system actually comes on shore (probably around the 00Z timeframe) and gets sampled by the RAOB sites, things may start getting a little clearer. It is also possible that the system will slow even further, and we will be changing threads again, especially if a deeper solution verifies...

 

[Amos Magliocco]

It seems like these the character of these transitional season systems is even harder to guess without real onshore sampling than mid-Spring or winter storms. I'm pretty happy, too, about the trend on the GFS and feel confident at least that the system will move in more slowly than progged, for whatever that's worth.

Taking a blend of the extended outputs so far in the last two series of runs, I'm leaning toward a central to southern Kansas area. The reasons are that moisture and instability progs have been consistent there, and the 12Z ETA showed 250 m2/s2 co-located near 1500 j/kg MLCAPE (to the south). Because I think the system will slow and because I think the sfc winds will back more than progged, I expect these values would verify or come in even better.

There are problems with deep layer shear this far south, it's true, but the region is in the rear exit of the jet on the last two ETAs and GFS operationals. Deep layer shear is certainly marginal and the warm front is far, far away, but I don't think lift is an issue. The dryline/sfc trough should suffice to initiate convection from the triple point all the way down to northwest Texas--all models have consistently shown precip trailing well to the southwest.

I admit some regional bias, as always, but not because Iowa or Nebraska is farther from me. I live in Indiana and it's about the same distance to Harper County as to O'Neill. What I'm nervous about is instability that far north that quickly in October, when insolation is so marginal anyway. I really like the 70F isodrosotherm peeking into southern Kansas at 18Z on the 12Z ETA, even if the veered LLJ erodes it back into Texas by 0Z. I am hoping this issue will be mitigated by a slower solution and (even more wishcastingly) a more neutrally or negatively tilted trough.

Still way early, but more fun than watching the 5400m line and thinking about how much salt I have on hand.

 

[Tony Laubach]

I'd make a chase into Kansas if Amos is right! Actually, taking a quick glance, I, too, am impressed with the late-season setup. Obviously timing will be an issue as I am smack in the middle of the semester.

I'll wait for the next couple days to pass by to get a better idea of what's going on. AFD here in Denver have talked about this system making a good change in the weather about Friday, but they are thinking slowing will occur as well, so they haven't figured it into their forecasts. Why am I mentioning Denver's AFD here? Well, normally they get concerned here with weather changes and the terrain effects on weather as these kcik through; and when it goes through, it usually pushes its way into the Plains. However, they mentioned in this morning's AFD that the big low will be well south of Denver, which if I followed this correct, would send the triple point right through Kansas on its way eastward.

Again, waiting for things to get sorted out before making judgements, but do have the weekend on standby just in case.

 

[Scott Olson]

Another day another trend... First off, for the northern plains Thursday Night- Strong lift and good moisture moving in and not to forget MUCAPE of 1500/ This is supported by ETA and GFS. And now it looks like the GFS has taken its que from the movie back to the future and amplified the system. Instability for the Northern Plains could reach a peak of 2000/ on friday with the main axis located near the great Lakes Wisconsin, into Iowa area. ETA seems more bullish with the instability with GFS going for about 3/5 of ETA's forecast. Will have to see if the models keep slowing and moving SW the location of the system.... Looking good though.

 

[Robert Dewey]

18Z ETA coming in, and it's pretty much stickin' to it's 12Z run. One difference I can see is that the 850mb low is weaker as it moves into the Plains/Midwest... But it's still as positively tilted as can be. The trough at 200-300mb is deeper and slower, which would be a slight trend towards the GFS...

What we really need, is the ETAs' forecast thermodynamics with the GFSs' forecast synoptics... Now thats really wishcasting it, LOL... (i.e., the ETA is putting 850mb temps in excess of 20C over northern IL!)

 

[Shane Adams]

I only looked at OK, and from what I see as of Tues evening it looks like you'll need a rocket strapped to your a** to keep up. Unidirectional, 50-70kt mean flow h85 through h3. Looks a lot like a 4-6-01 or a 3-4-04. I somehow manage to miss all severe weather on days like this.

I'll hold off on any real opinions until this thing is 48 hours out, but if it verifies anything close to what it's showing now, I'll predict a High Risk with a strong emphasis on damaging winds. One thing I've noticed through the years - a linear windfield with a 60-70kt average through h5 with a breakable cap, including any metropolitan area, equals a High Risk. If the event verifies but further east (away from DFW/OKC), I'll say Moderate.

 

[Chauncy Schultz]

Ahh, the wonders of long term forecasting.

The long wave trough currently situated across the western United States certainly does look to be moving out into the plains and upper midwest later this week, with emphasis on the Friday into early Saturday timeframe at this time when one considers all available model solutions. These solutions, of course, do leave quite a bit to be desired, which should be expected this far out, as everyone knows. But for some specifics... where the 12z runs of the major models are concerned: the ETA model maintains a positive tilt to the upper trough as it enters the plains Friday, with this nature resulting in quicker surface and upper air features when one compares the solution to the other models. Moreover...its tendency to move the dryline to the east so quickly may be overzealous considering its inability to resolve low level moisture profiles at such a range, when there is likely to be additional backing in the low levels in response to the increasing height falls, which could conceivably slow the dry lines' movement.

Considering, then, that the tendency for upper level troughs of this nature to slow and deepen is readily accepted, one leans toward the GFS model solution for the forecast of synoptic scale features. It should be pointed out that a major reason the ETA and GFS differ on their handling of the trough is the differences that exist in the models' solutions for the strength and amplitude of downstream ridging, an element directly tied to their handling of the upper low expected to develop off the coast of New England. It's here that the GFS gets my nod, which means that the overall pattern would slow and that the trough would have a more negative tilt as it emerges. Perhaps of greater importance when one is comparing the ETA and GFS today is the fact that the ETA suffered from a lack of RAOB data from the continental U.S. being ingested into the model due to problems with data flow to the supercomputer running the model. This in itself lends credence to a solution other than that of the ETA.

Of course, it does look like there will be plentiful moisture and instability available for active convection when the system does exit the Rockies, so its likely that someone....somewhere...is going to see some active storms late this week. The details will have to be hammered out as we move forward in time.

 

[Gabe Garfield]

I want to bring attention to the latest run of the GFS. It shows a considerable change from the last few runs with a more neg. tilt trough. It could be big if this verifies.

http://www.nco.ncep.noaa.gov/pmb/nwprod/an...8/fp0_078.shtml

Gabe