4/16/04 FCST: IA/MO

guest

The 84 hr eta and GFS are starting to present an interesting setup over IA/MO this Friday. With the trough setting up over the western CONUS, a decent sfc low is progged to setup somewhere in the general region, or perhaps to the north towards MN. Nonetheless, looks like the low could be drawing up sufficient moisture from the gulf to push dews into the 60s. In addition, the lapse rates should be fairly steep, providing for moderate values of CAPE.
Shear will not be a problem but hopefully the low will evolve far enough west and strong enough to put good helicity/shear further west. Looks like this region could be the starting grounds of a grand weekend tour. Look forward to other people's thoughts.

Chris
 
I was comparing notes on this morning's run with a friend of mine and there's a few elements of the 12Z ETA that don't makes sense to me. Mainly, where does all this moisture come from all of a sudden? There's no corn so it's not evapotransporation, and the low level trajectories are only favorable for a short period before Saturday 0Z.

On top of this, the GOM is getting blasted with northerly 850's right now, driving the best moisture deep into the Carribbean. Granted that today is Tuesday and we're in mid April now; things recover more quickly. But still, this return seemed sudden to me for a place as far north as Iowa.

Opinions?
 
I would suspect anything that would fire this early would have a very hard time becoming surface based. Moisture would be fairly limited at this point and dynamics would have to be the main ingredient to get anything going. It looks to be an elevated/mainly nocturnal event to me. These often can generate some incredible lightning however.
 
You mean the 12z eta for 18z Friday? Or the 18z eta? Says you posted at 11:55 a.m. so I'm assuming you meant the 12z eta. Take a look at the new 18z eta.

http://www.wxcaster2.com/CENTRAL_MESO-ETA_...NDSBLI_48HR.gif

That is for 18z Friday via the 18z eta(beings Earl's doesnt go out past 48hrs for the mesoeta. That is one hell of a warmfront.

http://www.wxcaster2.com/CENTRAL_MESO-ETA_...NDVORT_48HR.gif

40-50knts at 500 out of the sw.

http://www.wxcaster2.com/CENTRAL_MESO-ETA_...HSWEAT_48HR.gif

Yeah we still have to wonder about that, but even if we only got half that.

BUT... http://www.wxcaster2.com/CENTRAL_MESO-ETA_...WINDRH_48HR.gif

There is nothing good about that and the lack of moisture.

BUT...LOL... go down just a bit and http://www.wxcaster2.com/CENTRAL_MESO-ETA_...WINDRH_48HR.gif

The meso-eta is willing to break out precip between 18-0z now. IF there is deep enough moisture and we can get a storm up the shear says supercell riding a warm front. In my mind it bars some serious watching if you are anywhere close to a line from Omaha to Des Moines.

This setup reminds me ALOT like this storm that formed just west of Omaha and tor warned itself pretty much the whole way to Des Moines. http://www.extremeinstability.com/02-04-17.htm

Right now I'm living at my target for Friday....soooooooo I may be somewhat biased on how much I like the looks of this.

Mike
 
Ah I see. I guess they got rid of the part that says the user edited a post, because what you said, and, I edited mine to fix a url and it doesn't say I edited it either. That is useful info.

Yes, I'm ready for all these days, surely with the multiple ops we will see something cool over the period....right????? lol
 
After looking at the 18Z ETA for FRI/FRI NIGHT, I am wondering if the 18Z ETA is suffering from some convective feedback issues, especially 48HRs and beyond regarding this 4/16 system.

Checkout the QPF output from the ETA (top), and GFS (bottom)

**Edit: Edited to remove graphics, before they become outdated tomorrow**

The 18Z ETA looks like it develops a very compact and intense vorticity max at 500mb, which translates into impressive VV's in the mid levels, and generates quite a bit of QPF in a short period...Which looks a little suspect to me.

If it is not convective feedback...I would have to say that a rather significant outbreak of severe thunderstorms would occur over eastern IA/northern MO, with a decent shot at tornadoes given high instability and high helicity (400M2/S2 maxima over IL/IA/MO tri-state line at 00Z SAT).

What really interests me is that the 18Z ETA hangs on to instability through 06-12Z SAT...With close to 1500J/KG available along and south of the warm front from southern lower MI westward into northern IL. Very strong low and mid level forcing will likely keep the convection from IA going well into FRI night across this region. Wind profiles show little in the way of directional shear, but speed shear is excellent from the SFC to about 2.5KM AGL, and pretty much remains steady through 500MB. This is good for bow echos, but supercells would require excellent speed shear all the way through the 6KM AGL level, in addition to directional shear. To me, it looks like the potential for a strong MCS or possibly a serial DMCS (derecho), since several of the main ingredients are there.

But.....ALL of the above is based on the reasoning that the ETA is NOT suffering from convective feedback...Which to me it looks like it is.

Robert
 
I'm looking for mainly an elevated event. Widespread scattered elevated cells should pop up in the evening with the main threat being marginal hail and intense lightning. As the column slowly begins to fully saturate later in the night the storms may become more conglomerated and then begin to become slightly more surface based. The low-level jet will fuel this elevated activity so some very localized areas may see some heavy rain.
 
If sfc based CAPE does in fact reach 1250-1500J/KG for a nocturnal event, I would think most convection would be sfc based. I am still skeptical about this 18Z ETA run anyway...The more I look at it, the more it screams convective feedback to me...I wouldn't be surprised if storms don't even fire FRI/FRI NIGHT at all.

Robert
 
Yeah I'm very skeptical about those CAPE values, mainly because of moisture levels. As of late this afternoon (Wednesday) dewpoints are still in the 40's and even 30's(!!) all the way down to the Texas coast! I find it hard to believe deep moisture will make a return that quickly. As the weekend goes on though I think the excitement will really increase. :D
 
What exactly are those maps telling us about Friday afternoon beings they are for 6z Saturday morning? They are obviously showing the convective cluster it thinks will happen, which to me sounds great since initiation has been a little suspect.

The 18Z ETA looks like it develops a very compact and intense vorticity max at 500mb, which translates into impressive VV's in the mid levels, and generates quite a bit of QPF in a short period...Which looks a little suspect to me.

If it does it's AFTER 0z Sat, and would it do that if it thought an MCS was to develop?

It has a very weak sublte wave moving east across NE before 18z Friday, which would be GREAT. Point is who cares what issues it comes up with with this later in the overnight hours.

Wind profiles show little in the way of directional shear, but

Are we looking at Friday? http://weather.cod.edu/forecast/ETA/offeta...0mb_dewp_48.gif

Due east winds along the warm front turning to due sw at 500 and the boundary is lined up just right for something to latch onto it. I think the directional shear is there. I do not know what exactly will happen with moisture or that little wave.
 
Yes, moisture seems so odd with this whole thing, yet the models are SO consistant in this instability being here.
 
I am not an expert on convective feedback issues, as they are relatively new to me as well. I always look for things that just seem to "appear" in the model, or things that just pop-up without much cause. In this case...There is somewhat of a 500mb vort that comes across from the Rockies between 36FH and 54FH, and the it blows up for no particular reason at 54FH (see images below, I posted them in this forum so that way you can quickly glance between the two) -

**Edit: Edited to remove graphics, before they become outdated tomorrow**

The 500mb vorticity doesn't necessarily translate into vertical velocities as I said, but it does help them out somewhat (seems strong vorticity would cause air to rise, which is essentially what vertical velocity is, since vorticity is a measure of "cyclonic spin", but I am not positive on that). Another thing to note between 48FH and 54FH is the development of high RH values at 700MB across northern IA...RH values go from a dry 30-40% at 48HR, and jump to a humid 99.9% by 54FH...combined with the vertical velocities in the same layer, and you have very intense precipitation. While this can occur in the real atmosphere, it happens on a much smaller scale (mesoscale/sub mesoscale), but it appears as though the ETA is blowing it up into a synoptic scale feature, or roughly the size of its 40KMx40KM grid spacing, which then affects the other grid boxes around it.

Here is a link with more information, though it is geared more towards the GFS since it exhibits this BIAS frequently...http://www.hpc.ncep.noaa.gov/qpfbombs/

Robert
 
Originally posted by Mike Hollingshead
What exactly are those maps telling us about Friday afternoon beings they are for 6z Saturday morning? They are obviously showing the convective cluster it thinks will happen, which to me sounds great since initiation has been a little suspect.

The 18Z ETA looks like it develops a very compact and intense vorticity max at 500mb, which translates into impressive VV's in the mid levels, and generates quite a bit of QPF in a short period...Which looks a little suspect to me.

If it does it's AFTER 0z Sat, and would it do that if it thought an MCS was to develop?

It has a very weak sublte wave moving east across NE before 18z Friday, which would be GREAT. Point is who cares what issues it comes up with with this later in the overnight hours.

Wind profiles show little in the way of directional shear, but

Are we looking at Friday? http://weather.cod.edu/forecast/ETA/offeta...0mb_dewp_48.gif

Due east winds along the warm front turning to due sw at 500 and the boundary is lined up just right for something to latch onto it. I think the directional shear is there. I do not know what exactly will happen with moisture or that little wave.

When I was speaking of directional shear, I was talking about FRI night for points eastward (maybe I need to start a new thread for 4/17?). The point I am trying to make, is that the ETA is initiating convection over IA, and that may be convective feedback, meaning that convection may NOT actually fire over IA...00Z SAT is when the feedback first starts to come into play. My thought is that if it is indeed convective feedback, and the wave wont really be that strong, then what will initiate convection in IA?

Robert
 
Based off the bit of qpf, the sfc boundaries, and the little wave, the eta evidently has added up there should be convection....NOW....given this is wrong and the convection does not happen, any events happening after them(prog'd) would be convective feedback issues.
 
The point I am trying to make, is that the ETA is initiating convection over IA, and that may be convective feedback, meaning that convection may NOT actually fire over IA...00Z SAT is when the feedback first starts to come into play.

Yes and no, I think. The last half makes sense, but calling convection itself convective feedback wasn't making sense to me. You guys know more then me, so feel free to correct me here.
 
Robert, some great observations indeed. I don't think they pertain to the chase ops from 18z through and past 0z though. Is the precip suffering or is the 500 vorticity? The 500 vorticity. It's likely this little wave won't even happen and we wont' have to worry about anything....LOL. Nice to read from knowledgeable people on here. Thanks,

MIke
 
Sure - but I am confused with the real world Obs...


Yes, moisture seems so odd with this whole thing, yet the models are SO consistant in this instability being here.

Yeah that has been the topic for more then a week. We are all confused as to how this is supposed to happen. It's odd how confused the models are not. Run after run after run shows sfc TDs around or above 60 by Friday. And we've pointed out already how shallow this will likely be. I think one calls this talk, HOPE. Hope the models understand how this will happen. If nothing else we'll waste some shear and get an early bust out of the way.
 
Convective feedback is a very in depth subject, and is very complex, since it deals with model physics and dynamics.

After looking at the 18Z model data a bit more, and trying to trace individual lows...I think I see what is happening. It appears as though the "suspect" is in the 850MB level...It appears as though a piece of the 850MB low at 12Z THU breaks off and heads southeast into northern CO/NE...It then encounters slight lee side enhancement, making it a bit more defined by about 6Z/12Z FRI, with incresing vertical velocities. The low continues to track east into the very unstable air of IA/MO...Sparking the development of a MCS...which then basically creates a domino effect...The MCS increases the vertical velocity, and QPF explodes as a result of convection firing (which would be correct if the scenario played out).

So in actuallity...This scenario is possible, but very unlikely since all of the above factors must fall into place at the right time. And since the main "suspect" forms around 12Z THU...Any areas along its path would be subject to total model error, at least from the 18Z run. However; All is not lost for the southern IA/northern MO region! The 12Z ETA still looks like it could pose a decent severe weather threat across the region, with LI down to -10C (though I should be taking the 67F Td with a grain of salt, but thats a whole new can of worms)!!...

Ok, I think I'm gonna take a little break now...LOL

Robert
 
This system is getting more, and more fun to watch as comes closer to reality. I wonder if there is a chance that severe weather may affect more northern areas than Iowa, say SD or Minnisota? If it is at all close to me, I may take a trip south and see how far I get, lol.

can't wait for my first chase of the year,

Jared
 
I could post this to any of the forecast day threads but maybe its most pertinent to Friday first, at least. Scanning through the forecast discussions last night, I found one from OUN early Wednesday morning that reported an ETA six hour dewpoint forecast for a buoy point in the Gulf which was 6 degrees too high. Yesterday's Day 2 mentioned over ambitious dewpoints and again today: "LOW LEVEL MOISTURE RETURN TO VICINITY OF BOUNDARY ONCE AGAIN APPEARS TO BE OVERDONE IN ALL THE OPERATIONAL GUIDANCE."

Likewise the Day 3 this morning mentions the greater availability of moisture in the southern plains and the resultant tornado threat.

I'm not saying there won't be storms tomorrow, just that many forecasters think these moisture progs for far northern points are over the top. It's interesting and strange how the ETA and GFS have fallen into the same trap, nearly identical with the robust return.
 
Here are some links for people to conduct their own examination of the model initialization. The first is GOM buoy data:

http://www.ndbc.noaa.gov/Maps/WestGulf.shtml

Of particular interest (and this is the buoy cited in the OUN AFD from Wednesday morning, I think) is Station 42002, which described as its location: "W GULF 240 nm South-Southeast of Sabine, TX." As best I can approximate, this is about where this morning's 12Z ETA analysis (0 hour) shows a pool of 65F dewpoints. Yet at 14Z (nine minutes ago), the buoy reported a dewpoint of 51F.

Closer to shore, the readings are better, but ETA 12Z analysis still overplays them by four or five degrees.

For whatever reason, the model is grossly overestimating dewpoints in the western Gulf.
 
Looking at the RUC 12HR forecast for 00Z FRI...It looks much more realistic - http://www.rap.ucar.edu/weather/model/ruc1...hr_sfc_dewp.gif, than the ETA 12HR forecast valid for 00Z FRI - http://www.rap.ucar.edu/weather/model/eta1...hr_sfc_dewp.gif.

The 12Z ETA valid for 00Z FRI has mid 50's dewpoints all the way into northeastn KS, while the RUC has low 40's at the same time and area!
The reason I am using the RUC, is because it had very good initialization on Td's, whereas the ETA was overdone.


Robert
 
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