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

 

[Amos Magliocco]

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?

 

[Joel Wright]

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.

 

[Mike Hollingshead]

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

 

[Mike Hollingshead]

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

 

[Robert Dewey]

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

 

[Joel Wright]

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.

 

[Robert Dewey]

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

 

[Joel Wright]

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.

 

[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.

 

[Mike Hollingshead]

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

 

[mikegeukes]

Severe Weather Event is over, removed information.

Mike

 

[Robert Dewey]

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

 

[Robert Dewey]

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

 

[Mike Hollingshead]

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.