8/4/2004 FCST: Upper Midwest

Joined
Feb 8, 2004
Messages
1,975
Location
Detroit, MI
SWODY2: "THE COMBINATION OF BOUNDARY LAYER DEWPOINTS IN THE 70S AND THE INTENSE VERTICAL SHEAR WOULD APPEAR TO FAVOR A SIGNIFICANT TORNADO THREAT E OF THE SURFACE LOW"

The latest ETA is very promising for tornado potential... With substanial low-level moisture advecting into the Great Lakes region, leading to very strong instability (>2500j/kg CAPEs) and very strong helicities (>500m2/s2 0-3km layer). Hopefully something will turn out tomorrow...

..Nick Grillo..
 
Well, I originally thought this situation was very intense convective feedback in the ETA, but ALL of the 00Z suite (Canadian models/Euro models) show a very similar solution. The 06Z models are even stronger, with the GFS being most cosistant, while the ETA has pushed a little further south somewhat.

12Z models starting to roll in, and the ETA has the 250MB/500MB jet stronger at the 12Z analysis than the pervious 12HR forecast had, so it may yet again be a little stronger this run. If any of the situations were to verify, I would go as far as saying a significant outbreak of severe thunderstorms and tornadoes (maybe even strong tornadoes given the pretty intense shear for this time of year/good instability/SFC td's). My bet, is if anything close to these solutions occurs, expect at least a strongly worded MDT risk day... The GFS is even more ominous, and has been more consistant (its also in agreement with the Euro models). This may all be one big coincidance, and it may ALL be convective feedback, but thats just too many models (ALL) showing the same solution!

If I live in central or northern OH/IN, I would definately keep an eye on the situation, I may even decided to hit I75 and track on down there...
 
I'm defintely keeping an eye on tomorrow as I live real close to the sig. tornado bullseye in Ohio- about 2 or 3 counties sw of it :

http://198.63.55.43/CENTRAL_ETA212_ATMOS_STP_48HR.gif
http://198.63.55.43/CENTRAL_ETA212_ATMOS_SCP_48HR.gif
http://198.63.55.43/CENTRAL_ETA212_ATMOS_S...SIGSVR_48HR.gif

I'm a little skeptical right now - having a potential spring type of set up in August is way out of the ordinary here in the Ohio/In area- will see what the SPC says in their 1:30(1730 utc`) Day 2 outlook. But I am making preliminary chase preparations - "Be prepared"-Scout motto !
 
12Z Eta rocking the world to my south - helicities of 1000+ along the MI border with CAPEs to 3000 just south of the boundary. 9Z SREF from SPC also shows good agreement over IN/OH, I'm concerned if anything develops at all though along the boundary in extreme southern MI.

SREF also shows that all of the various schemes develop this system fairly close - 50% chance of SigTor > 3, Supercell index of 12, SigSvr 90% chance of being > 40000. My target right now is NW Ohio, where I can hit the stuff along the boundary or head south for the "typical" storms if nothing happens there.

- Rob
 
I'm gonna side with Rob, I will most likely be heading down into OH for this one... Also, that heavy QPF in MI is interesting (probably overdone, maybe)...

Man, these are some good probablities:

I suspect the afternoon AFD packages will feature more of the severe weather concern over that region (a 180 degree turn from there previous discussions of whether or not to add showers :lol:)...

[Broken External Image]:http://www.spc.noaa.gov/exper/sref/gifs/forecasts/SREF_prob_supercomp_3_f036.gif
 
I feel the pain... Sunday I had showers in the Wed forecast then Sunday night I went partly cloudy, then yesterday for the 6p I had mostly cloudy then added showers back in for the 11 ;>

GFS just trickling in now.

- Rob
 
I feel the pain... Sunday I had showers in the Wed forecast then Sunday night I went partly cloudy, then yesterday for the 6p I had mostly cloudy then added showers back in for the 11 ;>

GFS just trickling in now.

- Rob

LOL, what else can ya do though - The models went from nothing to an outbreak in less 06 hours, one must take that with a grain of salt...
 
I feel the pain... Sunday I had showers in the Wed forecast then Sunday night I went partly cloudy, then yesterday for the 6p I had mostly cloudy then added showers back in for the 11 ;>

GFS just trickling in now.

- Rob

LOL, what else can ya do though - The models went from nothing to an outbreak in less 06 hours, one must take that with a grain of salt...

Haven't the models been a little flaky in general lately? I am fairly new to weather forecasting but the SPC and the other forecasts that I have been watching have seemed to change dramatically from one day to the next in the last week. Is all the moisture at the surface to blame for the confusion or is it a problem with the upper level ?

I am cancelling any work for wednesday and hoping for the best, an outbreak in unpopulated areas with high visibility. I70 from Springfield OH to Indianpolis IN or I75 from Toledo to Cincinnati. If it turns into a bust it will be a 600 mile bust rather than a 1500 mile bust.

Visibility declines in Southern OH and IN. So the N 2/3 of either state is a better chase area. Corn and Soybeans in the North, trees and hills in the South.


I am uncertain about how to predict storm motion.
http://www.wxcaster.com/modelskewts.php3?f...STATIONID=_KIND

Shows storm direction/speed at 276 degrees and 26kts . Translated into english that is almost straight south ? and 27 MPH ? is that correct.
 
NW OH target certainly looks like the place to be. Everything seems to be in place, unless this is ALL convective feedback, which doesn't seem warranted like Robert said.

Initial target at this hour is somewhere around the Fulton, Hancock, Putnam county area. Leaving work at 13:00 so should be in the area around 14:30 at the latest.
 
OK, this could be the late-season Ohio chase I have been waiting for. Pending a data check in the morning, I will be out the door heading northwest on Route 35. Prelim target is somewhere NW of Columbus, the farther N and W the better. The uncertainty of tomorrow's situation has me a little concerned about making the drive, we'll see in the morning.
 
It's beyond my mind why the SPC would even consider not upgrading this area to a MDT risk... which they just did. It's still a slight risk? Unbelievable.

Probably because of the big swing in model guidance - To go from a "partly cloudy with showers forecast" to a "severe thunderstorms with tornadoes" is a bit dramatic for 6 hours, the difference between yesterdays 18Z and 00Z Init. One has to make sure, since the situation can flip just as fast - i.e the 18Z data may show nothing...
 
I'm trying to figure out exactly which features are suspected of over-amplification due to convective feedback. The low level wind fields?
 
They're still highlighting as a Slight due to the convective feedback problems with all of the models. Too much uncertainty, as whatever happens tomorrow will be solely based upon what does or doesn't happen today.

Sorry, a little late there. Robert already has it covered.
 
It wraps up some VERY strong winds in the low-levels, and the GFS does the same but not with that intensity. SPC should not upgrade to MDT given the unlikeliness of this event.

- Rob
 
I'm trying to figure out exactly which features are suspected of over-amplification due to convective feedback. The low level wind fields?

What can happen is that when the forecast models induce convection (such as today, over IA), it can contaminate the rest of the downstream grids. This usually results in abnormally high QPF, strong wind fields, intense 500mb vorticity centers (compact), and compact SFC lows. The models are suffering from all of these symptoms, but I am not so sure that they arn't correct in doing so... So to over-amplify would mean the flow/500mb vorticity/and depth of the hghts...
 
This is interesting because we know that clusters of storms can produce convectively induced vorticity maxima. Now I'm less certain about this, but I think I recall an instance a few years ago of either ETA or RUC actually anticipating that. I remember it struck me as bizarre because of how unusual the entire phenomena is so I wasn't exepecting numerical modeling to see it.

I guess tomorrow is another case of why it makes sense to ditch the models on Day 1 and dig through real data before making serious chase decisions.
 
This is interesting because we know that clusters of storms can produce convectively induced vorticity maxima. Now I'm less certain about this, but I think I recall an instance a few years ago of either ETA or RUC actually anticipating that. I remember it struck me as bizarre because of how unusual the entire phenomena is so I wasn't exepecting numerical modeling to see it.

I guess tomorrow is another case of why it makes sense to ditch the models on Day 1 and dig through real data before making serious chase decisions.

One thing to do is watch the RUC forecasts... Right now, the 18Z RUC 12HR forecast for tomorrow is pretty much identical to the 12Z ETA 24HR forecast - Except the low is a *bit* further north at 850mb, on the RUC (the RUC is also a little more widespread with the +40KNT contour at 850mb as well). The more I watch the evolution of things, the less I see convective feedback. The 12Z GEM/12Z UKMET both show the same solution as the USA models, which makes me *almost* positive that its not convective feedback since all of these models use different convective schemes.

Anway, check out this plot from UWISC, this is supposedly SFC winds - Check out the 50knts SFC winds in MI, just north of the heavy precip core! Their model usualy WAY over-predicts SFC wind speeds, but I just thought this was interesting to show...


bf72a5c7f5a80d7edd2a3b48b76bc90d.gif
 
One thing to do is watch the RUC forecasts... Right now, the 18Z RUC 12HR forecast for tomorrow is pretty much identical to the 12Z ETA 24HR forecast

A 12 hr forecast from the 18Z RUC would be valid 06Z, whereas the 12Z ETA 24hr hour forecast would be valid at 12Z - so this is really compairing apples with oranges.

Convective feedback is funny thing - generally only a problem when the explicit convective scheme fails and the much coarser convective paramterization scheme kicks in - generating convective overturning on much too large of a spatial scale - which can cause significant problems for the model solution usage in those areas impacted. However, upscale growth of convection should not be automatically attributed to convective feedback - the models are run at relatively high resolution these days and generally are capable of resolving mesoscale processes. Unfortunately, the operational ETA only has one shot at getting the mesoscale evolution right - so when you see these types of features you should automatically think this is one possible evolution subject to verification - but to literally say things will happen as shown, down to the county level, will generally leave you grossly disappointed. A good check is to look at the ensemble forecasts to see if they show a consistent signal, or if there is a large range of variability.

Glen
 
18Z Eta is more to the north - helicities of 400+ get up to a Grand Rapids to Flint line by 18Z with CAPE up to 1000. Best instability still over IN/OH but less directional shear.

Interesting over Iowa is that it whips up BOATLOADS of QPF overnight (7" of rain SW of DSM through 6Z tonight when there's not a drop falling now) and takes that max through Milwaukee (4" by 18Z) then towards Flint by 06Z tomorrow night. Another max develops near Toledo by 00Z tomorrow evening and extends up to Buffalo.

Local AFD's aren't saying squat other than "SVR STORMS POSSIBLE" at the most.

- Rob
 
A 12 hr forecast from the 18Z RUC would be valid 06Z, whereas the 12Z ETA 24hr hour forecast would be valid at 12Z - so this is really compairing apples with oranges.

Opps :oops:! What I meant meant was the 12Z ETA 18HR forecast (that truly is what I meant :eek: )...

Anyway, I am still trying to understand convective feedback and model physics/etc. I thought that if the model falsely initiates convection (on either scale), that it would contaminate the downstream grids in several ways -
1) Thunderstorm outflow/clouds would cause temps to cool
2) Model soundings for the particular region would show almost complete saturation (since the model is "raining)
3) Not sure, but wouldn't it also cause intense VVs?

All of which would be false, since there is no convection occuring (am I making sense? LOL)

As far as ensembles (mainly 09Z SREF), shows pretty much similar solution to the 12Z models...
 
Checking the WRF & 10km TAQ both have the same line of thinking with monstrous helicities over southern third of MI and extreme winds & CAPE in IN/OH.

- Rob
 
Checking the WRF & 10km TAQ both have the same line of thinking with monstrous helicities over southern third of MI and extreme winds & CAPE in IN/OH.

- Rob

I'm getting ready to run the WSETA on a 10KM grid using non-hydrostatic and no convective scheme (DTX suggested the no-convective scheme approach)... I am using the Tile 12 ETA to initialize) I could always use the GFS though...
 
Anyway, I am still trying to understand convective feedback and model physics/etc. I thought that if the model falsely initiates convection (on either scale), that it would contaminate the downstream grids in several ways -
1) Thunderstorm outflow/clouds would cause temps to cool
2) Model soundings for the particular region would show almost complete saturation (since the model is "raining)
3) Not sure, but wouldn't it also cause intense VVs?

All of which would be false, since there is no convection occuring (am I making sense? LOL)

You are correct that all of these things will make changes in the model forecast - and if the evolution doesn't reasonably match the forecast, then the model output is progressively degraded with time. I'd probably call this convective contamination though - not convective feedback. The "feedback" is the key term here - once convection occurs on the oversized scale (for example grid scale convection on say an 18 km square grid - which is one big updraft!!!) will cause considerable latent heat release within the model - quickly generating a small, compact and intense disturbance with mucho precip - and the impact to surrounding areas is strong convergence leading to further grid scale convection. This occurs on a much smaller scale with any model generated precip - but appears like grossly amplified in the case of true convective feedback. The AVN model is notorious for convective feedback problems - often showing up as a ringed bullseye of precip from seemingly no apparent forcing. In this case - the forcing is clearly evident in the model - and the upscale growth is at least reasonable. Will it actually happen? Guess we'll find out soon enough.

Glen
 
Back
Top