3/25/2007 DISC:MN/IA/WI

[Andrew Pritchard]

I'll answer your question with a quote from above cause it think it answers your question. I guess I dont consider mositure availability part of the system its self. So once agian I will try to simplify my statement for you, take a 985mb low put it in MN in March you might get 60 dp's in WI, but with a low of the same strength in the same location in June you might see 70dp's I guess if you consider the mositure source the system itself instead of the gulf then it wouldnt make sense. If you have anymore comments regarding my opinion please just PM me.

Okay, I see what you're saying, but I guess I don't see the point. Slightly higher dew points (60s would have been sufficient) and there could have been a tornado event today. You don't need 70F td's and the calender to say June for a tornado outbreak.

It reminds me of when people say things like "if he had made that shot, we would have won the game" Sure, if this and that was different it may have been different but it wasn't.

 

[Robert Dewey]

Sean;

I don't get the connection either - please clarify.

As for the "system in the summer", I again agree with Andrew and Rob Dale. Obviously if you change a parameter to be more favorable, you'll have a higher probability of tornadoes. I could also say that if this system had occured with lower LCL's, we'd be looking at more tornadoes. The main argument that was being made is that 75/65 T/Td with the same kinematic field in March would yield less tornadoes than an identical setup in July. The point is, 1500J/KG in March is the same as 1500J/KG in July (which isn't unheard of).

Also, the amount of shear today wasn't something that can't be achieved in the summer (or any other season). Thermodynamics are just as much a part of the system as the pressure depth and wind profiles.

 

[Dustin Wilcox]

Okay, I see what you're saying, but I guess I don't see the point. Slightly higher dew points (60s would have been sufficient) and there could have been a tornado event today. You don't need 70F td's and the calender to say June for a tornado outbreak.

I realize this I have seen a couple tornadoes on sub 60 dp days, I know there is a lot more besides moisture that goes into makeing a day a outbreak or a bust and I would like to hear some educated opinions on what besides moisture made today a bust.

Sure, if this and that was different it may have been different but it wasn't.

While this should probably be moved to DISC thread what is this and that in this case, beings tornadoes can and have occurred on sub 60dp days what other factors doomed today?

 

[Dustin Wilcox]

I opted not to chase today but long about noon or so I was thinking maybe I would be regretting that decision as the Satellite showed better clearing then earlier forecast, the RUC runs from this morning were pretty aggressive with precip over much of NE IA and CAPEs were already approaching 1000j/kg over much of central IA and that was beginning to surge North. Obviously veering winds didn't help the already marginal dp's, but even the SPC increased the tornado threat based on what they were seeing as of Mid-late morning. I was not around to monitor the situation this afternoon so I am not sure what went down after noon but I am curious as to what else made this event a non-event. Based on what I saw around noon with weakening cap and increasing instability I thought that NE IA into S WI would see a decent squall line.

 

[rdale]

The NOW thread pretty much describes the progression... Minimal surface moisture and high bases hurt.

RUC precip is pretty close to useless, far and away the worst of all available models. Better to use its diagnostic fields.

 

[afischer]

Obviously veering winds didn't help the already marginal dp's, but even the SPC increased the tornado threat based on what they were seeing as of Mid-late morning. I was not around to monitor the situation this afternoon so I am not sure what went down after noon but I am curious as to what else made this event a non-event. Based on what I saw around noon with weakening cap and increasing instability I thought that NE IA into S WI would see a decent squall line.

I think ultimately one would want to assess why the surface winds near/just ahead of the primary convective band ended up veering as much as they did... & then maybe watch for similar set-ups in the future for "pattern recognition." (FWIW, the initial Day 1 outlook for this event indicated there were in fact model discrepances with respect to how much surface veering would occur. I didn't personally look at any model data for this event though).

The compact shortwave trough itself appears to have had a definitively "positive" tilt, which in my experience doesn't bode as well for increased ageostrophy & backed surface flow via pressure falls. Like you say, the veered surface flow in the main action area probably hurt tornadic supercell potential via increased ML LCLs and decreased low-level SRH. These are the types of mesoscale details it would be nice to know of beforehand, but alas... it's not always that simple.

A SPC MCD hit well on the increased tornadic threat over central and eastern WI (obvious on 00Z GRB sounding) associated with a few rogue cells that fired ahead of the primary DPVA-induced convective band. I don't believe these storms were able to capitalize on this better environment (surface flow remaining backed & relatively rich BL moisture) due to the lack of mesoscale focus/synoptic scale vertical motion that far downstream of the shortwave trough. Regardless, by 03Z or so the cells were toast due to boundary layer cooling.

As for the lack of storms farther south trailing into northeast Iowa... probably can be attributed to a lack of vertical motion (or even large-scale subsidence... I've seen this before) immediately south of the compact shortwave trough moving ENE through the upper MS river valley.

 

[Beau.Gjerdingen]

I would just add that the mixing out of the moisture had a ton to do with the lack of instability present. 12z morning soundings had a huge dry surge just above the surface flying up towards northern IA and southern MN, these areas showed forecast 850 dewpoints of 6 and under by the early to mid afternoon. Strong winds allowed for plenty of mixing and if you watch the surface obs over southern MN as well as northern IA during the mid afternoon you will see a steady decline in dewpoints, even drying out into the mid 40's into north central IA.

The surface based instability forecasted was completely reliant on inflated low level moisture. The RUC didn't pick up on this until its afternoon runs which finally started spitting out almost NIL on the cape situation. Also the morning sounding from MPX had a fairly worked over almost moist adiabatic look to it, very poor lapse rates to work with and try to make big instability out of. Hindsight is 20/20 though. I was sitting down in Albert Lea, MN wasting away my Sunday as well. Good day to get all the equipment back in order though.

 

[Mike Hollingshead]

There wasn't anyting wrong with today, what wasn't right was your forecast, period point blank. Believe me, I wanted today to pan out just like everyone else but I just had to say to myself, "Its freakin March just be patient." Beleive me, I was ready to tear ass out to NC Iowa and I had to talk myself out of it. I'm just saying remember what time of year it is.

At least my period point blank wrong forecast was after more than just the fact it was March outside when I left. For what it is worth, I thought it was "wrong"(right) when I left to begin with, but thanks for letting me know all about my unposted thoughts...after the fact...and for the reason it's March. I guess some of us are more willing to try, regardless of the month(or distance in some cases). Wasn't it March out when you chased/busted in southern NE the day before?

 

[Damon Scott Hynes]

Wasn't it March out when you chased/busted in southern NE the day before?

Only March and SDS is epidemic, LOL...

 

[Rich Thompson]

I tend to agree with the folks "blaming" the moisture for the chase let down. It sure would have helped to have a sounding in central IA along about early afternoon. The DVN sounding revealed a rather deep moist layer at 18z, but it was tough to say how far west that profile extended. In retrospect, it obviously didn't extend far enough west as the moisture mixed pretty badly from the DSM area newd into WI - just ahead of the primary convective band.

We did get a few discrete storms with some supercell structure, and who knows how close we were to seeing more robust storms. A few degrees on the Tds through the boundary layer would substantially increase CAPE, and perhaps change the whole situation from a "bust" to a few solid supercells and perhaps a couple of tornadoes.

Forecasts are incorrect at times, and it's not always because the forecaster is a moron. We suspected the moisture was marginal, but SPC forecasts include the influence of other forecasters and previous outlooks. In this case, those influences didn't happen to help. Sometimes they do help. For those of you that thrive on criticizing public forecasts, do us all a favor and broadcast every detail of your erroneous forecasts. For those of you that have the guts to admit in public that you messed up, you have my utmost respect.

Rich T.

 

[Stuart Robinson]

Rich,
Working out why the forecast did not verify as planed is just as important (more so I would say) than scoring a successful forecast. Here I am talking from the stand point of a chaser who only has a busted day to loose and not official government output that will have people cancelling expensive events etc – that is a lot of pressure.
It troubles me when people slate the Government bodies for a poor forecast – you can only go on the information that that you to had right then and now.
It seems that when the SPC get it right – there is little credit given – get it wrong and you are slated.
As an aside this is just a US thing – Our own UK Metoffice gets the same treatment !!! which IMO is unfair.

 

[Brett Adair]

I tend to agree with the folks "blaming" the moisture for the chase let down. It sure would have helped to have a sounding in central IA along about early afternoon. The DVN sounding revealed a rather deep moist layer at 18z, but it was tough to say how far west that profile extended. In retrospect, it obviously didn't extend far enough west as the moisture mixed pretty badly from the DSM area newd into WI - just ahead of the primary convective band.

We did get a few discrete storms with some supercell structure, and who knows how close we were to seeing more robust storms. A few degrees on the Tds through the boundary layer would substantially increase CAPE, and perhaps change the whole situation from a "bust" to a few solid supercells and perhaps a couple of tornadoes.

Forecasts are incorrect at times, and it's not always because the forecaster is a moron. We suspected the moisture was marginal, but SPC forecasts include the influence of other forecasters and previous outlooks. In this case, those influences didn't happen to help. Sometimes they do help. For those of you that thrive on criticizing public forecasts, do us all a favor and broadcast every detail of your erroneous forecasts. For those of you that have the guts to admit in public that you messed up, you have my utmost respect.

Rich T.

Great post, Rich. There are always many factors in putting together the "perfect" forecast. Things happen.....and I can't count how many tomes that a tornado event has busted due to stout mixing across my region of the country (Southeast). It's just something that happens and there is really excellent way to forecast how much mixing will occur. So, I can understand why the SPC guys went MDT yesterday given the potential had mixing not been as strong in this area.

 

[Daniel Christianson]

Ok im not going to be bad guy here, i can see everyones opinion , im going to be OT.. i chase because i love it, its much like fishing to me, getting away and enjoying whats offered and sure we all bit** about busting , for me whether its December or a slight risk for something miles and miles away i go,( Chased in NE on WED, Chased in Southwestern NE the next day, and Chased in MN to WN on sunday) i will say yeah im impatient, i want things to happen now and not hrs later i think we all want stuff to happen right away just to please us all..

 

[rdale]

SPC forecasts include the influence of other forecasters and previous outlooks. In this case, those influences didn't happen to help. Sometimes they do help. For those of you that thrive on criticizing public forecasts

What sort of "pressure" is there to "conform" to earlier outlook? For example if you sat down yesterday to write the 4pm DY1 and concluded that this no longer was worthy of a PWO, after a few days of broadcasting this to be a big event, is there a rule (written or unwritten) that would make you reluctant to downgreade the MDT for whatever reason?

We have this debate in the TV side frequently - where some feel that you shouldn't change the forecast much from the previous met's to remain consistant, but others say you always give out your best (since the public forgets within 5 minutes of hearing in the first place ;> ) I guess my experience seeing mets give a forecast they don't agree with but "flows" better with preceeding outlooks is more bad than not.

And telling whiners to show their own forecast is a lost cause... The reason they rely so heavily on SPC usually has to do with their lack of ability, and regardless of how it happens - if a busted forecast impacts somebody, the American Way is to complain about the forecaster ;>

- Rob

 

[Melanie Metz]

I would just like to comment that we were concerned about the T/Td spread and lack of backed surface winds and didn't expect to see tornadoes. However, always the optimist, on days like that I just say "well, if the near storm environment is modified just enough and parameters unexpectedly come together for a tornado at least it will be highly visible and photogenic coming out of that elevated base!"

But March 55 dewpoints don't always equate to bust.

March 29, 1998 we had a large tornado in MN (St. Peter). Of course, the surface features were more conducive...nice backed winds with a surface Low and warm front. While dewpoints near St. Peter were only in the 50s, the Temperature wasn't much warmer thus LCLs were favorable.

And we have all been out on days later in the season with high instability, dewpoints in the 80's, nice backed winds, strong Low approaching..... but the shortwave just doesn't quite make it in time and the cap never breaks.

In the end, I just chase when there is a possibility. There are never guarantees. Just enjoy whatever the day brings! And sometimes it's a large wedge tornado with dewpoints at 55.

Melanie