Forecasting help

[Keith Mullen]

Perhaps someone could help me figure this out. I am apparently lacking on forecasting capabilities, as I just can't see much of any "bang" occurring tomorrow outside of what I see as a teeny possibility perhaps in a small area around the border of NE TX/NW LA/SE OK area.

I see potential for the possibility of some garden-variety rumblers, but what are (or what features are) the players responsible for the possibility of something severe?

I'm not seeing it - and I need to know what I am not seeing, and why I can't identify it. PLEASE.

I don't see enough deep moisture returning north over the next 24 hours - let alone moisture pumping as far north as forecast.

I don't see the lower level winds or 0-6 shear being more than ho-hum west of LA by afternoon.

...and I personally question the possibility of seeing strong convective potential. To me (remember, this is me looking at everything & my own probably poor predictions), it looks like the moisture may be insufficient, shear low-moderate at best, the dryline staying east in addition to not forcing well, MLCAPE and LI also overstated (IMO)...

What am I missing? What am I misenterpreting?

Please help, operaters are standing by waiting for your call...

 

[Robert Edmonds]

I haven't been following this day since I can't chase. However after just a quick look here are some parameters I noticed look good that perhaps you could take a look at. CAPE is close to ~2000J/kg (not bad considering what we've been chasing this year). There is also 500mb & 700mb bulk shear in the 40s and 60s (kt) with a good amount of helicity indicating possibility of rotating storms.

 

[Skip Talbot]

The shear is actually quite strong. What maps are you looking at? What numbers are you getting? The 12z WRF is showing 40-50 knots of 6km shear along the dryline at 0z. That's more than enough for supercells. Effective helicities approach 300 not far off the dryline as well. 0-1km shear approaching 30 knots is also supportive of tornadoes. That sounds pretty darn good to me.

As far as the moisture depth is concerned, I can't really tell you because I haven't looked at any forecast soundings. What is your reasoning for doubting the models? It looks like there is a strong LLJ thats going to advect moisture off the gulf the night before.

For the instability... if you are doubting the moisture values, than yeah your instability is also going to suffer. However, if cape values do indeed approach 2000 with the shear combo stated above, we have an environment that is favorable for tornadic supercells. The dryline looks quite sharp, and with the shear, and weakening cap initation should not be a problem either.

 

[Andrew Stoller]

The 18Z NAM is showing 60 degree dewpoints, 2,000 J/KG CAPE at 00z, along with 1KM EHIs getting up to 3, 3KM EHIs are getting up to 4, 3KM SRH is up to and past 300 along the dryline, and there's a fairly substantial cap through the day that erodes by 00z. Some of the NAM forecast soundings were showing a 99% supercell potential and 6KM shear of 50 knots.

If that doesn't produce something more substantial then garden variety rumblers, then I don't know what would!

 

[Keith Mullen]

Sorry, I'm at the office currently, so I can't really hop on and take another good peek at everything till I get home - which will make it that much more interesting to see how things have progressed.

Further north in the target area there appears to be a better setup for the changes with height but I see the T/Td depression and mixing being a bit too much...

Last I looked, it still appeared that the LLJ and moisture would still be barrelling in from the WSW and migrating easterly throughout the day - keeping the good moisture from moving to the KS border. Keeping an eye on High & Low systems tracking tonight.

...but it looked like the juice was still going to be forced on far too south and easterly towards LA. Heck, even Shreveport has been looking dry lately.

..and where the moisture is sure to return - speed with height yes, but turning looked sad.

There will be some storms, I don't doubt that, but I don't see anything that would make me want to drive more than an hour out of my way (at this time - watch me eat my words tomorrow).

The system that has been hovering over Idaho dropping tornadoes today isn't moving south at last peek - tracking ENE... but that's a whole nuther topic.

I know the forecast that folks who know what they are doing - says 1500-2200CAPE, but I can't visualize that occurring up into OK.

I guess I can revisit this when I am on my own PC at home - and closer to the target time.

This system/setup is stumping me, as I can't see the forest through the trees, and others seem to be quite hopeful.
...and I am not on track with the majority consent forecast.

I really appreciate your help in trying to show me what I am missing, and what I am misenterpreting.

Keith

** It is also good to be able to address this just before - and while - the event is setting up... so I can watch things unfold as they occur vs. looking back and scratching my head.

...again, thanks.

just snuck on and took a quick look at the current - and it still looks like LA/AR to perhaps TX is the only fair shot. I gotta be wrong.

 

[Jeff Snyder]

Keith,

Just for the record, nobody is thinking this will be an outbreak-type setup. It's marginal in the eyes of most folks I imagine (some may be more optimistic, others less so), but I think it's worth chasing. There are some marginal setups every year (marginal in the sense that model forecasts didn't indicate a particularly favorable environment for tornadoes and/or tornadic supercells) that surprise us... Every chaser has a different level of "risk vs. reward". Some chasers will chase marginal setups, bust a bunch of times, but also get to see some of the 'surprise' events; other chasers don't want to or can't chase as often (money, job or family committment, an unwillingness to drive long distances or spend much time for what may well be a busted chase), but they will invariably miss some of the more 'needle in a haystack' events.

It seems that you are pessimistic on tomorrow's threat for supercells because you think the models are overforecasting surface moisture return. That's a fair argument to make... If it's any consolation, there is decent agreement between models and between model run times (i.e. model-to-model and run-to-run consistency) of at least >55 F Tds returning to very near the sfc low by late afternoon. This may be overly optimistic, but we'll see.

I encourage you to post your thoughts in the FCST thread. There's room for some discussion there, and posting in the FCST thread is a good habit to get into largely because repeated forecasting is one of the best ways to improve your skills since you're forced to pay attn to and interrogate events that you may not otherwise.

 

[Keith Mullen]

Thank you

Thanks... well, my questioning here isn't so much of placing a forecast. I'm trying to put a beginner question in the beginner section on interpreting, analysis, and forecasting - that could be applied to any set up.

I'm just using the currently approaching event as the Guinea Pig - if you will.

I just didn't want to tie up the forecasting thread with my lines of questioning, nor with my failing at arriving at the same conclusions as others. It's oft hard enough to extrapolate info from the FCST/NOW without having to wade through my rubbish.

Not trying to poo-poo anything or anyone. Just trying to find out why the models say the event will bring a fairly decent shot - when I looked at it all with pen and paper, it fails to verify. So my thread is "where am I screwing up" I guess.

Perhaps if I just disect it down a bit.

Again, thank you.

 

[Rob Satkus]

So my thread is "where am I screwing up" I guess.



Again, thank you.

Something else to consider...just because your forecast doesn't match up with others, or even with the models, doesn't make it wrong.

RS

 

[Andy Wehrle]

I'm just using the currently approaching event as the Guinea Pig - if you will.

Actually, I think what we have coming up is a good "guinea pig" event to discuss without the restrictions of the Target Area. Common to many setups, it has two (or three) distinct potential target areas that may or may not produce. Each has its pros and cons (ignoring logistical concerns like terrain for the moment).

You have

A.) the warm sector surface low/triple point play

B.) the cold core play (which may not be geographically very far removed from A) and

C.) the farther south dry line/open warm sector play.

Does anyone else think there is potential for the surface low to "pull" moisture in and pool it against the warm front? If this happens, I'd bank on (B) being the place to be, if only to be assured of backed 850s and not having to worry about determining where along the dryline a storm is going to initiate.

 

[Keith Mullen]

Interesting

Forecasting: assistance is futile

Well, things have definately improved considering the timing and placement of everything involved with this system, compared with what I was looking at yesterday (re: 04/09/09 setup).

If anyone would like to take a stab at what influenced any of this, please do - it will help:

1. The low system maintained itself in a position a little more S and W of where it appeared to be migrating to - keeping lower flow more from the south & cutting down on veering. Result of the jet and upper levels influencing timing and placement?

2. UVV and shear profiles are positioned well in relation to the movement of the warm front.

3. Though not as weak as I was forecasting, the T/Td showed some improvement in advancing a little more NWerly. The better stuff still over AR/LA, but sufficient possibly approaching SE KS.

Though each of these movements are very minute when looking more on synoptic scale - where all their paths are progged to cross today is looking pretty darned explosive in a relatively compact area.

Wishing I was on the central border of OK/AR right now. For a second location, I would settle for a hair NE of Coffeyville.

Anyone else want to add/interject on this please? Thanks.

Oh, and thanks for the positive feedback guys.

 

[Derek Weston]

The 18Z NAM is showing 60 degree dewpoints, 2,000 J/KG CAPE at 00z, along with 1KM EHIs getting up to 3, 3KM EHIs are getting up to 4, 3KM SRH is up to and past 300 along the dryline, and there's a fairly substantial cap through the day that erodes by 00z. Some of the NAM forecast soundings were showing a 99% supercell potential and 6KM shear of 50 knots.

If that doesn't produce something more substantial then garden variety rumblers, then I don't know what would!

Certainly we did end up with a setup that produced storms of far greater intensity than garden variety -- 3 are dead in Arkansas after an encounter with a (likely) strong tornado. Perhaps violent. (though no specifics yet)

In taking a look at some of the data from Ark into Louisiana during this outbreak, I noticed some extremely strong Helicity values -- of significance was the 0-1km helicity values that were > 350 in areas across the region. (significant low level shear)

Decent CAPE was present, though, modest at up to 1500 J/kg or so where the most significant tornadoes took place. The area was *nearly* capped -- the extreme shear possibly overcoming.

Directional shear wasn't outstanding, with 850 flow having a definite westerly component -- however, enough to generate semi-isolated supercells capable of tornadoes. (if I remember correctly, however, anvil level winds were more favorably oriented for discrete activity as opposed to what we saw in Oklahoma -- this may have been a factor too)

The key further east in this outbreak, after dark, was the sort of sheared environment the storms had to work with, IMO. (from a forecast perspective, keep an eye on the low level nocturnal jet -- we usually see enhanced shear profiles after dark... the question, where tornadic storms are concerned, then is how much instability can still be realized -- if enough, you get what you saw Thur night)

 

[Keith Mullen]

things change

More moisture definately followed the leading edge of the low in a very tight line up to the KS border - a few points higher in localized areas than I had foreseen.

I hadn't taken the strengthening of the nocturnal LLJ into account in the later hours of the eve - was thinking it would go too linear & messy in the later hours as it passed the Western third of AR.

Movement of the system to the east after reaching the OK/AR line stalled a hair longer than I had anticipated as well.

Now that I have been spending more time on putting emphasis on the forecasting/prediction side of things, rather than wishcasting & then paying attention by late morning of - it's definately opened my eyes a little more to the behaviour of weather.

A little dash of this here, a tiny push of that there - alone doesn't necessarily amount to anything substantial... but, when each factor is given a small change all at the right time, it makes all the difference.

Question to add to this whole mix: Did the transition from the more flat terrain to the hills while moving across the state line potentially provide any influence in this - by providing another dash of orographic lift? Or was the already S winds relatively unaffected due to the direction of motion? Just another thing for me to muse.

Thanks.

 

[Neil Robinson]

This may seem like a daft question, but when forecasts refer to the 'Four Corners' region, where is that exactly?
Cheers

 

[Tim Vasquez]

The NM/CO/AZ/UT border junction.

http://en.wikipedia.org/wiki/Four_Corners

Tim

 

[Neil Robinson]

Thanks Tim. I should of course Wiki'd or Googled it myself but it's mid-afternoon on a warm, hazy day here and my brain isn't operating at full speed!