05/07/05 FCST:Central Plains

[Jared Mysko]

don't forget ND. Things look pretty good for this time of year up north. Keep in mind it is currently warmer in central Alberta than it is in Oklahoma at this time. Lightning strikes are being recorded way up north today in Alberta and forecast temps have increased daily this week since last weeks crappy cold. I'm excited either way since there will most likely be some storms happening into southern Manitoba on Saturday.

either way, wherever you are on Saturday, take care and have fun.

cheers,

Jared

 

[Justin Turcotte]

Models have gotten progressively slower with this system. A couple days ago I would have said Watertown, SD looked good now I'd have to shoot for Mobridge, SD, where the triple point might set up and where jet divergence looks the best. The warm front will extend east/southeast of here through Minnesota (outside the scope of most folks version of the central plains). There will be a fair amount of instability and shear along this feature and it may also be worth watching.

 

[nickgrillo]

I pretty much like Saturday, especially southcentral KS and northcentral OK, which is the area I'm focusing on. We're targettting Pratt, KS as of last night's 0Z run...

We'll have a cold front stretching from western SD south into TX. Excellent low-level moisture (dew points >60F) will continue to build ahead of the dryline in KS with strong low-level shear (>250 m2/s2 0-3KM SRH). This yields CAPE in excess of >4000J/KG in parts of SC KS SAT afternoon. Winds have gotten a bit stronger, but still not the best (wish we had more upper level support)... However, either way I believe there is enough to support supercells/tornadoes...

Note that there could be an outflow boundary in SC KS, which will be set down by tonight's convection and this could lower dew point depressions...

 

[Gabe Garfield]

I can't believe SPC is only going with 15% probs...it makes no sense. I really fail to see their reasoning.

The 6 Z run increased CAPE up to 3000 j/kg in a broad swath from north Texas to south central Kansas. In addition to this, the wind fields at all levels are more than sufficient (850 winds up to 40 kts, 500 winds at 45 kts, 250 winds at 70 kts) and are highly indicative of supercells, if storms fire (6z ETA breaks the cap in NW OK and C. KS). Also, Tds are forecast to be in the mid 60s, so dewpoint depressions won't be insanely large, provided temps don't exceed 80 by much.

In any event, supercells with large hail seem to be a good bet (if not tornadoes). Past model runs painted a somewhat marginal situation, but this one is getting better with every run.

Gabe

 

[Jim Bishop]

Originally posted by Gabe Garfield
I can't believe SPC is only going with 15% probs...it makes no sense. I really fail to see their reasoning.

The 6 Z run increased CAPE up to 3000 j/kg in a broad swath from north Texas to south central Kansas. In addition to this, the wind fields at all levels are more than sufficient (850 winds up to 40 kts, 500 winds at 45 kts, 250 winds at 70 kts) and are highly indicative of supercells, if storms fire (6z ETA breaks the cap in NW OK and C. KS). Also, Tds are forecast to be in the mid 60s, so dewpoint depressions won't be insanely large, provided temps don't exceed 80 by much.

In any event, supercells with large hail seem to be a good bet (if not tornadoes). Past model runs painted a somewhat marginal situation, but this one is getting better with every run.

Gabe

I agree, for the most part. As I briefly mentioned in the talk forum, I was surprised when I did not see a moderate risk for Saturday. IMO, there is a moderate risk for supercells producing large hail. The tornado threat will be there, but I wouldn't presume to be too agressive with that mentioning until the next update. But, forecast hodographs show a low level curve basically from southwest kansas to northwest oklahoma.

If I didn't think the tornado threat was going to be there, I wouldn't be planning on leaving Houston at 3am tomorrow to chase!

 

[Jeff Snyder]

Gabe,

I think the prob is only at 15% hatched because of coverage issues. It seems that storms will likely be isolated, so 15% is probably all that is needed unless it looks like there'll be more than a few storms in the area..

I currently have two more localized areas in mind. I've only really looked at TX/OK/KS area, since that's my chase domain tomorrow... Regardless, one is near I40 in the eastern TX panhandle / western OK area, and the other is up closer to the DDC area. The 12z NAM was showing a potential dryline bulge in the southeastern TX panhandle and the far wester part of the west north Texas area. In addition, the NAM brings up >65 Tds in a narrow corridor primarily south of I40. So, we may see locally backed flow if the feature mentioned above really is a dryline bulge, enhancing the low-level shear.

As for the "northern" local target near DDC... For whatever reason, my first hunch has been to target this area. The 850mb flow is stronger near and east of DDC than it is in the eastern TX panhandle and OK/TX border area, which yields a slightly stronger low-level shear profile. Unfortunately, the NAM is showing weak deep-layer shear up in this area, with 0-6km shear in the 25-30kt range. Given 2000-3000 j/kg CAPE, the deep-layer shear should be "sufficient" for supercells, but that's really on the low-end of deep-layer shear for supercells. For what it's worth, the NAM is showing deep-layer shear in the southern local target in the 35-40kt range, more favorable for supercells.

Right now, the NAM is telling me to choose the second local target based upon STP and SCP and some other parameters. We'll see though... magic seems to happen up in that part of KS, so I'm not so sure...

 

[Bill Tabor]

Folks any of you check out the EHI for tomorrow? I have a hard time getting excited when the only area with a decent number is SD at above 5. No way I'm gonna do SD on a one day shot. Looking down in Tx I see EHI above 3 which isn't bad but precip isn't shown to breakout.

Speaking of precip...based off of todays 12z NAM what will be the cause of initiation of convection in eastern OK/KS? NAM shows it between 18z and 0Z but it appears the dryline is still far west. There really isn't any mid level lift showing in these areas that I can see at all. Any ideas?

Edit**
Could it possibly be upper level divergence?

 

[Gabe Garfield]

Originally posted by Bill Tabor+--><div class='quotetop'>QUOTE(Bill Tabor)</div>

Folks any of you check out the EHI for tomorrow? [/b]

I'd be careful about reading too much into model-progged composite indices. Models have a +/- 30 % (I would say) error on values of helicity/CAPE. So, just a 1000 j/kg increase in CAPE and a helicity increase of 100 m2/s2 (which I've seen happen) can make a huge difference in a composite index.

<!--QuoteBegin-Bill Tabor
Speaking of precip...based off of todays 12z NAM what will be the cause of initiation of convection in eastern OK/KS?

Looks like ageostrophic curvature divergence to me (at the geopotential inflection point). So, yep, upper level divergence, I would say.

Well, I analyzed the daylights out of the 18z ETA model run...not much new to say. It does appear that there will be a significant backing of winds in W. Ok, which could really help the low-level shear. Kansas not looking better than W. OK, except, that it is closer to upper level support. All else being equal (between OK and KS), though, I'll go to Kansas.

At any rate, Nebraska doesn't look too shabby, provided the best shear can juxtapose with the best CAPE (which might be a chore, judging from the latest ETA/NAM).

Gabe

 

[Jeff Snyder]

Originally posted by Gabe Garfield

Well, I analyzed the daylights out of the 18z ETA model run...not much new to say. It does appear that there will be a significant backing of winds in W. Ok, which could really help the low-level shear. Kansas not looking better than W. OK, except, that it is closer to upper level support. All else being equal (between OK and KS), though, I'll go to Kansas.

At any rate, Nebraska doesn't look too shabby, provided the best shear can juxtapose with the best CAPE (which might be a chore, judging from the latest ETA/NAM).

Gabe

I agree with Gabe here... The 18z NAM is showing >65 Tds south of I40, with signficant backing in (primarily) southwestern OK by 0z. CAPEs >2500-3000 with the nice shear profile and decent Tds tells me that we this is as good a place as any south of Nebraska. Now, the 18z NAM is also showing precipitation (and associated cool sfc temps, etc) across western OK between 12-18z. So, if this garbage doesn't clear out in time, there'd only be a pretty narrow corridor between the dryline in the eastern TX panhandle and the grunge in western OK. Assuming with do get enough clearing, I like the area... Right now, I'd say west of I40 to Shamrock... The presence of Hwy 83 in Shamrock means that we'll have a good North/South option to reposition if needed, which means that I may end up in Wellington TX (far southeastern TX panhandle) or Sitka... LOL Obviously need to refine the target area later...

 

[Bill Tabor]

Originally posted by Gabe Garfield
I'd be careful about reading too much into model-progged composite indices. Models have a +/- 30 % (I would say) error on values of helicity/CAPE. So, just a 1000 j/kg increase in CAPE and a helicity increase of 100 m2/s2 (which I've seen happen) can make a huge difference in a composite index.

Yes it can, but the index has a purpose too and that is to calculate more or less an average of cape and helicity. This is pretty much what we do separately / manually anyway. I think the value of what it is showing is that at a glance it is summing up all the areas and showing more or less what is potentially more significant.

In the case for the 12z run of today most of the plains south of SD aren't too impressive. About all we can do is look at what the model offers us or wait for another run to see if it changes. I agree I shouldn't base my whole forecast / go no go decision on this alone as you say it can change. But I suppose what I am saying is it isn't a good sign. It's not consistently showing something strong such as it has in the SD area consistently.

No doubt it will change from run to run. Last night I could have sworn Medicine Lodge, KS was a great spot and I was going to leave earlier today but the 12z run just looks less intense than last nights 0Z. Granted 18z is out now.

I'm just trying to break it down into some workable consistent targets and right now I keep getting a poor solution overall except far north and that may have it's problems as well.

I'll keep looking at it. Maybe I'll figure something.

Today, kind of worked out the same way to some degree granted it was never as strong of a day. It ended up just getting a few storms with moisture weak and dynamics spread out. One storm got going well and may have dropped a tube. The rest didn't seem to do much.

 

[Mike Johnston]

Originally posted by Bill Tabor

Speaking of precip...based off of todays 12z NAM what will be the cause of initiation of convection in eastern OK/KS?
Could it possibly be upper level divergence?

I thought we were looking to the eastward movement of the dryline for initiation Saturday...seems to be pretty definite forecast of eastward movement all the way from central NE, through W Central KS and down through E panhandles, with most noticable bulge in lower E TX panhandle -at least that is what dewpoint gradients and accompanying surface wind shift line seem to indicate. Beyond that, there is an axis of 850mb divergence running N/S just to the east of the dryline. I just assume accum precip forecast over central and eastern OK/KS is result of eastward movement of storms so initiated, but maybe I am missing something.

 

[Michael P. Morris]

Looking at the 0Z run of the NAM, it appears that an area of precip will break out over west-central Oklahoma by 18Z as indicated by an area of lower temps around OKC. It does not appear (per mesoanalysis) that the ongoing convection has produced an outflow boundary yet, but that could come with time. I am considering revising my target area based on three significant factors - a strong divergent region at 300 mb over Western OK/TX Panhandles, increased instability by 0Z, and the likelihood of an outflow boundary from the convection during the day (as forecasted by the NAM). Depending on how things shape up overnight, I may be taking I-40 instead of I-35!

 

[Bill Tabor]

Originally posted by Mike Johnston

I thought we were looking to the eastward movement of the dryline for initiation Saturday...seems to be pretty definite forecast of eastward movement all the way from central NE, through W Central KS and down through E panhandles, with most noticable bulge in lower E TX panhandle -at least that is what dewpoint gradients and accompanying surface wind shift line seem to indicate. Beyond that, there is an axis of 850mb divergence running N/S just to the east of the dryline. I just assume accum precip forecast over central and eastern OK/KS is result of eastward movement of storms so initiated, but maybe I am missing something.

That's why I brought it up. It looked like it was too far east to be caused solely by the dryline. It didn't look like it was moving that far east that fast to me. Guess I'll check the new 0Z now and see what is up.

 

[Jay McCoy]

What I am starting to wonder is how far the dryline will actually progress east. The models for today showed the dryline was going to set up close to the NM/Tx border but it is still against the NM mountains and all the panhandle has SSE winds. Couple that with all the ground moisture we have from a wet past week and I dont see alot of mixing east. It wouldnt surprise me for the dryline to set up close to amarillo on Saturday and not the edge of the caprock unles it makes a b-line east overnight which is rare. Usually it backs west at night in this area so I see it still in NM at daybreak.

Will be interesting to see how the models initiate and handle it.

 

[Jeff Snyder]

As with my previous posts, this will only pertain to the southern KS / OK / TX area.

Well, run-to-run consistency isn't the best... I'm not quite as optimistic as I was with previous runs, largely due to the NAM decreasing 500mb wind forecast from an already marginal forecast previous... The 0z NAM is now showing 500mb winds of 30-35kts for the OK/TX/southern KS target. Surface winds back to nearly southeast by 0z east of the dryline in the TX panhandle and into western OK, but it looks like a grungefest in western OK tomorrow may suppress instability except for a relatively narrow corridor ahead of the dryline. This grungefest can be seen by the 850mb RH (90-100%), model QPF (widespread light amounts), and surface temperature plots (notice the upper-60 to low-70 temps in western OK). It is pivotal that this crap clear by afternoon, though it'll be a close call. Things should clear immediately ahead of the dryline in central and eastern OK/TX panhandles. The best 850mb flow is elongated N-N-NNW to S-S-SSE (LOL, so a very deviance from n-s), meaning there'll be slightly strong 850mb flow farther north across eastern OK ph, nw OK, sw/sc KS, than points nearer I40.

In terms of model QPF, the NAM is showing signs of convection by 0z immediately southeast of AMA, which is the only QPF behind the grunge in western/central OK.

All in all, it still looks like I'll be heading to Shamrock in the morning, and probably a little west given the westward shift in the NAMs dryline forecast positioning. Whatever the case, I do expect to either stay on I40 or head northward in time, but we'll see.

EDIT: I don't really agree with they 6z day1 outlook, as it nearly neglects discussion pertaining to the area from central KS southward... It mentions meridional flow in the mid-levels from centra/northern plains, but midlevel flow in the southern plains (i.e. southern KS, OK/TX) is NOT meridional. Additionally, if wind profiles were backing with height, we'd have negative helicity given likely storm motion, which would support left-splits / anticyclonic supercells over cyclonic supercells, and thus, the 5% torn prob would be for anticyclonic tornadoes primarily... Given the rarity of that, I doubt that'd be the case... LOL So, my target still holds.