4/06/06 FCST: KS/NE/IA/MO/OK/AR/TX

[Mike Hollingshead]

7pm forecast sounding for Sioux City

4pm forecast sounding for Norfork NE

Storm motions nnw at only 25 knots would sure be a nice change. I'll jinx it now and say Brady II somewhere in ne NE.

 

[Kevin Polston]

This forecast is based on the 00Z NAM (ETA) and if it is correct...or close to it (GFS is similar in placement of the synoptic features) then this is what I think will happen. It seems to me there are several ingredients coming together to promote tornadic supercells over portions of the plains. The threat area with the highest potential seems to be from eastern Nebraska through western Iowa into northwest Missouri. I like the potent mid level system entering the plains and spreading a large area of diffluent flow from KS/NE into IA/MO by 00Z Fri. Secondly the surface reflection of this system is a pretty rapidly deepening low pressure area...going from about a 992 low at 12Z over sw Nebraska to a less than 984 low over east central Nebraska by 00Z. That is a very good thing. The dryline surges eastward across the plains....and could occlude over northeast Nebraska with the warm front. This occlusion area I think could be the best area to target. Certainly the potential exists for tornadic supercells further south through western MO and far eastern KS....however...this eastern Nebraska area will be

1) on the nose of the dry punch pushing northward. There is a strong 700-500mb UVV max over north central Nebraska extending east along the occlusion and at the nose of the mid level dry punch;

2) the LCL heights will go quickly from over 1400(m) in southeast Nebraska to less than 800(m) over far northeast Nebraska and northwest Iowa. There is a corridor of low LFC heights from northeast Nebraska through western Iowa into northwest Missouri. This could be key.

3) 1km EHI values of 4-5 and 0-3km VGP values of .4 - .5 will be located over western Iowa and nw Missouri....arcing into the occluded boundary.

4) I dont think the area will stay capped as 700 mb temps cool to less than 4 deg C by 00Z under pretty good CAA at 700 mb.....and MUCIN values will be in the -25 to -50 range. More than sufficient forcing will exist to break through the weakening cap

5) wind shear will be more than sufficient for supercells...and augmented in the vicinity of the boundaries.

To summarize.....I think synoptically the pattern is quite potent for late Thursday afternoon into Thursday evening. I am reminded somewhat of the May 1975 Omaha tornado outbreak and how the surface pattern seems similar (ie, occluding boundaries and a deep low pressure system with a narrow tongue of moisiture and instability feeding into the system). I like the fact the system is deepening significantly up through 00Z. This is a real good indicator in my opinion of the potential for late in the day. Of course...it it still 48 hours out and alot can happen between now and then. But as of now....it looks good.

 

[Jayson Prentice]

I went through the 00z NAM as well as well as looked at some of the main features that the GFS had in so far. Kevin covered most things pretty well I think, the idea that LCL's might be too high isn't as much as a concern anymore. Models actually showing LCL heights to get down to around 500 in some areas of northwest Iowa. I had a nice long analysis of the model runs, but dont' know if its' worthwhile posting here. Its' on my website if you want to check it out.

Otherwise I'm thinking that this event is still looking mighty good, I like the cap that is in place and doesn't look like it will break until mid-afternoon. Much better than the previous events in which we saw the storms firing around noon already. Only question on that will be right along the low and to the northeast, if storms are there the whole day that might take away on northwest IA and even northeast NE's chances of significant severe weather. Models seem to agree that an area along the dryline, somewhere along the MO/NE/IA corners that may be a prime location.

Still 48 hours out and a lot of things to go through still... But, getting down with class at 3 and booking to the west sounds good so far!

 

[Matthew Havin]

Wow.....I didn't think they made fonts that big!

6Z NAM continuing to strengthen the land cyclone...... 980mb at 21Z Thursday.

Lemme repeat......980mb.

If memory serves me right, this is the strongest springtime low moving onto the Plains since 2001.

EDIT: Found it. April 11, 2001. Something like a 980mb low during the afternoon (983 at 00Z).

http://weather.unisys.com/archive/sfc_map/0104/01041200.gif

......which was a high risk day with 40 tornado reports. Shift the reports west, and you got tornadoes across E NE/W IA. Big difference between Thursday and April 11, 2001 will be the vertically stacking/slowing low Thursday versus a rocket takeoff of the system in 2001. We will see how this affects things.

Here is the SPC archive link:
http://www.spc.noaa.gov/exper/archive/even...0411/index.html

 

[Bart_Comstock]

In response to the Brian McKibben's post, yes it does appear that the SPC is thinking about the possibility of upgrading parts of the risked area to a High Risk. However you may want to edit your post, and tone the font down a bit as well as add a little more content to it. Not trying to be rude, just trying to help.

Originally posted by Chase Forecast Posting Rules
(3) Prohibited content. Users may NOT post the following:
* Weather bulletins and forecast images, except as brief excerpts, in moderation, and with an explanation of their meteorological relevance;
* Links without an explanation of their meteorological relevance;
* Noise: posts containing only exclamations, salutations, witticisms, or personal anecdote (e.g. "I sure hope we get a storm. Bye!");
* Content containing no information relevant to the topic.

As for the forecast....
Eastern Oklahoma dryline looks VERY impressive IF the cap is able to bust almost all the storms will be supercellular with fairly good tornadic potential. There's also a weak spot in the cap in SW Arkansas at noon on Thursday, isolated supercells could bust out there too. Overall, a big outbreak looks like a good bet. Hopefully most of the big action will happen in rural nothing and not affect too many people. The last thing we need is a big one to roll through KC or Ft. Smith (etc...). Also to those of you who are going to go out and chase this setup. Be sure to stay safe and watch your back, these suckers are going to be hauling across the plains and you wouldn't want one to sneak up behind you and catch you off guard with out an escape route, so do be careful.

 

[Scott Lincoln]

If memory serves me right, this is the strongest springtime low moving onto the Plains since 2001.

EDIT: Found it. April 11, 2001. Something like a 980mb low during the afternoon (983 at 00Z).

......which was a high risk day with 40 tornado reports. Shift the reports west, and you got tornadoes across E NE/W IA. Big difference between Thursday and April 11, 2001 will be the vertically stacking/slowing low Thursday versus a rocket takeoff of the system in 2001. We will see how this affects things.

[/b]

I remember that day. It was a high risk day, but didn't materialize to quite as severe as they were talking. We did, however, have a scary situation where a large tornado was on the ground for quite a while, heading right along I-35 towards the western part of the Des Moines metro. They ended up issuing the tornado warning for Des Moines before the tornado was even in the county to the south. Luckily it dissipated.
I believe all our storms that day were fairly quick moving mini supercells.

I'm still concerned about the moisture return. Tried to investigate this further with BUFKIT but it does not appear that my profiles are updating since Monday.

I will say just from looking at model runs that i could maybe see some storms form along the warm front into western Iowa while big stuff is going on along the dryline. Not alot of convergence along the boundary, but there is some, especially east of the low pressure area.

 

[Jeff Snyder]

Well, the models (NAM at least) are now undoing the changes that made in the runs from Monday and Tuesday morning, by speeding up the dryline passage. The new 6z run shows the dryline along the KS/MO border southward into se OK by0z, which is about 125 miles east of the position forecast several runs ago. With 500mb winds progged to be in the 80-90kts range, I have now completely questioned whether I'm going to chase. As it stands, I'm thinking similar to 3/12, but a tad farther east still. With significant forward motions and expected chase terrain, I'm not sure if it's worth the attempt for me (from OUN). I am surpremely disappointed that the dryline is hauling eastward so fast, but I still think it'll end up farther west than forecast. At least the trend has been to slowly shift the forecast surface low position by Thursday evening from Souix Falls southwestward (6z has it not too far from the central KS/NE border). If the dewpoints can recover, I'd think that a high risk is in order. However, this may be almost as un-chaser-friendly of a high risk as they come...

NOTE: Again, I speak of the target south of I70.

 

[Philip Flory]

Well, the models (NAM at least) are now undoing the changes that made in the runs from Monday and Tuesday morning, by speeding up the dryline passage. The new 6z run shows the dryline along the KS/MO border southward into se OK by0z, which is about 125 miles east of the position forecast several runs ago. With 500mb winds progged to be in the 80-90kts range, I have now completely questioned whether I'm going to chase. As it stands, I'm thinking similar to 3/12, but a tad farther east still. With significant forward motions and expected chase terrain, I'm not sure if it's worth the attempt for me (from OUN). I am surpremely disappointed that the dryline is hauling eastward so fast, but I still think it'll end up farther west than forecast. At least the trend has been to slowly shift the forecast surface low position by Thursday evening from Souix Falls southwestward (6z has it not too far from the central KS/NE border). If the dewpoints can recover, I'd think that a high risk is in order. However, this may be almost as un-chaser-friendly of a high risk as they come...

NOTE: Again, I speak of the target south of I70.
[/b]

The 12z moved the dryline furthur east as well. The dryline is progged E of 35 by 18z and in W Missouri by 00z. Actually, the latest NAM doesn't even break out precip at all in KS along the dryline, only in W MO around 21-0z. As previously said, I would bet that the NAM is forcing the dryline too far east and it is near I-35 near 12z... however... this seems furthur east than the last few high shear setups previous day NAM was pushing the dryline. Regardless... I think it's pretty safe to say initiation over E KS/NE OK will be in less than ideal terrain. I just don't know if I'll give this one a go, I have struck out the last few high-shear chases and they can be extremely frustrating.

 

[SteveCarter]

Amazing progs. This has the potential be something that will be memorable, to say the least.
1) Stronger, colder representation of upper level disturbance
2) Deeper surface pressure (as low as 980-987MB)
3) Pockets of intense upward vertical motion that mimic supercells
4) Line segments of strong UVV which represent possible LEWP, bow, and squall line formation
5) Two days of extremely unstable air through and near the warm sector from NE and KS into the Ohio and Tennessee Valleys
6) Extreme reflection of surface dry line in Lifted Index depictions on Day 2 and of "collapsing" cold advection from N MO into OH during Friday.
7) 500MB vorticity maximum exhibiting "swirl" pattern with core measures of 45 units
8) MuCAPE values exceeding 2500 j/kg near points of best lifting and forcing
9) Scattered helicity maxima along frontal structure and within warm sector.

Where to go? When to leave? What to do?? After my 1500 mile bust over the weekend, this DOES appear to be closer on Friday to where i live, but still looking at the Dyersville, TN area, but still pretty early. Will prob miss Thursday, but where on Friday?

 

[Kurt Silvey]

I have been watching and comparing today’s forecasted moisture return with the current metar data and so far things are looking good. The 14z RUC projects upper 50’s Td’s in nc OK by around 15z, 50 Td in central NE by 18z, and upper 50’s Td’s in c NE around 21 – 00z.
So far at 1516z there is a narrow plum of 60ish Td’s extending all the way to the OK / KS boarder. If this rapid return can be sustained we may hit the forecast for tomorrow. If it does return all the way to nc NE by 21 – 00z today, we may see some good storms fire along the NE SD boarder around 00z this evening, but that’s a different thread.

 

[Mike Peregrine]

Some nice thoughts being presented in this thread. Tomorrow looks like it has the potential to kick our butts yet again. If I had my choice tomorrow, I'd probably get up closer to the TP in south/central to east/central Neb ... for nothing else than forecast storm motion alone at this point. But also because I think vorticity will be maxi-crazy up in there.

Missouri and Iowa are looking like another screaming, frightening day setting up. I'm leaning toward storm initiation east of 35 in eastern Kansas by 0z, but likely earlier in the afternoon (if we are going to use 4/11/01 as a template, these COULD initiate much earlier, ladies and gentlemen ... so keep your eyes open all day). The storms should then sweep across the already battered and bleeding Missouri hills moving N/NE at 50-60kts, leaning more toward the 60s.

So ... take it from someone who just had his rear handed to him on a platter with a side of everything on it ... and is feeling a little humbled at this point. We're all going to have to watch our backs tomorrow.

 

[Jeff Snyder]

If the 12z NAM is to be taken as valid (or we assume the forecast will verify perfectly), I will most likley sit this one out. For whatever reason (intense mixing, etc) the NAM is now moving the dryline considerably farther east during the afternoon. Instead of being just east of the I35 corridor by mid-late afternoon as indicated several runs ago, it now appears as though the dryline will be located near a line from Tulsa to Emporia by 18z, before rocketing east into western MO by 0z. The 850mb flow looks quite veered overmuch of OK and southeastern KS, with SW or even WSW (over southern OK). This is likely helping to usher in very dry air air, which may be mixing downward and helping to move the dryline eastward.

The current progs show the mid-level and upper-level low centers located south of the surface low, which is resulting in an interesting shear profile for areas north of the NE/KS border. Winds seem to be back substantially in the 850-250mb layer (which isn't surprising given the location of the sfc low relative to the upper-level low). Instability may be significant in NE, but I'm very worried about the winds aloft, and the affect that they will have on storm evolution. Storm motions should be nearly due north (or even with a slight westerly component looking at the mid and upperlevel flow).

I'm still hoping that the system develops differently than the models are currently forecasting. With slightly flatter flow aloft (south of I70), shear profiles are decent in the southern 1/2 of the risk area, but I can't imagine I'll chase if the dryline forecast really appears as though it'll verify. I chased 3/12 when the DL was in eastern KS and OK, but I probably won't if it's in western MO. Maybe I can close my eyes, click my heels together thrice, and the forecast will revert back to the way it looked yesterday morning...

EDIT: I should note that OUN apparently feels that the dryline will be located near I35 by 4pm, per a graphic on their website. I thought this was old, but I see it was updated a little before 11am (several minutes ago), so I assume they've looked at the 12z model output...

 

[Chris Vagasky]

Jeff,

OUN has been showing the dryline in that same position for the past couple days. I haven't noticed much of a change in their placement of the dryline.

They may have some different thoughts than what the models are showing...I guess I'll be looking at the Mesonet data in the morning to see where the dryline is developing, and where it looks to be moving.

Of course, I think I'll be sitting this one out for a few reasons:

a. Work
b. Storm motions (I'm getting disappointed in all of these storms that are rocketing to the east)
c. Having to take the Ranger in for service.

Depending on how long © takes, I may be available for nowcasting for those who are out.

 

[Benjamin Sipprell]

04/05 12Z NAM and GFS output have fantastic hodograph profiles with significant CAPE and surface moisture extending from northern MO and along the anticipated dryline into northern AR ... southern Iowa and back into Nebraska aren't looking too hot for me to chase when things look so great and so close.

I'm thinking of traveling only slightly westward from St. Louis and north to set up and await storms to come to me seeing as how fast things will be flying.

 

[Todd Rasmuson]

In my best judgement i see this as a situation like some in the past
we need to wait until Thursday morning to be making judgements
on where to chase for one, i think the models could be wrong on
basically blasting the dryline into extreem ern ok into ar by thurs
afternoon... we need to closely watch central ks into central ok,
into n tx also very closely... the models have in the past have
done this, so i say its best if we wait until thurs mornin before
making decisions... attm iam thinking the front will be along
or e of i-44 to near highway 81 across central ok by 18z,
so we would have to watch for poss delvopment across
the central body of ok for poss delvopment.. just gotta
see what this dang dryline does....