04/15/2006 FCST: NE, IA, MO, KS, OK

[bbarjenbruch]

I'm not sure i agree with the SPC's outlook for tomorrow. Looks like the moderate risk is misplaced. It probably needs to be more of a KS/NE area. I dont think the system is going fast enough to take the area of possible strong tornadoes that far east. It looks to be after dark before the dryline makes it to western Iowa.

Looking at the BUFKIT ETA/NAM soundings quickly, Lincoln kinda looks crappy in general with unidirectional shear only during the afternoon and almost no CAPE; St Jo, MO looks like it has decent directional shear but it has a pretty much unbreakable cap; Topeka has an unbreakable cap and almost unidirectional shear.
According to GFS profiles, St Jo has a cap at 3pm and 6pm; Des Moines has decent shear and CAPE, but not until after dark.
These profiles were updated early yesterday, so i'm hoping that something has changed in the model runs and that when i get more updates it will look better.
[/b]

Apparently things have changed for the better as far as forecast soundings. KLNK is showing 1500 CAPE, LCL and LFC levels invof 1000 m, and 0-1 helicity consistently above 200. I can 100% agree with the SPC's forecast area just based on 0-1 and 0-3 helicity values alone for KLNK, KOMA, and KOFK. Although the model's "rain" functions are screwing the soundings up, CAPE is still adequate for vigorous updrafts, and there is MORE than enough shear in the low and upper levels. Hope I can get off of work...

 

[Paul Knightley]

Once again, it will be an armchair "virtual" chase for me, here in the UK!

Having looked at the various models, I will be planting myself (virtually!) in Lincoln, NE for the night, and then taking things from there tomorrow morning. ECMWF/ETA are hinting at eastern parts of NE, but 06Z GFS has been more bullish with the passage of the upper low, and favours western IA. A strong speed max should create a decent dry-line bulge by mid-afternoon, and I would be finding the DL/WF intersection. Anything which runs along the WF will have a good tornado potential, possibly strong, given the dynamics. I think Lincoln is a good place to start the chase, as GFS may be overdoing the speed of the system. There's also a good chance of some low topped activity for N NE and S SD.

 

[Rich Thompson]

Tomorrow might be a good time to play the "Davies" cold core setup beginning around 18z in central NEB. The system will tend to evolve into more of a closed/occluded low by Saturday evening, while the cap and moisture quality cast doubt on the warm sector along the dryline. You might be able to move E with the dryslot to catch other storms in SE NEB, but I'd be there earlier rather than sitting off too far E in the afternoon. The added advantage will be slower storm motions on the cyclonic side of the mid-upper jet.

Rich T.

 

[Mike Hollingshead]

If I were chasing tomorrow, which I am, lol, I'd want to be down the dryline arc a ways, stopping short of where it starts to turn more south. This location worked well April 6th. I guess I'd be in a location centered between the sfc low and the point where the dryline turns more n-s. I'd be on a good e-w highway as well. I'm betting this will wind up around the Hebron-Superior area. One thing I wouldn't mess with tomorrow is the warm front...it won't be lined up favorably to the upper-level winds. Sure something could still happen near it but I wouldn't make it my target.

I have a question for the real forecasters out there. Where exactly are the models coming up with this rapid increase in moisture between 18-0z? It isn't from transporting it north as it has looked just as good to the south. Is it from the evapotranspiration the model thinks will happen(which won't)? Or is this due to pooling ahead of an eastward bound boundary combined with backing low level flow as the system deepens? I'm assuming it is the pooling and backing(which would also help pool).

Thanks

 

[Rich Thompson]

I have a question for the real forecasters out there. Where exactly are the models coming up with this rapid increase in moisture between 18-0z? It isn't from transporting it north as it has looked just as good to the south. Is it from the evapotranspiration the model thinks will happen(which won't)? Or is this due to pooling ahead of an eastward bound boundary combined with backing low level flow as the system deepens? I'm assuming it is the pooling and backing(which would also help pool).

Thanks
[/b]

Mike,

The rapid moisture increase seems to be the result of the surface fluxes in the model - how it treats the soil moisture and vegetation. Most of these overblown moisture forecasts are most evident during the day, with big moisture increases at the surface from 15-21z. The problem is that moisture then becomes part of the first guess field for the next forecast.

There's a known problem with the current NAM which I hope will be fixed soon, so I'd be skeptical of the mid-upper 60 dewpoints shown on the dryline. Given the mediocre moisture all the way to TX in current obs, I'd ignore the dryline and play closer to the cold core where initiation and the cap won't be a big concern.

Rich T.

p.s. Do I qualify as a "real forecaster" after yesterday evening :unsure:

 

[Matthew Crowther]

The moisture situation right now looks very bleak- dewpoints in OK are now down to as low as 48- and soundings at OUN and FWD are pitiful in that regard as you might expect looking at the surface obs. Therefore the tornado threat tomorrow seems to be lower than even the last event in the Plains- as others have stated, the only hope may be for a few weak tubes up in the Sand Hills of NE over to near OFK or SUX by 00Z.

Matt C

 

[Kenny Drake]

I also notice about a 5F discrepency on what the Oklahoma Mesonet sites are recording for Td's and the METAR sites. I'm more inclined to believe the Mesonet Td readings over ASOS. If thats the case Td's over eastern KS right now are probably only in the upper 40's to low 50's. As of now, if I were chasing, I would follow Davies Cold Core Setup which is more favorable for lower Tds. I have not looked at his Cold Core article recently so I'm not sure if this setup will meet his requirements and im tired heh. Anyways for a chase zone I would target south central Nebraska. As I was suspecting the NAM (00Z Apr 15) has pushed the low farther west and north. This has moved the dryline to pretty much a I-35 location from KC to OKC by 00Z Apr 16. It is still showing mid 60F dewpoints which I don't think will ever happen tomorrow. I'm thinking this will be a mid to upper 50F Td day which will want to put me along the dryline/warm front boundary near the area of greatest lift (leading to my decision on chase location). LCL's are going to be quite high but I'm still expecting at least one good supercell with at the very least good sized hail and cells over NE and KS wont be breaking storm movement speed records either. Also another good thing going for tomorrow is the clear negative tilt of the trough leading to very cool 500mb temps over NE KS (-15 to -20C).

 

[Stan Rose]

Agreed that the moisture situation doesnt look great...but still think 60+ dews are attainable. at least the
nam and gfs now agree a bit more on the low and timing...with the cap breaking 22-00Z over n KS/S NE.
if so, manhatten north could see some action-S

 

[Kevin Scharfenberg]

The progged hodographs look pretty favorable for tornadoes over far northeast Kansas, southeast Nebraska, far southwest Iowa and far northwest Missouri. But looking at the morning surface map...the RUC looks much more reasonable (as it has all spring so far) on handling the boundary layer with 55-60 dewpoints, 30-35 dewpoint depressions, low CAPE and a strong capping inversion over the warm sector. I think initiation is somewhat questionable, and even if storms do go they'll be high-based and a little CAPE-starved given much lower dewpoints than progged by the NAM-eta.

If I was around KC/Topeka/Omaha this would be a much easier afternoon decision, but given the $2.70/gal gas prices and the numerous question marks about today, I'll pass on the long drive from Norman, and save time and money for better chances later in the spring.

 

[Jeff Snyder]

Well, I awoke this morning with every expectation to head up towards Concordia KS (be there ~1pm). However, looking at obs, I can't imagine we'll see any dewpoints within even 5 degrees of the NAM forecast. Current surface obs show the real 60-61F dewpoints entering southcentral OK, with mid-upper 50s in ne OK and se KS. I DO think at least the southern end of the MDT risk could see 55-59F tds by mid-late afternoon, barring sustained SSE 80mph winds in TX and OK. Looking at morning soundings, we should see the dryline mix pretty quickly to the east, as moisture on DDC is ankle-deep, dewpoints >50F on OUN is only ~25mb deep, and SGF's moisture is only ~50mb deep.

The shear profiles in the risk area is pretty nice, but I am concerned about the fact that we'll probably see a low-level veering wind profile beneath mid-level backing wind profile (as cold-air advection destabilizes the risk area from the top). The latest (12z) RUC indicates that the 60F isodrosotherm may make it to the I70 area by 0z... However, by that time, the dryline is progged to be just west of Kansas City.

So, though I had every intention on chasing today, I'm sitting this one out. It's a complete waste of a system/setup, however, given the nice shear profiles and the chaseable storm motions (<= 40 kts). But with my target area 4.5-5 hrs away, and with 25-30F dewpoint depressions, I guess I'll just have to wait for the next one. It's sad that the Gulf can get fropa'd 5 days ago and still not be open enough to give us real moisture. Then again, I'm not sure we've seen real (~>65f) dewpoints this year so far (not that that's uncommon -- it is only mid-April).

 

[Bill Schintler]

Target:
25 miles south of Lincoln, NE.

Timing:
Storm initiation along a Hastings to Beatrice line between 4 and 5 PM CDT. These will become severe and move into the target area through 6 PM.

Comments:
A significant event expected today, with a full spectrum of severe WX including tornadoes.

Discussion:
AM analysis indicates 110 kt H3 max over NM, with associated closed circulation over WRN CO. At the SFC, low pressure noted in NERN CO with developing WF roughly along I-70 in KS; while satellite imagery and radar indicate WWA cloud arc and along with developing precipitation in ERN and NRN NE. The 12Z NAM and RUC have finally initialized well with regard to SFC moisture, with a large portion of MO and ERN KS verifying with 55F dewpoints; while they have also initialized several degrees cool on temperatures. The RUC is considerably lower with regard to moisture in SERN NE later today, advertising Td’s in the 55F range. The RUC is probably more realistic then the NAM with moisture and resulting instability. At and just NE of the DL and WF triple point favorable instability (MLCAPE’s to 1500J/kG and LI’s to –10C) will be juxtaposed with deep-layer shear of 80 kts along with SRH (0-3km) locally in excess of 400m^2/s^2. A potential negative today may be dry air entrainment in the updrafts, with a very dry push at the H7 and H5 levels through 00Z.

- bill

 

[Paul Knightley]

Well, after looking over the various models through the day today, my virtual chase is taking me to Beatrice, NE, as a starting point. 00Z ECMWF was strongly hinting at this area (and being from the UK, I use it a lot here, and think it's often the best model)...it showed a strong dry-line punch across N KS, with the SE NE region being on the northern side of this. Strongly backed surface flow, and a brief but narrow window of strong lifting dynamics look like providing a window of oppurtunity for supercells, despite limited moisture.

Think the tornado threat will be limited by the lack of moisture, but any moisture pooling along warm front could yield something decent.

So, (virtual)n starting point is Beatrice, NE, but reckon that the best of the action could be a little further east, as the storms evolve, perhaps arounf Tecumseh, NE.

Good luck to anyone really chasing today, and stay safe.

Paul.

 

[Kenny Drake]

Latest RUC model finally picked up on the lesser amounts of moisture, showing only an isolated 60F zone in SE KS/NE OK/SW MO by 00Z Apr 16 with mostly 55-60F dewpoints ahead of the dryline. As Jeff noted the moisture layer is quite thin (ankle deep in DDC, literally looking at the sounding 12Z sounding.) OUN sounding the moisture layer a tad deeper but still not uniformally below 850mb. Winds are also veering south of KC so my target would be south-central to SE NE following the dryline advance where winds are backing ahead of the dryline. With very high DPD's I'd stick to the areas of greatest lift (i.e., near surface low). The one problem I have with this is the vertically stacked regime of the trough and associated surface low. This will give surface winds out of the southeast over SE NE, and nearly southerly winds at 500mb (maybe I am missing something, can someone explain why profiles still highly favor supercells?). Mean direction of storms in this area will be nearly north and will probably be moving along at a fair rate just looking at 500mb winds. Speed may also be influenced by the progged vertical stacking at 00Z.

From central KS southwards... if temperatures can control itself to under 85F, and dewpoints make it near mid 60s I wouldnt doubt a few isolated storms. Wind profiles will not be as favorable however, and being on the south side of the jet max is not promising either. Nonetheless, RUC does show isolated precip over NC OK at 2100UTC (15Z model run) and over NC TX (interesting.) If anything fires near Norman today I may check it out. But with a history research paper (blah), and 3 exams next week I wont go far from home. Good luck to all those who are chasing, hopefully better luck than the previous setups like this.

 

[Mike Johnston]

After looking at observations so far today, and progression of the RUC, I'll throw in a bit of a late forecast on today's setup. Although the higher probability target may be torwards SE NE, I think perhaps a higher payoff potential may be setting up over the eastern tier of KS, say from Allen Co. up through Johnson Co, for the following reasons:

1. Surface low appears to be slowing down forward progression and deepening even more than earlier models forecast. This may increase probabilities for backing surface winds further south than earlier anticipated.

2. Cloud cover over this region appears to be holding surface temps down by a few degrees, and dewpoints appear well on the way to building towards 63td or higher.

3. Crossover of winds with height appears to be the best out of the broader target area. As mentioned previously, somewhat stacked lows resulting in more uni-directional flow closer to the low centers, whilst in the SE warm sector, 500mb and 850mb crossover approaches closer to 90 degrees. SR helicity indications now appear very encouraging over this area.

4. Dewpoint gradient by 00z along eastern KS looks to be setting up very, very sharp, with >60td separated spatially with <35td by only a few scores of miles.

5. RUC now tries to breakout precip over the area.

6. Area is in exit region of maxima within southern branch of upper jet, and even some diffluence is apparant. Combination of this factor, along with #4 above, may very well set up sufficient lifting mechanism.

Realize that breaking the cap this far south is the potential limiting factor, but I can't help but believe at this point that - given convective initiation - chances for rotating supercells looks pretty decent.

Good luck to all chasing...should anyone need, I'm available this afternoon for nowcast support, just PM me.

 

[Mike Peregrine]

Just took a quick peek at RUC forecast soundings that make me feel that Falls City may have it over Concordia to Beatrice in terms of wind profiles and instability by 21-0z time frame. Falls City is also on the edge of a harder cap to the east. Wind looks unidirectional to the west ... although some nice convergence is now beginning to become pronounced along the dryline. I think I'm going to head up that way here in a bit (provided the chasemobile can do it ... it's having some 'issues' today). Storm motion is 232 degrees at 36 kts. Sig tor index sure likes to fire things up in NE Kansas/SE Nebraska around that time. Just don't know how much confidence there is in model guidance today.