6/6/07 FCST: ND/SD/NE/KS/MN/IA/MO

[Ross Lazear]

Okay, here goes Mr. Optimist =)

There are so many "ifs" with this set-up...but I think if I chose not to go and somehow the cap was magically broken over N.C. NE, I wouldn't be too happy with my choice. Nonetheless, it's looking pretty iffy.

I'm not sure how accurate model produced cinh is...but it does appear that the cap wants to erode around the dryline in central Nebraska by 00Zish (at least in the 00Z WRF run I just looked at). This is a big "if," though..and things look worse if you take away the magical 70F dewpoints the models generate out of nowhere.

Nonetheless, my chase team from U-Wisc is all ready to go, so we're just going to hit the road. At the very least, it'll be a fun road trip =)

We plan to head west on US-20 to Ainsworth/Valentine area, leaving Madtown at 3:30 AM (yikes!)

Good luck, all!

 

[Dan Robinson]

Wow. Glad we planned to stop and check the 00z models before continuing north. We're at The Trail's End truck stop along I-29 in Rock Port, MO. The first thing I did when we pulled in here was look at the surface obs, and after that I didn't even need to see any model image to know that we are not going any farther north. Gas prices will drop to $1 a gallon before 70F DPs make it north of I-80 tomorrow.

The good news for us is that we're not driving to Souix Falls tonight, saving us a tank of gas today. And we get a nice leisurely drive southwestward tomorrow to the dryline to watch the battle for the cap, rooting for the underdog. I agree the northern target is a waste of time and gas at this point.

 

[Bob Schafer]

A bit off topic, so I'll place a pemium on brevity:

Much hype about tomorrow for the last week. Stemmed from progged sfc L pressure+CAPE. How did models get Td's so wrong? Bigger question: Are they?

 

[Josh Richardson]

Have finally decided the best course of action tomorrow is to plan on being in O'Neill by early afternoon and making the decision to NW or SW from there. As many others have already said the Broken Bow area is looking pretty good but I would like to keep my options open for my original target of Winner SD as well. I guess we will see what happens early evening tomorrow.

 

[Bill Schintler]

Chase target for Wednesday, June 6

Chase target:
Hayes, SD (30 miles west of Pierre).

Timing:
Elevated storms and virga will reach the target area from the west through 6 PM CDT, and become surface-based. All forms of severe weather appears likely.

Synopsis:
00Z analysis indicated deepening ULVL trough in the PAC NW with attendant 55kt H5 max nosing into UT along with increasingly cyclonic flow over MT/WY/and CO. A couple of embedded mid-level S/WVs were noted on the H7 chart. A lead wave was over NERN CO with associated areas of convection there. An upstream wave axis was located over UT and very strong WAA was occurring E of this feature over CO and WY where a narrow 15C thermal ridge was located. A developing LLJ was transporting +10C H85 dewpoints into NEB and the Dakotas. At the SFC, deepening low-pressure was located in CNRTL WY; while dewpoints were increasing into the upper-50s F in WRN SD at 03Z along with a deep moisture layer as indicated on the LBF sounding. The NAM initialized well to most SFC and ULVL temperature and moisture parameters, however it does not seem to have as good of a hand on ongoing convective trends as does the GFS. The GFS is too weak with the present location of the WY SFC low, however.

Discussion:
SFC low pressure will rapidly deepen as it lifts into NWRN SD by early evening in response to unseasonably strong lift at the left-exit region of the 80kt H5 max. SFC moisture will increase dramatically as a result of both advection and evapotranspiration, and will reach the mid-60s by late-afternoon. MLCAPEs may reach 4000J/kg under steep mid-level lapse rates associated with the EML. Shear parameters appear equally impressive. In fact, the NAM advertises a 60kt WRLY H85 “jetletâ€￾, W and detached from the main LLJ, and this should arrive shortly after SFC-based initiation. If this feature verifies (the GFS does not indicate this), it would dramatically enhance hodograph curvatures after 00Z. Deep layer (SFC-6km AGL) will increase to 80 kts after 00Z.

Capping is a concern; however mid-level temperatures will cool several degrees over CNTRL SD by early evening with the advance of the stronger ULVL forcing. An area of virga in WRN SD should further cool the mid-levels through evaporative cooling. A CI shield also associated with this feature should not arrive in CNTRL SD until early evening, so insolation during peak heating hours should not be compromised as is often the case with very strong jet-stream level forcing.

11:18 PM CDT, 06/05/07
[FONT=&quot]- bill[/FONT]

 

[Mike Hollingshead]

http://wwwt.emc.ncep.noaa.gov/mmb/mmbpll/cent4km/v2/tcolc_f25.gif

Well that thing gives a little love to my triangle. To bad now it won't actually happen like that.

http://wwwt.emc.ncep.noaa.gov/mmb/mmbpll/cent4km/v2/

Certainly wants to shut down south of NE. Doubt that will happen either.

 

[Glen Romine]

Amazed that the NAM just won't let go of the idea of evapotranspiration compensating for dry advection. While the LLJ does seem to source from the DRT region, where at least modest moisture is in place, the net result overnight is minimal. With such strong low-level wind fields progged for tomorrow, and likely clear skies with deep boundary layer mixing - it is difficult to digest the advertised moisture return or prospects for evapotranspiration in a shallow layer. GFS is finally moving towards a drier solution - and is rather spartan in precip only over the rather road challenged areas of SD during the daylight hours - where as previously mentioned the shear is not that hot either. GFS does suggest a tendril of better moisture depth may try punching north of the NE state line near 00Z - which could just sneak in under the area of primary large scale ascent before dark - but without better prospects for daylight storms - this has the markings of a major bust up north. Agree with others that best prospects will probably come from rogue cells developing much further south from yet undetermined ripples in the flow.

 

[Ryan McGinnis]

I think I'm going to aim for the Kearney area, too, maybe a bit north depending on how the models look tomorrow morning. The way I figure, the wind profiles are great (seriously) in the area -- the hodo for KEAR at 0Z is nuts. If moisture is going to be a problem, there's a chance that it'll be less of a problem the further south you go. The cap seems a little weaker at 0Z in the latest NAM runs at 'only' 12-14C, so who knows. The mets at KLBF seem pretty pumped about central to NNW Nebraska in their discussion -- they single out Custer to Hooker county as the place most likely to pop, if anything does. Hopefully not as far west as Hooker -- I don't care if a tornado catches fire and begins talking, I'm not chasing in NW Nebraska any more!

It's also much less of a drive for me, and if all I see are puffy clouds, at least I've got family I can visit.

 

[Darren Addy]

I've been up and down like a yo-yo on this system, but the new SPC Day 1 outlook is going to have those who decided to stay home for Wed. either crying in their breakfast flakes or rapidly heading out the door in their pajamas. The word "outbreak" is back in the picture and the likely tornadoes are in the "narrow corridor" of central Nebraska to northern Kansas. Behold the power of the LLJ when it has a 778mb low sucking on the other end of the straw!

I'll be looking at more data in the morning, but right now I'd draw a diamond from Broken Bow to Cozad to Alma to Grand Island and back to BB, which puts Kearney just about square in the middle. There's plenty of free Wi-Fi in town, so it's a great place to sit and wait for the cap to break.

This message brought to you by the Kearney Chamber of Commerce

I can go to bed happy now. (Hopefully I'll be even happier tomorrow night!)

 

[Josh Richardson]

Man, I am sure glad I made the decision to be in the middle. It could be great down towards the Broken Bow area and now I can make that no problem and not limited to the northern play. Looking forward to today and good luck to everyone.

 

[Ryan Pfannkuch]

Final fcst thoughts for Wed.:

After considering a target yesterday well up into northern South Dakota, I have decided to compromise with my original thinking from a few days ago and go with something near the I-90 corridor. No matter how hard I try to convince myself that things will pop in NE before much before dark...I am just not sure enough to gamble on it...and I have a lot of respect for the many of you who are. I DO believe that NE could light up around 3z per the 6z NAM, but this is a little late for ideal chase purposes so I will focus a little closer to the surface low but still in the area where the low level shear is decent:

Final 4-county target area in southern SD:
Jackson, Mellette, Jones, Lyman
Including the cities of: Kadoka, White River, Murdo and Kennebec

Best of luck to all...as was earlier mentioned no matter what we will all look back on today as quite a forecasting exercise....as various targets all seem valid in various ways.

 

[Kurt Silvey]

Only time for a quick reply .... The cap should errode along the dryline in central NE, and appears to be a slight dryline bulge forecast. The biggest question is the juice. The Td's will be the key today. Follow the juice to the dryline and thats where you'll find me. There are Td's of ~ 59 / 60 already at the NE/KS border.

 

[Paul Knightley]

I would still favour Grand Island as a starting point - both GFS and ECMWF show the short wave pushing through NE this afternoon/evening, with evidence of a dry-line bulge in SW Nebraska. Warm front moves well north into the Dakotas, so it will be a case of playing the dry-line/moisture - instability axis. NAM breaks out some precip around the Grand Island area after 6pm CDT.
In light of all this, the triangle of Kearney - Grand Island - Hastings would be my target zone. As hodographs enlarge this evening due to the strengthening LLJ, a couple of strong tornadoes are possible, assuming storms can develop. The cap will be strong, but heating and the upper short-wave should allow isolated supercells at least.

The larger t/td spreads in the Dakotas probably mean a high wind threat is more likely in that region.

 

[Oscar van der Velde]

The 06Z GFS Convective Weather Maps are in.

http://lightningwizard.estofex.org/usa.html

At 21Z, a strip of weakly capped anvironment is found from SW Kansas down into Texas, and another area in SW South Dakota/NW Nebraska with strong deep convergence, and farther into the mountain states.
LCLs are pretty high in the SD/NE spot though, and also low-level CAPE only enhanced in Wrn North Dakota/SE Montana.

At 00Z, SREH3 over 400 m2/s2 from SD down into OK. Least capped in SE Montana, SW ND, and N/NW SD, and around the SW corner of Oklahoma.
Possibly as result of convection in the model, GFS makes a dip in deep layer shear over the northern area. Best 0-1 km shear is progged around the SD-NE border, LCLs not very low ahead there of the dryline (>1000 m, even over 2500 m where CIN low) and 0-1 km mixing ratios of 11-12 g/kg.

At 03Z, low level shear gets better up north, and uncapped CAPE mostly from N SD into W ND and Montana. Other areas get CIN back.

Seems South Dakota gets most favored, but W North Dakota and SE Montana get a rather stationary tongue of instability... the slow movement of this zone does not seem to indicate to me that it will become a squall line there, but I may be wrong. Shear is best southward though.

Note that MLCAPE sticks around 1500-2500 J/kg, but not 100% sure to trust this.

Good luck to all!
Oscar

 

[Bob Schafer]

A couple of my obs of the 12Z RUC (re:07/00Z):

DL bulge invof O'Neil, CINH holding it's own.

http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/ruc/hr3/images/ruc_cap_012m.gif

250 left exit region now situated in W SD/extreme NW NE (PH), and thus there may be subsidence near O'Neil. Practically under upper ridge.

http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/ruc/hr3/images/ruc_250_012m.gif

No precip at all anywhere near DL in 3 hours to 00Z:

http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/ruc/hr3/images/ruc_p01_012m.gif

Looks like a late show, for sure. Not to be preachy, but I do hope that anyone with intentions of chasing this system into the wee hours understands what they're getting themselves into. Huge CAPEs and helicities, and fast storm motions. NAM fSounding for 07/06Z for Yankton SD progs 44kts SM:

http://68.226.77.253/skewts/NAM-test/018/SKT_NAM__KYKN.png

Note that that fSounding progs modest CAPE, but it's for 06Z, and I didn't go looking at every station in the risk area. 0-3km SRH on there: 504. "Best CAPE": 2924. Sup potential: 70%.