07/02/2005 FCST: Central/Northern Plains

[Glen Romine]

Yeah, that's what seperates the recreational forecaster from the professional - they always take the time to verify the initial conditions and are familiar with model biases and common feedback problems. Nevertheless, I still don't see tomorrow as a total wash for supercell potential particularly into northcentral NE given most recent NAM and GFS model guidance. 12-13C 700 mb temps are quite reasonable for this time of year given strong enough surface convergence and both models yield a weak shortwave passage through the area near peak heating. The strong surface convergence is what doesn't appear to exist in either run - but given the extent of ongoing convection in NE, there is reason to believe a decent boundary will be heading back north capable of interacting with the dryline and potentially kicking off storms somewhere in NE. That said, agree the likelihood of storms will be higher further north based on what appears available now - but I'd still want to get up in the morning and check the obs before making alternate plans for the day.

Glen

 

[Mike Hollingshead]

I don't think NE was slighted today either was it, up by Valentine? Was that supercell out by Sidney earlier this weak slighted? My target remains around or nw of O'Neill, probably closer to Ainsworth.

 

[Mikey Gribble]

I think the forecast for tomorrow has been pretty well hashed out so I don't have a lot to add. The cap will be strong over Nebraska, but an ouflow boundary from overnight convection could increase convergence along the dryline and an isolated supercell or two are possible. I like the potential in Nebraska, but I am going with the safe bet in SE South Dakota. I think I will be able to get South in time if a storm should go up down in Nebraska. It looks like any tornado potential in SD should be later in the evening once the low and mid level winds improve. I was worried about the dewpoint gradient not being tight enough over SD, but I am not quite as worried about it anymore since the NAM shows it tightening up by 00Z. Forecast hodograph for Mitchell looks pretty good. LCL heights are a little high, but I won't let that stop me. I don't think we are going to get the dewpoints in the 70's that the NAM is forecasting since the good moisture resides all the way down in Oklahoma and Texas. The LLJ is going to have its work cut out for it. I would think we will come close to 70's with a few degrees help from evapotranspiration. I am still worried that LCL heights might be a little too high. I am planning on leaving by 7 tomorrow morning. Good luck to everyone who goes out.

 

[Steve Miller TX]

I'm with you Mike! LOL!!

Seriously, does anybody here think that 15-17C 700mb temps could be busted and produce an awesome tornadic supercell? Go ahead and formulate your answer.

If you said "No way! That's a super-thermonuclear cap that nothing could bust through!!" or something to that equivalent, then you might want to go back and look at a few case studies...in particular June 13, 1998. There are plenty of other case studies. The common denominator is strong dryline convergence and or extremely steep lapse rates from 700-500mb. The cap is ALWAYS a concern...and if it isn't, then you are looking at convective chaos and storms erupting everywhere.

Ok...enough of my rant regarding cap strength. :wink:

Here's my thoughts. Take a look at the temps derived from the 00Z Sunday forecast over the NE region:

SFC 33C
850 26C
700 13C
500 -10C

The lapse rates from 850 up are extremely steep! Keep in mind that the dry adiabatic lapse rate is 10C/km.

850-700 = 8.67C/km
850-500 = 9C/km
and importantly...700-500 = 9.2C/km

What I see are increasing 700mb temps while the 500mb temps remain almost steady through the day. I certainly see the capping inversion being pretty thin albeit strong regarding a surface parcel. I think convergence will be strong enough to get the parcel through this capping inversion to convective nirvana.

I'm certainly not expectind a widespread event by any means. But, like Mike H., I do expect at least one or two big monster isolated supercells to erupt in NE tomorrow with a reasonable chance as far south as the KS/NE border. I'm more pessimistic about KS based on the latest model run.

Oh, but wait! We are talking about models, right? LOL!! I'm not hanging my hat on such subtle thermodynamics nor the surface configuration. The NAM has been horrible this year in most regards in my opinion. Models should only be used as "guidance" and not the "gospel". What happens if the 700mb temps are 1-2 degrees cooler? What if the dryline convergence is stronger? What if the impulse is a bit slower kicking out? I could go on about reasonable variances in the model forecasts. Of course, they could swing the other way and I'll find myself with a nice suntan by Saturday evening. :wink:

What I see is outrageous CAPE and lapse rates, moderate to strong convergence, pretty good vertical wind profiles (especially with such high instabilities)...and it is Nebraska. 8)

We will certainly be looking at numerous outflow boundaries too to make things fun. I'm convinced 7/2 will be a great chase day somewhere in NE.

 

[Steve Miller TX]

Well, things certainly have changed a little since yesterday. The RUC/NAM squelch the dewpoints today more than I would have liked. Looking at current surface plots this morning, I still think upper 60Td are likely in KS into all of NE..especially with the aid of evapotranspiration. Of course, with surface temps progged to near 100F, that's some pretty serious dewpoint depressions. I'm hoping that surface temps in the lower 90's will be the case in NE today....we'll see.

An interesting thing I noticed this morning in the upper air analysis is the 500mb temps are certainly cooler than forecast with -10C all the way down into the TX PH and OK with -12C across NE. Upstream, -10C in CO and -12 in WY. So, I don't see these temps increasing to -8 to -9C today as forecast by the models across KS and NE. That's good news if we can keep the 500mb temps down to -10C. However, upstream 700mb temps are certainly toasty with 12 to 14C across WY/CO. It'll be interesting to see how the temps play out in the 700-500mb level today.

Vertical wind profiles still look better for NE and perhaps the KS/NE border region around Belleville. The convergence still looks great. It is interesting to note the big differences between the 12z RUC and NAM regarding surface features as well as the precip forecast with the RUC much more aggressive in breaking out a line of convection by 00Z and the NAM not even hinting at even a sprinkle. I'll take a compromise with a couple of big behemoth isolated cells exploding.

Gotta hit the road now from Liberal. See ya'll in the inflow.

 

[Glen Romine]

I guess since the discussion here is focusing on whether NE will or will not see storms today, I won't try changing the topic. So, after review of morning conditions, still looks quite feasible for northcentral NE to see a storm today. While moisture is limited from what was forecast, the LLJ did manage to transport reasonable moisture, and LBF sounding shows favorable depth at that. Appears consistent with obs and model forecast that a weak dryline surge will emerge from out of ne CO into central NE, and so north of the center of this feature could see adequate convergence to initiate a cell or two. 700 mb temps look decent this morning - and no really strong WAA in the short term, perhaps yielding ~13 C over the initiation area, but with the current clear skies this shouldn't be too great a hurdle. With expected high cloud bases, tornado threat in the region could be limited, but certainly still there. I'd certainly want to watch moisture trends and see how things evolve, but I think Mike's early targets still look about as good as any until things mix out a bit more.

Glen

 

[Bill Schintler]

Chase target for July 2, 2005

Target:
Atlanta, NE (60 mi SW of Grand Island)

Timing:
Possible storm initiation between 5 PM and 6 PM CDT, with storms evolving into a broken line between O’Neill, NE and Hays, KS through 8 PM CDT. There is a chance that the area will remain capped and storms will never initiate.


Storm type:
Isolated supercells between 5 PM and early evening, with hail to 3â€￾ diameter the primary severe risk and wind gusts to 80mph a secondary risk. Expect impressive and photogenic storm structure from some of the storms. There is also a small chance for weaker tornadoes in a few of the storms. Storms will move slowly to the east at 15 mph. storms in this area should weaken or dissipate by late evening

Discussion:
Today, the atmosphere has recovered nicely from the overnight MCS’s in NE. At 18Z SFC dewpoints were generally AOA 60F along and E of a CNK/MCK/FIF line in NE, while dewpoints in the mid-60’s were found in the ODX/LNK area. 19Z visible satellite showed a developing CU field in CNTRL NE although it now appears as though initiation is several hours away given the slow evolution and elevated character of this field, despite convective temperatures in the low-90’s as indicated by 12Z LBF and OAX soundings. KLBF also showed a 70mb deep moist layer along with a large curve in the hodograph between the SFC and 500mb, although much of the curve below 900mb was in response to an outflow boundary.

WV analysis and 12Z UA charts showed several shortwaves moving to the SE in 30kt 500mb flow, with the wave to affect today’s WX now entering the NE panhandle. The real question is whether this feature is strong enough to force SFC convergence along a DL/confluence boundary over the next several hours. This primary shortwave appears to be well sampled by the RUC and NAM, while the RUC is much more aggressive in developing QPF. Given storm initiation, MLCAPE’s to 4500J/kg along with deep layer shear to 35 kts will support storm organization and severe potential. Hodograph curves will increase in the evening with increased backing of the surface winds.

- bill

 

[Steve Miller TX]

Sitting here in Wakeeney, KS watching a nice line of TCu to my NW. This is starting to show up well in vis satellite. However, I'm not too crazy about the pitiful dewpoints...alot worse than I had expected today. KS looks like to me that the LCLs will be very high. I'm liking the NE surface obs right now...much more reasonable and of course better overall dynamics is here. So, I'm continuing heading north into NE. It looks like I'll be playing between Lexington and Ord.

Gotta run!!