10/22/04 FCST: Plains/midwest

Subsidence *and* cloud cover? Just kidding; I see what you're saying.

You don't like the dryline for lift in Kansas? Of all the ingredients in this brew, lift is one component I had hoped to cross off the worry-list. I think adequate lift will show up to the party all the way from Minnesota to ABI. In Kansas, I was counting on the surface trough / dryline, much as you mentioned for western OK. SWODY3 cites the dryline in their discussion of initial convection but in the context of western Missouri, and I see it firing earlier than that.

See exhibits A & B (maps relevant per 12Z ETA Wednesday):

http://weather.cod.edu/forecast/ETA/SP/eta...P_2_dewp_54.gif

http://weather.cod.edu/forecast/ETA/SP/eta...P_2_dewp_60.gif

In my experience, this is sufficient motion to initiate storms in a modestly unstable airmass so long as the inversion isn't thermonuclear. All this being said with caveat that models perform poorly mixing drylines, etc etc. We have to accept the numerical flaws for any of these discussions, of course.

As for western Oklahoma, I'm all ears! The more west we can initiate in daytime, the happier I'll be. If I find myself watching towers somewhere near Clinton (or Altus!) on Friday afternoon, I won't complain one bit. It's quite a puzzle trying to match the probabilities for discrete storms in daylight in chaseable terrain. Always a compromise for sure.

Great forecast discussion!
 
The 12z ETA continues the westward trend for the dryline positioning in the southern plains. In fact, the 18z Fri forecast now has the dryline on the western OK / eastern TX panhandle border (as mentioned in yesterday's OUN AFD). Looking at UVV plots valid 18z and 0z Friday afternoon and evening, there is tremendous lift / UVVs along the surface "cold" front from DDC northeastward, which is strongly indicative to squall line development. On the other hand, forcing along the dryline in OK is not nearly as strong, yet still pretty signficant. Depending upon what happens to the convective complex that the ETA brings across southern OK Friday morning and early afternoon, we could be game down here... Despite upper 70 Tds along the TX coast, the ETA only brings up upper 60 tds into OK and northward, which is likely the reason for the ETA-forecast SBCAPE only being in the 1000-1700 range. The low-level 0-3k helicity progs, however, are awesome in northern OK and southern KS by 18z (300-350 m2/s2), and only increase in time. My current "target" is the area between Enid and Wichita, perhaps Harper for old-times sake...
 
You don't like the dryline for lift in Kansas?
Click to expand...

Yeah, KS poses a unique mix of pluses and minuses in my view. Again - I should offer the disclaimer of a fairly literal interpretation of the model output for details that are really too small to be looking at this far out - but for fun I'm doing so anyway. Last night's GFS run is slower with the southward march of the cold front behind the dryline - never really catching up in KS but maybe down to around OMA by 00Z. The ETA is more agressive with this, with the dryline CF intersection perhaps near Salina KS by 00Z. This is getting down near the region where persistent cloud cover is forecast by the model - so I'm modifying the instability in my mind based on expectations of somewhat cooler conditions across much of central KS than forecast. Strong surface wind fields will result in strong mechanical mixing and minimize the thermal effects from cloud cover - but I don't think to the extent shown by the model - with essentially no cooling shown in the cloudy region. I'm fond of extreme southern KS to western OK largely owing to forecast cold air advection in the OK and TX panhandles at 700 mb overspreading the dryline in that region (see the 700 mb T&rh plots at 54 and 60 hrs) which would favor early convective development there - despite the model not doing so.

Glen
 
Friday afternoon temps...

Anyone have any thoughts as to the extent of the jet stream related CI shield Friday (which will be a major player in insolation)? At 18Z Friday, it looks like significant CI S and E of a CDS-ICT-OTM-DBQ line, based on 250 mb RH.

bill
 
Re: Friday afternoon temps...

Anyone have any thoughts as to the extent of the jet stream related CI shield Friday (which will be a major player in insolation)? At 18Z Friday, it looks like significant CI S and E of a CDS-ICT-OTM-DBQ line, based on 250 mb RH.

bill
Click to expand...

Now that the models have "settled down" somewhat, when it comes to agreeing that there will at least be a storm, I think we should wait until tomorrows runs before trying to pinpoint such finer details WITH accuracy. Anyway, setting accuracy aside - The ETA looks like it would be rather cloudy - during the afternoon/evening FRI, RH values between 850-250mb are quite high, with some slight vertical motion between those layers...

Just remember, the GFS/ETA flipped in one model run, and they can do so again...
 
Some of what is coming out of NWS offices:

FSD out of SE SD is mentioning mini supercells and supercells in NW Iowa with capability of tornadoes.

Norman office touches on it briefly mentioning the possibility for supercells.

But the real banger is out of Missouri, here is the quote:

HOWEVER...BY FRIDAY AFTERNOON THUNDERSTORMS WILL BE LIKELY...AND THE THREAT FOR WIDESPREAD SEVERE STORMS IS EXPECTED DURING THE AFTERNOON AND OVERNIGHT HOURS. SEVERE WEATHER PARAMETERS INDICATE THAT FRIDAY COULD SEE MANY SUPERCELL THUNDERSTORMS...EACH CAPABLE OF PRODUCING LARGE HAIL...DAMAGING WINDS...AND TORNADOES. LARGE SEVERE WEATHER OUTBREAKS
ARE RARE ACROSS THE OUTLOOK AREA FOR THIS TIME OF YEAR...BUT THEY DO OCCUR.
Click to expand...
 
Yeah.. I'm doing the happy dance with Amos right now in terms of glancing at the CAPE/SRH maps.. Missouri may go for the gold, but my season in south Kansas can't be looked over, either.

Going to make tentative arrangements just in case I head out Friday, but will wait until later runs can narrow down more what's going on. I'm praying deeply for something along or just west of the I-35 corridor. Sumner County would be a good start! *LOL* Anyone been there yet this season? :lol:

Again, I'll bust into more detailed forecasting of my own come tomorrow morning. Still too far out to get real hopeful just yet.
 
I think I'll have to keep waiting before I get an idea where to head, if at all. I don;t crunch numbers and equations with this stuff, I just put everything into one hand, add em up, and then go where the sum tells me. We're still too far out because right now equations make more sense than intuition as far as guesses, but we all know the reverse becomes true on chase day. If these runs keep promising something, I'll be poised for a risk-taking jaunt to the southern end of the love zone, playing a better cap and instability for isolated convection. I honestly don;t see anything at this point that makes me excited; I've tried to run down 85mph storms, doesn't work. However, my hopes of convection Thursday night may be coming true. I love treading that fine line of "too much convection/just enough convection" pre-initiation, the latter can be a bigtime instability booster this time of year, when thermos just aren't reliable on their own.

Where ever the bullseye is, it will be painfully obvious Friday morning.......if it isn't, I'll probably stay home.

FWIW, I'm still not seeing the good supercell shear in these runs, looks very fast and very linear to me, given the lack of CAPE. With 60-70kts of steering flow, we'll need something on the order of 2700-3000j/kg to make it through.
 
I think I'll have to keep waiting before I get an idea where to head, if at all. I don;t crunch numbers and equations with this stuff, I just put everything into one hand, add em up, and then go where the sum tells me. We're still too far out because right now equations make more sense than intuition as far as guesses, but we all know the reverse becomes true on chase day. If these runs keep promising something, I'll be poised for a risk-taking jaunt to the southern end of the love zone, playing a better cap and instability for isolated convection. I honestly don;t see anything at this point that makes me excited; I've tried to run down 85mph storms, doesn't work. However, my hopes of convection Thursday night may be coming true. I love treading that fine line of "too much convection/just enough convection" pre-initiation, the latter can be a bigtime instability booster this time of year, when thermos just aren't reliable on their own.

Where ever the bullseye is, it will be painfully obvious Friday morning.......if it isn't, I'll probably stay home.

FWIW, I'm still not seeing the good supercell shear in these runs, looks very fast and very linear to me, given the lack of CAPE. With 60-70kts of steering flow, we'll need something on the order of 2700-3000j/kg to make it through.
Click to expand...

Helicities are in excess 300's, which would be good enough for tornadoes... You are right about things being linear though - Looking at the forcing along the front (using vertical velocities, wind/moist convergence through the low levels), forcing is VERY strong, and of course VERY linear... My guess is that when storms first develope they will be supercellular, but then evolve into a rather significant squall line. Given that... Your best chances would be to catch things in the west, and catch them fast, or you will be chasing the back of a squall line...

As far as shear being too much... That is possible, and another reason why linear convection would be the mean mode - i.e. a low topped convective line...
 
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