04/18/05: FCST: Central Plains / Upper Mississipi Valley

Feb 8, 2004
Detroit, MI
Making it short... 00z GFS shows a strong front pushing across the central plains with substantial low-level moisture and instability setting up in the warm sector, from IA southwestward into OK -- with excellent deep-layer and low-level shear for supercells and possibley isolated tornadoes.

Latest Outlook (Noon):

This system definitely has more to work with than the last few systems that have moved into the area. The main problem will be whether or not to trust the position of the system for the afternoon on monday. The models recently have not been doing that great of a job getting the systems placed right until almost the day of the event.
I would be really excited if after several days other models go over to the GFS timing and solution. In the northern plains temps reach into the 80's and dewpoints are progged at 60, more likely mid 50's. Still this creates some very strong instability. However, it appears that the 4-8 day severe weather outlooks from the SPC for this day mentions that the SPC does not believe that there will be a very amplified system and instead a couple less weak systems. I'll just have to wait and see.
Disclaimer as always: I'm new at this forcasting thing, so if I say something silly, feel free to point it out! :)

Not sure if anyone is following the 18th right now (it's pretty far out and the low is progged really north), but I'm hoping it'll turn into a chase day. GFS and NAM have the dryline sweeping over the CP. 250 jet is nonexistant, but the 12Z NAM is showing a nice LL jet and a good northern moisture punch in by 0Z Tue with temps in the 80s across NE and KS. Still way out there & maybe I'm wishcasting since I have Monday off. 8)
Well Models seem to be all over the place with this one. At this point, looks like severe weather is most likely north of I-80 in Iowa. however, run to run consistency is terrible. Will most likely have to wait till later to make even a halfway decent forecast.
Monday still looks like it has some potiental. Albeit rather conditional. The threat here is probably going depend a lot on whether the slower NAM or the faster GFS verifies. As with the NAM cape and shear look fairly good but with our front still out west there will be little to help overcome the strong cap. The 0Z run of the NAM had a much more pronouced CAP than the 12Z and also actual shows precipitation. SPC is mentioning a possibility for upgrade to slight risk for the northern plains and just like the last one this is probably with the intended time frame of mainly 0z-06z.
The 0Z NAM has a nice little shortwave trough ejecting into eastern NE and into northwest Iowa at around 18Z Monday. If that'd slow down just a wee, it could be fun day in Nebraska.

edit And the OZ GFS has the shortwave coming through slower and further south; exit region is SE Nebraska at 18Z, as opposed to W Iowa with the NAM.

Disclaimer: poster is very new at forecasting
I think water is still pretty muddy with this one. GFS is still bouncing around. might be Sunday night before we see for sure whats going on. however, at this point I only expect some marginal severe weather on monday.
Chase target for today, April 18

Chase target:
Blue Hill, NE (about 15 mi S of Hastings).

Storm initiation 3 PM, for new convection to develop in the wake of the current convective complex tracking NE through KS and NEB.

Storm type:
Hail to 1â€￾ diameter.

AM surface analysis showed a weak outflow-enhanced boundary from about 40 mi N of CNK to 20 mi S of EAR. Meanwhile, scattered convection was occurring along and NE of a GRI to MWK line in response to a S/WV lifting slowly NE out of SWRN NEB. This feature will be the focus for renewed convection early this afternoon. MLCAPE’s to 1500 J/kG along combined with marginal shear (0-3km SRH around 150 m^2/s^2 combined with 0-6 km bulk shear AOB 30 m/s ) will result in some storm organization capable of moderate hail.

- bill
Well, it's day 1 - so might as well give today a quick rundown. Area I find most interesting right now is the small but intense shortwave slowly migrating across KS this morning will slip into NE, continueing to offer enhanced lift ahead of the wave. Weak and widely scattered showers are present across portions of NE and KS, within inflow rooted around the 900 mb level. 50 knot WSW flow at 250 mb sampled this morning at DDC offers a glimmer of hope that reasonable speed shear could be in place along the southern edge of the wave - but whether convection can develop in wake of subsidence from mid-level short wave, as mentioned in the SPC discussion, is certainly tough to buy. RUC and NAM both consistent with intense convective development in the se NE area, where it appears sufficient shear will be in place for rotating storms, with the main instability axis sliding in from the sw edge of what is shown as a small convective cluster. At least upper 50 dews look to slide into the region by later today, with clearing appearent in the 'mini' dry slot that should offer a decent chance for keeping up with the strengthening cap. So, I guess the thing to watch for over the next few hours is whether the current elevated convection can start to get better organized, then there may be a chance for the tail end cell to be of interest. Model guidance suggests a Hastings to Beatrice area right now - too early to pinpoint until the current evolution becomes more clear. But, if I were working at SPC, I'd consider adding a 5% torn bullseye in this region at the 1630 outlook.

Currently am targeting the Hebron/Fairbury area for a target this afternoon, leaving ICT in less then 1 hour. Obviously, shear profiles are more then acceptable for tornadic supercells, as SPC has mentioned. Td's reaching the upper 50's seems reasonable with 1500-2500 J/KG SBCAPE by late afternoon N KS/SE NE. Subsidence concerns me greatly, however you have to take chances with a setup like this. Today's chasing also will allow me to be in place to play Western NE tomorrow if I choose to do so.

Good luck everyone
With position of dry slot and 500mb winds now forecast at 30 to 40 knots this afternoon, I would position in north central to northeast Kansas, perhaps along US 75 between Topeka and the Nebraska border - even though current meso dicussion is focusing a bit further north.
Slow but steady increase in convective activity around the Hastings, NE area could finally signal the anticipated storm development in the next hour or so. As expected earlier, mid-upper 50 dewpoints are now entering the region, where despite subtle moisture/thermal contrasts, persistent equivalent potential temperature convergence remains focused, particularly extending along a short axis from near Hastings back to near Topeka, sliding slowly northeastward with time. Water vapor shows band of weak ascent overspreading the best instability at this time - so it remains possible more interesting convection will get going soon. Need to see convection build down to near the KS state line to improve the chance of getting favorable deep shear to interact with whatever manages to go up. No change in target thoughts yet.

There is currently a lot of convective garbage at the moment in my area. I'm currently planning on sitting tight and seeing what happens over the next few hours. I'll be playing the Gage/Jefferson area today if things go well.

Current dewpoint in Beatrice is 55, forecasted to get up around 60. Helicity looks like it should be sufficient. 700 mb temps look to be a bit warm, though.

So right now it's a waiting game.
SPC hasn't mentioned, but a look at both north central and south central KS shows some severe parameters inching up: an area of 40kt winds at 500mb with good directional sheer in north central KS, 100MB mean layer CAPES of 1,000 to 1,500 in the south, 35-40kt effective bulk sheer...perhaps lack of a strong enough forcing mechanism thus far?