04/05/05: FCST: Central Plains/Upper Mississippi Valley

[Jeff Snyder]

"Haul" seems to be a good word, Marcie. With 500mb winds in the 50-75kt range, the storms will indeed be hauling. OUN AFD seems to hint that they expect initiation a little farther westward than NAM/GFS hint...

I find it interesting that the non-NCEP models (namely, the UKMET and the ECMWF) show the surface low into central OK by 0z, which is markedly different from the NCEP models (namely, the NAM and the GFS), which semi-agree with a surface low placement in the far eastern KS / KS-MO border / or KS/MO/NE border areas. Regardless, dewpoints are still in the low-50s in the Gulf off the TX coast, so...

Right now, I'm actually liking the ne TX/se OK area, though we'll have to see in later model runs if it appears that surface flow will remain non-veered enough for a tornado risk. The Gainesville to Paris area was very good chase territory when we were down there on 3-21, so I'm favored to that area. CAPE should be okay for April (this isn't going to be a 4-26-91 event), though we'll have to see what the low-level shear does.

EDIT: It's important to note that some NWSFOs and the HPC are siding strongly with the more southwestern route of the surface / upper low features, more in line with the UKMET/ECMWF forecasts. Refer to http://www.hpc.ncep.noaa.gov/discussions/pmdhmd.html for more information on this. The ICT NWSFO actually mentioned this in their discussion as well --> http://kamala.cod.edu/offs/KICT/0504032035.fxus63.html ... So, per ICT NWSFO and HPC, it appears that the surface low may be considerably farther west by Tues afternoon, which would put the ICT/OUN/TSA CWAs into play...

 

[Mike Umscheid]

EDIT: It's important to note that some NWSFOs and the HPC are siding strongly with the more southwestern route of the surface / upper low features, more in line with the UKMET/ECMWF forecasts. Refer to http://www.hpc.ncep.noaa.gov/discussions/pmdhmd.html for more information on this. The ICT NWSFO actually mentioned this in their discussion as well --> http://kamala.cod.edu/offs/KICT/0504032035.fxus63.html ... So, per ICT NWSFO and HPC, it appears that the surface low may be considerably farther west by Tues afternoon, which would put the ICT/OUN/TSA CWAs into play...

I was on the day shift and was part of the internal discussion among all us neighboring offices and with HPC... it's a good thing we have non-NCEP models to use in the forecast process. When there is a dichotomy between NCEP's NAM and GFS vs. ECMWF/UKMET/Canadian.. usually the latter ends up verifying closer to reality. Fore more, read the DDC AFD

Mike U

 

[Amos Magliocco]

It appears that the 18z run of the NAM places most features aloft and surface about 75-90 miles southwest of the 12z run, but none as slow or southerly as the UKMET, which at 0Z Wednesday has the center of the sfc low in northwest Oklahoma.

I'm curious how autonomous these 18z runs are. What I means is how likely are they to replicate the poor initializations of the morning run given that they ingest some of the same data (I think is what I remember having read--that much of the UA data is the same since there are no launches between 12z and 18z)?

I like the trend for sure, and am hoping we can get back to some modicum of agreement in time for long-distance chasers like me to make a choice with some confidence.

PS: Great AFD, U. It's cool when chasers are writing text products!

 

[Kurt Silvey]

Well the system has slowed since late last week, which is not surprising. But, Tuesday may present the first chase opportunity for those of us in the north central plains. I see two areas of interest; the first would be the n or ne area of the surface low. If the low tracks along the NE KS boarder this area would include se Nebraska and sw Iowa. This area of the low proved productive in two other systems this spring, 3/21 & 3/30. But the low may slide further south into srn KS. The second area would be the cold front as it moves eastward through se SD and nrn IA. It appears there could be some capping in this area which will allow instability to increase ahead of the front. But if the cap is too strong and there is no isolation just ahead of the front, it could lead to a squall line type of event as the front moves through. In either case moisture needs to return to the area. Td’s are prog to be around 55 – 60 in these areas. We’ll have to see what tomorrow brings.

 

[Ryan McGinnis]

Caveat: I am new to this whole forecasting thing. Take everything I mention for what it is -- half statement, half desire for correction.

Looking at the latest NAM runs, it looks like this system may pull pretty good moisture (TD's almost to 60) all the way up to where I live -- SE Nebraska -- but that there is almost no shear in the atmosphere up here and a fairly pathetic 300mb winds. For chasers out this way, it looks like a linear event along the cold front.

Another thing I'm not understanding (and hopefully someone can explain this to me) is that the ETA is progging a good amount of cape in Central NE around the 12Z on the north end of the low -- despite the fact that the winds are northerly in this area. Is the moisture wrapping around the low? I usually think of northerly winds as being a lot drier than the southerly winds south of the low.

Thanks!

 

[Glen Romine]

Some improved run-to-run consistency with the most recent NAM cycle. Surface low is slightly further south and west, particularly early, but with slightly improved moisture forecast. Upper level system weaker this run, yet is still a potent and compact system. Because of the stacked nature of this system, some question as to whether adequate deep layer shear will be present colocated with a forcing mechanism. Most recent cycle added a secondary warm front to potentially force convection - but such small features are notoriously unreliable this far out. So, I wouldn't completely discount this system's possiblilities - but it isn't very attractive either. Further south storms could fire in a more linear fashion, NAM suggests after 00Z, but too early to nail that down yet.

Glen

 

[Chris C Sanner]

I'm watching the ECMWF very closely this run as soon as it gets itself out to see what the prospects are. I like the ~60 TDs forecasted by the NAM all throughout the area, and I also like that the CAPE is in the ~2000 range in OK. What I don't like is that the winds suck if the Low is faster and more north, which would kill any supercell chances right off. IMHO, if the system is further west/south as the ECMWF dictates, it might be worth chasing for folks down here, as the shear might be a bit better in Oklahoma, but if things are going to be east of me here in Velma by 18z, I'm sitting this one out, ONLY because this upcoming weekend looks very promising in terms of chase potential in the flatlands of Western Oklahoma for a 3 day period.

 

[DanHinch]

As it stands with tonight’s 00Z model run it looks like I could be chasing from my front porch on this one. I am not one to have a ton of faith in a 48 hour forecast but there has been pretty good consistency in the NAM in the last couple of runs. I think I would pick a target somewhere between Sedalia, MO and Columbia, MO. Looking at soundings for SZL and COU the NAM seems to break down the cap and start convection between 21Z and 00Z. If the cap can hold this strong all day, things could really get juicy and be quite explosive. Looking at a JEF sounding south of COU the NAM forecast CAPE over 2000 J/KG, SRH of 313 lending to an EHI of 4.1. These numbers are hard to ignore especially backed up by LI's around -8, and deep layer shear ~35knts. I think that there is enough deviation in storm motion from the mean shear that they may remain discrete for a while. LCL heights are reasonable around 940 meters, sure I would like to see lower but that could get it done. The hodographs for this area look very nice as well with a good curve. I wouldn't put all my money on a 48-hour forecast, but the way things look I won't have to travel far.

Dan

 

[Jeff Snyder]

This model flip-flop-aroo is pretty interesting... The 0z runs from tonight's NCEP models are not showing a whole lot of run-to-run consistency (the NAM is a tad more consistent in the past couple of runs), with a general (and hoped-for) trend towards the non-NCEP model solutions (from ECMWF, UKMET, and Can.) discussed previously. While the 0z NAM is slightly to the southwest of its previous positions with the surface low, the GFS is now showing the surface low along I35 in northern OK and southern KS by 0z. Meanwhile, the UKMET run is pretty similar to it's earlier 12z run, with the surface low in the OK panhandle/TX panhandle/southwestern KS area by 18z, shifting southward by 0z, with the surface low centered along the western OK and TX panhandle border. Certainly, this is a healthy 150-250 mile difference compared with the NAM... I am liking the general trend that the NCEP models have in bringing the surface low a little farther southwest, since it continues to make the prospects of chasing in central/eastern OK a little better.

 

[mikegeukes]

Based on a quick glance of the 00Z models runs.

NAM continues to be the outlier so far, moviing the system further north compare to the Canadian, ECMWF, GFS and UKMET models, which has it much further south. Would favor the more southerly placement of the system.

Some questions to ask about the NAM:
The positives, difluence, dry slotting, moisture increases at H85, steep lapes rates to name a few. The negatives, How much is the NAM over doing the surface dew points, still a bit of a spread of T-Td, not much moisture in the lower layers at 42 hrs, will capping be a issue, especially over IA, vertically stacked, to name a few, be intersting to see if the NAM verify.

Still would expect some storms to develop along the dryline from eastern KS, eastern OK, and northeast TX, moving into MO, AR, later on and more storms forming along the warm front, in NE, IA and southern MN. Good lapse rates and cold air at H5 for some good hailers in some of the storms.

Mike

 

[Chris C Sanner]

Alrighty then, looks like the NAM is finally in line with the ECMWF. The Low is progged about DDC at 0z. Depending on how fast the dryline mixes eastward, it looks like this could be a more central Oklahoma show. Cape looks about ~2500, and if the winds remain more southerly, we will have some mean shear. Only concern is storm speeds, as they look to be moving tommorow. Things look much better with this run in comparison to the last couple. Now waiting on the other models to really make a good forecast.

 

[Mike Hollingshead]

http://www.wxcaster2.com/CENTRAL_ETA_SFC_S...INDSLI_30HR.gif

http://www.wxcaster2.com/CENTRAL_ETA_SFC_S...INDSLI_36HR.gif

Interesting winds in central IA. They back strongly along the wf between 18z and 0z.

http://www.wxcaster2.com/CENTRAL_ETA_500_G...NDVORT_30HR.gif

http://www.wxcaster2.com/CENTRAL_ETA_500_G...NDVORT_36HR.gif

500mb winds try to stay more veered(less backed than most places not southeast of the low) along the nw side of the bulging ridge. There should be a nice shear profile along the wf. Not sure this is a wise choice but I'm not leaving home to drive well south to find the non-unidirectional shear again when this option is overhead. Target of Blair Nebraska(to say Des Moines IA).

 

[Karen Politte]

For this date - and indeed any date for the next 7 days outlook, I don't like what I see. My opinions may be influenced by the fact that gas is now 2.19 in Norman - but I guess I'm just not that desperate to go and chase eastern Oklahoma. Ye-es I may chase it if it was looking like the all-time tornado outbreak.....but it's not.

Moisture will be limited because of the battering the Gulf has taken with last week's system, and by 0Z Wednesday 6th April the only place left to play is extreme eastern Oklahoma & Kansas, and western AR. That doesn't get me excited, for some reason.

Also - not to pull this thread off topic but has anybody looked at what this next system's front is due to do to our beloved Gulf? It's a repeat of last week - bringing 50-degree dewpoints well into the northern Gulf and pushing the 60-degree line waaaay down there. I think I'd be discarding any hopes of chasing this weekend.....

KR

 

[Nic Wilson]

The NAM Monday 12z run has finally come in line with its European and Canadian counterparts. At 18z it has a 992mb surface low sitting in southwestern KS with a dryline extending south towad Enid, to Lawton and points south. Set-up looks similar to March 21st since it appears the dryline will pass thru OUN around 18z and initiation should be shortly thereafter.

Td's are currently up to as high as 56 in southern OK. Using the "glass is half full" mentality the best we can expect for Td's tomorrow would have to be in the mid 60's....NAM progs low 60's. This still doesn't get me too excited considering temps should be around 80 ahead of the dryline, so LCL's will be much higher than climatological numbers wanted for tornadogenesis.

My current target is to hang out in Norman until 18z and see where the dryline bulge will occur and then make a decision to head out or not based on how the Td field and storm motions are looking.

 

[Amos Magliocco]

Well, after finally getting the ETA to do what we want and keep the important surface features in chaseable terrain, I'm going to leave her at the altar, I think. I can't sell myself on the stacked-low shear structures (though they paid off for some on March 21st), the modified Gulf air, the narrow moist axis (given storm motions), and how fast the storms will fly even during the short window before the massive forcing lines out the convection.

My favored region for this event, around TUL to McAlester, is about nine hours from here, and I'd have to leave this afternoon. I guess an ecstatic Day 2 later might persuade me, but I don't see that happening.