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

Joined
Feb 8, 2004
Messages
1,975
Location
Detroit, MI
I'm thinking there is some pretty good potential for Tuesday ... We'll have an open GOM, with southeasterly surface flow advecting >55F Tds all the way north into MI, with >65 Tds into central/eastern OK... Yielding relatively strong CAPE across the region. Wind fields are a bit better than the last run (500mb slightly stronger). Here is my latest outlook graphic:

Latest Outlook Graphic - http://www.midwestchase.com/wxforecasts/ap...pril5-2.gifhttp://www.midwestchase.com/wxforecasts/april5-2.gif[/b]


..Nick..
 
I'm thinking that the potential is there for a good severe weather event on Tuesday, moisture this time should not be a problem! :D

I am thinking at the moment that the best potential for severe weather would be focused around north central Oklahoma, eastward (Ponca City, Bartlesville, Tulsa, maybe as far southeast as McAlester). NWS's (Pleasant Hill, Wichita, Springfield, Tulsa) HWO mentions of severe for Tuesday. GFS has dewpoints in this area of around 60, but the only thing I am concered about is where the GFS is tracking this low. Previous runs have had this further north, centered around the Kansas/Oklahoma border, but its taking the low down to the Oklahoma/Texas border at the moment. I have looked at the ECMWF model and it has the low at the moment for 0Z on Wednesday at the Kansas/Oklahoma border, so the models are still disagreeing, but later runs will better refine my forecast.
 
Originally posted by Ben Prusia
I'm thinking that the potential is there for a good severe weather event on Tuesday, moisture this time should not be a problem! :D

I'm not convinced that moisture won't be a problem. The models are showing northwesterly flow through the Gulf though Sunday, with some 20-25kt northerly surface winds tomorrow. Winds in the western Gulf don't start to turn southerly until Sunday afternoon evening, but by then the moisture will have been pushed all the way south of the Yucatan, so it'll take plenty of time to get it back into the plains. With two days of strong northerly flow, I'd expect we'd need at least two days of strong southerly flow to get the moisture back up here, which means it'll be a close call, IMO, for Tuesday. We may end up with some modified continental air like we've had a couple other times this year -- with Tds in the 50s. Yes, we've had tornadic events with such dewpoints, but it's certainly much easier to get significant potential instability with Tds >60. It appears that we'll be depending upon Gulf modification of the continental air, so I'm not sure that we'll be able to do this. If we can slow this system down a day or two, I think we'll have a better chance of seeing some TRUE Gulf air (Tds in the 60s and 70s).
 
It's always hard to find late-May air in early April; you're usually dealing with some post-FROPA modification like this and I think in the case of last night's GFS concerning the southern plains, it could be worse.

The model develops high pressure over the GOM as early as Saturday night, and as low-level winds calm, the water will have undisturbed insolation both Sunday and Monday, with the fetch beginning Sunday afternoon. If this run verifies, I think there's time to create enough "new" Gulf air to sweep back up into Oklahoma and at least offer the possibilty of a decent chase. We can probably rule out a big tornado day, but then there's a good reason why the climatology looks like it does. Still the southern plains can recover very rapidly.

Rich Thompson's name always comes up this time of year as he has written quite a bit about return and recovery topics. Sea surface temperatures and gulf buoy data are available here:

http://fermi.jhuapl.edu/avhrr/gm/05apr/ind...humb_short.html

http://www.ndbc.noaa.gov/rmd.shtml

It's interesting to 'keep score' and see how the air flowing into the basin changes and what effect it has on SST's.

My bigger problem with Tuesday is what a radical departure last night's solution was from the one before it. I'd like to see two or three more runs show consistency before I believe what we're seeing.
 
Originally posted by Jeff Snyder+--><div class='quotetop'>QUOTE(Jeff Snyder)</div>
<!--QuoteBegin-Ben Prusia
I'm thinking that the potential is there for a good severe weather event on Tuesday, moisture this time should not be a problem! :D

I'm not convinced that moisture won't be a problem. The models are showing northwesterly flow through the Gulf though Sunday, with some 20-25kt northerly surface winds tomorrow. Winds in the western Gulf don't start to turn southerly until Sunday afternoon evening, but by then the moisture will have been pushed all the way south of the Yucatan, so it'll take plenty of time to get it back into the plains. With two days of strong northerly flow, I'd expect we'd need at least two days of strong southerly flow to get the moisture back up here, which means it'll be a close call, IMO, for Tuesday. We may end up with some modified continental air like we've had a couple other times this year -- with Tds in the 50s. Yes, we've had tornadic events with such dewpoints, but it's certainly much easier to get significant potential instability with Tds >60. It appears that we'll be depending upon Gulf modification of the continental air, so I'm not sure that we'll be able to do this. If we can slow this system down a day or two, I think we'll have a better chance of seeing some TRUE Gulf air (Tds in the 60s and 70s).[/b]

I totally agree with Jeff - and bear in mind that even when we DO get some southerly flow back from the Gulf, it could very well be a bad fetch. I don't have time to digress largely here - but I just posted more lengthily on another thread in TA about the current prospects:

http://www.stormtrack.org/forum/viewtopic.php?t=5768

Regards,

KR
 
Originally posted by Amos Magliocco

Rich Thompson's name always comes up this time of year as he has written quite a bit about return and recovery topics. Sea surface temperatures and gulf buoy data are available here:

Last nights runs do show a little more hope than previous, but I'm still skeptical. I'd say that I'd watch for the NAM to enter this forecast period, but the 72-84hr NAM forecasts have been horrible of late. LOL...

For those who are curious about SSTs, return flow, etc, you may find the following to be interesting:

Thompson, R.L., 1996: Buoy Observations from the Western Gulf of Mexico during the
1993-1994 Cool Season. {HTML}


Edwards, R. and S.J. Weiss, 1996: Comparisons between Gulf of Mexico Sea Surface Temperature Anomalies and Southern U.S. Severe Thunderstorm Frequency in the Cool Season. Preprints, 18th Conf. Severe Local Storms, San Francisco CA. {52K HTML}
 
From the 12z 84 hr runs of the NAM and GFS this morning there is definitely a wide divergence in the solutions of the two models.

The GFS has the 500mb vort. max. sitting in Western Idaho with relatively zonal flow whereas the NAM has the 500mb vort. max. in northwestern Arizona with a much deeper trof axis.

The GFS and NAM both begin returning Gulf moisture northward in the afternoon on Sunday. I don't think Tuesday afternoon will be an ideal set-up but the shear will be there (although it likely will be another stacked low) and dew points should be sufficient for weak tornadoes somewhere in the Southern Plains.

There is also a huge discrepancy in the placement of surface lows by Tuesday evening by the ECMWF and GFS which should really come as no surprise considering how far out we are still.

GFS: Elongated 1005 L in southern Wisconsin with no associated L in the Southern Plains

ECMWF: 999 L near Wichita with deeper associated trof
 
I'll make this brief since I have to be up at 6am to cram for a Marketing test in the morning (don't ever take a Saturday morning MBA level course :evil: ).
The 00z NAM is falling into a similar solution as the ECMWF so I'd say my confidence is increasing for a Tuesday severe outbreak across southeastern KS and eastern OK.

The NAM has a nice fetch of 55 Td's into southern KS on Monday, with a tongue of 60 Td into southern OK...so I'd say its safe to assume that moisture return would be even better on Tuesday ahead of the low with 35 to 45 knot 850 mb winds progged. The only concern is there is noticeable veering of the 850 winds by 12z Tuesday at 850 mb, but the surface wind field looks good out of the south.

Both the NAM and ECMWF have the surface low in northern KS at 12z on Tuesday with the NAM at 1001 mb and the ECMWF stronger at 997mb. The GFS has it further south in northwest OK at 999 mb.

Nice insolation across the Southern Plains starting tomorrow will atleast create high confidence in the presence of instability across the region by Tuesday, we'll have to wait and see if the progged moisture returns are realistic. If the system slows slightly from its current track then things are looking good for a possible chase.
 
I have been continuing to monitor the severe weather that is possible on Tuesday over southern Kansas and northern Oklahoma. ETA at 84 hours (Wednesday at 0Z, Tuesday at 7:00PM CDT) shows a CAPE value of anywhere of 1000-1500 J/KG from a line east of Interstate 35 in northern Oklahoma and also east of a line from Salina to Omaha. CAPES from 1500-2000 J/KG are also progged in southeastern Oklahoma and northern Iowa. Td's are progged to be in the lower to mid 60's in northeastern Iowa and also in extreme eastern Oklahoma. Surface temperatures are going to be up to 80 degrees in an area from Emporia, Kansas northeastward to the Minnesota State Line, also along and south of Interstate 40 in Oklahoma. LI's are right now progged to be -4 from Emporia northeastward and also in Oklahoma. The low will continue to track from Kansas on Tuesday into extreme northern Oklahoma, maybe hugging the border of Kansas/Oklahoma throughout the active part of the day.

I think the best bet for severe weather on Tuesday will be in Oklahoma, along and mainly east of Interstate 35, and a little south of the Kansas border. I will update my forecast tomorrow!

EDIT: I viewed the new 12Z GFS which shows the Low now tracking over central Kansas during the day Tuesday which may shift the severe weather risk a little north, but there are still differences in the ETA and the GFS to settle, but until then I am still banking on the Low tracking near the Kansas/Oklahoma border.
 
Hmm, the 18z runs of GFS and NAM are not looking good for those wanting to chase in OK/KS/TX/NE... The NAM is signficantly farther east with the dryline and surface low by Tues afternoon, which is more inline with GFS forecasts. The 18z GFS shows the dryline near the OK/AR border by 18z, with the low near Kansas City during the afternoon. The 18z NAM follows the same eastward trend, indicating the dryline along the OK/AR border by 0z. For what it's worth, that means that the 18z NAM solution is 140 miles east with the dryline position compared to the 12z NAM run. It continues to look like there will be two instability bullseyes, associated with two moisture bullseyes. One will be from eastern OK/western AR southward, and one farther north into Iowa. Between the two, it appears that the strong 850mb flow will result in the mixing out of the surface moisture. To the south, the moisture should be deep enough to maintain 60 Tds, while, to the north, the mixing should be less vigorous, thus allowing IA to maintain decent surface moisture.

I usually don't like commenting on a single model run, but the eastward trend was supported of the NAM puts it more in agreement with the GFS... Hopefully this trend will reverse itself on the 0z runs, since I'd REALLY like to chase KS/OK/northern TX on Tuesday. I'm also hesitant an any runs that deviates the 140 miles that the 18z is from the 12z run.

For what it's worth, the GFS is a tad farther south with the surface low (just south of MCI instead of just north of MCI by 0z) and a TAD farther west (slower) with the mid-upper level low/wave.
 
I would place bets on eastern KS southward into northeastern TX, as far as chaseable storms goes.

IA and NE due appear to have good instability, but wind fields are terrible. For starters, the 500mb jet streak never really peaks in, and the 500mb low is SSW of the region. The 850mb/700mb winds are really weak, as that area is in the center of the trough. Also, helicity values in that area are horrible as well by the time the CAP/CINH errodes and the best instability moves in, so don't expect too much tornadic stuff in that area. You can also see the CAP using the 700mb temps, where there is a ridge of higher temperatures across most of IA.

Further south in southeastern KS, OK, and northeastern TX... Instability looks decent (similar to the areas further north), these locations are east of the main low/trough, so wind fields aren't really a problem, though the strongest low level wind fields don't really develop until the 6Z WED. The strongest 500mb jet streak is also moving across this region during peak heating/instability, between 18Z and 0Z. As far as storm mode is concerned... This system does appear to be strong, and with that comes some pretty strong mass forcing along the dryline/cold front, as evident on the vertical velocity fields, so things could go linear quite fast, with few isolated supercells. But, given that, I believe during the first several hours of initiation, storms will most likely be "isolated", and that's where the best chance of catching the supercell exists, though I'm not seeing a significant tornado threat as of now.

The rest of the event could possibly be a squall line during the night time hours from LA to MO (6Z onward)... During that timeframe, a pretty strong dry punch develops at 700mb and 500mb, vertical velocities explode, and the nocturnal LLJ develops... Increasing helicity values significantly. But, MLCAPE drops significalty during that timefram, enough so to leave the threat mostly linear, and eliminate a significant supercell and tornado potential.

Too bad this system doesn't slow down some/spin up further west... If you took that same 6Z model forecast (from above) and move it back to 21Z, where significant instability could be realized, things would likely become very active.

Of course, most of this is pure speculation at this point, which is always fun to do.
 
I think the models are coming into a better agreement as to the position of the Low during the day on Tuesday. It appears now that the Low will track along the Kansas/Nebraska border. 12Z NAM has the Low just north of the Kansas/Nebraska border at 0Z Wednesday, while the 0Z GFS has the Low centered around Kansas City. I think the best position for severe weather will be east and northeast of the Low which will make, in my opinion, the area from Nebraska City southward and eastward into Kansas and Missouri as the best bet for severe weather. Td's are progged to be up to the 50's or even the 60's, with CAPE values of 1500 J/kg to 2000 J/kg.

I am thinking that any tornado threat will be at a minimum across Kansas and Missouri as a squall line could develop as soon as any storms fire. I do see that the NAM has indications of -8 LI in north central Iowa, but I am not convinced about storms developing that far northeast of the Low, especially any severe. I will post an updated forecast tomorrow.
 
Nebraska and Iowa certainly don't look too impressive for Tuesday. Yes, the NAM shows plenty of CAPE and some nice, low LIs, but what else does it show? It shows practically no wind over OMA at 850mb. Thus, the helicity is meh. Dynamic support is better over eastern Iowa...still come CAPE there, but it's very CINful. The NAM also shows warmth around 700mb. Looking at the BUFKIT sounding for OMA, there's a nasty inversion until about 21Z...and by that time the helcities have dropped considerably.

Right now, it looks as if the best potential will be a very skinny region along the OK/AR border into western AR. The dynamic support is better there, but it looks like not too much will go on prior to evening. All-in-all, I'm not tremendously impressed, but its still 60 hours out and the first week of April.


Ben
 
I'm forcing myself to post this for accountability and learning. But, 850 and 700 winds show a good chance at anything forming going linear fairly quickly. Best bet would be intercepting anything early on in initiation in E. OK or extreme SE KS, as the line looks to haul eastward once it gets organized.

Marcie
 
"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...
 
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
 
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!
 
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.
 
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!
 
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
 
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.
 
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
 
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.
 
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
 
Back
Top