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

[nickgrillo]

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..

 

[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!

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.

 

[Jeff Snyder]

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!

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).

 

[Amos Magliocco]

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.

 

[Karen Politte]

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!

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

 

[Jeff Snyder]

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}

 

[Nic Wilson]

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

 

[Nic Wilson]

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.

 

[Ben Prusia]

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.

 

[JHadorn]

Correct me if I'm wrong, but the latest GFS shows what appears to be a half-decent jet streak forming around the 5th.

How will this come into play?

This is what I'm talking about, just so we're clear:

http://www.rap.ucar.edu/weather/model/disp...hr042hr048hr060

http://www.rap.ucar.edu/weather/model/disp...hr042hr048hr060

 

[Jeff Snyder]

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.

 

[Robert Dewey]

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.

 

[Ben Prusia]

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.

 

[Ben Cotton]

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

 

[MMartin]

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