05/07/05: TALK: Southern/Central Plains

[Mike Hollingshead]

It THEN progs a VERY rapid turnaround in the afternoon bringing 60s across the board all the way through SPS, western OK, and up into South Dakota!!!

http://www.rap.ucar.edu/weather/surface/sfc_ict.gif

http://weather.cod.edu/forecast/ETA/previo...0mb_dewp_18.gif

Last nights 0z eta at 18z looks pretty dang close to me(actually almost spot on up here). Temps have now risen and the sfc tds are holding nicely in the upper 50s with some low 60s in most of KS, NE and western IA. It is called pooling. If a convective cluster forms in sc SD or ne NE today and plows se I think one can count on that much more pooling south of it tomorrow.

http://www.rap.ucar.edu/weather/surface/sfc_aus.gif

Even did well down south too. This isn't saying tomorrows progs will be spot on, but at the same time I don't see it as being all that crazy.

Also, the gulf intrusion shunted decent moisture westward and that is likely what has travelled up here...just the long way into Mexico and sw TX. With the flow starting to come more off the gulf it is going to start pulling up that recycled air, but the good stuff isn't far behind. Maybe that is why the tds are falling off like rocks with heating down there right now. I hope that isn't what is in place up here on Saturday...though with added pooling and rapid transport it should all be ok.

 

[Mike Johnston]

Regarding Karen's question about the veractiy of quick dewpoint recovery, I believe in the case of this system, it has at least as much to do with the dynamics of convection as the source/quality of the heat and moisture. The height lines at 850mb are oriented very much north/south. Advection does not occur when the height lines are parallel to isolines (eg., isotherms); can't advect warm/moist air where it is already equally equally warm/moist as the "source." When the flow meets a more perpendicular isoline, however, positive advection occurs. That is why we are seeing with this system the phenomenon of dewpoints pooling in various places (eg South Dakota) over the plains. Think of it like a comet soaring overhead with a long, thin tail. In this particular case, it looks like we have a somewhat e/w isotherm kind of dropping south over night, perhaps in the wake of today's convection up north, and then tomorrow - boom - the 850mb flow hits it perpendicular and we see dewpoints rise rapidly during the day on Sat in places like N Central TX.

 

[Jeff Snyder]

Originally posted by Karen Rhoden
What are other's thoughts on the ETA's very aggressive progged moisture recovery for this Saturday's timeframe?

Today's 12Z May 06 ETA run forecasts a \"dry hole\" (due to overnight precip/MCS?) to move from central TX to around the SPS area by 1200UTC Saturday morning - with this area containing sub-50oF dewpoints. It THEN progs a VERY rapid turnaround in the afternoon bringing 60s across the board all the way through SPS, western OK, and up into South Dakota!!! By 00Z Sunday it plays around with 65oF dewpoints near SPS, too.

How realistic does the list think this is?? I don't quite know where it's getting it's moisture from - especially from taking a look at the current surface pattern and noting that there are NO 60-anything degree Tds onshore ANYWHERE in Texas, and also looking at buoy data and seeing that the highest dewpoint locatable in the Gulf is 63.0oF at Scenic-Route Station 42020 in the north-western Gulf.

I am wondering just *how* we are going to realize these ETA-progged 60-65oF dewpoints on Saturday evening from San Angelo to Fargo.

:?

I'm not being pessimistic - goodness only knows I want this higher-moisture resolution to verify......because I will, barring unforeseen circumstances like grungefest - be out there.

KR

Karen,

I think that, with May now, we're starting to see the NAM pick up on diurnal increases in Tds courtesy of evapotranspiration (thank you plants!). There seems to have been nice daily diurnal fluctuations the past several days, so I think we can attribute the increase in Tds not to advection, but rather to evapotranspiration. Afterall, as you inferred, you can't get >60 tds from TX to the Dakota's in 12 hours. LOL I suppose you could, but would we really want to be chasing with synoptic-scale flow from the south at 80mph? LOL..

EDIT: Moved my discussion over to FCST thread.

 

[Mike Johnston]

Jeff Snyder wrote:

There seems to have been nice daily diurnal fluctuations the past several days, so I think we can attribute the increase in Tds not to advection, but rather to evapotranspiration

Oh, I agree - in general - the improvement in daytime Tds has much to do with evapotranspiration at this time of year. However, I think to explain the apparent anomaly of higher dewpoints much further north on the plains than dewpoints further south - followed by a reversal the next day - you have to look at the mechanics of advection, especially with a system such as the one we are forecasting now. That is why I mentioned not to worry too much about the source - the molecule pooling up in SD may not have travelled all the way from the gulf in a few hours - but it likely did advect from somewhere south, be it air over greener pasture or whatever.

 

[Karen Politte]

I've spent this morning and afternoon looking at this.....still don't quite know what I'm thinking LOL, but...

Yes it's May and yes we have to be wary of evapotranspiration. I wonder if the massive amounts of ground saturation in the TX Panhandle over winter will come into play at all.

But aside from that - what I really think will be the driving factor behind attaining true moisture tomorrow may just be the Scenic Route. I would keep an eye south and west for your moisture......don't sit watching Houston's harbor......cause that ain't where it's going to come from this time!

Thanks to all who've discussed the mositure with me this afternoon. I agree with all of your points.

KR

 

[Jeff Snyder]

Originally posted by Mike Johnston
Jeff Snyder wrote:

There seems to have been nice daily diurnal fluctuations the past several days, so I think we can attribute the increase in Tds not to advection, but rather to evapotranspiration

Oh, I agree - in general - the improvement in daytime Tds has much to do with evapotranspiration at this time of year. However, I think to explain the apparent anomaly of higher dewpoints much further north on the plains than dewpoints further south - followed by a reversal the next day - you have to look at the mechanics of advection, especially with a system such as the one we are forecasting now. That is why I mentioned not to worry too much about the source - the molecule pooling up in SD may not have travelled all the way from the gulf in a few hours - but it likely did advect from somewhere south, be it air over greener pasture or whatever.

Mike,

My comment was in connection to the increase in Tds from the 50s in the morning to the 60s by afternoon across most of the plains. A large-scale increase in Tds in ~12 hours during the day signals evapotranspiration primarily. This higher-Td air can then be advected elsewhere, as you noted in your example of advection from some greener pasture. There will also probably be some moisture pooling owing to decent surface convergence, especially in the northern plains. Minor large-scale moisture advection has been occurring courtesy of the southerly flow bringing up SOME moisture from the Gulf as well. At any rate, I should end this since it's going off-thread.

 

[Billy Griffin]

Evapotranspiration !! Look at the amount of rainfall we've had (heck, even snow) over the plains/high plains regions. OK Mesonet already shows 60 degree dewpoints in Altus, and many other places... even as far north as Alva, OK.

That's my answer. I don't think this is TRUE gulf flow of 70 degree dewpoints, I think it's modified continental air that, by this time of year, coupled with evapotransporation, can get DPs well close to 70 degrees.

The moisture, however shallow, is moisture, and I'll take it !!! :wink:

In addition, I don't want HP cells anyway. Too tough to mess with. Give me a few classic dryline cells and keep them out over some picturesque countryside, oh what fun !!

 

[Karen Politte]

I note an area of thundershowers/precip located around Midland TX and moving far northeast of there towards the Oklahoma border. Much of this may not be reaching the ground nearer OK, but the Midland stuff is moving NE and definitely raining on somebody.

It will be interesting to see what effects this precip. causes over tonight. Will it moisten things a bit more? Will it lay down boundaries around CDS that get long-forgotten by T-time tomorrow?? Is this a sign of moisture creeping northwards??

Hmmmmm......

KR

 

[Billy Griffin]

All of the above, Karen. :wink:

Any moisture will only enhance what we already have in place, and boundaries left over from any overnight convection can only help as well.

As far as an indication of returning moisture, I just don't think it's TRUE gulf moisture returning. As Jeff refers to it quite often, I think we're just seeing modified cont. air returning on the southerly winds. I think now that we've pretty well reached capacity on our vegetation "greenage", it's now going to be very difficult to supress our dewpoints lower than ~45 degrees, even after the dryline passes (speaking for central Oklahoma). Yes, I know, high plains, different story. Later in June, different story... as vegetation is cut and dries with the summer sun.

I think the next 4 weeks are our best time, as everyone will likely agree, for seeing action in our area (central Oklahoma), but I still don't see a major gulf airmass today, more moisture flux coming in by Sunday leaves me VERY optimistic then, and ESPECIALLY NEXT WEEK, but keeping on focus for this particular talk thread for tomorrow, I think the excitement should be building in everyone for some good potential dryline stuff tomorrow afternoon.

 

[Mike Johnston]

Dick McGowan and I will be heading out west from KC area by 9:00 this morning. Our plan is to make directly for the crossroads of Salina via I-70, to arrive by noon, and pause to evaluate guidance at that point. Our current thinking is Salina will put us at the SE base of a target box extending to Hayes area to the W, and up through Concordia, KS to York, NE to the N via US 81. Like the chances for greater upper level flow and proximity to approaching dry line to the W of Salina, but SPC's higher tornado probability area currently forecast to the N of Salina. Hopefully, we will at least have a mesoscale discussion out by shortly after noon that we can hang our hat on.

Good luck to all chasing today!

 

[Philip Flory]

I am leaving ICT now for Shamrock, TX. Really do not have a target as I will just target wherever the best SFC conv takes shape that will hopefully lead to initiation of an isolated supercell or two in E TX pan. RUC/NAM have been trying to indicate a dry punch the last few runs now in W TX. RUC/NAM also continue to indicate an isolated precip area SE AMA by 00z... we will see. May stop for lunch in OKC considering initiation likley will not take place until late afternoon. Have mixed feelings about today, feel that if storms go though that photogenic supercells are a good bet and hopefully we have low enough LCL's and can squeak out enough low-level shear for a couple tornadoes. Im much more concerned right now with convection even going.

Have fun everyone!

 

[Adam Atkins]

Wow

12z RUC has the 60's Tds creeping up into the Western OK, E TX panhandle this morning COMPLETELY MIXING OUT. We'll be dealing with upper 50's dewpoints, yet again. May see a local diurnal maximum in W OK near some of the baby winter wheat fields.

There is a dying trend in the shower/t-storm activity currently over the area probably due to some convergence aloft in the right front quadrant of the jet. I actually like these early showers because they'll leave boundaries all over the place.

The best storm may be the tail end charlie today because of the only 1500-2000 CAPE in the target, so I may target somewhere S of I-40, might head down I-44 and west towards Childress. Hopefully these storms are more isolated in nature than yesterday when there was storm negative storm interaction all day, killing tornado chances.

EDIT:
12z NAM shows better moisture and similar kinematics as RUC. Seems NAM places the better helicity farther north. I like the small 40-50 kt mid-level flow in the E TX panhandle by 0z. This has the potential of being a beautiful W OK dryline chase if the better moisture can drop anchor today.

 

[Verne Carlson]

Leaving Denver soon and hope to high-tail it east to about Goodland, KS and then adjust from there. Good look to everyone going out today!

 

[Mikey Gribble]

Today is a tough call. Everwhere looks marginal. I have been looking at the same stuff for over an hour now and can't make up my mind. I have to leave now though, so I have decided on DDC to the Oklahoma border. Good luck to all who are going out today.

 

[nickgrillo]

I just got done looking at everything and I feel the same way. I ain't sure where to go, but DEFINITELY not north of DDC...