4/17/04 FCST:PLAINS

[Anonymous]

I was just thinking what Scott was thinking, I came to post a possible severe weather event in or near the plains and here we are, over 20 posts into this topic already.....I fortunately have the weekend off (for once) this weekend so I will be out if the weather continues to follow our predicted track. I will be where the weather is, I live in OK so I am hoping for somewhere in southern or central OK. We will see.

 

[J.B. Dixon]

The latest GFS (120 hr) is putting the warm front action right over SE Nebraska, with a good punch of 60+ dewpoints. If you can get over the horrible visibility aspect, these kind of early north season setups can pay off big time (I'm thinking 8 Apr 99, SW Iowa outbreak).

Why I'm getting fired up this early is beyond me. I know I'm in for a letdown.

 

[Matthew Havin]

For the late nite dreamers:

The 0Z Tue 13 Apr AVN run is up....... so let's highlight a few things.

At 0Z Sun (5 days out):


1. NE and IA in left exit region of 250mb jet maxing over NE NM at 117kts.
2. 850mb LLJ from S near 45kts over N central OK and E KS.
3. Central pr near Goodland KS a bit under 996
4. Sfc T >75 and near 80 over W KS, E NE, and S IA (Sat evening)
5. LI -6 over much of IA (CAPE likely >2000)
6. Veering profile 60-70 degrees over KS, IA
7. Model showing 2 good days of Plains warming (Thurs and Fri >75 highs)

I'm not allowing myself to get excited yet, but if the models keep up continuity until Thursday, I'll start packing.

 

[Tony Laubach]

Things look like they'll be a bit closer to home for me, at least in terms of a not-so-marathon chase as March 27. If things maintain about the same position, I think I'm going ot head out regardless because I can.

Temps will stay pretty warm throughout the week, and looks as if the moisture will get in there as well. Everything else is still a ways away, enough not to warrent too close a look, but CAPE values look like they could punch 2000, so maybe that'll hold (or get better 8) )... my only concern is the April curse I've had for 4 years now, but with one chase under my belt, I'm hoping to shake that curse.

Still waiting til about Thursday before making any real decisions or excitment, but it gives me something to watch for the next few days. I imagine I'll go as long as the position of things remains about the same in later runs simply because I can be up and back in a day (less mulah). Also have a light week in terms of take-home work as I have exams Wednesday, and had one last Thursday, so nothing too major to keep me in chains. Just hope the car hangs on a bit longer!

 

[Ben Cotton]

I've mostly been looking at Iowa because that's about as far out as I can go for a Saturday event (a Sunday event would have to be even closer, of course). Given that I live in Indiana, a severe Saturday in Iowa might be my only chance for a while. That having been said, the 12Z GFS doesn't
instill a whole lot of confidence. The shear profile is very nice on
Saturday, in both direction and speed. 2M temps should be in the upper
60s, and there's the chance of some Gulf moisture being brought up by the
850 winds. The big concern is the location of the surface low. 18Z
Saturday, the low will be over southeastern WY, with a warm front
extending across the NE/KS border and just south of IA/MO. By 0Z, the low will still be in sern WY, but the warm front will have moved north into
southern IA and the cold front will be along the CO/NE border and across
the OK/TX panhandles.

It looks like Iowa will be out of the warm sector for most of the day, so
northern Missouri might be a better option. Then again, the target area
might have to be moved further west due to the timing of the system.
Still...this is 100 hours out, so there's plenty of time for conditions to
improve. Tomorrow's 12Z Eta will start picking up on this, and we'll see
where it goes from there.


Ben

 

[Robert Dewey]

I have to agree Ben, I'm gonna wait and see what the ETA does, since it is higher resolution and can get a better handle on things in general. I don't have time to head over into IA this weekend, but I'm hoping any leftover activity will be able to make its way into IN/MI region late Sunday.
Anyway, late FRI also looks like it could feature a couple of severe storms across the Great Lakes, with a nice trough swinging through and a bit of directional/speed shear and instability.


Robert

 

[Gabe Garfield]

Whoa.

Major turn-around from the 12Z models (and the 18Z ETA) with regard to moisture availability for this weekend. The ETA and now even the GFS (which typically underforecasts moisture) are indicating at least lower 60s dewpoints starting Friday. ETA progs mid-upper 60 dewpoints across the entire southern plains by Friday evening. The Gulf looks like it will open wide, so we should see our first maritime tropical airmass of the season in the southern plains.

With this in mind, I believe this weekend(and into next week) WILL be awesome. Wind fields are now the concern, not the moisture. Mind you, wind fields already look decent (as progged by the models). I have been extremely cautious with this system (since models vary so widely 5-7 days out), but it looks like the moisture issue (which was my main concern) won't be one after all.

Gabe

 

[Blake Naftel]

Discussing the upcoming system with others off the forum; Not a fan of model wishcasting until down to the final 36-24 hours before a chase, however GFS is staying persistent (shifting the low slightly east). Now swaggering into a "believable" time frame -- I think this is one point that should be noted!

Similar to 30-April-2003, it appears there will be a secondary target of interest much further from the surface low along the warm front where the LLJ noses in at about 0Z. Waterloo is "squeezed" between the right entrance region of the mid-level jet and the left exit of a screaming LLJ. The flow is similar to 30-April-2003 where there were a couple fairly significant tornadoes in IL well away from the surface low NW MO/SW IA where 99% of chasers were. I had to blow off this day for the most part as I was due in OKC the following day to start work for Tempest Tours (still got on early evening convection E of ITC). Like the southerly surface flow with NNE flow immediately north of the warm front giving ample push from the surface.

Yet another significant factor to be noted is that if Td's which are progged verify along the warm front, a rough calculation would give ~2500-3000 j/kg of MUCAPE.

Wait... hold the beans here... I'm talking UP IOWA!?!?! That is whacked out and trippin'!!!

..Blake..

 

[Austin Ivey]

I guess I will throw in my two cents on the prospects for this coming wknd. There's no use repeating what others have said, especially with several days until the possible event. However, one interesting thing of note are the extremely saturated grounds along almost all coastal areas of Texas extending several hundred miles inland in some cases. Some areas have received 5-7 inches of rain in the past week+. I've never read any research about this but it seems to me the abnormally "wet" soils and terrain would undoubtedly help the moisture recovery and possibly drive dewpoints to higher levels more quickly than if the soils were drier.

One possible example of this can be seen by examining the NWS observation from the Brazoria County Airport on the immediate Texas coast (south of Houston) from tonight. The dewpoint at 5pm local was 44 but after the winds calmed down the dewpoint rose to 52 by 9pm. I think this dramatic increase speaks to the extremely waterlogged soils mentioned earlier. 8 degrees is a large difference! Certainly the models don't account for soil moisture/evpotransporation because it's hard to quantify. Then again I'm not an expert on the schematics of the models. Any comments?

Brazoria NWS station:
http://weather.noaa.gov/weather/current/KLBX.html

 

[Kevin Scharfenberg]

Good observation Austin. The southern plains should see a lot of sunshine the next couple of days to aide in evapo-transpiring the water on the ground. I believe there is some element in the eta model that tries to take this into account based on what soil moisture observations are available, but I think its success is mixed (no pun intended!).

That said, the Gulf is being hosed of the deep, tropical moisture, and despite the sun, will probably not reach full equilibrium in time for the weekend (still, 60ish dewpoints will not be too shabby). That said, the forecast pattern suggests that even if the first wave were to go by with limited moisture, the gulf will not get scoured this time, and there is still plenty of energy crashing into the southwest U.S. during the next week. So, stay tuned...

 

[Jim Bishop]

Kevin raises a good point. Even if the abundant moisture isn't available this weekend, there will not be a cold front to affect it due to the southwesterly flow aloft. And, the GFS is showing shortwave further upstream being very intense. So, cross your fingers for a possbile west Texas chase early next week.

Jim Bishop
http://stormgasm.com

 

[Amos Magliocco]

I agree next week looks enticing too, and probably wetter. But ETA and GFS both insist on lower 60 dewpoints east of the dryline over the weekend, despite all the objections we've raised about the condition of the Gulf, unfavorable trajectories, lack of corn, etc etc. LOL. So if you can't beat em, join em, right?

With a jet streak progged to reach the Texas panhandle around peak heating on Saturday, combined with the strong height falls, vorticity advection, and favorable deep layer shear, I have to like that area again for severe on Saturday. We even have something of a strong cap forecast that could help keep storms isolated. Or, with the depth of moisture problems, keep them from appearing at all--heh.

Perhaps I'm reading too much into RH values at 850? I surfed around for forecast soundings that far out and found no sites that offer them past 60 hours. I had to surf because I don't trust forecast soundings and so I never use them and don't know where they are. Living 1000 miles away from Vega, though, forces you to use all tools at your disposal, no matter how blunt. So I know I sound like a broken record with my depth of moisture worries, but otherwise the setup looks solid.

There is a second area of interest up north along the warm front. At this point, I think a single topic can handle both discussions. But if it the volume gets heavy and people want to split the topic for the two target regions (north plains and south plains), we can do that too.

 

[Amos Magliocco]

Originally posted by Jonathan Merage
I'm based out of Lafayette, IN, (Purdue U.) and based on current model ouput, especially the most recent ETA, my prime target location is definitely southern IA. According to the 12Z ETA, all areas around DSM will have the highest CAPEs (~3000 J/kg), with the best mix of deep-level moisture and frontal lift right around there on Sat, not to mention LIs down to -8!!. ETA also projects that area to be in the right-exit quadrant of a decent jet streak, which will provide the upper-level support the supercells need once they get started. As far as the central & Southern Plains are concerned, good LUCK to all chasers headed out there! Even with a fairly potent dryline, assuming CI starts up on Sat., the CAP's gonna make targeting the right cells a chore!
I'm going to base myself somewhere in western IA and wait for the warm-front to come through,Jon

I'm including a lengthy quote from Jon because I believe he intended to post about Saturday in this thread, so any replies should be in here of course.

My take is that the cap is strong in Oklahoma, definitely, and that's not a bad thing--LOL--as long as it breaks. What will also be in Oklahoma is a strong belt of midlevel winds, rapid height falls, vorticity advection, and a tight dryline. I also prefer the southern target because the moisture should be at least as rich in western Oklahoma as in Iowa. I know what the model shows, but the southern plains have the distinct advantage of being closer to the Gulf. Here's a snippet from today's SWODY3, which I think could easily apply to what we're seeing on Day 4:

"AS WAS THE CASE IN THE DAY 2 PERIOD...BOUNDARY LAYER MOISTURE RETURN FORECAST BY THE 00Z/14 ETA AND GFS MODEL RUNS APPEARS TO BE OVERDONE ON DAY 3 OVER THE CNTRL PLNS."

Iowa is enticing because its so much closer for me (I'm in Bloomington, Indiana) but as of the 12Z run, I really think the eastern Texas Panhandle and western Oklahoma have more going for them.

 

[Jeff Snyder]

I agree... I think Saturday could be significant for the OK/KS area. On top of >2500 CAPE and nice shear, the 12z ETA does break out convective precip across western OK by 0z. Check out http://www.wxcaster2.com/CENTRAL_ETA_SVR_C...HSWEAT_84HR.gif if you read this before the 0z runs come out... There seems to be a CIN minima immediately ahead of the dryline by Saturday afternoon. The capping will likely ensure that convection stays isolated, as does the fact that 0-6k shear vector is perpendicular to the dryline.

I'm not really concerned about moisture return, as the models have been persistant in giving us decent dewpoints. I'm slightly concerned about high LCLs, but we're still too far away to give that much thought.

Beyond Saturday, I think Sunday could be decent too, though I'm not as thrilled about it as Saturday.

Getting slightly beyond the scope of this thread, the longer-term model seem to keep the western US in a mean trough through at least the next 2 weeks. Also, the CPC seems quite favorable towards numerous severe weather outbreaks for the next two weeks... check it out at http://www.cpc.ncep.noaa.gov/products/pred...ts/threats.html ..

 

[Bob Schafer]

Having looked at the 18Z ETA, I am beginning to become concerned with timing. The upper level dynamics may arrive just about 6 hours too late to get the cap broken and get convection in PH's/KS before dusk Saturday.

Bob