10/22/04 FCST: Plains/midwest

[David Draun]

Hey, that means on TWC tomorrow evening, Dr. Greg Forbes will forecast "about 2 dozen tornadoes," for Friday just like he did that Saturday, April 17th

Still looking good, IMO. I'd like to see forecast temps come up though. Even with the dynamics as they are.

 

[rdale]

Hopefully Dr Forbes won't be on-air tomorrow - he's scheduled to come to Michigan State Univ for a talk in the afternoon, weather depending, and I'd like to hear him!

- Rob

 

[Dan Cook]

Newest AFD from Davenport mentions that if enough instability, significant tornadoes and hail would be possible.

 

[Jeff Snyder]

Interesting changes in the latest 0z ETA run... In general, the slowing / westward trend is continuing, both in jet streak positioning and trough positioning, as well as in the associated surface low positioning. Now, for those who didn't want the widespread >75kt 500mb winds, there is good news -- the "slower" timing of the jetstreak means that the area from central KS is ~70kts, with 60-70kts in eastern KS, and 40-55kts in western MO. Whereas the old run had a 988 low near Mankato MN, the latest run has a 992 low in far SW MN. In addition, the dryline, which the 12z ETA had from OMA to END to Vernon, TX, the new 0z ETA shows the dryline from OMA to Woodward to south of AMA by 0z. Since the trough is coming through weaker and a little slower than previously forecast by the ETA, the relatively warm 850-700mb temps are remaining in eastern KS and eastward from there. It's important to remember that model forecast CAPE is pretty poor, but the 0z ETA shows >1500 SBCAPE basically north and northeast of OKC to Kansas City and up to near FSD at 18z Fri, though decreases that significantly by 0z, with the main precip well east of this area from STL to SPS perhaps. The warmer 850-700mb temps are making for a thermonuclear cap (unbreakable CINH) from eastern KS southwestward into OK. Now, again, models tend not to do well on CAPE/CINH forecasts, so take it for what it's worth... I'm still banking on nc OK and sc KS, however.

I think the OK potential hangs a lot on what happens with the ETA-forecast convective complex overnight Thursday and Friday morning. This could either mix over the atmosphere on the mesoscale and kill the potential, or it could provide us a boundary that would work northward through the day on pretty strong southerly synoptic-scale flow. In addition, we may get some mesoscale subsidence surrounding and nearby the complex, which may help clear out some clouds and increase the potential instability...

 

[Mike Hollingshead]

LOL, Go GFS!!!!!!!!! Target remains the same......

That is just beautiful. Screw all the finite details. It looks MUCH MUCH better then the ETA and anything we've seen thus far.

 

[Jim Bishop]

Yeah the trend of slowing down this shortwave had continued in the latest ETA run. I don't like how the ETA is veering the 850mb wind during the day across west Oklahoma. I'm affraid this will advect in too much dry air and scour out a lot of the good low level moisture, which will limit CAPE, already a concern. But also increase the cap as Jeff mentioned.

The shear still looks great for tornadic supercells by 00Z across west centra/central OK and southern Kansas. But when will the 850 winds actually back??? Very concerned about that. As long as they back by 3 or 4 pm tornadic supercells should initiate along the dryline across western OK and race northeast...

The shear looks even better for tornadic supercells across Iowa, and the low level moisture may actually be better due to more backed 850winds. I must say that area really does look the best right now.

Overall, this setup still looks like a potential tornado outbreak. Lots of low topped tornado supercells. In my experience tornadic storms moving faster than 35mph tend to produce long track tornadoes...

The ETA should have a great handle by tomorrow morning. We'll see what's in store....

 

[Robert Dewey]

LOL, Go GFS!!!!!!!!! Target remains the same......

That is just beautiful. Screw all the finite details.

A little wishcasting, Mike? LOL

It looks MUCH MUCH better then the ETA and anything we've seen thus far.

Just to hastle ya, the 18Z GFS was actually deeper... Other than that, I would like to see the GFS win this one - I just might have to make a trip out there...

 

[Jeff Snyder]

I should have mentioned on my post that my post was based entirely on the 0z ETA. Having now just looked at the 0z GFS, I can say that the two models are very different. The 0z GFS looks a lot like previous runs of both the ETA and GFS. I mean, looking just at the upper trough at 500mb, the 0z GFS still has a slight negative tilt to it, and about the same intensity/depth as before. As I said in my above post, the 0z ETA has significantly weakened the forecast intensity of the trough and has brought it out with more of a positive tilt. On consistency alone I'd choose GFS. This is one of the less common cases where there are very significant model discrepancies just 42-48 hours before the event.

As Mike said, "GO GFS, GO!"

 

[Amos Magliocco]

I agree that it's a remarkable discrepency and I'll trust the GFS as well, based on run to run consistency. If you A/B the 42h panel at h3, you get like a 45 degree difference in the trough axis. Wild stuff!

I'm still looking at south central to southeastern Kansas.

 

[Mike Hollingshead]

Just to hastle ya, the 18Z GFS was actually deeper...

Don't hastle me...lol. And besides.....the sfc low is basically as deep as the 18z gfs...BUT....it's slightly further w/sw.

 

[Jim Bishop]

I just now looked at the GFS myself. Wow, it looks like this morning's ETA run. I'd say also say go with the GFS for tonight as the ETA may have had problems with this run.

 

[Jamie Lahowetz]

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
950 PM CDT WED OCT 20 2004

...IF SECOND ROUND OF CONVECTIVE INITIATION(PROBABLY
SUPERCELLULAR) OCCURS IN TIME ACRS SOUTHWEST-SOUTH CENTRAL IA FRI
AFTERNOON...AND COMES INTO THE LOCAL AREA BY FRI EVENING...EXTENT
OF SHEAR AND ACTIVITY PROGRESSING ALONG ANY LINGERING OUTFLOW
BOUNDARIES OR WARM FRONT ITSELF SUGGEST A TORNADIC THREAT.
SOME FOOD
FOR THOUGHT...BLEP CALCULATIONS FOR FRI AFTERNOON/EVENING TAKING
INTO ACCOUNT IF TEMPS CAN ATTAIN 77 DEGREES WITH A SFC DPT OF 65...
SUPPORT STRAIGHT LINE WINDS OF 57 KTS...ROTATIONAL WINDS OF 91 KTS...
AND HAIL ENERGY LEVEL POTENTIAL SUPPORTS 1.3 INCH DIAMETER HAIL.

Maybe I shouldnt of sold my digital camera yet, damn.
http://iwin.nws.noaa.gov/iwin/ia/discussion.html

 

[Amos Magliocco]

Re: 10/22/04

Is it just me or does this setup look almost like the April 18, 2004 setup last spring..

In that same vein, the GFS output for Thursday's 0Z run, at 36 hors, looks somewhat similar--specifically at 500mb and 850mb-- to April 25th, 1994. For those of you with Tim Marshall and Tim Vasquez's old Tornado Forecaster's Workbook, this is Case #3. However, some important surface features are different than what we're exepecting, so the similarities are probably not too useful.

For curiosity's sake, this was the day of the Lancaster, Texas tornado, when the end of a squall line broke into discrete storms and produced an F3 and F4. There were also F0's in central Colorado near Ft. Carson and Limon.

 

[Mike Peregrine]

ETA forecast SRH looks pretty healthy for 0z anywhere from Emporia, KS up through Cameron, MO.

SFC based CAPE appears substantial in this area as well -

http://beta.wxcaster.com/models/eta/centra...S_CAPE_48HR.gif

Very powerful system and deep low for this time of year. Hopefully wind fields are not overblown ... also wondering about storm speed ... these things have the potential to get fast, and chasing across northern Missouri at light speed just isn't my idea of a good time ... still, this has the potential to be a really exciting day. Can't help but get a little psyched when we're talking about a potential outbreak situation anywhere from NE Iowa down into Oklahoma in late October.

 

[Amos Magliocco]

For what their worth, the 6Z runs of ETA and GFS would seem to side with the 0Z ETA on a slower, more-positively tilted trough with weaker instabilities and convergence along the dryline / pac front.

The eastern half of Kansas still has issues with midlevel moisture and potential cloud cover to further limit instabilities. I have a hard time seeing how storms will survive with such marginal lapse rates in a highly-sheared environment. On pure momentum, I'm heading west, but expectations are pretty low.

I know another system is expected next week, but we're getting so late in October that instabilites aren't likely to improve. I think this is our last best shot for supercells and tornadoes in 2004.