5/4/07 FCST: KS/OK/TX

[Rich Thompson]

Fortunately at work here, I have the luxury of comparing the NAM up against higher skill global spectral model solutions like the GFS, UKMET, ECMWF and the Canadian (on the web). At first, looking at the NAM, I was like "uh oh, long-track tornadoes possible and a busy night for me on the radar here in SW KS".... but the NAM is currently outlier in the surface response and convective feedback issues. The convective parameterization of the NAM are quite bullish when it comes convective initiation. My gut instinct is that the May 3rd version of the NAM model looks far too bullish on surface based convection over a lot of Kansas... and thus, it impacts the near surface kinematic fields. The GFS, Canadian, and UKMET show far much less QPF in KS... except for the northwest corner of the state over a good portion of GLD CWA. I would be quite cautious of going too far south tomorrow. I think the best area for tornadoes will be just north of the greatest surface response to the larger-scale dynamics at play... which will be along the KS-CO border by "go time". I think Pratt-GBD is too far east and also too far south? This thing will be coming out slow... and the response in the low levels will be farther west... any dryline storms developing against the +9 to +10C @ 700mb will be isolated and farther west as well I would think. I just don't trust how the 30-36hr NAM is handling this thing yet.. This looks like a GLD CWA show to me.

Hey Mike,

Are you sure it's truly convective feedback in the NAM? The NAM has more precip compared to none in the GFS, but it hardly looks like a convective feedback signature w.r.t. the deep tropospheric system. The GFS is more known for this sort of feedback (not apparent in this case). I'm not saying the NAM will be correct, but convective feedback doesn't look like the reason for its forecast evolution. FWIW, the developmental 13 km RUC run at 30 h shows a similar pattern to the NAM, with convection just W of Great Bend by 00z.

Obviously we have two general scenarios here, one with the dryline bulge into SW KS and storm initiation near and NE of the triple point, and the other scenario is slower and limits all convection to N of I-70. One question I have about the slower GFS is why it's moisture gradient is so out of phase (to the E) with the surface trough? I recall it doing the same thing back on 21 March 07, and it's precip was slow to develop that day as well. I guess what I'm trying to say is it's nothing more than a guess that the NAM is right or wrong. Just because it was bad a few months ago beyond 48 h doesn't mean anything right now. The GFS has just as many problems. I don't have the luxury of looking at comparable graphics for the ECMWF at home, so it's tough to judge its performance against the NAM in the short term.

Rich T.

 

[Donald Giuliano]

Some things of interest regarding this NAM dryline bulge are the impressive lapse rates, very deep boundary layers, and strong mixing shown on soundings throughout the desert southwest. Given the significant westerly component forecast at 500mb and boundary layers that extend nearly up to that height, it's not too hard to imagine that some of this deep mixing could be advected eastward tomorrow, leading perhaps to a dryline farther east than when boundary layers were more shallow a month or two ago. Not sure how much of an impact this might have, but I think it's worth noting, though I don't know how well the NAM's PBL scheme handles these sorts of differences.

 

[Ryan Pfannkuch]

After taking a cursory glance at some of the developmental 13km and 20km RUC data from the ESRL page...I found it very interesting that these various models DO NOT generate convection along the E-W boundary in west-central/southwest KS through at least the 0-3z time frame. Nothing. Instead the focus is on convection developing along the inverted trough extending northward into western Nebraska...which is well north of the main CAPE axis along/south of the E-W boundary in KS.

http://maps.fsl.noaa.gov/

This solution seems to be much more in line with the 12z/18z GFS which as earlier discussed is much less aggressive convecting the KS boundary and showing considerable more CINH. At any rate, I am becoming more convinced that this will likely be a rather late show with most of the severe weather focusing later in the evening/overnight farther north into NE as the instability shifts northward.

It looks to me like the NAM is becoming more and more of an outlier in promoting the earlier big show in western KS...and it will be interesting to see which way the forthcoming 4/4.5km explicit WRF reflectivity progs lean.

 

[Jim Tang]

I'm not sold on a thermonuclear cap from the OK/KS border north. In fact, the models still show an leading impulse that could spark thunderstorms. QPF outputs are not dependable enough for me to make a forecast off of. Problem of course is if the system slows down, a legit possibility.

One thing that perks my interest, as Donald above mentioned, is that it doesn't seem the moist layer will be as deep as previous events. In addition, the H5 wind barbs seem to be more veered compared to previous events. The ground is still wet, but I think the dryline could make it near DDC.

 

[Bill Schintler]

Chase target for Friday, May 4

Chase target:
Ness City, KS (35 miles north of Dodge City).

Timing:
Storm initiation: 5 PM CDT.

Storm mode:
Supercell storms will produce a full spectrum of severe weather, including a few tornadoes.

Synopsis:

Evening analysis showed blocky pattern with deepening negatively-tilted trough in the WRN CONUS and weakening UA circulation over OK. Numerous waves were embedded in these features: In association with the ULVL circulation over OK, an area of assent was noted over ERN TX into LA, while a potent wave was lifting into NERN CO and was associated with an expanding area of unsettled WX in ERN WY into MT. Further to the S and W, several compact waves were translating through SRN CA, NV, AZ, and into CO. A 35kt LLJ had developed in the high plains E of the H85 trough, and this feature was transporting 10C dewpoints NWRD. Area soundings (LBF, DDC, RAP) were all nearly saturated in the lower levels, while soundings in NM and AZ showed nearly dry-adiabatic lapse rates through the 600mb layer.

Discussion:

Models (NAM, GFS, UKMET) have initialized well to SFC and H85 moisture, and strength and track of SFC features. Curiously, however, they differ considerably with QPF with the NAM producing strong QPF signals while the GFS holds off until early evening. The NGM appears weaker and more disorganized with the evolution of the SFC low however it sides with the GFS with QPF. Differential advection of steep mid-level lapse rates in the southwest with LLVL moisture transport should result in an EML over much of the plains on Friday. Meanwhile, SFC low pressure will deepen through the afternoon hours as it tracks towards the WRN OK panhandle with a WF extending NE of this feature by 00Z. Impressive instability should remain capped until late-afternoon when the strongest forcing in the left-exit region of a 60kt H5 speed max approaches the area while the DL surges EWD towards US-283 in KS. Backing SFC flow beneath a 35kt LLJ will result in impressive hodograph curvatures while SFC-6km bulk shear will increase to 50kts by 00Z. Overnight, storms will expand in coverage and track E across KS as a 60kt LLJ noses into the area.

- bill

 

[Mike Umscheid]

Hey Mike,

Are you sure it's truly convective feedback in the NAM? The NAM has more precip compared to none in the GFS, but it hardly looks like a convective feedback signature w.r.t. the deep tropospheric system. The GFS is more known for this sort of feedback (not apparent in this case). I'm not saying the NAM will be correct, but convective feedback doesn't look like the reason for its forecast evolution. FWIW, the developmental 13 km RUC run at 30 h shows a similar pattern to the NAM, with convection just W of Great Bend by 00z.

Rich T.

Hey there Rich,

The convection from the NAM model appeared to impact the surface winds from what I was looking at on AWIPS 12km NAM...although looking at it closer again, perhaps not... but in several cases I've certainly noticed surface winds and subsequently divergence fields really being impacted in mainly the 12km NAM... an impact in surface winds over a larger spatial area than one might usually expect with one or two supercell storms or small scale area of storms. Anyway, I guess it's how one interprets the output... pretty complicated obviously trying to decipher fields of a very high resolution model when you have convection being generated.

Regarding tomorrow, the new 00z NAM is slightly farther north with its convective QPF signal, but still shows quite a bit of convection along this east-west axis of convergence... which looks to be largely at the nose of the advancing dry intrusion northward. If this is legit, then Ness City to Hays looks prime for sure. I am still leery about this though. At the same time though, I think the dryline to the east of this "punch" will also sharpen somewhat by 00z and isolated supercells might exist up and down the dryline from Ness City south through perhaps Ashland shortly after 00z? This is fairly low probability though, but even the UKMET shows a lot of 700mb UVV along the dryline in Northwest OK. Something to watch as there may be an enhancement of convergence in this area farther south.

Tomorrow looks like a real complex day at the surface with significant cyclogenesis occurring to the west along the KS/CO state border. Where will the best *convergence* set up though? It could actually be in any number of areas along the 1) inverted trough/baroclinic zone north of the sfc low... 2) this east-west axis of convergence at the nose of the dry intrusion that the NAM is so keyed up on... 3) somewhere along the dryline where convergence might be maximized south of the dry punch. The greatest probability significant severe storms, to me, appears to be in area #1 with convergence/frontogenesis being maximized in the area of greatest cyclogenesis/isallobaric response. Good luck chasing tomorrow, I'm jealous!

Oh yeah, my target = Ness City... a nice little middle ground, just in case the NAM is on to something

 

[Mikey Gribble]

Good god! If the NAM is telling the truth and something goes up on the N-NE side of that bulge it is going to be intense. GBD has an EHI of 10.4!!! Are you serious? Supercell potential at 99.8%. I'm not a fan of composite indices, but that's impressive. MLCAPE at 4,000J/KG. Dewpoints are finally realistic in the mid 60's. I buy that after looking at the surface chart. The cap is eroded by 00Z, so everything is looking good IF the NAM is telling the truth. I am becoming more and more convinced that it is with each run. If this does come close to verifying I think tornadoes are very likely over a small area N-NE of the dryline bulge. I do agree that there is a decent chance that storms won't get going until after dark, but living in ICT I am not willing to risk missing what happens if the cap does break, so I will be heading West tomorrow.

 

[Jeff Snyder]

I can't really add much beyond what I've previously written and what others have noted recently. I will, however, point out that the the 4 km WRF explicit convection run from 00z tonight is quite interesting --> http://wwwt.emc.ncep.noaa.gov/mmb/mmbpll/cent4km/v2/ ... A look at the 2m temperature field indicates that it brings the cold front down into the western OK panhandle, and a couple of discrete supercell develop between approximately Liberal and Ashland, KS, areas by 0z and 1z tomorrow. Of course, Mother Nature seems to hate Oklahoma, so I chuckle when I see convection develop immediately north of the OK/KS border... T

he exact positioning of this convection should be taken too seriously, but it certainly is a good sign IMO. Not surprisingly, the model indicates a discrete storm mode until ~6z, when things get a little more messy. I certainly wish we had access to more model fields (e.g. 2m Td, lowest-model-level winds, 500mb winds, etc)...

I'm preparing for Great Bend Chaser Convergence -- 2007! The NSCC has nothin' on tomorrow! Maybe we should gather guest speakers... ;-)

EDIT: In addition to my high-resolution WRF trifecta (4.5km WRF, 4km WRF, and 3km WRF), I'll add the 2km WRF (run by OU CAPS) and each of the 10 members of a 4km WRF link --> http://www.caps.ou.edu/wx/spc/20070504/ ... The 2km WRF run is only out through 8z, but it'll be interesting see how things verify tomorrow. I've learned really to like the explicit convection, high-res WRF runs in terms of forecasting storm mode, but I have no experience with the 2km WRF hosted by CAPS. Thanks to Dan Dawson for bringing this 2km WRF run to my attention. It's now the WRF quadfecta, I suppose.

 

[Van DeWald]

I'll bring the hibachi and some charcoal. Anyone want to bring along a cooler full of steaks and drinks for the victory dinner? LOL. I think there still is some question as to the initiation point tomorrow. GFS looks too far north, Nam is a little further north than previous runs, and 4km WRF is even further south. Somewhere between the Nebraska and Oklahoma borders should suffice. Seriously, am sticking pretty close to my original target of Great Bend, but perhaps a little west now toward Ness City or Rush Center.

 

[Gabe Garfield]

I can't chase tomorrow, but I thought I'd offer my two cents on the forecast. To put it succinctly, it stinks to be at home for this one.

This setup is oddly reminiscent of May 12, 2004. On May 11th, most people were targeting Great Bend to around I70, only to find that the cold front had advanced further south than previously anticipated.

Other similarities:
The cap was an issue that day, there was a baroclinic boundary intersecting the surface low, extreme instability was present along and south of the boundary, and the day started out low-hype.

I'm not saying this is going to be a repeat, but the similarities are striking.

Furthermore, I like the fact that the S/W trof is just entering the Plains by 00z. This has been associated with big tornado events in the past. Because of this, I think that tomorrow will probably be the better of the two-day event, since things could get messy on Saturday.

Gabe

 

[Jeff Piotrowski]

Significant Tornado's Possible Kansas

I like the Ness City over to North of Great Bend for a few significant tornado's along the boundary after 23Z. Based on the 0Z 12KM NAM!!!

OH NO !!!!!!!!! The WRF is now updated how about Protection Kansas again???

Now for the rest of the story tonight the new 0Z 4KM WRF says storms explode at 23Z on the Kansas/Oklahoma border near Ashland Kansas SE of DDC. Track ENE watch out!!!

Also the 4KM WRF says maybe tornadoic storms form SW of OKC and move toward or just South of OKC.

Bottom line their will be tornado's in Kansas & Oklahoma on Friday.

SPC MOD outlook is very good.




The next fours days their will be a lot of tornados in the Plains.

Good Luck to all that go chasing.

Jeff Piotrowski

 

[Jason Bolt]

I'll be starting off tomorrow in St. John, Kansas. Seriously though, if any of the Great Bend chaser convergence members need some free wireless or a place to sit for a while my office in St. John is two blocks off 281 on 4th street. Brown building, south side, fire/EMS station. You all are welcome anytime.

 

[Gerard Jebaily]

Things are looking pretty nice. Almost too nice. I dont want this to end up like an April 1, 2006 event. But if I only have to goto Woodward, OK to have a look, thats worth it to me (which is my target attm). I have a crew, we will be headed there from norman tomorrow AM. We might move further north into DDC depending how things look tomorrow. The biggest con for tomorrow, is not weather related...its the price of fuel. 2.89 is way steep for a chase day, I hope it will be worth it. I will be monitoring 146.550. My call sign is labeled on the vehicle KI4LJT but I will have other hams with me. Good Luck to all.

Chip Legett: WX9EMT
Zach Flamig: KE5KJA
Andrea Dittman: KE5NXG

 

[Jason Boggs]

I have a pretty good feeling about Friday. I'm not so sure about the MOD risk all the way down to Childress though, but we will see. I'm willing to be that the MOD will be shaved to just include the extreme NE TX panhandle.

Obviously, moisture isn't a problem with this event. High Td along with steep lapse rates and temps in the mid 80's will result in CAPE from 2000 to possibly 5000. Very nice directional and speed shear will result in storms going supercellular very quickly. I hope the cap is moderately strong so that only the strongest updrafts will survive resulting in discreet tornadic cells.

Not sure where I will end up since I chase for a TV station here in AMA and our viewing area is in the moderate risk. We will see what happens.

Good luck to all that will be out and remember to be courteous to other chasers and above all, STAY SAFE!!!

 

[mark plate]

Fortunately at work here, I have the luxury of comparing the NAM up against higher skill global spectral model solutions like the GFS, UKMET, ECMWF and the Canadian (on the web). At first, looking at the NAM, I was like "uh oh, long-track tornadoes possible and a busy night for me on the radar here in SW KS".... but the NAM is currently outlier in the surface response and convective feedback issues. The convective parameterization of the NAM are quite bullish when it comes convective initiation. My gut instinct is that the May 3rd version of the NAM model looks far too bullish on surface based convection over a lot of Kansas... and thus, it impacts the near surface kinematic fields. The GFS, Canadian, and UKMET show far much less QPF in KS... except for the northwest corner of the state over a good portion of GLD CWA. I would be quite cautious of going too far south tomorrow. I think the best area for tornadoes will be just north of the greatest surface response to the larger-scale dynamics at play... which will be along the KS-CO border by "go time". I think Pratt-GBD is too far east and also too far south? This thing will be coming out slow... and the response in the low levels will be farther west... any dryline storms developing against the +9 to +10C @ 700mb will be isolated and farther west as well I would think. I just don't trust how the 30-36hr NAM is handling this thing yet.. This looks like a GLD CWA show to me.

Based on the full set of 00z models, I agree with this...it will mainly be a GLD CWA show today. Moderate risk all the way down through OK is a stretch and seems highly conditional. The better bet is no storms at all in OK...and maybe not too far south into KS per GFS/Canadian. We'll see...