6/6/07 FCST: ND/SD/NE/KS/MN/IA/MO

[Mikey Gribble]

I really like the Kearney area. I could make the SD border area tomorrow, but I am going to gamble too and play the dryline farther South (at least right now that is my thinking, it could very easily change tomorrow). The setup is just too good around Kearney Nebraska to pass up. There really isn't too much to say that hasn't been said already. The cap and moisture return are both big problems. Both should become much more clear with morning obs. I agree with Rich that this is going to be an amazing feet of advection if the moisture forecast verifies. I am anxiously awaiting tonights run of the WRF radar product and tomorrow mornings soundings. That should answer a lot of questions. My plan is just to head North to the Kearney area, check data, and move from there if neccessary. I can't leave town until 9:30, but that should be early enough, especially if I end up playing southern Nebraska, which as of now I am planning on doing. NAM has 3km EHI at 12.6 in Kearney tomorrow night. That is insane. The paramaters vary slightly between the GFS and NAM. GFS has a better hodograph, the NAM has better instability. Both show SR 1km winds >30kts, 5km SR winds >15kts, and excellent 1km SRH, which when combined with everything else has tornadoes written all over it if the cap breaks. I am leaning towards the GFS at this time. Everything is extremely favorable for strong tornadoes provided moisture return is adequate and the cap breaks. I definitely think the SD target is a safer bet, but the payoff is much less as well IMO. Tornadoes are a good possibility up there and in higher concentrations, but if storms fire further South in Nebraska better shear should lead to strong-violent long track tornadoes (once again assuming moisture return is adequate and the cap breaks early enough, both of which are very big ifs).

 

[Dick McGowan]

http://beta.wxcaster.com/cgi-bin/parse_skewt_trace.cgi?model=META&fcsthr=030&STATIONID=KHLC

Skew- T for Hill City, KS at 0z (per 18z wrf). Little cinh left......LCL's are high, but I'm not expecting any tornadoes till after dark.
Waiting on the 0z runs....

 

[Brandon Sullivan]

Quick question for all of you... We have some impressive heat being put out by forecasts in Western KS/ OK, and Western Texas..

With this heat, I assume the lifting will be alot better, then lets say if its only 82F outside. I've often heard meteorologists talk about a magical temperature the temperature needs to get to for a cap to break, what would this temperature be?

Well you need to reach convective temperatures. This varies on a daily basis..

I am really worried about the capping inversion.. Pretty Strong Cap advertised.. Also, timing is looking worse given slowing of the system.. With initiation after penetration of the cap after 00z Thursday..

 

[Nick Hartley]

FSD is thinking like this:
http://www.crh.noaa.gov/crnews/display_story.php?wfo=fsd&storyid=8516&source=0

Their latest forcast discussion is kind of bleek sounding:

http://www.crh.noaa.gov/product.php?site=FSD&product=AFD&issuedby=FSD
Per their latest discussion:

WEDNESDAY MORNING LIKELY TO SEE SOME ONGOING SCATTERED ELEVATED THUNDERSTORMS OVER THE EASTERN CWA. .... THIS ACTIVITY SHOULD LIFT RAPIDLY NORTHEAST DURING THE MORNING...THEN A MASSIVE CAP...IN THE FORM OF 200-300 J/KG CIN...WILL DEVELOP. THIS SHOULD PRECLUDE ANY DEVELOPMENT FROM OCCURRING UNTIL MAIN UPPER WAVE MOVES INTO THE AREA LATE IN THE AFTERNOON. WOULD EXPECT SEVERE THUNDERSTORMS TO DEVELOP IN CENTRAL NEBRASKA AND CENTRAL SOUTH DAKOTA BY ABOUT 22-23Z...THEN QUICKLY TRANSITION INTO A SQUALL LINE AND LIGHT NORTHEAST FORM HERE. THE MAIN THREAT FOR SEVERE WEATHER APPEARS TO BE WEST OF A MARSHALL TO TYNDALL LINE...AND WOULD NOT AT ALL BE SURPRISED TO SEE IT END UP WEST OF A DE SMET TO LAKE ANDES LINE. SOUTH AND EAST OF THE MAIN UPPER LEVEL SUPPORT...THERE WILL BE MAJOR PROBLEMS GETTING CONVECTION TO GO AS UPPER LEVELS BECOME LESS SUPPORTIVE AND CAP REMAIN VERY STRONG. WILL LIKELY DECREASE POPS...ESPECIALLY IN NW IA.

Less than 24 hours away from this event. Will be interesting to see what the set up is tomorrow morning before heading to work for about 5-7 hours of work depending on the set up. That will definately have a lot of impact on where I would like to target.

 

[Shane Adams]

I popped in here quickly before I hit the road hoping for some encouraging wordage.....instead I feel just as worried about tomorrow as I did before popping in LOL. Someone mentioned last night in the chatroom that tomorrow would be a choice of unidirectional/moisture-starved storms in the daytime or a perfectly-sheared capbust further south. I tend to agree with that scenario, though the closer we get to gametime the more I feel there will be a surprise popper somewhere in the southern half of the target tomorrow. Maybe this doesn't qualify as forecast material, but if the dewpoint forecast is on crack, I don't see why the capping inversion isn't either. Both have been consistent but as Rich pointed out, the dewpoint thing is gonna require biblical porportions to be realized. Call me crazy or just a wishcaster, but I get the feeling something is gonna go somewhere in Nebraska or north Kansas, insdie that delicious pocket of extreme instability/shear.

Leaving DFW now to Norman, a few hours' sleep on a motel floor, and off to where ever tomorrow. Good luck to any who dare tempt fate tomorrow.

 

[Edward Ballou]

I would agree with others' observations that the models seem to indicate that the cap is weakening somewhat. Also that moisture - if it can some how leech or suck out some of that moisture that's farther east then it would be much better. The setup still looks promising and I don't think anyone can blame the chasers that make the long trips to roll the dice. One of our local tv stations is downplaying the whole event but left in the cautionary - ready your weather radio.

I haven't really changed my target and regardless of the outcome, it would be a great chance to see some fellow chasers. Cautionary tale: per Chris Collura's unfortunate incident a while ago - watch your goods in your cars people.

 

[Dustin Wilcox]

Even though the CAP is still there, it is some what weaker with CINH forecast to down around 30 by 21Z in Broken Bow, the parameters and curving hodograph are tough to overlook, 1km EHI of 10.4 at 3Z. Plan to be in NCNTRL NE early to make the crucial call as to head North or stick along the DL in NE where if the cap erodes impressive supercells are a sure bet.

http://beta.wxcaster.com/cgi-bin/parse_skewt_trace_all.cgi?model=NAM&STATIONID=KBBW

 

[Dick McGowan]

http://beta.wxcaster.com/cgi-bin/parse_skewt_trace.cgi?model=NAM&fcsthr=024&STATIONID=HLC

Looks better than the 18z, with LCL's/LFC's lowered and closer to each other and also less cinh. I'd say anywhere from dodge city up to the SD border is game. (Haven't looked further south than Dodge.)

 

[Mike Hollingshead]

I'm starting to lean towards a spot somewhere in a triangle from North Platte to Lexington to Broken Bow.

http://beta.wxcaster.com/cgi-bin/parse_skewt_trace.cgi?model=NAM&fcsthr=024&STATIONID=kbbw

Forecast sounding for Broken Bow at 0z.

My biggest concern is actually this.... http://www.wxcaster2.com/CENTRAL_ETA_500_GPHTMPWNDVORT_24HR.gif
.....southwesterly mid-level flowing ending up much more backed in nature over said target. I've just seen it so many times it's frustrating. That'll ruin a good setup nice and quickly. But, then again, the GFS backs the sfc more than the nam(at least old runs had....new one not out yet).....so things could still be ok if that were to happen and have more backed mid-level flow.

 

[Rich Thompson]

The evening soundings/upper air analyses confirm the potentially strong cap with 700 mb temps of 15-16 C from Riverton, WY down to El Paso, and 850 mb temps around 30 C. This very warm mixed layer will be poised to overspread the Plains tonight and tomorrow as flow over the Rockies increases.

The moisture is just as lame as feared. All of the soundings N of I-20 have mean boundary layer dewpoints in the mid-upper 50s, with only 65 F available for the "scenic route" through DRT. You'll need surface temperatures of 90-95 F to minimize CIN at the elevation of LBF tomorrow, and T-Td spreads will be rather large with only low-mid 60 Tds. You'll have to hope that the dryline circulation is strong enough and parcel residence time is long enough to pop a storm or two on the dryline south of the low.

None of the previous mentions the relatively weak vertical shear forecast near the surface cyclone in wrn SD, or it's certainly much weaker than farther south in NE/KS in proximity to the low-level jet. This will be an interesting forecasting exercise at the very least...

Rich T.

 

[Darren Addy]

Rich, I appreciate your expertise and am not asking this to challenge your conclusions. I'm just wondering if you could guess what LBF is seeing when they say (in recent forecast discussion)

THE NAM SOLN THIS MORNING IS CONSISTENT WITH PVS RUNS...DEVELOPING A STRONG 978MB SFC LOW ACROSS SWRN SO DAKOTA TOMORROW AFTERNOON. A SHARP DRYLINE WILL DEVELOP SOUTH OF THIS FEATURE INTO SWRN NEBRASKA BY MIDDAY...WITH MID 60 DEW POINTS PUSHING INTO CENTRAL AND ERN NEBRASKA. -7 TO -8 C TEMPS AT H5 WILL EFFECTIVELY CAP THE ATMOSPHERE UNTIL LATE AFTERNOON BEFORE THE MID LEVEL COOLING CATCHES UP WITH THE DRYLINE. AS IT STANDS...WEAKEST INHIBITION POPS UP FROM WESTERN CUSTER INTO HOOKER COUNTY AT 21Z. IF THE DRYLINE SURGE IS STRONG ENOUGH TO OVERCOME THE CAP...EXPLOSIVE THUNDERSTORM DEVELOPMENT WILL RESULT. SVR PARAMETERS AND INDICES CONTINUE TO INDICATE LIKELY SEVERE STORMS WITH A STRONG POTENTIAL FOR TORNADOES. FOR NOW...WILL PAINT HIGHEST POPS EAST OF LBF...AS DRYLINE IS EXPECTED TO BE EAST OF HERE BY 21Z.

 

[Donald Giuliano]

As Rich mentioned, the moisture situation is not looking pretty, and the shear situation has steadily gone downhill near the left-exit region of the upper jet in SD over the last 5-6 model runs. At this point, I'd say that points north of I-70 are pretty much toast, as low-60s mixed layer dewpoints are the best that can be hoped for, and even that is probably being optimistic. Note that surface dewpoint observations tomorrow could be deceiving due to strong surface moisture flux caused by the massive rain the Plains states have had recently...just look at today's sounding from Lake Charles, LA. Yuck.

So anyway, north of I-70 there's simply no way Gulf moisture can make it back up there in time...a look at this evening's soundings and the 850/925mb mixing ratios forecast by the RUC for 12Z tomorrow morning is enough to see that. All the good moisture is progged to still be locked up south of Waco, TX by the RUC (which I see no reason to doubt), and even assuming an average of 50kt due south winds through the low-levels during the next 12 hours only gets it as far north as maybe I-70 by 00Z. Toss in very shallow moisture on even the best sounding from this evening (Brownsville, TX), and the only area I'm really interested in chasing is the TX panhandle into southern KS, as I don't think real moisture will get any further north than that.

I'll be re-evaluating tomorrow morning, but right now I'm thinking maybe head to the Pampa, TX area. That is, assuming it looks worth chasing at all based on morning obs/models. Kind of a bummer, really, given the strength of the system, which looks like it could rival a lot of east coast winter storms, at least in terms of minimum central pressure. I don't think I've seen a Plains system quite like it this late in the year before, but then I haven't been around as long as some others. Rich, if you're still reading, do you recall any ridiculously dynamic systems like this so late in the season from past years?

 

[Brandon Sullivan]

I am noticing a very strong inversion as Rich Said based on the 00z soundings. From BIS to OUN. A cap such as this takes quite a while and very strong temps to overcome..

No need to rehash what Rich said, but I do agree with all aspects of his posts. I dont feel confident enough that the Cap can be broken.

Im catching the Thurs System.. Good luck all..

 

[Rich Thompson]

Rich, I appreciate your expertise and am not asking this to challenge your conclusions. I'm just wondering if you could guess what LBF is seeing when they say (in recent forecast discussion)

Darren,

There's no need to worry about challenging my "expertise". This is a chaser discussion board where we're supposed to *discuss* these things. Plus, I'm wrong a good portion of the time

The "mid level cooling" is a reflection of the mid level ascent spreading eastward. Unfortunately, at least during most of the afternoon/evening, I think this strong lift will be back in the dry air over the high Plains. The NAM and GFS precip signals suggest some sort of high-based junk forming in the dry air and surging into the dryline/frontal zone. It's my experience that this is not a particularly good way to initiate tornadic supercells along and east of the dryline, and often leads to more linear/forced convective modes.

Rich T.

 

[Mikey Gribble]

I do agree with Rich in regards to the weak shear for the surface low target. SRH drops off quickly as 850mb is halved relative to the dryline target from Hill City to Kearney. If you hug the Neb. border it is still good with Winner showing 45kts deep layer, 1km SRH at 180, and 1km SR winds at 24kts. That is certainly supportive of tornadic supercells, but if you go a little farther North to Pierre the deep layer shear drops off to 35kts which is borderline supportive of supercells (adequate given the high CAPE), but the hodograph looks pretty crappy.
http://beta.wxcaster.com/cgi-bin/parse_skewt_trace_overlays.cgi?fcsthr=024&STATIONID=_KPIR
Anyways, I am going to go with the Hill City to Kearney target assuming I chase tomorrow. Morning obs will make that decision for me. There are some very impressive parameters in that area if we can realize tds in the mid to upper 60's. If that happens then the cap is the only issue. Best of luck to anybody chasing tomorrow.
edit - I am optimistic enough to think that mid to upper 60 dewpoints could reach as far North as northern Kansas and far southern Nebraska by 00Z. I am always amazed at how fast the moisture makes its way North on days like tomorrow.