5/6/10 FCST: KS/OK/MO

[Ben Prusia]

An "if" day is progged for tomorrow in the central Plains. 12Z NAM shows 994mb low centered over SW Kansas with front extending eastward and dry line near or along the I-35 corridor by 0Z Friday. The models shows instability around above 2000 J/Kg, and CIN weakening to 0 late in the day which could provide the grounds for some convective development along the warm front and possibly along the dry line, but should remain capped further south. Am monitoring this day for a potential chase in Kansas.

 

[Mike Johnston]

I agree, Ben, that this setup deserves at least some attention. SPC's Day 2 outlook is citing only low 60s dewpoints, but this morning's NAM run seems fairly emphatic in introducing a band of 65+ tds over east central Kansas. While overall wind flows are only moderate, the surface-850-500 crossovers look very good. LCLs should be workable at <1,200 meters. Convective precip should break out along the warm front at or shortly after 00z.

Right now, parameters seem to look best along the southern edge of the slight risk area. Will need adjustment tomorrow am, but initially an area from Ottawa to Garnett thence eastward to around the state line, and perhaps even southward as far as Ft. Scott bear watching.

Hopefully, this setup will at least give the Kansas City area chasers something to consider.

 

[Brian Stertz]

Lifting warm fronts always mean trouble this time of year. Tomorrow could be a
good surprise set up and one worthy of keeping a very watchful eye on. 12z NAM
has some very good pluses (strong veering profiles and decent CAPE) to offset minuses (modest lapse rates). Right now I am thinking there could be tornadoes within 30 miles of the KC Metro (southwest and south). Storm motions should be very manageable too.

 

[Mike Johnston]

Anyone know if the Vortex II armada will be in Kansas tomorrow? Have they made that call?

Yes, that is what Mike Bettes is indicating on his Twitter messages...evidently they're traveling to central Kansas today and eastern Kansas could be their target for tomorrow.

Getting back to the forecast, I guess I don't understand why SPC is standing by their forecast of 50's to low 60's td in the target area tomorrow. Both the NAM and GFS are indicating 65+, and the latest Day 2 outlook was written several hours after these models had run. I'm sure I'm probably missing something, but if anyone can see it, please point it out. Thanks.

 

[Skip Talbot]

Yes, that is what Mike Bettes is indicating on his Twitter messages...evidently they're traveling to central Kansas today and eastern Kansas could be their target for tomorrow.

Getting back to the forecast, I guess I don't understand why SPC is standing by their forecast of 50's to low 60's td in the target area tomorrow. Both the NAM and GFS are indicating 65+, and the latest Day 2 outlook was written several hours after these models had run. I'm sure I'm probably missing something, but if anyone can see it, please point it out. Thanks.

The NAM and GFS are in pretty good agreement that the richest moisture will not be sharply focused on the dryline or the warm front. These boundaries that will act as the lifting mechanism for initiation are defined more with upper 50's and 60's dewpoints. Now, if we can get storms to fire on the dryline and move into the richer moisture then we are probably talking about much more formidable supercells (with the capping caveats). Storms firing on the warm front and triple point will have less moisture and be working with more stable air, but these storms may still pose a tornado threat as they work with the enhanced directional shear along the warm front. Of course this all relies on storms breaking the cap, but both the 12z NAM and 4km WRF are hinting that they might.

 

[GPhillips]

Getting back to the forecast, I guess I don't understand why SPC is standing by their forecast of 50's to low 60's td in the target area tomorrow. Both the NAM and GFS are indicating 65+, and the latest Day 2 outlook was written several hours after these models had run. I'm sure I'm probably missing something, but if anyone can see it, please point it out. Thanks.

Raw model dewpoint forecasts verifying at 00Z have been biased several degrees high across eastern KS this spring. GFS and NAM statistical guidance for dewpoints have, on average, been better than the raw grids. For example, from this morning's runs, for Chanute (CNU), the 36 hr forecast NAM grids have a dewpoint near 67 while the NAM MOS has 56 at the same time (00Z Friday). For the GFS, the gridded output has 64 or 65 while the GFS MOS has 61 at the same time. SPC is no doubt taking into account this bias in their forecasts. Note, I am not saying the NAM MOS will verify with mid to upper 50s dewpoints, just that the grids do have biases which the statistical guidance attempts to adjust for.

 

[Rich Thompson]

SPC is adjusting the moisture downward because the NAM forecasts will almost certainly verify too high. Take a look at the current (19z) observations across TX/AR/OK/LA...all I see are a bunch of Tds in the 50s where this morning's NAM is forecasting 60-65 F this evening. I have a hard time believing we'll see legitimate mid 60s along the warm front in KS tomorrow when Tds have mixed into the 40s and 50s today across TX/LA/AR.

The message in all of this is to not be surprised when CAPE is smaller, CIN is larger, and LCL heights are higher than currently forecast for KS tomorrow.

 

[Jared Farrer]

Makes sense what Rich was saying. I am kinda expecting dews to be in the middle to upper 50s. But if we can keep spreads down below 20 we still could be in for a few decent supercells tomorrow. If things can manage to fire. The overall setup looks pretty decent. But Vortex 2 is out their and they will probably Jinx the whole mess??!!

 

[Jeff Passner]

It looks like late development, maybe too late for a good chase. Let's see if anything fires before 0000 UTC.

 

[Jeff Snyder]

I want to point out the consistency of the forecasts from the 00 UTC runs of the 4km NSSL WRF and the 4 km EMC WRF... Despite what the operational NAM is forecasting, both of these high-res WRFs have a very similar forecast in terms of convective evolution tomorrow evening. In essence, they both have convection firing late afternoon in far NW KS or extreme SW NE. With time, both are showing fantastic supercells along and N of the I70 corridor tomorrow evening; unfortunately, the best updraft helicity and supercell-like reflectivity structures are a few hours after sunset, in the 3-5 UTC time frame.

For the eye candy... Check out the 27h-30h reflectivity on the EMC WRF, and the 24h-29h reflectivity and updraft helicity on the NSSL WRF. Many of these supercells may be slightly elevated (with 1500-2500 j/kg MUCAPE and sfc tds in the mid- to perhaps upper-50s), but that's tough to judge since those two sites don't really give an exhaustive list of model parameters and levels (e.g. can't even see Td forecasts from the EMC WRF).

 

[matt patterson]

It is interesting to note that the 17z RUC Breaks out Precip Just East of Wichita at about 5-6 PM today.. This was also on the 15z.. If a storm could form the parameters support several modes of severe wx...

 

[Chad Cowan]

Well the new Day 1 outted my favorite lesser-known forecast reflectivity model so I don't mind talking about it now... the HRRR has been absolutely stellar this season with predicting initiation (timing AND location). For each of the last 6 hourly runs (up to 18z) it has been initiating convection between 23z and 01z along the nose of the strengthening LLJ in essentially the same location in eastern KS. With +60kts of effective shear, supercells will be the dominant storm mode. The question is whether or not the storms will be able to form south of the warm front and root in the boundary layer, not atop the stable layer north of the warm front. If they do become surface based and then interact with the boundary, there is a good chance of tornadoes in the 7-9pm time frame, given the strong low-level turning. That's a big if, though. As of right now, I don't think the dynamic ascent and surface heating will be enough to break the cap, I think isentropic lift will be needed for that. Regardless, I'm expecting to see a few significant hail reports to the south and southwest of the KC metro area this evening.

Below is a composite map I threw together of the 17z HRRR's output for 7pm. The fcst composite reflectivity shows a nice blob southwest of Lawrence, right on the WF, and other updrafts further south, into the warm sector. The underlay is the sfc CAPE chart, showing +2000 j/kg south of the front. The white line is the 1500 j/kg isoline from the MUCAPE chart (not shown), which indicates ample elevated instability north of the warm front.

 

[B. Hey]

The latest 00z RUC run show precip breaking along and just south of the I-70 corridor. The SPC has also upgraded the area to 5%. The moisture and timing is going to be the limiting factor as the dew points are about 15-20 higher 100 miles to the south. Maybe we will get lucky before dark.