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6/4/05 FCST: KS/OK/MO/IA/NE

I’ll start a forecast thread since Saturday is looking interesting. Also, being a weekend, many chasers who can’t chase Friday will have the opportunity Saturday.
According to the GFS (00Z June 3), there is 30-45 flow at 500 mb from the southwest across Oklahoma, Kansas, eastern Nebraska and western Iowa at 0000 UTC on June 5. Interestingly, there is a bulls eye of 50’s in southern Minn. Looking at the 700 level, the cap shouldn’t be a problem. Li’s from -6 to -8. I am concerned looking at the surface as the low is over central Minn with backed winds to the east of it. There are also backed winds in southeastern Kansas, western Missouri though not as strong. Precip is across northern and eastern Kansas, Missouri and southern and eastern Iowa. There is an area of 75 dewpoints for most of extreme eastern Kansas and approaching dryline form the west. The Eta shows a nice 40 max of 500 mb winds through eastern and central Kansas though their main area of precip in northern Minn. (init June 3 00Z) I do like the Eta showing a low that moves into south eastern Kansas by 00 Z June 5th and 3000 to 4000 CAPE in eastern Kansas and northwestern Missouri. I wish the models would better agree (and they are often wrong anyway.) Saturday will also depend of the results of Friday’s convection. Overall, I see Saturday as better than Thursday and possibly Friday with a strong chance of supercells, some of which will be initially tornadic. I think the Iola area in southeast Kansas is the best compromise.
 
I hope you are right about southeast KS, Bill, since that will make a much shorter drive for me after chasing S KS or N OK tomorrow. NAM actually has the highest EHI farther east near STL at 0Z Sun, and suggests strong instability along a curving boundary (warm front?) from Kansas City through northern MO back to STL. I do think the best potential will be along the western part of this boundary, so am tentatively thinking maybe somewhere near Kansas City, i.e. a little farther north that what you are thinking about - but time will tell.
 
I don't think the CAP will be a much problem at all, really digging the mid 70 dewpoints that we'll probably see across SE Kansas.

I think I'm going to head to Emporia early AM and then go from there.
 
It seems to me that there are two areas of possible tornadic storms.
One would be in accordance with the latest SPC outlook, mostly in the area of southwest to south central Iowa. If left-over convection and clouds are not an issue, that area will have the best shear and instability combination. Good forcing and an approaching shortwave make this area my target for right now. The main problem I see is that the winds are not changing direction enough with height at the low levels, and that the surface winds may be too light.

Down in eastern Kansas through eastern Oklahoma would be my other area to watch. Seems that there are better wind fields, but there wont be as much shortwave support as up north. The forcing also does not look as good to me.
 
Tomorrow looking very interesting over the northern/central plains. Latest SPC outlook is still mentioning the upgrade to moderate, so will have to wait until the 1 am issuance to see if that holds out.

GFS strengthens the low to a 990 mb low pressure system. At 250 looks like a lob of stronger winds from the southsouthwest (around 50 kts). A huge area of vorticity along the low pressure system as well as areas just to the south. Mid levels have the southwest winds around 40 kts. Low level winds will have the counter clockwise rotation around the low at 25-35 kts.

Td's look to be in the mid to upper 60's for the most part, with LI's well below the -3 range. Not all of the GFS svr parameters are in. But using the text extraction on some places in central IA is showing capes ranging from 2000 to 5000 j/kg in central IA. LCL heights look to be below 750 meters across central IA as well... EHI's are ranging from 2-3 over IA as well.

Overall not looking to shabby over central IA. Target area would depend on tonights convection, and the exact location of low... Prelim guess would be around the FOD area.
 
GFS is quite a bit stronger than the NAM, but it really does look like some sort of feedback issue... The only consistancy in the models is that there will be plenty of low level moisutre, with Td's of ~70F pushing as far north as MN/WI/MI.

Hopefully we can get some decent supercells over the IA/MN area, which will then rapidly congeal into a fast moving and powerful derecho which will track from WI all the way to NY... now that's just beyond wishcasting (or is it stepping back in time to May 31, 1998?). 8) :lol:
 
I'm about to leave work, so I don't have time to post too much, but after several adjustments, it looks like Atlantic, IA will be the initial target. The NAM has us chosing between the instability and the dynamics. The minimal capping over ern KS has us a bit concerned about there being too much going on to get a clear shot at anything. Southern Iowa, central Missouri, that's where it seems like the action will be. Myself, Kevin Peters, and Angie Woolard will be leaving shortly. If we get to the hotel at a reasonable hour, I'll take a look at the 0Z runs a post a better fcst.


Ben
 
Something good I've noticed in the model trends... more backing of the surface winds. This looks to be best in the southern Iowa, northern Missouri area. I think this will help increase the tornado threat for the areas of central and southern Iowa, between the areas of highest instability but also near the low.

Here is the question you have to ask yourself if chasing...
Close to the low? More instability?

A few areas of convergence are being forecasted in the models.... one near Fort Dodge, IA, another east of St Joseph, MO, and some other areas near Omaha and central Kansas.
If you like being closer to the low, I would head to central Iowa northwest of Des Moines. If you like more instability, head for NW Missouri. As long as the models are not way off, I think those are the two areas where we will see the best chances for storm development.
 
For tomorrow I’m interested primarily in the area from Lamoni, Iowa through NW Missouri (STJ) and into eastern Kansas near and south of Ottawa, due to favorably backed winds and instability. Along this corridor, 0z GFS progs values around 0-1 km shear of 100-125 m**2/s**2, with CAPE ranging from 2750 J/kg from Lamoni, Iowa to 3500 J/kg in eastern Kansas, and EHI of 3 in southern Iowa and 4 in eastern Kansas, with LCL heights of 1000 m in both areas, and LFC of 1300 m. 18z NAM is faster with progression, showing 249 m**2/s**2 in NW Missouri, EHI values ranging from 2 in southern Iowa to 4.2 in eastern Kansas, MLCAPE ranges of 2000-3000 J/kg, much more reasonable lid strength of -1 to 1 across this area, and LCL of 1000 m, LFC ranging from 800 to 1200 m.

Tomorrow is therefore looking MUCH more favorable than today, with better and earlier agreement between the models than today, deeper low pressure, and parameters that approach the ‘strong’ range for tornadic thunderstorm development. I will likely stay home most of the day to see what happens with all of this ongoing convection (hopefully this will clear out by tonight). I’m also torn between Iowa and eastern Kansas, but since I’m smack in the middle of both I would say that St. Joseph, Missouri is an excellent place to start from tomorrow to monitor data as the day progresses.
 
Generally agree with the E KS / NW MO / S IA targeting for tomorrow for same reasons as mentioned in previous posts. Main concern is with overnight convection - if the MCS currently in E Central KS heading NE is all there is and dies a natural death, I doubt that alone would throw a huge monkey wrench into tomorrow's setup. However, once again the LLJ is expected to intensify overnight (40-50 kt southerly flow at 850mb over eastern KS), and any new major convection initiating overnight could really scramble the atmosphere, overriding the synoptic setup as the several MCS did over many areas of the plains today. The small t/td spreads and low forecast LCL's are great - but if due more to low temps because of cloud cover, then it's a moot factor. Likewise with the cold pools and outflow boundaries, but not when they're so numerous, bumping into each other, and convection is so widespread as to create too much sinking air (high pressure at the surface.) We'll need a decent area of clear skies by early afternoon to make this dog hunt.

At this point, I'll probably wait until at least getting satellite pictures in the morning before making a forecast target for chase tomorrow.
 
6/4

Southern end of the risk area looks incredible via latest RUC model run. 6 utc RUC shows the dryline in W OK by 18z, beneath 50 knot 500 mb flow. I'd suggest just a bit farther north where the 0-3 km flow is stronger near the surface low (ie. 40 kt 700 mb flow). CAPE will also be maximized just ahead of the dryline where it is approaching 5000 j/kg. The downside to the southern part of the target area will have to be the large scale descent associated with the right exit region of the jet streak. However, strong positive vorticity advection and ageostrophic curvature divergence should be enough forcing to overcome a moderate capping inversion.

I imagine I'll target somwhere near Wichita, KS, initially. Long track supercells with possibly strong tornadoes appear likely tomorrow across a very large area which could spell disaster for a large part of the plains. Hopefully our photogenic storms stay as far away from communities, to prevent major damage, and so we have a better view!

We'll see exactly what the plan is tomorrow morning when some hard data is available. It's about freakin' time we had synoptically forced dryline to provide a focus area for sustained surface convergence! No more retreating dryline and dying Cu....PLEASE.
 
I like the southcentral KS / extreme northcentral OK target for today. Rich boundary layer moisture, characterized by dewpoints in the low-70s, along with strong insolation, with yield extreme instability by late afternoon, with NAM forecasts of 3500-4000 MLCAPE and RUC forecasts of >5000 SBCAPE. A near-perfect timing of a shortwave trough, with enhance mid-level flow, should provide strong enough upper forcing to, with strong surface heating, weaken the cap sufficiently for convective initiation. With the NAM forecasting a surface low near Lamont, a dryline bulge is forecast to the east/southeast/south of this low. A strong low-level jet will enhance low-level speed shear, though the RUC and NAM both show winds to be SSW for the most part (exception: NAM forecasts for farther east into eastern KS are SSE), which results in non-impressive low-level shear profiles. In addition, the veered low-level flow (925-850) results in rather weak 0-6km deep-layer shear values across most of the area south of a McPherson to Emporia, with NAM forecasts of 30kts, owing largely to a relative lack of directional shear.

There does appear to be a weak OFB invof the nc ok / sc KS border region, which be be a play later today. I'd sit near the apex of the dryline bulge near Wellington, KS, today. The 18z OUN and LMN soundings should be nice to see. The 12z RUC run did break out a convective cluster in this area as well. The OFB / dryline intersection may yield a convergence maximum (if the OFB doesn't mix out, which is quite possible). In addition, the backed flow along and immediately north of the OFB MAY locally enhance low-level shear.

I'm not so hot on the 25% hatched tornado risk, however, unless winds back more than model progs. I'd prob sit at 15% hatched for now, but just my forecast.

Virtual starting chase target: Wellington.
 
Chase target for today, June 4

Chase targets:
1) 20 mi N of Topeka, KS
2) 30 mi E of Winfield, KS (about 50 mi SE of Wichita)

Timing:
Both targets should see storm initiation around 4 PM CDT.

Storm type and intensity:
Significant outbreak of supercell storms with large hail, transitioning into a severe wind threat in the evening through the overnight. There is also a small chance for tornadoes.

Discussion:
WV imagery showed two important S/WV’s rotating around the base of the WRN trough in 55kt ULV flow. The lead S/WV, responsible for ongoing convection in IA and MO, was lifting through NERN KS at 12Z. The upstream wave, lifting through WRN KS, will be the afternoon WX maker. Extrapolation of the motion of this feature brings its effects into NERN KS around 20Z. Notable in the visible satellite was a huge outflow boundary in MO and OK in the wake of the departing MCS, while another “wakeâ€￾ was lifting slowly WWRD in ERN and SERN KS, which should reach an Emporia to Independence KS line by mid-afternoon. Also, skies had cleared through most of KS.

Surface dewpoints were in the mid-60’s although moisture was somewhat shallow as was indicated by TOP sounding. As a result, models will be somewhat over optimistic on afternoon dewpoints and resulting CAPE’s as they likely will not resolve the amount of boundary layer mixing that may occur despite NWRD moisture advection at the surface through 850mb as the OUN sounding only indicated a 40mb deep moist layer while at LMN the 850mb dewpoint was only 14C. RUC and NAM probably have also overdone moisture return at 850mb. Nevertheless, MLCAPE’s to 4000J/kg will be found along and E of I-35 in KS. Favorable thermodynamics along with 50kt deep-layer shear and (0-3km) SRH’s to 300m^2/s^2 will support supercell storms. However, large dewpoint spreads approaching 25F will not be conducive to tornadoes.

- bill
 
I'm glad to see others are thinking along the same lines as myself. South central Kansas-se kansas/north central Oklahoma looks like a good target.

Forecast hodographs looks incredible for tornadoes. The RUC is forecasting on the order of 5000 J/kg CAPE as well.

There's going to be a lot of tornadoes today. Wish I could chase!
 
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