2/28/07 FCST: TX / OK / KS / NE

And we have another <990mb low in the Plains... Forecast models indicate another strong upper-level trough will move out of the western US and into the plains during the middle of next week. As it is 5 days out, the timing may change, obviously. Yet again, it appears, at this time, that moisture return will be the biggest question mark, and that will depend upon the amount of time for moisture return and how far the cold front associated with the current cyclone makes it into the Gulf. The NAM at 84hrs is more favorable for moisture return (extrapolating to 108hrs, or Wednesday afternoon/evening), with >60F Tds just southeast of Dallas - Fort Worth; the GFS is less favorable, indicating another marginal-moisture setup. Regardless, flow will be very strong at all levels (e.g. >50kts at 850mb from Texas to Minnesota), and the environment should be characterized by very strong low-level and deep-layer shear. The system looks like it'll eject a little farther north than the current system, so I included Nebraska in the thread.
 
Also, it looks like the trough this time around will be of a longer wavelength and thus somewhat less progressive, which would tend to leave more margin for error timing-wise. Also, check out the 300-250 mb jet. The left exit region is almost perfectly placed at 18 and 00 Z over the dryline. I, too, noticed the lack of decent instability in the warm sector on the GFS (partly due to the presumed extensive cloud cover in the warm sector per the 850 mb RH prog), but simply looking at the time available for moisture return (at least 24 hours) leads me to believe that we may be in somewhat better shape instability/moisture-wise than with Friday's system. At least the potential is there.
 
This setup looks very interesting 4 days out. Like Jeff said moisture return is the biggest question mark at this time. The GFS does forecast dewpoints in the mid 50's range for northeast/north central Texas and very extreme south central Oklahoma. Dewpoints are forecasted in the 60-65 range in south central/southeast Texas. Last nights 00z run now shows the surface low in the Texas panhandle at 992mb. The previous 12z run yesterday showed the surface low in Kansas. A little off but not too much. At least there is some confidence that a fairly deep low should be in this general area on Wednesday. Winds shear with this system looks excellent with 850mb winds forecasted at 30-50 knots, 500mb winds 60-80 knots, and 250 winds in excess of 100 knots. Vertical shear looks good as well. Surface winds are slightly backed. All of this data is for 00z Thursday. This could really be a good day, esp. if the models stay consistent and moisture can at least push mid 50's like they did last Friday. The further south in Texas you go the higher the dewpoints (into the 60's.) Worth keeping an eye on for sure as it is on the SPC 4-8 day outlook. Will be interesting to see what the day 3 shows and also how the NAM compares with the data that the GFS is putting out right now.
 
After a quick glance at this mornings model runs wed seems like it actually may be a decent chase day. not to get into too much detail (84 hours out) storm motion and speeds dont seem impossible and if we can get some decent moisture (greater than 55-57) things may look up. also a noteworthy thought is that the target area may be right smack in the middle of oklahoma which makes for some real healthy chase terrain...
we will have to see how this works out!
 
In Kansas we may see another cold core setup over portions of E/C Kansas during the afternoon to early evening timeframe. Dewpoints in the low 50s and temps reaching the mid 60s will be in place over the area. A cold front will move in during the afternoon hours and be the focal point for severe convection. Vertical wind shear may be supportive of low-topped supercells, that will eventually converge into a squall line.

Here is the 0-3km CAPE for 00z Thur:
http://grib2.wxcaster.com/wxcaster4/CONUS_ETA_0-3KM_CAPE_84HR.gif

500mb Winds 00z Thur:
http://www.rap.ucar.edu/weather/model/eta84hr_500_wnd.gif

Surface dewpoints 00z Thur:
http://www.rap.ucar.edu/weather/model/eta84hr_sfc_dewp.gif
 
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As of the latest NAM & GFS the possible cold core setup in Kansas won't be happening. Still four days out maybe things can change.

I do see a pretty significant severe wx event shaping up for the S Plains. dewpoints in the 60s will reach E OK by 00z Thur. CAPE will range in the 1000-1500j/kg area across NE OK/ SW MO/ and Ex SE KS extending into NC Texas. Still like I said earlier lots can change, but definetly something to watch closely.
 
Definately seems like some nice parameters are coming into place for Wednesday in NE Ok and adjacent areas. Heres some model extraction data from 12z NAM at Tulsa for 60 hours out (0z Thur).

temp = 66
dew = 59
cape = 941
Lifted Index = -5.6
0-3km helicity = 300

850 wind dir/vel = 196/32 kts
500 wind dir/vel = 245/52 kts
200 wind dir/vel = 266/150 kts

It actually gets better at 6z with cape up to 1200, 0-3km helicity at 552, LI down to -7.4, with dewpoints getting into low 60's. Cap strength could be a problem though.
 
Im concerned abit with the dry warm air advecting in at 850mb, other than the cap issue i think that we have a legitamate chase day in this great sooner state.
 
After looking at the 18z gfs im a little more intrigued about the possiblity of severe wx across oklahoma. The is a lot of concern in relation to moisture/moisture depth and and warm 850 flow due to veering of the winds. However, the 18z run puts a little more moisture at the 850 layer and draws it a little closer to the target area. this has been a trend (if you can call 3 model runs a trend), so im hoping this continues.
 
There continues to be some potential for Wednesday, but the setup faces similar obstacles as the previous one (namely, questionable moisture and initiation). Last night's NAM was forecasting southwesterly 850mb across most of the southern plains, which was ushering in very warm and dry air just above the surface. Through the past few model runs, however, the NAM appears to have backed off this forecast, with the more recent 00z run backing the 850mb flow to SSW by Wednesday evening. There appears to be an opportunity for a rogue supercell in a relatively narrow zone of reduced CINH in northcentral Oklahoma (+/- 50-75 miles), as upper-50s Tds (and maybe even >60F) combine with 65-75F temperatures ahead of the dryline to produce ~1500 j/kg SBCAPE. Questions of initiation remain, as there remains some capping which may suppress convection until after dark. There is a hint of a lobe of mid-level vorticity swinging through the area near 00z, but the "big kahuna" hangs back until ~12z the following morning, so we won't have much DPVA to help out. It'll be a tough call, but that's relatively common for this time of year.

The NAM forecast sounding valid 00z/01 at OKC looks rather tempting: http://beta.wxcaster.com/cgi-bin/parse_skewt_trace.cgi?model=NAM&fcsthr=048&STATIONID=_KOKC

It's important to note that the GFS is considerably less aggressive with moisture return, indicate pitiful moisture depth (and magnitude). If this verifies, I'll look back at this post and shake my head, for it'll feel silly to even consider chasing given the look of the GFS forecast soundings....
 
While i was waiting on 12z to render i figured that i would see what the great crystal ball 6z output (GFS) had to say and was pleasently surprised. The models all continue to bring moisture back further to the west into E and NE oklahoma. Li values max out around the TSA area at 00z and the 850 winds continue to back more to the ssw. the only caveat to this entire post is that when 12z comes out everything may be different so as our Roman friends used to say "Cum Granis Salis". (I knew 6 yrs of latin would be useful someday.)
 
The 00z NAM continues to indicate potential for supercell development tomorrow (and in central Oklahoma -- a close chase for me and many others). I won't rehash much, since the two primary issues remain (moisture depth/quality and initiation questions). However, I will say that, if the following verifies, I think we'll see a pretty good potential for a rare late-February tornado event in Oklahoma --> OKC SkewT forecast from NAM valid Wednesday evening. I'm still a little concerned about the moisture quality, since I think the 00z NAM initialized dewpoints a little too high in central Texas (the 55-60+ tds). In addition, the models do not initiate convective precip in the central Oklahoma, so I'm not getting too excited yet.
 
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The latest run is very interesting, there is little to no CIN from the red river northward by 00z. Soundings are pretty promising with backed winds especially ADM and PVJ. I was almost surely sitting this one out but if the tds get to 60 and if the cap does in fact erode, we could see some interesting storms for sure. The LCLs look at bit high AoA 1000m, but there are a number of factors that could make those lower. I guess its wait and see time, I'll be very interested to see if the SPC pulls back the slight risk further into Central OK now.
 
Taking a look at the 00Z model runs here is my analysis. Both GFS and NAM seem fairly consistent in the timing of the 500mb trough ejecting out into the plains. By 6pm Wednesday the trough is progged to be centered over NE Utah. Out ahead of this OK Mesonet readings are showing a frontal boundary draped across northern OK with Tds reaching the upper 40's across southern OK. What is interesting to note is a 54F Td reading at Ardmore (or near Ardmore). IMO, this may be instrumentation problems as all readings nearby are in the mid to upper 40's. 00Z soundings from OUN and FWD show signs of a developing LLJ (but still very weak.)

Both NAM and GFS are progging the dryline associated with the sfc low to be near or just west of I-35 by 6pm Wednesday. Given what happened last Friday, I am expecting this to be the farthest possible extent of the dryline before nightfall (dryline was progged to be across western OK last Fri by nightfall, ended up being about 60 miles west of there.) The first noticeable difference between the NAM and GFS is forecasted Tds. NAM is progging solid 60 Td's almost to the KS/OK border by 00Z. GFS is being a lot more conservative with the 60s holding to southern OK with mid 50s across the rest of the state. Forecast soundings for OUN show the potential for a clear air bust tomorrow. Both models are progging a relatively deep layer of dry air above 850mb. If the dryline ends up being slightly farther west than models are forecasting than this layer of dry air may not be as pronounced across central OK. Also interesting to note is the difference in the wind vectors between the two models. GFS is tending towards a much stronger wind speed solution between 850 and 700mb than the NAM. However, both models show supercell favorable dynamics. For this time of year I would actually prefer the weaker solution (with respects to wind speed) due to the weaker CAPE. NAM is forecasting an enhanced area of CAPE at 00Z from near Ardmore north through OKC and then stretching NNE towards Stillwater and over towards Tulsa. If the dryline ends up being slightly farther west than current model prognosis this area will more than likely shift westward slightly. The majority of the 850mb moisture looks to be well east of the forecasted dryline location, presenting the overall problem. Dry air at 850mb will make initiation difficult for an adiabatically rising parcel. If the air dries up too quickly with height than a rising parcel will never reach condensation before it loses all of its vertical momentum. Along with this LCLs may be too high for those looking for naders before dark.

Regardless, tomorrow looks promising for seeing some Cu billowing over Norman. :) The main event will surely be after dark, but the chance of at least some isolated cells before dark looks like a possibility. I have class all day until 5:15pm CST (Shapiro's handing back our dynamics 2 exams @4.) For me, the best situation will be getting out of class and seeing a cell right over Norman. Of course, then I just have to figure out how to bike back to my apartment.
 
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The 00z NAM continues to indicate potential for supercell development tomorrow (and in central Oklahoma -- a close chase for me and many others). I won't rehash much, since the two primary issues remain (moisture depth/quality and initiation questions). However, I will say that, if the following verifies, I think we'll see a pretty good potential for a rare late-February tornado event in Oklahoma --> OKC SkewT forecast from NAM valid Wednesday evening. I'm still a little concerned about the moisture quality, since I think the 00z NAM initialized dewpoints a little too high in central Texas (the 55-60+ tds). In addition, the models do not initiate convective precip in the central Oklahoma, so I'm not getting too excited yet.

Jeff why does that skew T not match the forecast sounding off the Storm Machine?: http://weather.admin.niu.edu/machine/fcstsound.html

It shows cape 563 and cinh 76 at 0z on Mar 1.
 
Jeff why does that skew T not match the forecast sounding off the Storm Machine?: http://weather.admin.niu.edu/machine/fcstsound.html

It shows cape 563 and cinh 76 at 0z on Mar 1.

It looks like the difference in the calculation of CAPE. It looks like Storm Machine uses 100mb mixed- or mean-layer CAPE, while it looks like wxcaster uses surface-based CAPE (i.e. tracing a surface parcel). The near-surface temperature profiles looks a little different on each site as well, with the wxcaster site showing nearly well-mixed from the sfc to ~825mb (with dry adiabatic temperature profile and constant-mixing-ratio moisture profile) and the Storm Machine site showing less steep near-surface lapse rates and shallower moisture.

EDIT: To me, it looks like the Storm Machine Skew-T only plots T and Td every 50mb, while the WxCaster Skew-T plots T and Td every 25mb.That said, the Td profile in the low-levels is much drier on the StormMachine skewt than on the wxcaster SkewT. For example, note how there is almost saturation at 825mb on wxcaster, while it is very much unsaturated on Storm Machine. If Wxcaster does indeed use more data (in the vertical), we could see significant differences, especially as in this case, where the moisture extends to 815-825mb, something that is not captured if Storm Machine only plots 850mb and 800mb data. Just a guess. If Storm Machine uses MLCAPE, such a difference could be very important, since it would mix in much drier air (between 825-800mb) in the calculation of the ML parcel. This would explain the lower CAPE and higher CINH (since it results in lower Theta-e of the updraft/parcel).
 
Guys....could it be that it is a different model? On the storm machine site it says it is the WRF.....while what Jeff posted was the NAM output. I looked at the NAM output on NSHARP and the profile is the same as off of the wxcaster site. A slight difference in CAPE calculations (~1700 off of wxcaster and 1543 off of NSHARP). I also agree that it looks like the storm machine output is not as high resolution as wxcaster or what I am looking at on NSHARP.
 
I was using StormMachine quite heavily last Friday and I noticed some really crazy CINH/CAPE numbers, such as something like 500/50 in an environment where those numbers should have been almost opposite (50 CIN, 500 CAPE). Is there possibily a third party forecast sounding site I can take a look at because if wxcaster's forecast sounding for KOKC @ 00Z verifies, WoW! The StormMachine sounding is far from impressive with much drier air near the LCL height from wxcaster. And of course, it depends on what type of CAPE each of the two sites are calculating... surface based and mean layer can make a huge difference in dry layers like Jeff mentioned.

Kevin: ETA/NAM should be the same model. I guess its possible that either site may have confused the names.
 
Guys....could it be that it is a different model? On the storm machine site it says it is the WRF.....while what Jeff posted was the NAM output. I looked at the NAM output on NSHARP and the profile is the same as off of the wxcaster site. A slight difference in CAPE calculations (~1700 off of wxcaster and 1543 off of NSHARP). I also agree that it looks like the storm machine output is not as high resolution as wxcaster or what I am looking at on NSHARP.

The NAM used to run on the Eta, and it now runs on the WRF (i.e. the WRF model runs in the NAM timeslot, having replaced the Eta in that same timeslot last year). I assume any difference are merely typographical (i.e. the person who sets up the script to create the graphics hasn't changed it from Eta to NAM or WRF). There is a very, very outside chance that Storm Machine actually locally runs the Eta, but I can't imagine that'd be the case. So, as Kenny said, I think both sites are using the same model output.

EDIT: http://wwwt.emc.ncep.noaa.gov/mmb/mmbpll/cent4km/v2/ The latest 4.5km WRF with explicit convection shows a strong, isolated storm developing just northwest of OKC and moving northeastward at and after 00z (use Total column condensate product). That run also indicates that the storm is the only storm to develop and sustain itself (more than an hour) in Oklahoma tomorrow and tomorrow night (though convection does develop near 12z in extreme ne OK).
 
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I've been looking at the model output this evening and I don't know...maybe it's just me....but I am impressed by the severe potential towards 06Z in southeast KS/southwest MO/and northeast OK. I agree that there could be some storms develop back towards central OK along the dryline before sunset. However...parameters really become focused (according to the NAM) over the se KS/ swMO/ ne OK areas by 06Z. The surface low has deepened to 986 near CNU by then....which has brought the 60 degree dewpoint line into far se KS and sw MO. I think the difference between the NAM and the GFS is that the NAM starts deepening the low a little sooner...allowing for the quicker return of moisture. The GFS has a 990 low near Tulsa at 06Z then deepens it to a 982 low between MKC and COU by 12Z. What impressed me however was the combination of parameters focusing in on this area. VGP values of .4 to .5, 0-1KM EHI of 2-3, LCL's below 1000m, (LFC's are also quite low....less than 2000m in se KS dropping to 800m in sw MO), 0-1km SRH is in the 300-350 range and the nose of the mid level jet - with 60kt winds - is punching into this area as well. So with the tightening dewpoint gradient along the dryline and the upper support it seems things look favorable for supercells and tornadoes into and possibly through the night. Looking at point forecast soundings....it is remarkable to see the changes in the profile over a few hours. The lapse rates steepen, the cap erodes, and the shear is impressive. Oh...also 0-3km CAPE values increase during the night...suggesting storms can get rooted close to the surface. So...that's what I am thinking. I am curious to hear other opinions on this.....as it is based off the NAM and maybe its not correct. Nevertheless...if it is close to accurate then it appears to me that some "stuff" is going to happen.
 
Here is a somwhat crude looking forecast sounding from EMC.....but it shows the same sounding as what was seen on wxcaster.

http://www.emc.ncep.noaa.gov/mmb/soundings.nam/stations/723570.html

The CAPE value is not as high as wxcaster (I've noticed over the years some of the values seem a little high) but it is ~1200 which is a far better number than 500! Also...not much CIN showing up....somaybe this can help validate the wxcaster model sounding. Besides....I always like to say choose the model which shows the better numbers! :)

Here is one other site you can check out. Unfortunately it looks like the page is slow in updating. Check out http://www.nssl.noaa.gov/wrf/ and then click on the OUN and HUN sounding areas. You may already know about this site in which case just disregard this.
 
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One last tidbit before I go to bed...

I tried to do a similar crude dewpoint analysis as was done by Jeffrey Miller before the 2-23 event. As you can see, moisture recovery is much further ahead currently than with the previous event.

0640z 2/28 Td analysis
0440z 2/23 Td analysis

Note that is doesn't speak to the depth of the moisture, however! An 850mb Td analysis would show considerably more dry air compared to the last event. Fortunately, 850mb is quite a ways higher off the ground in central and eastern OK than it is in the western TX panhandle, so a 1 to 1 comparison may be slightly misleading.
 
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