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

Dec 9, 2003
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:

500mb Winds 00z Thur:

Surface dewpoints 00z Thur:
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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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