1/28/2006 FCST: TX / Southern Plains

[Bill Tabor]

Ok, so 1/26 fell apart with a tragic death! Lying GFS. Here I go out on a limb again with our GFS friend. This time it seems to be a little friendlier, but still no guarantees.

Basically I like the area around Wichita Falls near 0Z right now. The GFS shows the approach of another mid level low (positive tilt) but this time it isn't cut off and perhaps will really materialize. Instability, dewpoints and temps look relatively better this time as the flow from the Gulf has been in progress for at least a couple of days and warmer temps are forecast prevailing over Tx and the Gulf. Instability is forecast to reach -4 near SPS at 0Z which is just east of the srfc low (1007mb) that will form nearby, and northeast of dryline bulge. Dewpoints will be a little weaker than preferred at 50F to 55F and deep layer may be a bit thin still. Temperatures are expected to get up to 70 and should aid in convective initiation in late afternoon assisted by approaching mid level wave. Additionally deep layer shear appears sufficient for supercells assuming ample moisture but weaknesses for tornadoes include fairly weak surface winds and somewhat large directional shear discontinuity between 850mb winds and sfc. SPS and the area just south of it appears to also be in the left exit quadrant of the 500mb wind max. Upper winds are supportive also.

I have some concern for the smaller mid level wave that appears to pass thru much of Tx earlier in the day. It could kick off precip early and contaminate my target area. My other concern is better parameters for SPS only seem to really come together near dark making it limited for chasing this time of the year.

Not sure how good of a chase opportunity this is with it being so close to dark. Assuming the above GFS verifies on Saturday, I expect there will be at least a breakout of some thunderstorms with some having the potential to have rotating updrafts, and possibly severe hail. I'd say tornado potential is limited.

 

[nickgrillo]

I don't see any potential in this system (besides some very welcomed heavy rainfall possibilities across TX/OK) besides the potential for a few isolated marginally severe hail reports. There will already be widespread cloud cover / precip aided by continued low-level WAA/isentropic ascent (and increasingly diffluent upper flow) which will make it very tough for any SB/near SB buoyancy to develop... The best turnout I could see would be some marginally severe hail in any areas which recieve some elevated instability (mid-level wave approaching the area will help steepen lapse rates) with all activity likely being elevated given the stable near-surface layer.

 

[Bill Tabor]

I don't see any potential in this system (besides some very welcomed heavy rainfall possibilities across TX/OK) besides the potential for a few isolated marginally severe hail reports. There will already be widespread cloud cover / precip aided by continued low-level WAA/isentropic ascent (and increasingly diffluent upper flow) which will make it very tough for any SB/near SB buoyancy to develop... The best turnout I could see would be some marginally severe hail in any areas which recieve some elevated instability (mid-level wave approaching the area will help steepen lapse rates) with all activity likely being elevated given the stable near-surface layer.

Yeah, don't get me wrong. I'm not saying this is a great chase opportunity. I'm just pointing out the increased potential in this area. That said, I don't expect a whole lot - thunderstorms - possibly somewhat elevated, with some potential for rotating updraft and yep - marginally severe hail. However I just checked the GFS and it's already pulled the vort max back a bit more west at that timeframe which may leave not much of anything.

Once again GFS accuracy sucks. It can't get the timing of these waves down.

 

[Robert Dewey]

The ECMWF and UKMET's accuracy has been doing good over the past several months. I would always consult with those models after looking at the GFS to see just what the general trend is.

 

[Bill Tabor]

Check out the SPC Ensemble Composite Severe for Saturday. Interesting...
http://www.spc.noaa.gov/exper/sref/

 

[Bill Tabor]

As expected NAM seems to have a totally different take on this system than the GFS did. Nam doesn't show a concentrated low pressure center forming west of SPS, and the strong vorticity max headed near SPS is WAY further north on the NAM now - LOL! I suppose it's worthless to speculate on the GFS that far out - which I believe is the point I already made - here reaffirmed.

Now a more reasonable scenario seems to take place. Lower sfc pressures to the north of SPS and a trough extending down into Tx. Appears in the morning a warm front will be mostly E/W across south Tx and work it's way north during the day to eventually have some interaction with the trough and windshift boundary SW to NE through middle of Tx. A weak mid level wave comes in early kicking off probably a good amount of precip throughout much of TX up through the center SW to NE. Dewpoints up to 55 will be in place and NAM shows perhaps up to a bit over 1000 cape and fair amounts of helicity throughout the day and I notice forecast EHI may be over 1.4 in parts of central Tx later in the afternoon. LI may be up to -4 or -6.

So my take is probably a fairly widespread rain event provided much needed rain which we are way behind on. This will include thunderstorms. Check NAM forecast soundings I see potential for scattered weak rotating updrafts, and forecast parameters for supercell composite over most of the active portion of Tx indicate this as a weak possibility. Seems best soundings though are down between CRP and HOU near the coast. Small hail should be a potential throughout the active portion of Tx.

 

[nickgrillo]

Hmm... Both the latest NAM and GFS runs make the system way more interesting... Slightly more robust boundary layer moisture, much deeper sfc cyclone (per GFS, which drops the sfc low by 8mb between 12-00z) and both stronger mixed-layer CAPE and low-level shear (with some backing sfc flow ESE of the low, per GFS) with very cold H5 temps. Not saying it's a biggie, but the GFS has been pretty acurate these past few monthes... So, I think there is some potential for isolated, low-topped supercells close to the sfc low (wherever it lands... With the latest GFS bringing it in ne KS).

The NAM is quite a bit weaker with the system (GFS shows the sfc low 10mb deeper by 0z SUN)... Yet these comps still show some impressive figs:
http://grib2.wxcaster.com/wxcaster4/CENTRA...OS_STP_45HR.gif
http://grib2.wxcaster.com/wxcaster4/CENTRA...OS_STP_48HR.gif

 

[Bill Tabor]

Changed the subject to include a wider area than just north Tx.

I glanced at the lastest 12z NAM, forecast soundings, forecast ehi, and Earls severe indices. Interesting. Not sure what to make of all of it yet, as I don't have time to fully analyze. I'll take a further look in a bit.

 

[nickgrillo]

Originally posted by nickgrillo
Hmm... Both the latest NAM and GFS runs make the system way more interesting... Slightly more robust boundary layer moisture, much deeper sfc cyclone (per GFS, which drops the sfc low by 8mb between 12-00z) and both stronger mixed-layer CAPE and low-level shear (with some backing sfc flow ESE of the low, per GFS) with very cold H5 temps. Not saying it's a biggie, but the GFS has been pretty acurate these past few monthes... So, I think there is some potential for isolated, low-topped supercells close to the sfc low (wherever it lands... With the latest GFS bringing it in ne KS).

The NAM is quite a bit weaker with the system (GFS shows the sfc low 10mb deeper by 0z SUN)... Yet these comps still show some impressive figs:
http://grib2.wxcaster.com/wxcaster4/CENTRA...OS_STP_45HR.gif
http://grib2.wxcaster.com/wxcaster4/CENTRAL_ETA212_ATMOS_STP_48HR.gif

Glad to see SPC agreed ... Broyles just introduced a SLGT to eastern KS...

Latest GFS is even stronger with the surface low, bringing it to 997mb by 0z SUN -- with cyclogenesis leading to a strong isallobaric response -- which is backing boundary layer flow across eastern KS/western MO near the low. Very cold 500mb temps around the low is leading to steep mid-level lapse rates (evident on both NAM/GFS fcst soundings for the region) and is increasing SB/MLCAPEs.

Looks to be a somewhat repeat of 11-27-05, IMO....

<img src=http://members.cox.net/jondavies4/112705cks/112805etasfcTd00f24anno.gif>
<img src=http://www.rap.ucar.edu/weather/model/gfs036hr_sfc_dewp.gif>

If this continues, I might leave for TOP late tonight...

 

[Dick McGowan]

Nick Grillo wrote:

Glad to see SPC agreed ... Broyles just introduced a SLGT to eastern KS...

Latest GFS is even stronger with the surface low, bringing it to 997mb by 0z SUN -- with cyclogenesis leading to a strong isallobaric response -- which is backing boundary layer flow across eastern KS/western MO near the low. Very cold 500mb temps around the low is leading to steep mid-level lapse rates (evident on both NAM/GFS fcst soundings for the region) and is increasing SB/MLCAPEs.

Looks to be a somewhat repeat of 11-27-05, IMO....



I agree for the most part. 500 temps are around -20-22 except for maybe SE KS via GFS. Cape is in place with ~500 j/kg, but very thin.

My target Emporia KS attm, anxious for 0z runs. It's January and I need to see convection.

I think it goes early, 1-2 pm. If I bust, oh well, I've wasted a few hours, and a little gas.

This is my first forecast (not much of one). Jinx.

 

[Mike Hollingshead]

Going strictly off today's 12z GFS I'm almost thinking somewhere south of Concordia KS between there and Salina around noon and following it ene to somewhere just north of Topeka.

http://www.wxcaster.com/modelskewt.php3?mo...&STATIONID=kcnk

Concordia fcst sounding at noon.

That dryslot, which will be quite cold has me interested in the day.

http://weather.cod.edu/forecast/AVN/avn_us...500_rhum_30.gif

Under the mid-level dry slot and north or nne of the sfc low.

http://weather.cod.edu/forecast/AVN/avn_us...S_0_lift_30.gif

Now if I can figure out a way to skip my nephew's b-day party.

 

[Ryan McGinnis]

Tomorrow seems marginal to me, but marginal on a Saturday is like a godsend in the middle of January. It does seem like a bit of an early day from the 12Z GFS. The 850 winds back as the low slides in, and the GFS is progging them at a good 30 knots over NE Kansas. The 500 jet is going a good 50 knots. The ETA doesn't seem so bullish on the drypunch. The limited instability makes me think of mini sups, but the SPC is talking about isolated supercells & large hail, so maybe the models are underestimating the instability in the dryslot sector. The fact that I'll be getting the car ready tonight is almost a sure omen that nothing will come of this, but, again, it's January and a little wishcasting seems in order.

I'll postfix that with the usual "I suck at forcasting, don't give what I say too much weight, feel free to tell me where I'm wrong" line.

 

[nickgrillo]

Originally posted by Ryan McGinnis
Tomorrow seems marginal to me, but marginal on a Saturday is like a godsend in the middle of January. It does seem like a bit of an early day from the 12Z GFS. The 850 winds back as the low slides in, and the GFS is progging them at a good 30 knots over NE Kansas. The 500 jet is going a good 50 knots. The ETA doesn't seem so bullish on the drypunch. The limited instability makes me think of mini sups, but the SPC is talking about isolated supercells & large hail, so maybe the models are underestimating the instability in the dryslot sector. The fact that I'll be getting the car ready tonight is almost a sure omen that nothing will come of this, but, again, it's January and a little wishcasting seems in order.

I'll postfix that with the usual "I suck at forcasting, don't give what I say too much weight, feel free to tell me where I'm wrong" line.

Any supercells in KS tomorrow will be shallow ("low topped") given the low equilibrium levels and the main threats from any of the storms will be tornadoes and large hail (given very favorable low-level shear profiles) in the region immediately near the surface low (and in region of backed boundary layer wind fields)...

The NAM is weaker with the system -- and brings the surface cyclone further south and east (by about 50-100 miles) with slightly more veered low-level winds ahead of the dryline... The NAM also brings in a narrow swath of 1000 j/kg SBCAPE (stretching from the sfc low and trailing down into TX along the dryline) while the best 0-1km SRH is left slightly further to the east... Now, the GFS solution is one I favor the most... It brings the sfc low further north and much deeper (with isallobaric forcing strongly backing low-level wind fields near the low) with frontal lift increasing ascent by just after noon... Making me think SSW of KTOP would be a good area to start with (perhaps around Manhatten by 16-18Z).

I'll probably not be going tomorrow... I have to remind myself that it's JAN, and driving 14 hours for a cold-core setup (and end up spending $100-$150 in the long run) isn't the wisest decision

 

[Bill Tabor]

Ok I've looked at the 0Z run (both GFS and NAM). I prefer the NAM solution because I'm tired of GFS lying and moving the vortmax all over the place. However the way the GFS moves it all north and east faster is probably more realistic based on climatology. But who cares I'll choose the one that gives the better shot down here - LOL - the NAM.

NAM pulls the 500mb vort down into the Big Bend of TX and through the day between 18z and 0z moves the center up to SE of ABI. However the area it's lift will influence is much greater and comprises much of the north central Tx area including along the I35 corridor. At the surface a trough will extend N/S through western Tx and by 0z should be just east of I35. 55F to 60F degree dewpoints will be in place with sb cape near 1000, LI's between -2 & -4 throughout central Tx and partially extending into OK. Helicity readings are reasonable and EHI is forecast to over 1.0 in places. Additionally mid level temps will be approaching 20F north of an E/W line through AUS. During the day light to moderate and slightly backed sfc winds be from the S to SSE & will cover eastern Tx. H85 level winds while somewhat veered as the daylight wears on should still provide fairly strong low level directional shear. Also between 18z and 0z 500mb jet left exit region should pass over north central/north eastern Tx and should contribute to lift and instability.

Tonight, storms / showers are already ongoing NNE/SSW across central Tx. While this should limit instability, it should nevertheless still be reasonably unstable for some severe storms tomorrow. Expect showers to continue along with weak advance waves. Tomorrow I'd expect the potential for some severe throughout much of eastern Tx (eastern 1/3) including the coast and extending into parts of south and southeastern OK.

Tomorrow afternoon between 18z and 0z and with approach of very strong vortmax I expect some supercells. If NAM verifies and low is as strong as forecast and down into TX - expect some slight backing of sfc to 850 winds providing a minimal environment for some tornadoes particularly north of an E/W line through the AUS area.

After examining many forecast soundings I like Corsicana approaching 0Z for a target for supercells and a possible tornado.

 

[Chris C Sanner]

I think, to see a tornado today in my part of the woods you will have to be pretty dadgum lucky but the chances are nowhere near 0. OUN already mentions low cloud bases and decent LL shear, but the fact they're expecting a line kind of dulls the tornado risk a bit in their minds. I think that if a storm can get going on a local outflow boundary from the convection this morning (which there looks to be a couple) and stay discrete for a little while, well..you figure it out :lol:

But, instability is a concern, we're 3 hours from the forecasted initiation and its thundering, raining, etc. here with no sun in sight. Satellite shows a sharp edge well W of here (Velma/Duncan), so I'm rather curious about whether we can get that 1000 cape the ETA was giving last night, my gut leans to no, but my heart to please :wink:

All in all, if you have no other plans, really need to see a storm, and don't have any expectations coming in, I see no reason not to chase just for the fact there is an alright chance of a supercell today...

PS...Just for those on the edge, storm speeds are going to be 45mph or so, not the fastest I've ever chased, but its not easy keeping up with em either!