05/01/10 FCST: TX, AR, LA, OK

[Niccolò Ubalducci]

Hello everyone,

Take advantage of the time available for groped a preliminary forecast for May the first.

The area that seems most interesting is the triangle formed by I30 and I20 from Dallas to East.

The moisture from the Gulf slope after 3 days of strong south flow will bring dewpoints between 70 and 75 F, with values of approximately CAPE 3000/3500 J/Kg over the area indicated.

The directional shear seems excellent with backing of low-level winds to its east of Dallas. The LLJ will be around 30 kt while the upper winds will be between 50 and 60 kt.

The conditions seem very favorable for supercells initially that will evolve into squall line with the passing hours and moving to East.

The frontal convergence line SW-NE passing through Dallas could provide the right trigger for starting early in the afternoon.

So now, my target is preliminary Sulphur Springs TX.

 

[Eric Bucsela]

I agree Sat looks good (better than Friday) in E TX, especially if you believe the 48 hr NAM, which has best parameters displaced further west than the 48 hr GFS. My concerns are relatively weak surface winds and decent but not outstanding instability - also the possible effects of earlier convection. Will have to wait and see how all this plays out in later model runs.

 

[Jonathan Whitehead]

Tomorrow could be a high end MDT risk day for parts of SRN & ERN AR/WRN TN/WRN MS.

A very strong SWLY upper jet (bulk shear of at least 50kts) combined with very rich tropical moisture (dewpoints in upper 60s to near 70) will yield a moderately unstable airmass across SRN & ERN AR/NRN LA/WRN TN/WRN MS tomorrow. A sfc low is forecasted to develop along the front across WRN AR which will back sfc winds across ERN AR tomorrow afternoon resulting in high 0-1 Km helicity values. A stratus overcast will limit daytime heating through midday but by mid-afternoon enough breaks in the clouds should occur to yield 2000 J of CAPE. Additionally very saturated soils and high moisture content will result in low LCLs resulting in high 0-1Km CAPE values. Supercells should fire by 2100 UTC across NRN LA/SRN AR out ahead of main line of storms that should fire across ERN TX around mid-morning. Supercells should progress NEWRD through the late afternoon and evening hours across ERN AR. All modes of severe weather will be possible, with the threat of a strong tornado or two. Another dangerous threat is flash flooding. High PW values will result in very efficient rainfall producing storms with some supercells becoming HP. WFO MEG (MEM) has already hoisted a MDT risk for ERN AR and I expect SPC to follow suit.

I should also point out that this weekend is Beale Street Music Fest weekend in downtown Memphis. Having grown up and spent my first 19 years in Memphis, I can tell you first hand this is a major event, with 50,000 people expected downtown and along the River for outdoor concerts by major big name bands. Concert goers should pay carefull attention to the weather and be prepared to seek shelter during the late afternoon and evening hours should severe storms threaten.

 

[beaudodson]

I have been concerned for the KPAH region since Thursday night. Everything points to backing winds late this afternoon and evening. This line of storms is moving right on through (2 AM now). It should clear the area leaving behind some boundaries.

If we can see instability realized then I think we see the risk for supercells. I would add areas further north to this thread.

The new day one moderate is currently centered on west TN into this area.

Defin some potential later today for some significant weather over this region.

 

[Jesse Risley]

The real deciding factor for today, in my opinion, will be the extent of any diurnal heating that occurs, mainly when and where any pockets of instability might develop between breaks in the current cloud cover. The area appears fairly overcast at the present time, though the RUC wants to break out some respectable instability in the ARKLAMISS region, extending northward into the Ohio River valley by early afternoon.

By 20z Bulk Shear values on the order of 50-70 kts, EHI (0-1 km ~ 2.5; 0-3 km ~ 4.5), SFC LCL (500-1000), LI (~-6) and 0-1 km SRH values (~200 m2**s2) all appear sufficient for a decent severe weather even today.

 

[Michael O'Keeffe]

If the RUC is right and brings in CAPE over 2000 j/kg over Arkansas than today could be HUGE! Really wish I could be there as today looks like a textbook AR/MS/LA/TN outbreak day.

If I were chasing I would start just east or maybe NE of Little Rock. Storms will likely fire in the Arklatex first and blast NE into C/E Arkansas and with the good directional shear discrete supercells appear likely. Moisture and CAPE look to be very good in fact unusually high but not out of the question if we can get some heating. Once the LLj gets cranking after 21z then things could get ugly with strong tornadoes a good bet maybe even some long track tornadoes given storm motions. Pray for the folks down in Arkansas as it is not easy for an area to be battered two days in a row by tornado outbreaks.

 

[Trey Thee]

If the RUC is right and brings in CAPE over 2000 j/kg over Arkansas than today could be HUGE! Really wish I could be there as today looks like a textbook AR/MS/LA/TN outbreak day.

If I were chasing I would start just east or maybe NE of Little Rock. Storms will likely fire in the Arklatex first and blast NE into C/E Arkansas and with the good directional shear discrete supercells appear likely. Moisture and CAPE look to be very good in fact unusually high but not out of the question if we can get some heating. Once the LLj gets cranking after 21z then things could get ugly with strong tornadoes a good bet maybe even some long track tornadoes given storm motions. Pray for the folks down in Arkansas as it is not easy for an area to be battered two days in a row by tornado outbreaks.

All things point to a substantial severe weather event today. SPC seems to agree iwth your assessment that today will be huge. This afternoon is going to pose some problems as there are some populated areas namely Memphis right smack in the middle of the high risk area. With Little Rock on the western edges they can't let their guard down.

We definately need to pray for everyone in this area, they were hit fairly hard last week and some areas were hit yesterday.

 

[Ryan Wichman]

I worked on a forecast last night, with the concerns of cloud cover, instability and low level backed winds being in question. But short-range model runs are indicating that all of these ingredients are coming together for a major tornado outbreak AGAIN.

Full write up on the forecast can be seen here: http://convectiveaddiction.com/2010/05/01/050110-forecast-tornado-outbreak/

 

[Jeff House]

The flat region of eastern Arkansas, with relatively fewer trees, is in play today. I would not bother with initiation in the mountains of central Ark. Instead I'd be patient and wait for it to roll into eastern Ark.

East/west outflow boundary (and Gulf dews boundary) intersects CF/DL in central Ark. The OFB is lifting north as of late morning as the CF/DL inches east. The intersecting boundaries should be in the flatter territory by afternoon. If I were able to chase I'd position around Bald Knob (road choices) and wait for action to come off the mountains of central Ark. My goal would be to stay in the vicinity of the boundary intersection once it is out of the mountains.
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EDIT: Probably pre-position along I-40 east of LIT due to how the OFB sank south. Also CAPE better south. However watch out if the OFB reverses. The rate of destabilization can be more important than a snapshot of CAPE.

I second Trey's prayers for the Deep South. Been a tough couple weeks with tornadoes and oil. We always chase in hopes it is away from populated areas. Good luck and chase safely!

 

[Andrew Stoller]

Western AR is clearing out and good insolation/surface heating is occuring this morning. A few recent RUC runs were hinting at 3,000 + J of CAPE in southern AR today, and if the cloud cover can stay at bay, it may be realized. Given the surface cyclogenesis in northwest AR with the approach of a strong impulse rounding through the base of the large northern upper trough, deep layer shear looks very strong across southern/southeast AR. The forecast hodographs on various RUC runs look dangerous. I'd say today possibly has higher potential then last Saturday during the Yazoo City incident, given the juxtaposition of instability and shear.

 

[Mikey Gribble]

I haven't done much forecasting, but from what I've seen it looks great for strong tornadoes over the southern half of the high risk area. The shear profiles look more like a plains outbreak than what I'd expect to see in the southeast with backing 850mb winds and 500mb out of the southwest. There is a good 90 degrees of turning in the 0-6km layer at 00Z this afternoon over southern Arkansas. I don't want to type much again so I'll just copy and paste from my blog...

It looks great for tornadoes today, especially over the southeastern quadrant of Arkansas where the low level shear and CAPE will combine for a potent combination. Storms will fire west of there a ways, so I don’t know how many storms will get to tap into this environment. Don’t get me wrong the entire southern half of the area SPC highlighted with a high risk looks good for tornadoes, but the best spot is about half way across the state of Arkansas along their southern border and northeast from there.
If I was chasing today my initial target would be Magnolia Arkansas. That is downstream a little ways from where storms will develop later this afternoon. It has good road networks leading out of it so you can move in on a storm easily once it fires to your southwest.
The area near Magnolia and downstream of there looks awesome for tornadoes. The 850-500 crossover is insane with 850 winds out of the southeast at 35kts and 500 out of the southwest at 75kts. That is amazing. The 00Z hogograph is very good. There is about 90 degrees of turning in the 0-6km layer with 0-1km SRH around 300m2/s2. Combined with moderate to strong instability and very low LCL heights the environment will be exceptional for tornadic supercells. Given the strong wind fields in place at all levels (and SR wind profile) any storm in this area over southern Arkansas will be capable of strong or possibly violent (EF4-5) long-track tornadoes.
So again Magnolia Arkansas is where I’d be. I haven’t spent hardly any time forecasting for today so I’m sure I’ll tweak my forecast later. God I wish I was chasing for the last two days.