April 3, 2012 chase

This was definitely a surprise chase day for me. 

Synoptic environment:

A compact upper level low was spinning over NM by 12Z and the associated 500mb low was progged to move slowly NE throughout the day. 

A 60kt jet streak was located at the base of the 500mb low and was forecast to move over the N TX area during the early afternoon. 

Note the SW 55kt flow at DFW.

The upper level low moved N throughout the day and we actually had southerly 55 kt flow by 00Z. 

850mb flow was southerly and around 25-30 kts. 

At the surface, there was appreciable moisture with dewpoints in the upper 60's.  Winds were ESE at around 5-10 kts. 

There was a definite outflow boundary from previous night's convection in OK that was making it's way south.  Notice the easterly and northeasterly winds running roughly along a line from DFW area to Texarkana.  I noticed this in the morning and it was plain as day on vis satellite.  I didn't know at the time that this would help to contribute to the mini-tornado outbreak that I was to commence later in the afternoon.

A line of elevated storms had already developed along the dryline in western North Texas and was making a slow progression to the east.  I decided, after getting back from the doctor's office, that I would go out west and do a test run with the video stream.  Although there were some breaks in the cloud cover to the east of the line of storms, I didn't think that discrete convection would fire around the metroplex so I headed west to Weatherford.  I set up at a truck stop along I-20 and started streaming the rotating, yet elevated, storm that was moving into that area.  I messed around with that storm for about 15 minutes until I noticed a cell developing south of the metroplex and ahead of the main line.  I quickly jetted east on I-20 and by the time I had reached western parts of Fort Worth, the storm became tornado warned.  I figured that I would be able to intercept somewhere east of I-35 and eventually made my way into the strong winds and heavy rain of the FFD around the Kennedale area.  I knew that the meso had to be to my south because of the northerly winds.  When I got into the clearing in the bear's cage, I turned off onto Little Rd near the I-20/287 interchange.  As I made my way down the road I caught the first glimpse of the tornado.

I headed to the on ramp of 287 and stopped to set up.  The tornado was less than a mile to my SW and I was able to get out and make a quick judgement call that the tornado was going to move just to my south. 

What commenced was the best footage of my life:

The tornado passed 1/2 mile to my south and displayed varying shapes (cone/stovepipe, multi-vortex, no condensation funnel, ragged tube) as it moved to the northeast.  This is the first time that I have seen multiple vortices up close and personal.  Pretty interesting how it did that while on the highway.  I couldn't believe cars weren't bailing out of there.  I don't think some of them knew what was actually going on or didn't realize the situation until it was upon them.

The descending RFD was a pretty dramatic sight.  When you get this close you really lose sight of the massive wall cloud over your head.  After losing sight of the tornado, I quickly drove down to the place where the tornado crossed and turned around.  I snapped a few photos of the damage.

 The tornado continued into the Arlington area causing EF-2 damage.

I drove back to I-20 and headed east to see the tornado roping out. 

I was quite worried because my wife was working at a nursing home in the Euless/Bedford area and the meso was heading in her direction and still showing strong rotation.  After calling and warning her about the incoming storm, I headed east and then north to reposition on the storm.  I wasn't able to get another good vantage point of the base of the wall cloud, but I did get a few structure shots of the meso with a beautiful RFD cut. 

Called it a day to the east of DFW airport at around 2:00 pm.  This was the earliest that I had returned home from a successful intercept! 

Here are the storm reports for that day:

Radar image of supercell at approximate time of my footage:

www.srh.noaa.gov/fwd

4/2/12

I've been watching this system evolve over the past couple days and haven't posted about it.  The closed 500mb low is currently over NM and an attendant 90kt jet streak is rounding the base of the low.  The position of the low is far west of the dryline placement today, which is located roughly from Canadian-Childress-SW TX with a slight bulging near the Red River.  This morning the WRF 4km models were showing CI occurring around 23-0Z from far Western OK down to just a couple counties west of Fort Worth.  The HRRR was also showing CI closer to the SPS area.  The problem I'm seeing right now is that it looks like the thin layer of moisture (around 100mb deep) is being mixed out ahead of the dryline south of Childress.  This could make it harder for CU to break through the cap to the west of Fort Worth.  Now, the HRRR is only showing CI in Western OK closer to the surface low. 


If storms can fire, they will become severe very quickly with MLCAPE values AOA 3000 J/kg.  If storms can remain discrete, I believe that as the upper level support increases from the west and bulk shear values increase AOA 40kt, then we can get some massive HP supercells with few reports of weak tornadoes.  If I were positioning today, I would be parked in Altus, OK (where a cu field is developing) and watch to see which storm becomes dominant.  The slow storm speeds today should make for easy viewing of the storms.  Structure shots will be a premium today! 

I will be sitting at home tonight watching KU try for another basketball championship.  GO JAYHAWKS!!

3/19/12 Forecast

The main trough and associated line of convection is crawling east towards the DFW area today.  The environment out ahead of the line in N TX is characterized by excellent speed shear, moderate instability, high ESRH values, low LCL's, and clearing skies.  As of now, the wind profilers are not showing a lot of turning between 850 and 500mb.  This worries me.  I'm afraid this broken line of storms will congeal and move through the area with no discrete supercells.  I will nervously watching sat and radar and waiting for anything to become dominant on the line or for something to fire out ahead of it.

If something can become discrete, it has a high probability to become tornadic.

3/18 reports

Convective initation occurred west and southwest of Childress, TX last night (forecasted pretty well by HRRR).  3 supercells became dominant, 1 southwest of Childress and the other 2 were relatively close to one another in SW OK and eventually merged to form the only tornadic supercell of the afternoon in OK.  Here are the reports from SPC:

The cap held strong near my original target area of Pampa.  However, looks like I would have been able to intercept this storm had I been out that day.

3/18 update

Still armchasing and wishing I was out there today!  :(

Here is what it looks like at the surface at 1843Z:

The dryline hasn't tightened up yet and convergence is still a bit weak because of the strong pressure falls to the west that are backing winds behind the dryline.  The best convergence is to the west and southwest of Childress, TX:

The cap is still holding on and don't have a cu field developing yet:

Upper level support is still in NM and will take some time to overtake the area and combined with dryline convergence, should break the cap with isolated storms.

The HRRR is indicating that the cap will break where convergence is strongest right now (west of Childress, TX):


It keeps that storm isolated and tracks it into a favorable supercell environment characterized by relatively higher SRH values and lower LCL's.

We will see what happens!

3/18 Forecast

The upper level support is still well behind the surface features and we will likely only see 40-50 kts of mid-level flow over the highlighted area.  However, 0-6 bulk shear vectors crossing the dryline roughly at 70 degrees should promote discrete storms early on.  Storms will probably cluster into a line after a few hours because of the meridional component of the upper level flow above 500mb.  Moisture doesn't look to be a problem today.  Already, low 60 dews from TX Hill Country up through W OK to the KS border.  There are minor discrepencies between the RUC and the NAM on dryline placement and surface flow.  The NAM is progging more backing to the sfc flow and thus stronger convergence at the dryline in the TX/OK panhandle.  The NAM is less bullish with moisture advection though, and thus shows weaker instability over WC OK and the panhandles.
A few storms should fire along the dryline in the Eastern TX panhandle between 20-23Z.
The NAM is showing a narrow tongue of MLCAPE values of 2000 J/kg and 0-3 SRH values >200 m/s2 in WC and NW Oklahoma.  If storms can move NE into this narrow corridor of higher instability and remain discrete, then I wouldn't be surprised to see a report of a strong tornado in that area.


Based on what I'm seeing, I would still probably sit tight in Pampa, TX or and await initiation.

Severe weather - March 18, 2012

It appears that a fairly potent severe weather outbreak will occur in the TX and OK panhandles and north into western KS and NE.  The SPC has issued a slight risk for their Day 2 convective outlook with hatched 30% probabilities in aforementioned areas.  

A strong, upper level trough is currently digging along the west coast of the US and moving eastward.  

 

The models are in pretty good agreement that the trough will traverse the 4 corners region and become slightly negative-tilted as it ejects into the plains.  The NAM and GFS are in slight disagreement in regards to the position of the dryline in the panhandles (NAM being farther west), but both models are showing decent destabilization east of the dryline (MLCAPE values 1000-1500) and a backing sfc wind profile.  Models show sfc dews will be in the upper 50's to low 60's east of the dryline in the eastern sections of the panhandles.  However, i believe the models are underforecasting the moisture and I believe we will see dews in the low to mid 60's as far north as WC OK, thus increasing instability.  The 850 winds are in the 30 kt range and are backing SSE.  If that holds true, then we should see some tornadoes tomorrow if storms can stay discrete.

   I expect that  storms will fire in the early afternoon hours along the dryline in the central Panhandles and stay semi-discrete for a couple hours.  Then, as the main jet streak approaches and lift increases, several clusters of storms will merge into a solid squall line with embedded supercells and trek east with a risk of strong damaging winds and isolated tornadoes.  I wouldn't be surprised if SPC puts a MOD risk for tomorrow in these areas (especially for high wind threat).  We will probably see a handful of tubes tomorrow too.

 

You can see the negative tilting to the trough!  Speed max present over northeast NM and into OK panhandle.  

 

Notice backing sfc wind profile east of dryline!

Here is a forecast sounding for 00Z for Childress, TX (KCDS):

 

 

Great directional and speed shear!  Cape values are meager because of low dewpoint values, but this may be due to convective feedback in the models.  

 

Some cons with this system are the strong meridional component of the upper level flow; storms could become linear quickly.   Also, the possible lack of stronger instability due to a cirrus shield and less moisture (assuming the models are accurate).  

I'd be chasing this event but I have work obligations until 3 and I recently had back surgery again and don't know if I can take the several hours of driving to get to the storms before dark. If I were chasing I would park myself near Pampa and await initiation.  Storms to the north will have stronger mid level flow and upper level support but less instability.  

 I will probably be chasing the next day nearer to home.  Will post more on that tomorrow.

We'll see how the day unfolds!