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!