4/9 & 4/10 Severe Weather Update ***Updated***

Updates coming this afternoon once ARW and NMM are available...

Alright since Dima did a pretty good layout of the forecast based on the 12z runs this morning I'll focus on a few other areas we may have over looked. How and why has the entire system slowed down over the past 3 days in the models and now the evolution goes from a positively tilted trough off in Cali to a negatively tilted trough in MN?

First of all since there are no observations off the west coast the model does not know the strength or location of the subtropical jet. Once it moves on shore where radiosondes are launched a much different evolution occurs. Due to the location of the upper trough from the mid latitudes this allows for the angular momentum to be reduced allowing for the subtropical jet to be further north (Due to the angular momentum typically out flow from tropical convection struggles to make it past ~20N). This allows the unstable tropical air to get wrapped up in the upper wave producing a much higher tropopause! What are the implications of this higher tropopause? Simple really, greater instability! Lets look at some observation and forecast soundings...

First 12z from this morning

The air above 200mb is the first we see of this tropical air being included into the wave. Below is another look at it from a forecast sounding 6hrs later in the same region.

It appears the tropopause begins at 250 but then the thermal profile suggest there is something else present...
Here is what a cross section through the area would look like...

Once these two jet structures "phase together" (for lack of a better term) the tropopause is consequently higher, moving the EL closer to 150mb. All the while the subtropical jet has been destabilizing the air out ahead of the upper wave at 500mb, setting the stage for 2,500+ J/kg of CAPE, seen below.

Then, as a result of this destabilization convection occurs, transportating low PV air near the surface upward and eastward, enhancing the jet along the ridge, amplifying it, enhancing the dynamics and the entire upper wave in just 48hrs goes from this...

to this...

Pretty crazy? And now the jet structure has a greater depth, with the subtropical and polar jet vertically stacked, enhancing the upper level dynamics and forcing...Sounds like a moderate and potentially major tornadic outbreak set up to this guy.

Did I say, "Can't Wait!"?

Convergence