Thursday, April 7, 2011


It's going to be a very interesting day in northern Utah.  The morning sounding shows steep lapse rates extending through the middle troposphere.  CAPE is limited, but with some surface heating, may get sufficiently high for us to see good rumblers in northern Utah.

Source: NCAR/RAL
At present, precipitation and a sharp wind shift and temperature contrast are draped across extreme northern Utah.

The NAM, however, generates a new band to the south over Salt Lake, that becomes dominant and quite intense.  At issue is why this occurs, although it forms along the Great Basin Confluence Zone that frequently forms during large-scale southwesterly flow.  

We're still not sure why this kinematic feature forms, but it appears to play a role in frontal development (West and Steenburgh 2010) and I guess we'll see today if perhaps it can contribute to convective initiation.  

Will we be Thunderstruck?  Perhaps only Angus Young knows.  


  1. I think that the Uinta Range also plays a major role in convergence and frontal evolution here. The Uintas cause a major diversion of pre-frontal southerly flow, much of which seems to get channeled around the west side of the range and may contribute to development of a convergence zone in the greater SLC area. It seems that the Uinta range also tends to slow cold frontal passages in this area considerably, due to a mesoscale pre-frontal surface high upwind (to the S/SW) of the Uintas.

  2. In a situation like this, the blocking effect of the Uintas would be confined to very near the range. Typically blocking is confined to within about a Rossby radius of a barrier (=NH/f) where N is the Brunt-Vaisala frequency, H the scale height, and f Coriolis. Today, with the lapse rates so steep, N is quite small, and so is the Rossby radius. I suspect the Uintas today are not having a strong impact on the broad convergence zone, which appears to extend across much of the Intermountain West.

  3. I am certainly in agreement about today's situation, especially since the convergence band is continuous all the way back across Nevada. I was looking at the paper that you linked to in your blog post, so I guess my comment is more general. But it seems to me that in some cases the Uintas may have a big impact on frontal evolution in the SLC area, especially when more low-level stability is present. The E-W orientation I think is also important in terms of influencing the low-level southerly component wind field, and I have noticed a large region of low-level easterly flow to the SW of the range in many pre-frontal cases.

  4. I am glad there are some weather sites that are not complete jokes.

    It appears people here actually are interested in learning and not random chatter. It's fun learning lake effect setups. No two are ever alike.